The Weapon and Science


In this section, the weapons used to destroy the Twin Towers and the other buildings in the WTC complex, as well as the weapon that caused the massive crater and seismic activity in Shanksville, Pennsylvania, are examined here.

Fatman – bomb dropped on Nagasaki

IMAGE: Nagasaki-type Atomic Bomb “Fatman”. The Nagasaki atomic bomb was nicknamed “Fatman” because of its shape. The TNT implodes on the core of plutonium, causing nuclear fission.

The Bomb Called “Little Boy”

Through self-sustaining nuclear fission (chain reaction), an atomic bomb emits a huge amount of energy instantaneously.
The atomic bomb dropped on Hiroshima was a gun-barrel bomb. The uranium was divided into two pieces, both less than a critical mass and placed at either end of a cylinder. When one piece was fired into the other, critical mass was achieved.
Though the bomb was long and thin in shape, it grew shorter over the course of the project. Hence, the final bomb was called “Little Boy.”

Shockwave video: “Little Boy,” the Atomic Bomb Dropped on Hiroshima

VIDEO: “Little Boy” the atomic bomb dropped on Hiroshima (Dailymotion)

Larger version hereSource URL

1. A detonator was used to trigger the explosion.
2. One mass of uranium was fired into the other.
3. The neutrons created by that firing started a fission chain reaction, generating a tremendous amount of energy instantaneously. URL






Images were taken from the swf file above

RNEP Nuclear Bunker Buster

Dailymotion | Youtube: RNEP Nuclear Bunker Buster (from Union of Concerned Scientists) “RNEPFallout” (SOURCE URL 1 | SOURCE URL 2)

Nuclear fission

The nuclear fission reaction

VIDEO: “Nuclear fission reaction” (Dailymotion)

Caption: “When a neutron strike the nucleus of a uranium (or plutonium) atom, the nucleus splits, releasing two or three neutrons and a large amount of energy (as radiation, heat, etc.). The neutrons thus released strike other nuclei, and the repetition of this nuclear fission is known as a “chain reaction.” When a chain reaction occurs in an extremely short time, a tremendous amount of energy is released. The atomic bomb utilized this synergy as a weapon.” (URL)

Watch larger version of video here


IMAGE: Fat Man – internal components

Fat Man: Implosion-type bomb


IMAGE: “The initial design for the plutonium bomb was also based on using a simple gun design (known as the “Thin Man”) like the uranium bomb. As the plutonium was produced in the nuclear reactors at Hanford, Washington, it was discovered that the plutonium was not as pure as the initial samples from Lawrence’s Radiation Laboratory. The plutonium contained amounts of plutonium 240, an isotope with a rapid spontaneous fission rate. This necessitated that a different type of bomb be designed. A gun-type bomb would not be fast enough to work. Before the bomb could be assembled, a few stray neutrons would have been emitted from the spontaneous fissions, and these would start a premature chain reaction, leading to a great reduction in the energy released. Seth Neddermeyer, a scientist at Los Alamos, developed the idea of using explosive charges to compress a sphere of plutonium very rapidly to a density sufficient to make it go critical and produce a nuclear explosion.” URL:

The Structure and Explosive Mechanism of the Hiroshima Bomb

Caption: “The Hiroshima Bomb (Little Boy). About three meters long and weighing about four tons, the bomb dropped on Hiroshima was called “Little Boy” because it grew shorter over the course of the project … The Hiroshima bomb was designed to use gunpowder to blast one piece of uranium 235 into another, in order to reach a super-critical mass instantly. Roughly 50 kilograms of uranium 235 were packed into the bomb, of which less than one kilogram instantly underwent sustained nuclear fission, releasing energy equivalent to 16,000 tons of chemical high explosives. Highly sensitive radar attached to the bomb enabled it to explode at the altitude calculated to maximize the effects of the explosion.” URL:

The Hiroshima Bomb (Little Boy)

IMAGE: “About three meters long and weighing about four tons, the bomb dropped on Hiroshima was called “Little Boy” because it was relatively thin.” URL:

The Hiroshima Bomb

The Hiroshima Bomb (Little Boy)

Because of its long, thin shape, the Hiroshima bomb was called Little Boy. The fissile material was uranium 235. The uranium was divided into two parts, both of which were below critical mass. It was a “gun barrel-type” bomb that used an explosive device to slam one portion of uranium into the other, instantly creating a critical mass.
When a critical mass is available, a chain reaction takes place instantaneously, releasing energy far beyond the capacity of ordinary explosives. The energy released by the Hiroshima bomb was originally thought to be equivalent to the destructive power of approximately 20,000 tons of TNT. Later estimates based on damage to buildings and studies of the bomb’s structure have reduced that figure to approximately 15,000 tons. It is believed that this enormous energy was released by the fission of slightly less than one of the 10 to 35 kilograms of uranium 235 in the bomb. (original link)

Alternative link:

Little Boy – a gun-type bomb


Caption: “In essence, the Little Boy design consisted of a gun that fired one mass of uranium 235 at another mass of uranium 235, thus creating a supercritical mass. A crucial requirement was that the pieces be brought together in a time shorter than the time between spontaneous fissions. Once the two pieces of uranium are brought together, the initiator introduces a burst of neutrons and the chain reaction begins, continuing until the energy released becomes so great that the bomb simply blows itself apart.” URL:

Fizzle yield

Even a sub-kiloton bomb can cause considerable damage

Reasons for a fizzle are examined. A fizzle yield is a yield that is less than expected. A nuclear bomb with a fizzle-yield could have caused considerable damage in the WTC attacks. It’s possible that the perpetrators deliberately employed a bomb that would “fizzle” so as to limit the scope of the nuclear destruction and disguise the fact that a nuclear device was used. In other words, the perpetrators would have selected a detonation size that would be less than typically seen for a nuclear attack but of a size that would cause the damage they wanted to cause. A “fizzle-yield” nuclear bomb would fit the bill: it would cause a detonation half-way between that caused by conventional explosive devices and a small (1 kiloton) nuclear bomb.

Reasons for a fizzle

There are several reasons why a nuclear test might fizzle. Indeed, “fizzle yield” is a recognized nuclear term, indicating the complexities of igniting a fission bomb, especially one that is made from plutonium.

A fizzle can happen when the bomb literally blows itself apart too fast for the nuclear chain reaction to take place properly and generate the large amount of energy needed for a full-scale explosion. Should that happen a bomb meant to be in the Nagasaki range (20kt) may yield only about a kiloton.

There are two ways this can happen. One is contamination with Plutonium-240. The key ingredient for a plutonium bomb does not exist in nature; it is manufactured in a nuclear reactor when atoms of Uranium-238 capture loose neutrons and are converted to Plutonium-239, the stuff of bombs.

But these plutonium atoms can, in turn, capture neutrons, becoming Pu-240 and even Pu-241. With a bomb contaminated with Pu-240, the probability of a fizzle is very large. The US maintains a standard that none of its bomb-grade plutonium will have more than 6% Pu-240. [..]

The other problem concerns detonation. Plutonium bombs work on the “implosion” principle. A sub-critical core of plutonium about the size of soft ball is surrounded by conventional explosives. The pressure from the explosion squeezes the plutonium into a critical mass, setting off the nuclear explosion.

But the shaped charges must be so precisely engineered that they go off simultaneously. If even one charge explodes prematurely, even by a nanosecond, it may blow the bomb apart, cutting short the chain reaction and reducing the yield.

Of course, even a sub-kiloton bomb can cause a lot of damage. A one kiloton bomb will have the radius of destruction of about a third of the Hiroshima bomb, not exactly a city-flattener, but perhaps something that could work as a terrorist weapon.


1) A fizzle yield, for those just coming in, is a bomb failure where the chain reaction blows the fissionable material apart, curtailing a complete explosion. Interestingly, the typical yield of fizzle explosion is a kiloton or under.

2) a ‘fizzle yield’; that is, the smallest nuclear yield this particular device could provide.

Reasons for a fizzle – more

Plutonium weapons have several ways of misfiring. The first depends on the triggering of the plutonium by an implosion process. The implosion must be extremely symmetrical to be fully successful. Typically a combination of fast and slow conventional explosives surrounds a sphere of plutonium (the “core” or “pit”). Engineers must carefully machine all the pieces that make up this explosive shell into shapes that, when detonated simultaneously, produce a precisely spherical shock wave that compresses the plutonium to two to five times its normal density (the more compression, the greater the explosive yield). At the higher density, what was a subcritical mass of plutonium becomes supercritical–that is, one in which a sustained chain reaction takes place, producing the blast.

If the shock wave fails to be completely symmetrical–for example, if a detonator goes off 100 nanoseconds later than the rest–the compression will be less efficient because the core will tend to squirt out in the directions where the shock wave is weaker or arrives late. Another potential troublemaker is the initiator, a small device at the center of the core that emits a burst of neutrons to start the chain reaction reliably at a precise stage of the implosion. An initiator going off early or late–or not at all–reduces the yield.

Early triggering of the explosion, a kind of fizzle called a predetonation, can also occur when too much of the isotope plutonium 240 is present. The fuel rods of nuclear reactors produce the desired isotope, plutonium 239, but the longer it remains in the reactor, the more of it becomes plutonium 240. Plutonium 240 constantly emits tens of thousands of times more neutrons a second than plutonium 239. Although neutrons are the key particles in producing a nuclear chain reaction, an excess of them early in the implosion is a recipe for predetonation.


Reuters: “Gary Gibson, senior seismologist at Australia’s Seismology Research Centre, said a 4.2 magnitude quake would be the result of a one kiloton explosion.”

Reason for a fizzle – chain reaction starts too soon

One of the key elements in the proper operation of a nuclear weapon is initiation of the fission chain reaction at the proper time. To obtain a significant nuclear yield, sufficient neutrons must be present within the supercritical core at just the right time. If the chain reaction starts too soon, the result will be only a ‘fizzle yield’, well below the design specification; if it occurs too late, there may be no yield whatsoever.



In the underground nuclear testing (the testing of nuclear weapons), decoupling refers to the attempt to prevent some of the bomb’s energy from transmitting as seismic waves. This makes it more difficult for outside observers to estimate the nuclear yield of the weapon being tested.

On North Korea’s nuclear test

“I am still puzzled as to why the possibility of a decoupling cavern has been totally ignored.

Some of the early reports were that the test was conducted in abandoned mines, which would have a network of tunnels and shafts that I would expect could serve to decouple the blast.”

”… even a 1 kiloton explosive would still be a terrifying weapon. Recall that the 1995 Oklahoma City explosion involved only a few tons of ANFO. A 1 kiloton (1,000 ton TNT equivalent) bomb could kill people in an area of about one square mile and would partially destroy a much larger area. Most of these deaths would be from fire or from the prompt nuclear radiation.”

“A fizzle is simply a detonation of lower yield than designed. It does not mean a dud. Wrong words leads to wrong thinking.

The 1/2 kiloton NK fizzle would kill with immediate radiation over a 2 square kilometer area.

The area in the red ring in this image of Manhattan is the >500 REM lethal zone. The yellow arrows show the World Trade Center for scale purposes:”

IMAGE: Aerial view of the WTC site in lower Manhattan

Seismic and decoupling

Detonation of a sub-kiloton bomb would cause destruction of several buildings although it would not flatten a city. The radiation that would have been released was not a desired effect. The attack on the WTC was not a terrorist attack like the one described below, where the aim was to simply cause as many deaths as possible. The terrorists in the 9/11 attack faced restrictions of having to hide the authorship of the attacks. Saudis did not have nuclear capability at the time of the 9/11 attacks so the destruction of the buildings had to look like they had been caused by something else.

South Korean authorities said they monitored a seismic event of 3.6 on the Richter scale that was not a natural occurrence and corresponded in time to the claimed test.

A yield of 550-800 tons (.55-.8 KT) is not too small by any means as an achievable yield.

It’s also worth pointing out that an atomic bomb of .6KT or so is no city flattener, but would work quite spectacuarly as a terrorist weapon. If detonated on the ground or from the top of a building, it would also result in serious fallout, increasing the terror effect and the number of deaths. Further, it would contaminate the terrain at and near ground zero for a long time. Cleanup and decontamination would be lengthy and very expensive. Imagine such a weapon being detonated in an American harbor [..]

Calculating yield from body wave

DefenseTech explains how yields are calculated from seismic readings:

You’re thinking, 3.6, 4.2, in that neighborhood. Seismic scales, like the Richter, are logarithmic, so that neighborhood can be pretty big.

But even at 4.2, the test was probably a dud.

Estimating the yield is tricky business, because it depends on the geology of the test site. The South Koreans called the yield half a kiloton (550 tons), which is more or less — a factor of two — consistent with the relationship for tests in that yield range at the Soviet Shagan test site:

Mb = 4.262 + .973LogW

Where Mb is the magnitude of the body wave, and W is the yield.

3.58-3.7 gives you a couple hundred tons (not kilotons), which is pretty close in this business unless you’re really math positive. The same equation, given the US estimate of 4.2, yields (pun intended) around a kiloton [..]

Using the US Geological Survey figure of 4.2 magnitude body wave of the seismic shock, giving a 1 KT achieved yield, actually buttresses the case that this test was not a fizzle, in my view. For battlefield purposes, say, against the South Korean or US forces on the peninsula, a 1 KT device is more usable than a 20 KT bomb. A 1 KT weapon is smaller, thus easier to conceal, and can be designed to be fired from existing artillery pieces, whether cannons or rockets. A Nagasaki-yield weapon would be of little military utility in fighting against South Korea or American forces. And you much more easily can get from a tested 0.6-1.0 KT proof-of-concept device to a usable terror weapon of the same yield, than from a test of a much larger yielding device. (DEAD URL)

Detecting nuclear tests


Caption: Seismic detectors form the backbone of the nuclear monitoring system.

Seismic detectors

Information is collected from 500 seismic detectors around the world. Scientists are tasked with distinguishing earthquakes and nuclear testing blasts.

Seismic detectors—the same ones used to study earthquakes—form the backbone of the monitoring system. At the National Earthquake Information Center in Denver, information from about 500 seismic stations around the world is collected and analyzed, yielding information on 30,000 earthquakes a year, says Harley Benz, the U.S. Geological Survey scientist in charge of the center. But not every “event” is an earthquake, so the scientists have developed techniques to distinguish quakes from blasts. “We do this all the time in the western U.S.—there’s lots of quarry blasts, and the signal looks quite different,” Benz says.

Explosions tend to blast outwards in all directions evenly, producing a strong compression wave. Earthquakes, in contrast, are produced by rocks sliding against each other along a fault line, yielding strong shear waves. The waves travel at different speeds, with the compression wave arriving at detectors before the shear one. And if that first wave is the stronger of the two, Benz says, it suggests the event was an explosion. Other characteristics of the wave patterns, such as the frequency spectrum and how much of the wave traveled along the surface as apposed to through the bulk of the Earth, can also help distinguish blasts from quakes.

The equivalent magnitude of an earthquake and nuclear explosion

A magnitude 4 earthquake releases energy on the order of a one-kiloton nuclear explosion. – Lawrence Livermore National Laboratory

Decoupling – methods

Disguising nuclear testing can be done by decoupling. Another method is to camouflage the blast with mining explosions (mine masking). Decoupling requires exploding the device near a large underground cavity. The “Bathtub” underneath the WTC complex could have served as the large underground cavity that served to reduce the seismic activity of the nuclear detonations in the WTC attacks.

There are several ways to fool a seismic detection system. One way is to camouflage the blast with conventional mining explosions; another method, known as “decoupling”, involves exploding the device in a large underground cavity designed so that the energy of the explosion will go to compressing the gas in the cavity instead of melting and compressing rock. A U.S. experiment in 1966 showed that decoupling could reduce the seismic signal by a factor of 70. Both decoupling and mine masking are extremely difficult to carry out in practice—but just in case, there are several other detection techniques.

The most definitive signature of a nuclear explosion is the presence of radionuclides, a collective term for the radioactive isotopes produced by a nuclear reaction. While “fallout” was most obvious when early tests were conducted above-ground, underground and underwater tests also tend to leak radiation into the atmosphere. The detection process, which looks for key indicators like the ratio of different xenon isotopes, takes several days and can’t pinpoint the exact origin of the blast. But once a signal is detected, there’s no doubt a nuclear explosion has taken place.

Decoupling – effects

Decoupling can reduce the magnitude of a seismic reading. A fully-decoupled 1 kiloton nuclear test can cause an earthquake of magnitude 2.7. An earthquake of this magnitude is rarely felt by anyone.

Small Earthquake Near Russian Test Site Leads to U.S. Charges of Cheating on Comprehensive Nuclear Test Ban Treaty

On August 28 the Washington Times carried a lead story “Russia suspected of nuclear testing.” It was followed up the next day by the Washington Post and the New York Times, the latter with the headline “U.S. Suspects Russia set off Nuclear Test.” In the body of those and other press reports, however, the nature of event on August 16–whether it was a nuclear explosion or an earthquake at or near the Russian Arctic nuclear test site at Novaya Zemlya–was expressed as being still in doubt. [..]

[An] earthquake of magnitude 2.7 is a very small event, one that is rarely felt by anyone. In his executive summary of 1993 about the 1992 event, Ryall states that its magnitude was appropriate for a fully-decoupled 1 kiloton nuclear test. This begs the question Is fully decoupled or highly decoupled nuclear testing possible at Novaya Zemlya? In a 1996 review paper on decoupled nuclear testing I argued that large decoupling factors could be obtained only for explosions with yields in excess of 1 kiloton when they were detonated in huge cavities constructed in salt domes. The decoupling factor is the amplitude ratio of a well-coupled, non-evasive explosion to that of one of the same yield detonated so as to decouple or muffle the size of its seismic waves. Large cavities constructed in hard rock and used for clandestine nuclear tests are likely to leak bomb-produced radioactive isotopes to the surface by way of joints and faults. Hard rock contains such imperfections on a scale of meters and larger. A cavity with a radius of about 28 meters and at a depth of 1 km in salt is needed to fully decouple a 1 kiloton nuclear explosion. […]

A few kilotons tested with a decoupling factor of 70 times corresponds to an mb of about 3.0. A capability better than that is being achieved now for Novaya Zemlya. Probably decoupling factors no larger than a factor of two, however, are possible at that test site for yields of a few kilotons. An explosion of that size would correspond to mb 4.0.


IMAGE: The Bathtub. This underground basement held six floors of a parking station, a metro line and offices. This space underneath the towers would have acted as a decoupling cavern for any bomb detonated within or above it.





Report on the seismic recordings of Ground Zero

The seismic recordings during the collapse of the towers were 2.1 and 2.3. These recordings are consistent with the detonation of a small nuclear device. In contrast, the recordings obtained during the plane crashes were 0.9 and 0.7. These recordings were not of a sufficient magnitude to cause the collapse of buildings.

Seismic recordings of the World Trade Center collapses

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On September 11, 2001 Columbia University’s Lamont-Doherty Earth Observatory recorded seismic signals produced by the impact of the two aircraft hitting the Twin Towers of the World Trade Center. The ground shaking was consistent with the energy released by small earthquakes, however, it was not sufficient to cause the collapse and damage to the surrounding buildings. The buildings around the Twin Towers were damaged by the kinetic energy of the falling debris and the pressure exerted on them by the debris and particle laden blast produced during the collapse of the two towers. Learn More at the Earth Institute at Columbia University.

Seismographic recordings of the tower collapses were recorded in five states, as far away as 428 kilometers [266 miles] in Lisbon, New Hampshire. Lamont’s home station, in Palisades, New York, is located above the Hudson River, 34 kilometers [21 miles] from downtown Manhattan, where the towers stood. The aircraft impacts registered local magnitude (ML) 0.9 and 0.7, indicating minimal earth shaking as a result. The subsequent collapse of the towers, on the contrary, registered magnitudes of 2.1 and 2.3, comparable to the small earthquake that occurred beneath the east side of Manhattan on January 17, 2001. Source: November 20, 2001, issue of Eos, published by the American Geophysical Union, seismologists from Columbia’s Lamont-Doherty Earth Observatory

Seismic recordings captured


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Figure 1: Seismic recordings on E-W component at Palisades for events at World Trade Center (WTC) on September 11, distance 34 km. Three hours of continuous data shown starting at 08:40EDT (12:40 UTC). Data were sampled at 40 times/s and passband filtered from 0.6 to 5 Hz. The two largest signals were generated by collapses of Towers 1 and 2. Eastern Daylight Time (EDT) is UTC minus 4 hours. Expanded views of first impact and first collapse shown in red.

Seismographic recordings of the tower collapses were recorded in five states, as far away as 428 kilometers [266 miles] in Lisbon, New Hampshire. Lamont’s home station, in Palisades, New York, is located above the Hudson River, 34 kilometers [21 miles] from downtown Manhattan, where the towers stood. The aircraft impacts registered local magnitude (ML) 0.9 and 0.7, indicating minimal earth shaking as a result. The subsequent collapse of the towers, on the contrary, registered magnitudes of 2.1 and 2.3, comparable to the small earthquake that occurred beneath the east side of Manhattan on January 17, 2001.

The Lamont seismographs established the following timeline: 8:46:26 a.m. EDT [1240 UTC] Aircraft impact – north tower, Magnitude 0.9; 9:02:54 a.m. EDT [1302 UTC] Aircraft impact – south tower, Magnitude 0.7; 9:59:04 a.m. EDT [1359 UTC] Collapse – south tower, Magnitude 2.1; 10:28:31 a.m. EDT [1428 UTC] Collapse – north tower, Magnitude 2.3.

In addition, the seismic waves were short-period surface waves, meaning they traveled within the upper few kilometers of the Earth’s crust. [..]

The paper by Won-Young Kim, Lynn R. Sykes, J.H. Armitage, J.K. Xie, Klaus H. Jacob, Paul G. Richards, M. West, F. Waldhauser, J. Armbruster, L. Seeber, W.X. Du, and Arthur Lerner-Lam, “Seismic Waves Generated by Aircraft Impacts and Building Collapses at World Trade Center, New York City,” appears in Eos, Volume 82, number 47 (20 November 2001), page 565.

DPRK Nuclear Test 10-9-06: seismic record


Seismic activity is used to estimate suspected atomic weapon’s yield, or destructive power. The activity measured 4.2 on the Richter scale, as recorded by USGS. Initial reports regarding this event were mixed. Russian authorities said the test was equivalent to 5,000 to 15,000 tons of TNT (5-15 kilotons). The bomb dropped on Hiroshima, Japan in August 1945 had a yield of approximately 15 kilotons. “We have no doubts that it (the test) was nuclear,” Russian Defense Minister Sergei Ivanov said.

Comparisons of signals from different sources

Although the signals from the WTC collapse and earthquakes are of similar magnitude, the character of the seismographs are quite different. Differences in P and S waves are observed.

Comparison of World Trade Center collapse signals with signals from earthquakes, gas explosion and mine collapse

The signals at PAL from Collapse 2 and a small felt earthquake beneath the east side of Manhattan on January 17, 2001 are of comparable amplitude and ML (Fig. 4). The character of the two seismograms, however, is quite different. Clear P and S waves are seen only for the earthquake. The 7-km depth of the earthquake suppressed the excitation of short- period Rg, which is so prominent for the collapse. The difference in the excitation of higher frequencies also can be attributed to the short time duration of slip in small earthquakes compared to the combined source time of several seconds of the complex system of the towers and foundations responding to the impacts and collapses. The waves from the WTC events resemble those recorded by regional stations from the collapse of part of a salt mine in western New York on March 12, 1994 (ML 3.6). That source also lasted longer than that of a small earthquake. A truck bomb at the WTC in 1993, in which approximately 0.5 tons of explosive were detonated, was not detected seismically, even at a station only 16 km away.

An explosion at a gasoline tank farm near Newark NJ on January 7, 1983 generated observable P and S waves and short-period Rg waves (ML 3) at PAL. Its Rg is comparable to that for WTC collapse 2. Similar arrivals were seen at station AMNH in Manhattan, which is no longer operating, at a distance of 15 km. AMNH also recorded a prominent seismic arrival at the time expected for an atmospheric acoustic wave. [..] [The] seismic waves excited by impacts and collapses at the WTC are short-period surface waves, i.e. seismic waves traveling within the upper few kilometers of the crust.

Authors Won-Young Kim, L. R. Sykes, J. H. Armitage, J. K. Xie, K. H. Jacob, P. G. Richards, M. West, F. Waldhauser, J. Armbruster, L. Seeber, W. X. Du and A. Lerner-Lam, Lamont-Doherty Earth Observatory of Columbia University, Palisades, N.Y. 10964, USA; also Dept. Earth and Environmental Sciences, Columbia University.

The above is an html-version of the following pdf-document:

Differences between seismographs of nuclear explosions and earthquakes

The earthquake source differs appreciably from that of an explosion in that the former involves shearing motion along a fault. Consequently, earthquakes typically generate larger shear (S) waves than explosions when the two sources are normalized by the size of the compressional first-arriving (P) waves.

Detection of nuclear testing has increased in reliability

Detonations of yields of a kiloton can be detected anywhere on Earth.

Advances in Monitoring Nuclear Weapon Testing – 2009 report

Detecting a test of a nuclear weapon has become so effective and reliable that no nation could expect to get away with secretly exploding a device having military significance.

Seismic monitoring can now detect a nuclear explosion with a yield of a kiloton or more anywhere on Earth. In many places, detection is far more sensitive than that. – By Paul G. Richards and Won-Young Kim (March 2, 2009)

Seismic disturbances of nuclear blasts

9/11 WTC collapses produced seismic disturbances equivalent to a 4.2 magnitude earthquake. A magnitude of that size would indicate a nuclear blast of 1-kiloton yield.

How do scientists determine if a nuclear blast has occurred? By Julia Layton

Another method of detecting a nuclear blast is by seismograph, the device that monitors Earth tremors to pinpoint and analyze earthquake activity (among other ground-shaking events). There’s actually a whole network of 500 seismograph stations positioned around the world whose job is to report ground-shaking incidents, and that includes any evidence of bomb blasts. NPR’s “Detecting Underground Nuclear Blasts” reports that the seismic activity recorded on Monday indicated a ground disturbance that would be the equivalent of a 4.2 magnitude earthquake. That magnitude indicates a blast with about a 1-kiloton yield, which is equal to the power of 1,000 tons of TNT.

Figuring out if a seismic event is an earthquake or a bomb blast is relatively easy. Scientists perform analyses of wave patterns that can accurately confirm an earthquake-versus-explosion determination. In highly simplified terms, in an earthquake, the ground starts shaking slowly as plates slide against each other, and then the seismic activity slow picks up as the ground really starts to move. In an explosion scenario, the initial blast is extremely power­ful, and the subsequent shaking of the ground grows progressively less severe. But figuring out it’s a blast and not an earthquake is only part of the process; seismographs can’t really determine if the blast was nuclear or conventional in nature. Also, it’s possible to “hide” a nuclear blast, for instance by detonating it in a tremendous underground cavity, which decreases the effects on the ground because the blast’s energy goes into compressing all that gas in the huge hole.

Seismic recordings of underground nuclear blasts

The explosion recorded in the 9/11 WTC attacks was the equivalent of a 4.2 earthquake and would translate into an explosion of 1,000 tons of TNT.

Detecting Underground Nuclear Blasts – by David Kestenbaum

Earthquake monitors around the world picked up vibrations from North Korea’s nuclear test range, but those signals alone are not enough to prove that it was a nuclear blast. […]

A large underground explosion generates a shock wave that travels great distances through the Earth. Seismic detectors register the vibrations. The U.S. Geological Survey says the explosion they recorded Monday was the equivalent of a 4.2 magnitude earthquake. Assuming the test took place in rock, this would translate into an explosion equivalent to roughly one kiloton, or 1,000 tons of TNT. For comparison, the “Little Boy” bomb dropped on Hiroshima in 1945 exploded with an energy of about 13 kilotons. In 1952 “Mike” — the first hydrogen bomb — created a blast of more than 10 megatons, 1,000 times more powerful. – NPR October 11 2006

P and S waves are the key in distinguishing earthquakes and nuclear explosions

Indian nuclear tests and seismic signature


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As part of DOE’s effort, teams at Livermore and Los Alamost have been working to improve ways to seismically characterize clandestine underground nuclear explosions and differentiate them from other sources of seismicity, such as earthquakes and mining explosions. Much of Livermore’s work has centered on developing regional discriminants, which are characteristic features of a seismic waveform (for example, the peak amplitude at a particular frequency, within a specific time frame) recorded at distances less than 2,000 kilometers away. These discriminants are used to differentiate between explosions and other types of seismic sources. [..]

As seen in Figure 2, the seismogram from a representative earthquake clearly differs from that of the May 11 test. Livermore-refined discriminants based on P and S waves were strongly indicative of an explosion, not an earthquake or other seismic source, at all frequencies tested (0.5 to 8 hertz). Livermore seismologist Bill Walter explains that the differences in seismic P- and S-wave energy provide one method of discriminating explosions from earthquakes. Seismic P waves are compressional waves, similar to sound waves in the air. Shear (S) waves are transverse waves, like those that propagate along a rope when one end is shaken. Because underground explosions are spherically symmetric disturbances, they radiate seismic P waves efficiently. In contrast, earthquakes result from sliding or rupture along a buried fault surface and strongly excite the transverse motions of S waves. Thus, we expect that explosions will show strong P waves and weak S waves and that earthquakes will show weak P waves and strong S waves, as seen in Figure 2.

According to Walter, one way to quantify this difference is by determining the ratio of P-wave to S-wave energy measured from the seismograms. Explosions should have higher P/S ratios than earthquakes.

The seismograph of the World Trade Center tower collapses compared with the seismograph of nuclear test


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Img: URL: Source: Science and Technology Review Dec 1998


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South Tower collapse and North Korean nuclear test


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Caption: Figure 3: Record section of vertical-component seismograms from stations in Fig. 2 following collapse of north Tower of WTC. Zero corresponds to computed origin time of 10:28:31 EDT. Data filtered for passband 0.5 to 10 Hz. Three velocities indicated by dotted lines.

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Caption: Figure 3: Record section of vertical-component seismograms from stations in Fig. 2 following collapse of north Tower of WTC. Zero corresponds to computed origin time of 10:28:31 EDT. Data filtered for passband 0.5 to 10 Hz. Three velocities indicated by dotted lines. Img: URL:

Caption: Seismograph of North Korean nuclear test.  Modified image from URL: – NY Times: Seismic Readings Point to a Small Nuclear Test (May 25, 2009)

Caption: Seismic Readings Point to a Small Nuclear Test (May 25, 2009) Img: URL: – NY Times

Report: Initial seismic readings from the underground blast in North Korea were consistent with a relatively small nuclear test, but it will be days or weeks before the United States and international organizations can determine whether it was a nuclear detonation and how successful it might have been, experts said Monday. [..]

Martin B. Kalinowski, a nuclear expert at the University of Hamburg, said a magnitude of 4.7 corresponded to a nuclear explosive yield of about three to eight kilotons of high explosives, with the most likely yield being four kilotons. A blast that generated a tremor with a magnitude of 4.5 would be smaller.

In contrast, the primitive bombs dropped on Hiroshima and Nagasaki had explosive yields of 15 kilotons and 22 kilotons, respectively.

A senior Obama administration official said Monday afternoon that based on seismic data alone, officials estimated the explosion at “several kilotons.”

URL: – NY Times


Img: URL: Caption: Collapse of South Tower


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Ground-shaking insignificant in Twin Tower collapses

“During the collapse, most of the energy of the falling debris was absorbed by the towers and the neighboring structures, converting them into rubble and dust or causing other damage — but not causing significant ground shaking.” — Dr. Arthur Lerner-Lam, Director of Columbia University’s Center for Hazards and Risk Research, as quoted in Earth Institute News

More discussion at

Plane impacts probably involved explosions


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Caption: Seismic Readings Point to a Small Nuclear Test (May 25, 2009). Modified image from URL: – NY Times.


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Comparisons with other nuclear events

Caption: Onset of P waves from a Soviet underground nuclear test monitored at a relay station in England. Img: URL: (Ground Zero-The Nuclear Demolition of the Twin Towers – Copyright © 2007 by Niall Kilkenny)


Caption: Seismic signature from the North Tower nuclear explosion. Img: URL:

Reversed Rayleigh Waves

Reversed Rayleigh waves are consistent with an implosion rather than an explosion.

Reversed Rayleigh Waves


Caption: Interestingly, the observed Rayleigh waves are reversed, consistent with an implosion rather than an explosion source. Image: URL:


The last underground nuclear tests were conducted by India and Pakistan in May, 1998. [..] The IRIS station NIL (Nilore, Pakistan) is close to a planned IMS primary station and recorded some very interesting seismograms from the May 18, 1998, Indian test. We carefully calibrated the path to NIL using a prior Mw 4.4 earthquake that occurred on April 4, 1995, about 110 km north of the Indian test site. [..] Interestingly, the observed Rayleigh waves are reversed, consistent with an implosion rather than an explosion source. The preferred explanation is that the explosion released tectonic stress near the source region, which can be modeled as a thrust earthquake of approximate Mw 4.0 earthquake plus a pure explosion. This tectonic release is sufficient to completely dominate the Rayleigh waves and produce the observed signal (Walter et al., 2005). We also examined the explosion at high frequencies of 6-8 Hz where many studies have shown that relative P/S amplitudes can discriminate explosions from a background of earthquakes (Rodgers and Walter, 2002). Comparing with the April 4 1995 earthquake we see the classic difference of relatively large P/S values for the explosion compared to the earthquakes despite the complication of the large tectonic release during the explosion. (This is LLNL report UCRL-TR-211315).

Rodgers, A. J. and W. R. Walter, Seismic discrimination of the May 11, 1998 Indian nuclear test with short-period regional data from station NIL (Nilore, Pakistan), Pure Appl. Geophys., 159, 679-700, 2002.

Walter, W. R., D. Bowers, N. Selby, A. Rodgers and D. Porter, Tectonic Release from the May 11, 1998 Indian Nuclear Tests, LLNL report UCRL-JRNL-202983-DRAFT (to be submitted in 2005).

Date Taken: January 29, 2009

Photographer / Contributor: William R. Walter, Arthur J. Rodgers • Lawrence Livermore National Laboratory; David Bowers, Neil Selby • Blacknest, United Kingdom



Caption: Record section of vertical-component seismograms from stations in Fig. 2 following collapse of north Tower of WTC. Zero corresponds to computed origin time of 10:28:31 EDT. Data filtered for passband 0.5 to 10 Hz. Three velocities indicated by dotted lines. Img: URL:



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Comparison between North Korean test and World Trade Center Tower collapses

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Caption: DPRK’s seismic signature of their nuclear test  Img: URL:

Caption: Seismic record of explosion from digital station Vladivostok

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Source: CEME – Geophysical Service of Russian Academy.

TEXT: On October 9, 2006, North Korea’s Korean Central News Agency announced that it had successfully conducted an underground nuclear test. The test was reported to have taken place at 10:36AM, local time, in Hwaderi, near Kilju city, in North Hamkyung province. According to the KCNA statement, no radioactive leakage had taken place as a consequence of the test. [..]

The nuclear test was reported to have had a yield equivalent to between 500 and 2000 tons of TNT. By 15 October 2006 US intelligence estimates of the test put the size of the blast as low as 0.2 kilotons, the equivalent of 200 tons of TNT. According to some reports, the North Koreans had informed the Chinese government that the planned test would produce a 4-kiloton explosion.


Underground nuclear explosion appears in the seismograph

A sharp spike of short duration appears in a nuclear explosion, says a seismologist.

Strange anomaly noted in World Trade Center collapses

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Caption: These unexplained “spikes” in the seismic data lend credence to the theory that massive explosions at the base of the towers caused the collapses [..] A “sharp spike of short duration” is how seismologist Thorne Lay of University of California at Santa Cruz told AFP an underground nuclear explosion appears on a seismograph [..] Experts cannot explain why the seismic waves peaked before the towers actually hit the ground.


The Palisades seismic data recorded a 2.1 magnitude earthquake during the 10-second collapse of the South Tower at 9:59:04 and a 2.3 quake during the 8-second collapse of the North Tower at 10:28:31.

However, the Palisades seismic record shows that—as the collapses began—a huge seismic “spike” marked the moment the greatest energy went into the ground. The strongest jolts were all registered at the beginning of the collapses, well before the falling debris struck the Earth.

These unexplained “spikes” in the seismic data lend credence to the theory that massive explosions at the base of the towers caused the collapses.

A “sharp spike of short duration” is how seismologist Thorne Lay of University of California at Santa Cruz told AFP an underground nuclear explosion appears on a seismograph.

The two unexplained spikes are more than 20 times the amplitude of the other seismic waves associated with the collapses and occurred in the East-West seismic recording as the buildings began to fall.

Experts cannot explain why the seismic waves peaked before the towers actually hit the ground.

Asked about these spikes, seismologist Arthur Lerner-Lam, director of Columbia University’s Center for Hazards and Risk Research told AFP, “This is an element of current research and discussion. It is still being investigated.”

Lerner-Lam told AFP that a 10-fold increase in wave amplitude indicates a 100-fold increase in energy released. These “short-period surface waves,” reflect “the interaction between the ground and the building foundation,” according to a report from Columbia Earth Institute.

“The seismic effects of the collapses are comparable to the explosions at a gasoline tank farm near Newark on Jan. 7, 1983,” the Palisades Seismology Group reported on Sept. 14, 2001.

One of the seismologists, Won-Young Kim, told AFP that the Palisades seismographs register daily underground explosions from a quarry 20 miles away.

These blasts are caused by 80,000 pounds of ammonium nitrate and cause local earthquakes between Magnitude 1 and 2. Kim said the 1993 truck-bomb at the WTC did not register on the seismographs because it was “not coupled” to the ground.

“Only a small fraction of the energy from the collapsing towers was converted into ground motion,” Lerner-Lam said. “The ground shaking that resulted from the collapse of the towers was extremely small.” – American Free Press: New Seismic Data Refutes Official Explanation By Christopher Bollyn (Sept. 3, 2002)

Other graphs of seismic disturbances at the World Trade Center

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Other seismographs of Twin Tower Collapses


Caption: 1st collapse south tower  Img: URL:


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Audio accords with the seismic evidence

Booms heard before collapse

VIDEO: Rick Siegel 9-11 Eyewitness-Booming sounds  Dailymotion

Audio wave and seismic record of the North Tower

VIDEO: 911 Eyewitness video of the audio wave for the North Tower Dailymotion

Audio wave supports explosives

VIDEO: 911 Eyewitness – Sound analysis shows explosives Dailymotion

Witnesses reported rumbling and dust clouds before collapse

VIDEO: 911 Eyewitness – Witnesses reported rumbling and dust clouds before collapse Dailymotion

Complete Rick Siegel documentary 

VIDEO: Rick Siegel 9 11 Eyewitness Video  ArchiveOrg

Distinguishing nuclear explosions from other events

Distinguishing an earthquake from a nuclear event requires a close examination of the seismic waves. Such waves fall into two major categories: surface waves, which move along Earth’s surface, and body waves, which move through Earth and bounce off structures inside. Body waves may be primary (P) or secondary (S). Seismic P waves are compressional waves, similar to sound waves in the air. S waves are shear, or transverse, waves, similar to those that propagate along a rope when one end is shaken. Underground explosions radiate P waves in a relatively symmetric spherical shape. Earthquakes, which result from plates sliding along a buried fault, strongly excite the transverse motions of S waves, producing a distinct radiation pattern. Explosions thus show strong P waves and weak S waves. Earthquakes, in contrast, typically show weak P waves and strong S waves.


Img: URL: Caption: Various kinds of seismic events can be grouped on a source-type, or Hudson, plot based on their ground motion. A perfectly symmetric underground explosion would appear at the apex of the plot. By analyzing the seismic waves produced by the disturbance that rocked the Crandall Canyon Mine in Utah in August 2007, Laboratory seismologists determined that the event was an implosive tunnel collapse, not the sideways slippage of an earthquake.

But this information alone is not foolproof because the structure of Earth imparts an imprint on the signal. One way to quantify the difference between these seismic disturbances is to determine the ratio of P-wave to S-wave energy measured from the seismograms. Explosions should have higher P:S ratios than earthquakes.

Recent Livermore work led by Walter sought to clarify the characteristics of the P:S ratios that distinguish nuclear weapons tests from other tectonic activity. By examining regional amplitude ratios of ground motion in a variety of frequencies, his team empirically demonstrated that such ratios indeed separate explosions from earthquakes. The researchers used closely located pairs of earthquakes and nuclear explosions recorded at monitoring stations at or near the Nevada Test Site; Novaya Zemlya and Semipalatinsk, former Soviet Union test sites; Lop Nor, China; India; Pakistan; and the North Korea test.

“At high frequencies, above 6 hertz, the P:S ratio method appears to work everywhere we looked,” says Walter. “Explosions have larger P:S amplitude values.” For example, a test in India on May 11, 1998, compares well with the October 9, 2006, North Korea test.

Bill Walter is quoted. Lawrence Livermore National Laboratory Operated by Lawrence Livermore National Security, LLC, for the U.S. Department of Energy’s National Nuclear Security Administration

Caption: Seismograms recorded during the explosion (red wave) and a recent earthquake (blue wave) near that experiment show the different seismic patterns produced by these geologic disturbances.

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Differences between nuclear and earthquake seismic signatures

Differences between nuclear explosions and earthquakes

• Explosions produce strong compressional wave (P-wave). Seismic signals are depleted in S-wave.

• Earthquakes produce strong S-waves.

Explosions and earthquakes

• Explosions produce strong compressional wave (P-wave). Seismic signals are depleted in S-wave

• Earthquakes produce strong S-wave.


Explosion Yield and Magnitude

The energy releases (yield Y in kt TNT) of tamped (no decoupling) underground nuclear explosions have been calibrated against their measured seismic magnitudes using some NTS tests:

mb = log Y + 4.0

Ms = log Y + 2.0

So a 1 kt explosion is equivalent to an earthquake of mb 4.0.

Differences between nuclear explosions and earthquakes

• Explosions have much smaller source dimension.

Log R (in km) = (1/3) log Y – 2

It’s ~ 1 km for a 1 Mt device. An earthquake of this size (Ms 8) usually have a dimension of 100 km.

• Explosions have shorter time duration

A Mt device has a duration of ~ 1 sec, as compared to 30 sec for a similar sized earthquake.

• So explosions generate more high-frequency signals than earthquakes.

Difference in Radiation Pattern

• Earthquakes have much more complicated radiation patterns than explosions

• Explosions tend to have nearly isotropic radiation patterns (the same in all directions) while earthquakes have many “lobes” in their patterns

• Therefore the observed radiation pattern of a source can be used as a discriminant


Powerpoint: Detect and Isentify Nuclear Explosions by Lupei Zhu Fall 2004

Comparing the seismic records of World Trade Center collapses and Indian nuclear test

More comparisons with Indian nuclear test URL: Img 2: URL: Alternate URL: URL: Img 2: URL: Alternate URL: URL: Img 2: URL: Alternate URL:

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Caption: Seismic shockwaves from the latest test were recorded in South Korea. IMG: URL:

Cavity decoupling

Because of the drawbacks of all of these scenarios for clandestine testing, partial or full decoupling of subterranean tests is widely viewed as the only serious threat to monitoring a test ban. Decoupling involves conducting a nuclear test so as to reduce the amplitudes of seismic waves to levels below those for a contained, tamped explosion. One less effective way to do this is to conduct the test above the water Table in a large body of dry, porous sediment. Far more effective, in principle, is testing in a large mined underground cavity.

In a tamped underground nuclear explosion, large volumes of rock are exposed to overpressures far beyond the limits of elasticity, causing them to yield and suddenly to be displaced outward a large distance, generating large and easily detected seismic waves. If the explosion takes place within a very large cavity, however, the pressure of the shock wave in the surrounding rock remains below the elastic limit and produces relatively small displacements. Some early work suggested that, with “full decoupling,” seismic amplitudes transmitted into the earth at some frequencies could be reduced by over two orders of magnitude. Later studies indicate that decoupling factors of ≈70 may be achieved at low frequencies but decoupling factors at high frequencies are likely to be much smaller. Hence, broadband seismic instruments can be extremely useful in test ban monitoring. Joints or other fractures in the surrounding rock may lead to somewhat lower decoupling factors. If the cavity is too small for full decoupling, the seismic waves are reduced by a value smaller than that for full decoupling. The effects of a nonspherical cavity can be quite complicated.

Proc Natl Acad Sci U S A. 1999 September 28; 96(20): 11090–11095.

Copyright © 1999, The National Academy of Sciences Geophysics

Geologic constraints on clandestine nuclear testing in South Asia

Dan M. Davis and Lynn R. Sykes

Large factors can be achieved by decoupling


• Another way of decoupling is to fire the explosion in a large cavity.

• A factor of 120 can be achieved in theory if the cavity is large enough so that the shock-wave deformation is elastic (fully decoupled).

• A factor of 70 was achieved in one US test in which a 0.38 kt explosion was detonated in the cavity produced by a 5.3-kt explosion (see movie)


• To reduce seismic signal strength by firing the explosion in low-coupling medium (such as dry alluvium) or in a cavity.

• The decoupling factor is defined as the amplitude ratio of the seismic signals from a fully contained explosion in hard rock to from a decoupled explosion.

• A decoupling factor up to 10 can be achieved for dry alluvium.

• A problem is to avoid leakage of radioactive material and surface deformation. This demands thick alluvial deposit (~600 m for a 1 kt shot).

URL: (Detect and Identify Nuclear Explosions – Lupei Zhu Fall 2004)

Seismic signature

IMG: Seismic waveform nuclear vs. earthquake URL:

Richter magnitude and TNT-equivalent seismic energy yield

Richter Magnitude TNT for Seismic Energy Yield Example (approximate)
-1.5 6 ounces Breaking a rock on a lab table
1.0 30 pounds Large Blast at a Construction Site
1.5 320 pounds Large Quarry or Mine Blast
2.0 1 ton
2.5 4.6 tons
3.0 29 tons
3.5 73 tons
4.0 1,000 tons Small Nuclear Weapon
4.5 5,100 tons Average Tornado (total energy)
5.0 32,000 tons
5.5 80,000 tons Little Skull Mtn., NV Quake, 1992
6.0 1 million tons Double Spring Flat, NV Quake, 1994
6.5 5 million tons Northridge, CA Quake, 1994
7.0 32 million tons Hyogo-Ken Nanbu, Japan Quake, 1995; Largest Thermonuclear Weapon
7.5 160 million tons Landers, CA Quake, 1992
8.0 1 billion tons San Francisco, CA Quake, 1906
9.0 32 billion tons Chilean Quake, 1960
10.0 1 trillion tons (San-Andreas type fault circling Earth)
12.0 160 trillion tons (Fault Earth in half through center, OR Earth’s daily receipt of solar energy)


Seismic waves


The mechanical properties of the rocks that seismic waves travel through quickly organize the waves into two types. Compressional waves, also known as primary or P waves, travel fastest, at speeds between 1.5 and 8 kilometers per second in the Earth’s crust. Shear waves, also known as secondary or S waves, travel more slowly, usually at 60% to 70% of the speed of P waves. P waves shake the ground in the direction they are propagating, while S waves shake perpendicularly or transverse to the direction of propagation.

Seismic detection of nuclear tests can pose some challenges

Seismic detection of nuclear tests


Meeting Monitoring Challenges Zucca points out that under the current Threshold Test Ban Treaty (banning explosions exceeding 150 kilotons), determining accurate explosive yield is the critical issue. Most nuclear tests near the threshold treaty’s limit generate seismic magnitudes of about 6 or greater on the Richter scale. Seismic signals from these tests travel thousands of miles through Earth’s relatively homogeneous core and mantle and are readily picked up by far-away seismic stations for relatively straightforward characterization (Figure 2a). Under the CTBT, however, the critical issues will be to determine that a nuclear explosion no matter its size took place and to pinpoint its location accurately. A nation attempting to conceal a test could attempt to minimize the seismic signals. Such signals from a small nuclear test could be well below magnitude 4, with resulting measurable signals traveling 1,000 miles or less. What’s more, the signals would likely be confined to Earth’s upper mantle and crust, an extremely heterogeneous environment that distorts, and even blocks, parts of the signals (Figure 2b). Accurately locating and characterizing signals at these so-called regional distances pose a significant challenge, says seismologist Bill Walter. It’s a much harder job because we can’t use global models of Earth. We have to calibrate region by region, seismic station by seismic station. Successfully meeting the regional distance challenge, says seismologist Marv Denny, has been the most difficult aspect of the Livermore effort over the past several years. Denny says that complicating the task is the huge number of events that, at first cut, can resemble a small nuclear detonation. Stations will be recording a constant stream of background noise that includes earthquakes, lightning, meteors, sonic booms, navy armament testing, mining explosions, construction activities and other industrial operations, nuclear reactor operations and accidents, natural radioactivity, and even strong wind and ocean waves.

Analysis of nuclear test seismic wave pattern

Indian nuclear test seismic wave pattern


Figure 5. An international monitoring station in Pakistan detected the Indian nuclear test of May 11, 1998, about 740 kilometers away. (a) Analysis of the seismogram showed a P-wave-to-S-wave ratio strongly indicative of an explosion and not (b) nearby earthquakes [..] Key algorithms provide discriminants, characteristic features of a waveform (peak-to-peak distance, height, width, or some ratio). A particularly useful discriminant, for example, is the ratio of P-wave amplitude to S-wave amplitude. The P (or primary) wave is a compressional wave that is the first to arrive at a station. The S wave or shear wave has a slower propagation speed and arrives behind the P wave. The seismogram from the Indian nuclear test of May 11, 1998, as recorded by an international monitoring system station in Pakistan about 740 kilometers away, showed a P-to-S ratio strongly characteristic of an explosion and not an earthquake (Figure 5).

Comparison of the aircraft impacts and collapse of towers

The aircraft impacts registered local magnitude (ML) 0.9 and 0.7, indicating minimal earth shaking as a result. The subsequent collapsing of the towers, on the contrary, registered magnitudes of 2.1 and 2.3, comparable to the small earthquake that had occurred beneath the east side of Manhattan on January 17, 2001. The Lamont seismographs established the following timeline:

8:46:26 a.m. EDT [1240 UTC] Aircraft impact – north tower Magnitude 0.9

9:02:54 a.m. EDT [1302 UTC] Aircraft impact – south tower Magnitude 0.7

9:59:04 a.m. EDT [1359 UTC] Collapse – south tower Magnitude 2.1

10:28:31 a.m. EDT [1428 UTC] Collapse – north tower Magnitude 2.3

In addition, the seismic waves were short-period surface waves, traveling within the upper few kilometers [miles] of the Earth’s crust. They were caused by the interaction between the ground and the building foundations, which transmitted the energy from the impacts and collapses.

Ground shaking

Oral reports of ground shaking before collapse

Brian Becker — Lieutenant (F.D.N.Y.) [Engine 28] We felt — our whole building that we were in, when World Trade Center 2 collapsed, that was the first one to collapse. We were in World Trade Center 1. It was a tremendous explosion and tremendous shaking of our building. We thought it was our building maybe collapsed, there was a collapse above us occurring. It was tremendous shaking and like everybody dove into this stairwell and waited for, I guess, 20, 30 seconds until it settled, and that was our experience of the other building collapsing.

Interview, 10/09/01, New York Times

Michael Beehler — Firefighter (F.D.N.Y.) [Ladder 110] I was by I guess the outer part of the building and I just remember feeling the building starting to shake and this tremendous tremendous like roar and I just — I kind of didn’t even notice it, but like out of the corner of my eye, I saw out of the building, I saw a shadow coming down. At that point I thought it was the upper part of the north tower that had just basically like toppled over, fell off. I didn’t actually see the building part go by me, because I think I was on the opposite side. But I just remember feeling this tremendous tremendous shake and hearing this, like, noise. Again I can’t describe. What I did was I ended up running out.

Interview, 12/17/01, New York Times

Jody Bell — E.M.T. (E.M.S.) I lost track of time. You start to hear this rumble. You hear this rumble. Everything is shaking. Now I’m like, what the hell could that be. I’m thinking we’re going to get bombed. This is an air raid. You hear this thunder, this rumbling. Then you see the building start to come down. Everybody’s like, “Run for your lives! The building is coming down!” At that moment when that building was coming down, I was strapping a patient onto a stair chair.

Interview, 12/15/01, New York Times

David Blacksberg — E.M.T. (E.M.S.) I lost track of time of when the second building was coming down. It sounded like one big rumble, and then it just sounded like it just continued, and I was — I wasn’t really paying attention. I was looking at the sound.

Interview, 11/23/01, New York Times

Nicholas Borrillo — Firefighter (F.D.N.Y.)on 23rd floor of North Tower:
Then we heard a rumble. We heard it and we felt the whole building shake. It was like being on a train, being in an earthquake. A train is more like it, because with the train you hear the rumbling, and it kind of like moved you around in the hall. Then it just stopped after eight or ten seconds, about the time it took for the building to come down.

Interview, 01/09/02, New York Times

Peter Cachia — (E.M.S.) [Battalion 4] I was like a little too close to the tower when it started coming down, because when I started running, I knew I was too close and I really didn’t think I was going to get out of there. So about halfway up Liberty Street I saw a truck, I guess an SUV. It wasn’t a police or a fire vehicle. It was just a car that was parked there. I went under the truck while the tower came down and the ground was shaking and the truck was shaking and I thought that was it for me. I thought I was done. I stayed under there until I guess everything was over.

Interview, 10/15/01, New York Times

Paul Curran — Fire Patrolman (F.D.N.Y.)North Tower:
I went back and stood right in front of Eight World Trade Center right by the customs house, and the north tower was set right next to it. Not that much time went by, and all of a sudden the ground just started shaking. It felt like a train was running under my feet.

The next thing we know, we look up and the tower is collapsing.

Interview, 12/18/01, New York Times

Timothy Julian — Firefighter (F.D.N.Y.) [Ladder 118] You know, and I just heard like an explosion and then cracking type of noise, and then it sounded like a freight train, rumbling and picking up speed, and I remember I looked up, and I saw it coming down.
I made it right to the corner, and there’s a column right there, and I was with my guys. We all made it to like the column, and I remember it was plate glass behind me, and I’m thinking I’m going to get hit by this glass and like a porcupine. I’m going to get it, you know, but nonetheless, it rumbled.
It was the loudest rumbling I ever heard. The ground shook, and I got thrown down, and I remember it just got black, and I got knocked down. I remember geing buried.

Interview, 12/26/01, New York Times

Bradley Mann — Lieutenant (E.M.S.) Shortly before the first tower came down, I remember feeling the ground shaking. I heard a terrible noise, and then debris just started flying everywhere. People started running.

Interview, 11/07/01, New York Times

Keith Murphy — (F.D.N.Y.) [Engine 47] At the time, I would have said they sounded like bombs, but it was boom boom boom and then the lights all go out. I hear someone say oh, s___, that was just for the lights out. I would say about 3, 4 seconds, all of a sudden this tremendous roar. It sounded like being in a tunnel with the train coming at you. It sounded like nothing I had ever heard in my life, but it didn’t sound good. All of a sudden I could feel the floor started to shake and sway. We were being thrown like literally off our feet, side to side, getting banged around and then a tremendous wind starting to happen. It probably lasted maybe 15 seconds, 10 to 15 seconds. It seemed like a hurricane force wind. It would blow you off your feet and smoke and debris and more things started falling.

Interview, 12/05/01, New York Times

The “Bathtub” and slurry wall of the World Trade Center

Genesis of the Bathtub

The WTC complex consisted of seven buildings on a 16-acre site in lower Manhattan. The deep basement (bathtub) portion of the site covers a four-city block (980 foot) by two-city block (520 foot) area some 200 feet from the east shore of the Hudson River (Figure 1). The deep basement occupies only about 70 percent of the 16-acre WTC site and is just west of the place where the Dutch landed in 1614. The size and depth of the deep basement and the alignment of the perimeter wall were dictated by several requirements: the construction of a new interstate commuter railroad (PATH) station parallel to the Greenwich Street east wall; support for an operating New York City subway tunnel located just outside the east wall; protection of the entry points of two 100-year old, 17-foot diameter PATH tunnels on the east and west; and the foundation of the twin towers (WTC 1 and WTC 2) on bedrock within the excavation (Figure 2).

The geology of the WTC site varies from east to west. On the east (Greenwich Street), 15 to 30 feet of fill cover as much as 20 feet of glacial outwash sand and silt, below which are 5 to 20 feet of glacial till/decomposed rock. The Manhattan schist bedrock is found at depths of 65 to 80 feet. A knoll of quartzite rock intrudes into the site at the southeast corner. On the west (West Street), the fill is 20 to 35 feet thick and is underlain by 10 to 30 feet of soft organic marine clay (river mud). Below the river mud is a 20-foot thick layer of glacial outwash sand and silt and 5 to 20 feet of glacial till/decomposed rock. Bedrock is found at depths of 55 to 75 feet. Groundwater levels were within several feet of ground surface. [..]

The basement was bounded by a 3,500-foot long, 3-foot thick slurry wall (perimeter wall) constructed from grade and socketed into rock located at depths of as much as 80 feet.

[The slurry walls contained bentonite at first which was replaced with concrete.]


DIAPHRAGM WALL CASE STUDY #4: World Trade Center Recovery, NY, NY

The tragic events of 9/11/01 have left few people untouched. One of the greatest “heroes” of the day has been the “bathtub” of the World Trade Center, being able to resist the tremendous forces generated by the destruction while holding back the Hudson river from entering the New York City tunnel system. The “bathtub”, is actually a 3 ft thick (0.91 m) structural slurry wall that keeps water and soil out of the excavation.

Description: Img: URL: World Trade Center Bathtub and Original Conditions (adapted from NY Times 9/18/01)

Caption: The bathtub contained the footprints of the Twin Towers and Buildings 3 and 6.

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Caption: This illustration shows a cross-section of the bathtub tall. The diagonal lines represent the post-tensioned tie-backs: cables that resist pressure pushing inward on the bathtub.

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Caption: This photograph shows the bathtub wall after most of the rubble from the 9/11/01 attack was removed. Portions of basement floors are visible in the right-hand side of the photograph.

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Bathtub covered 9 blocks

About half of the superblock that the World Trade Center occupied contained a deep basement, the so-called bathtub. It was a skewed rectangle with sides about 980 and 520 feet, and a depth of about seven stories.

The bathtub is the 9-block area of the World Trade Center site that is excavated down to bedrock and hard soils and ringed by the slurry wall. The bathtub was created to enable the building of the Twin Towers’ foundations, and was ultimately filled with seven stories of basements housing the parking garage, mall, and building services. Since the ground water level at the World Trade Center site was just a few feet below the surface, while bedrock was about 70 feet below the surface, creating the bathtub required first building a 7-story dam below the water level of the adjacent Hudson River — the slurry wall. [..]

Four of the World Trade Center buildings — the Towers and Buildings 3 and 6 — rested on foundations entirely within the bathtub.

Building the slurry wall

The question was how to keep the Hudson out.

Jack Kyle, chief engineer at the Port Authority, came up with an answer. It was known as the slurry trench method. Excavating machines with clamshell buckets dug a three-foot-wide trench right down to bedrock 70 feet below. They did it in 22-foot-wide sections all the way around the site. As they removed fill from each section, they pumped in a slurry of water and bentonite, an expansive clay. The clay naturally plugged any holes in the sides of the dirt walls.

When they had fully excavated a section of the trench, workers slid a 25-ton, seven-story-high cage of reinforced steel into the section, then filled that portion of the trench with concrete from the bottom up. The yard-thick wall became known as the “bathtub,” though this bathtub was meant to keep water out, not in.


Caption: (1) Builders of the “bathtub” wall first excavated a three-foot-thick trench segment that was 65 feet deep by 22 feet wide and filled it with a stabilizing slurry. (2) They then lowered a giant steel cage into the trench, with attachment points for reinforcing tiebacks that were later anchored to bedrock outside the wall. (3) Finally, they poured in concrete, which, as it rose from the bottom up, forced out the temporary slurry.

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The World Trade Center was built on bedrock

Caption: The soil on the island of Manhattan is perfect for building skyscrapers. In midtown Manhattan, BEDROCK is only about 10 feet or 3 meters deep. However, at the location of the Twin Towers in the lower part of Manhattan BEDROCK is about 100 ft or 30 meters deep. There is also the problem of water from New York harbor and the Hudson River. Midtown Manhattan was thus the IDEAL place to build the Twin Towers.

When it comes to demolition by nuclear weapons the deeper the foundation the better because depth of soil hides the effects of RADIATION: “By testing underground, man has placed a shield around most radioactive by-products from nuclear explosions. In contained underground detonations of fusion devices, radioactive products are trapped in cracked rock and rubble beneath the ground’s surface. The gaseous products such as water vapor, carbon dioxide, iodine, and tritium gradually cool. Most of the water and iodine condenses to a liquid. Neutrons promptly interact with lithium in the rock minerals to produce the radioactive isotope tritium (see Box 2.1), and this heavy isotope, in part, replaced ordinary hydrogen in water to form tritiated water. The radioactive water mixes with natural ground water and moves with it through the surface rock.”(Bolt, Nuclear Explosives and Earthquakes, pp. 83-84).


The Hiroshima Bomb

Because of its long, thin shape, the Hiroshima bomb was called Little Boy. The fissile material was uranium 235. The uranium was divided into two parts, both of which were below critical mass. It was a “gun barrel-type” bomb that used an explosive device to slam one portion of uranium into the other, instantly creating a critical mass.
When a critical mass is available, a chain reaction takes place instantaneously, releasing energy far beyond the capacity of ordinary explosives. The energy released by the Hiroshima bomb was originally thought to be equivalent to the destructive power of approximately 20,000 tons of TNT. Later estimates based on damage to buildings and studies of the bomb’s structure have reduced that figure to approximately 15,000 tons. It is believed that this enormous energy was released by the fission of slightly less than one of the 10 to 35 kilograms of uranium 235 in the bomb.

The Hiroshima Bomb (Little Boy)

Hiroshima Bomb Diagram

Length: Approx. 3 meters (120 inches)
Weight: Approx. 4 tons (9,000 lbs)
Diameter: Approx. 0.7 meters (28 inches)
Element: Uranium 235 (dead link)

Alternative link:

The Nagasaki Bomb

Compared to one used on Hiroshima, the Nagasaki bomb was rounder and fatter, so it was called “Fat Man.” The fissile material was plutonium 239. The plutonium was divided into subcritical portions and packed into a spherical case. To cause the chain reaction, gunpowder around the periphery of the case was used to force the units to the center. Thus, it was called an “implosion-type” bomb.
The fission of slightly more than one kilogram of plutonium 239 is thought to have released destructive energy equivalent to about 21,000 tons of TNT.

The Nagasaki Bomb (Fat Man)

Nagasaki Bomb Diagram

Length: Approx. 3.2 meters (128 inches)
Weight: Approx. 4.5 tons (10,000 pounds)
Diameter: Approx. 1.5 meters (60 inches)
Element: Plutonium 239 (dead link)

Project Plowshare

Caption: Project Plowshare sought to use peaceful nuclear explosions for civil engineering purposes. One proposal envisioned the nuclear excavation of a new Atlantic–Pacific canal in Central America. Some of the routes considered are shown in this map.

Plowshare and the quest for peaceful nuclear explosions became one of Livermore’s major programs in the 1960s. Initially, the program focused on large-scale earth-moving, or nuclear excavation, with the long-term goal of using nuclear explosions to excavate a new Atlantic-Pacific canal through Central America (Figure 6).

Peaceful nuclear explosions – Sedan test

Caption: Sedan test (underground test) only a small amount (of radioactivity) released into the atmosphere. (at 5:50 min). (Screen capture)

“(4:35) The results of Plowshare work in controlling and limiting the rate of radioactivity released by a nuclear explosion have been and continue to be highly encouraging.

Scientists have already determined that when a nuclear explosives are buried at a depth that will produce the biggest crater, a major part of the radioactivity is swallowed up in the rubble of the crater. But the most promising results have been gained by improving the design of the explosive itself and by improving emplacement techniques. Both of these specifically calculate to reduce the release of radioactivity.

In the 1962 Sedan event, for example, only a small fraction of the radioactivity produced by the explosion was released to the atmosphere. If Sedan were conducted with the improved design and techniques available today (1965), there would be even less radioactivity and more reduction is still expected. A hundred-fold reduction from the radioactivity levels from 1962 through more improvement in explosive design and emplacement techniques.

When this prediction is realized, it will mean that the main limitation of nuclear excavation projects will not be radiation. It will be other potential hazards of explosions, nuclear or conventional: the ground shock, the air blast, and the dust cloud (6:22 min).”

Layer cake design

Image from movie (dead link)

“In Andrei Sakharov’s Layer Cake design, several layers of light and heavy elements were alternated. High explosives surrounding the Layer Cake would be used to implode and ignite the atomic bomb at the center of the device. The atomic explosion would then set off a fusion reaction in the deuterium.”

Caption: “Implosion-type weapon. Fat Man, the Nagasaki bomb, used 13.6 lb (6.2 kg, about 12 fluid ounces or 350 ml in volume) of Pu-239, which is only 39% of bare-sphere critical mass. (See Fat Man article for a detailed drawing.) Surrounded by a U-238 reflector/tamper, the pit was brought close to critical mass by the neutron-reflecting properties of the U-238. During detonation, criticality was achieved by implosion. The plutonium pit was squeezed to increase its density by simultaneous detonation of the conventional explosives placed uniformly around the pit. The explosives were detonated by multiple exploding-bridgewire detonators. It is estimated that only about 20% of the plutonium underwent fission; the rest, about 11 lb (5.0 kg), was scattered.” URL:

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Camp Desert Rock


Image from video below:

VIDEO: Camp Desert Rock  Dailymotion

At Camp Desert Rock in Nevada, the U.S. military began using smaller atomic blasts to learn how to fight a nuclear war. On April 22, 1952 approximately 2,000 Army personnel conducted maneuvers beneath the mushroom cloud of the Charlie nuclear detonation. The 31-kiloton explosion was one of the largest ever conducted in Nevada to that date. This government film claimed that with a few basic precautions, U.S. troops could fight and survive an atomic attack.

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Video: “Survival Town”

VIDEO: Dailymotion | Youtube

Caption: Survival Town atomic bomb blasts. Army destroys a fabricated American town. Real-size dolls are the only inhabitants in “Survival Town”.

“Survival City was built by the Army for Operation Cue. The goal of the test was to observe how houses, shelters, power lines, a radio tower, metal buildings, food, clothing, and actual people would survive at various distances away from a nuclear blast. Mannequins sourced from J. C. Penney, populated the city.

The May 5th 1955 explosion was dubbed Apple-2. The all-clear was finally given at 8:10am.

The 31 kilotons explosion blast area extended 3 miles out from Ground Zero. Approximately 6,000 spectators watched from about 6 miles. Army troops in tanks and trenches were positioned at a mere 2 to 3 miles from the epicenter.”

Stills from the video:

Video: “Atomic Doomtown”

VIDEO: Atomic Doomtown. Big dolls were the sole inhabitants of this town. Filming was done inside the house to show the effects of nuclear explosions on the interior of nearby houses. Nevada desert in 1955. Dailymotion | Youtube

Some stills from that video:



Operation Cue

VIDEO Dailymotion | Youtube: Beginning in 1953 the Federal Civil Defense Adminstration, working with the Atomic Energy Commission, set up an atomic test program to investigate the effects of nuclear weapons on typical American homes and their furnishings. (“OperationCue1955”) Original movie link | Original URL


U.S. nuclear reactor locations (dead link)

May be archived under

Caption: The yield of a hydrogen bomb is controlled by the amounts of lithium deuteride and of additional fissionable materials. Uranium 238 is usually the material used in various parts of the bomb’s design to supply additional neutrons for the fusion process. This additional fissionable material also produces a very high level of radioactive fallout.

Caption: Nuclear energy can also be released by fusion of two light elements (elements with low atomic numbers). The power that fuels the sun and the stars is nuclear fusion. In a hydrogen bomb, two isotopes of hydrogen, deuterium and tritium are fused to form a nucleus of helium and a neutron. This fusion releases 17.6 MeV of energy. Unlike nuclear fission, there is no limit on the amount of the fusion that can occur.

Portable nuclear munitions

Caption: Special Atomic Demolition Munition (SADM), a Navy and Marine Corps project that was demonstrated as feasible in the mid-to-late 1960s. The package shown was intended to be used by UDT/Seal Special Forces, delivered into water by parachute along with a two man team, then floated to the target, set in place and armed by hand. Designed to attack a harbor or other strategic location that could be accessed from the sea.


The answer to the existence question is certainly yes, at least for “trunk size” devices. Unclassified sources have reported that small nuclear devices were developed by both the United States and the Soviet Union during the Cold War, a direct result of the work on tactical nuclear weapons. [..]

The U.S. developed a class of devices called “Atomic Demolition Munitions” (ADM), intended for use as atomic land mines. ADMs were in the U.S. inventory from the late 1950’s until such weapons were phased out by arms-control agreements in the 1980’s. A version of the ADM for use by Special Forces, the “Special Atomic Demolition Munitions” (SADM), was suitcase or duffle bag size, weighing less than 100 pounds [..] The top photo on this page is from a declassified film showing a demonstration of the SADM in the late 1960s. [..]

The Soviet Union’s small nuclear devices were developed for nuclear mines and possibly for Spetsnaz attacks (Special Forces). In 1997, General Aleksandr Lebed claimed that the Soviet Union created one hundred and fifteen atomic demolition munitions (ADMs), low-yield, one kiloton devices that were small, portable, and without safety devices to prevent unauthorized detonation. Lebed further raised the issue of whether the ADMs were all in proper custody and accounted for. Others have contradicted Lebed — the issue is unsettled, but it is most likely that the Soviets did produce small atomic munitions, similar to the U.S. SADM.

An important point is that all nuclear devices require routine maintenance to remain viable. Small devices are no exception and, in fact, may require more frequent maintenance than larger weapons. Therefore, a diverted weapon from military stocks will become ineffective in a matter of a few years even if its control systems can be bypassed. The main danger, after the device has lost its original effectiveness, is its use as a source of weapons grade plutonium.

Caption: SADM packing case small atomic munition

Caption: H-912 transport container for Mk-54 SADM.

Text: A suitcase nuke is a tactical nuclear weapon which uses, or is portable enough that it could use, a suitcase as its delivery method. Synonyms include suitcase bomb, backpack nuke, mini-nuke, or pocket nuke. [..]

The lightest nuclear warhead ever acknowledged to have been manufactured by the U.S. is the W54, which was used in both the Davy Crockett 120 mm recoilless rifle–launched warhead, and the backpack-carried version called the Mk-54 SADM (Special Atomic Demolition Munition). The bare warhead package was an 11 in by 16 in (28 cm by 41 cm) cylinder that weighed 51 lbs (23 kg). It was, however, small enough to fit in a footlocker-sized container.

Background on Suitcase Nukes

A “suitcase” bomb is a very compact and portable nuclear weapon and could have the dimensions of 60 x 40 x 20 centimeters or 24 x 16 x 8 inches. The smallest possible bomb-like object would be a single critical mass of plutonium (or U-233) at maximum density under normal conditions. The Pu-239 weighs 10.5 kg and is 10.1 cm across. It doesn’t take much more than a single critical mass to cause significant explosions ranging from 10-20 tons. These types of weapons can also be as big as two footlockers. The warhead consists of a tube with two pieces of uranium, which, when rammed together, would cause a blast. Some sort of firing unit and a device that would need to be decoded to cause detonation may be included in the “suitcase.”

Another portable weapon is a “backpack” bomb. The Soviet nuclear backpack system was made in the 1960s for use against NATO targets in time of war and consists of three “coffee can-sized” aluminum canisters in a bag. All three must be connected to make a single unit in order to explode. The detonator is about 6 inches long. It has a 3-to-5 kiloton yield, depending on the efficiency of the explosion. It’s kept powered during storage by a battery line connected to the canisters. Source: – Department of Homeland Security (Dept of Homeland Security)

Too Few Labs To Test ‘Dirty Bomb’ Fallout

Report Finds U.S. Lagging In Resources To Test For Radiation Exposure

AP) The U.S. has a shortage of laboratories to test the thousands of people who might be exposed to radiation if a “dirty bomb” detonated in a major city, according to a recent congressional investigation.

The federal government established 15 disaster scenarios for federal, state and local officials to plan for, including one in which a dirty bomb goes off in a major downtown area and potentially exposes 100,000 people to radioactive materials.

A dirty bomb would contain some radioactive material that could cause contamination over a limited area but not create actual nuclear explosions.

Should this happen in real life, America would not be able to quickly conduct tests for these people, because there are few labs capable of doing so in the country; and the tests available only address six of the 13 radiological isotopes that would likely be used in a dirty bomb, according to the report prepared for the House Committee on Science and Technology. Instead, it would take four years to complete all these tests, according to the report to be released Thursday. [..] – Copyright AP WASHINGTON, Oct. 25, 2007

Caption: A congressional report found it would take four years to test the thousands of people who might be exposed to radiation of a dirty bomb detonated in a major downtown area. (CBS/AP)

Video: Declassified US Nuclear Test Film #31

VIDEO URL: Title: Declassified U.S. Nuclear Test Film _31 Dailymotion | Youtube | ArchiveOrg

“SADM Delivery by Parachutist/Swimmer (Special Atomic Demolition Munition) – The Special Atomic Demolition Munition (SADM) was a Navy and Marines project that was demonstrated as feasible in the mid-to-late 1960s, but was never used. The project, which involved a small nuclear weapon, was designed to allow one individual to parachute from any type of aircraft carrying the weapon package that would be placed in a harbor or other strategic location that could be accessed from the sea. Another parachutist without a weapon package would follow the first parachutist to provide support as needed.

The two-man team would place the weapon package in an acceptable location, set the timer, and swim out into the ocean where they would be retrieved by a submarine or other high-speed water craft. The parachute jumps and the retrieval procedures were practiced extensively.

The video shows a man in a wet suit donning his parachute, the weapon package, and a reserve parachute. After he jumps from the aircraft and is nearing the water, he drops the weapon package down on a 17-foot line to lessen the impact of his landing. He then floats the weapon package to the desired location.”

A still from that film:

VIDEO: American SADM

Dailymotion: American SADM. American Special Atomic Delivery Munitions. A shorter film (28 sec)

A still from that film:

Nuclear bunker buster – mini-nukes


The RNEP would be used on targets that may be immune to conventional weapons. Its backers claim it would create little contamination above ground, but critics say that it would produce huge amounts of nuclear fallout. The RNEP may also remove the distinction between a nuclear deterrent and conventional weapons, increasing the risk of a nuclear exchange.

US law prevents development of new “mini-nukes” that have an explosive yield of less than 5 kilotons. But the RNEP falls outside this ban because it is not a new weapon.

Rather, it will be a modification of an existing nuclear bomb, probably a highly modified B61, sources say, a weapon whose explosive yield can be set from anything between 0.3 and 340 kilotons. The bomb uses fission at low yields but is a fusion (hydrogen) bomb at high yields. The Hiroshima fission bomb had a yield of 12 kilotons.

Underground explosions are 10 to 15 times as effective against buried facilities as airbursts. A conventional bunker-buster is dropped from high altitude and hits the ground at enormous speed. It penetrates earth, rock and concrete before exploding. A nuclear version has the advantage of a far more powerful shock wave, increasing the depth of its destructive effect.

The US already has around fifty ‘penetrating’ nuclear weapons in its stockpile, but these can only reach a depth of six metres in earth. David Wright, a nuclear-weapons expert at the Union of Concerned Scientists in Washington DC, says this would not be nearly enough to contain the radioactivity.

“Even for a 0.3-kiloton explosion, you would need a burial depth of about 70 metres in dry soil and about 40 metres in dry, hard rock to contain the blast,” Wright says. An explosion at the maximum depth achievable so far would throw thousands of tonnes of highly radioactive debris into the air.

Nuclear bunker buster

Fig. 2 The Pentagon has a growing collection of high precision conventional weapons capable of defeating hardened targets. In this sled-driven test, the GBU-28 laser guided bomb with its improved BLU-113 warhead penetrates several meters of reinforced concrete.

Underground detonations limit collateral damage

Fig. 1 Diagrams like this one give the false impression that a low-yield earth penetrating nuclear weapon would “limit collateral damage” and therefore be relatively safe to use. In fact, because of the large amount of radioactive dirt thrown out in the explosion, the hypothetical 5-kiloton weapon discussed in the accompanying article would produce a large area of lethal fallout. (Philadelphia Inquirer/ Cynthia Greer, 16 October 2000.)

The B61-11 Nuclear Bomb

[M]ini-nuke advocates — mostly coming from the nuclear weapons labs — argue that low-yield nuclear weapons should be designed to destroy even deeper targets.

The US introduced an earth-penetrating nuclear weapon in 1997, the B61-11, by putting the nuclear explosive from an earlier bomb design into a hardened steel casing with a new nose cone to provide ground penetration capability. The deployment was controversial because of official US policy not to develop new nuclear weapons. The DOE and the weapons labs have consistently argued, however, that the B61-11 is merely a “modification” of an older delivery system, because it used an existing “physics package.”

The earth-penetrating capability of the B61-11 is fairly limited, however. Tests show it penetrates only 20 feet or so into dry earth when dropped from an altitude of 40,000 feet. Even so, by burying itself into the ground before detonation, a much higher proportion of the explosion energy is transferred to ground shock compared to a surface bursts. Any attempt to use it in an urban environment, however, would result in massive civilian casualties. Even at the low end of its 0.3-300 kiloton yield range, the nuclear blast will simply blow out a huge crater of radioactive material, creating a lethal gamma-radiation field over a large area.

Bunker buster in action

VIDEO: “CNN_bunkerbuster” Dailymotion (URL)

COMMENT: Notice that the blast is from a below ground explosion, similar to the WTC ones which were buried in the basement and were encased (in concrete and steel).

The fact that the explosions occur underground in the case of the bunker buster means that the effects of the nuclear explosion are all reduced (blast, thermal and radiation effects).

Bunker buster video

VIDEO Dailymotion: Nuclear bunker buster. From Federation of American Scientists. (“Nbbd_hi”)

Images from the video:

Robust Nuclear Earth Penetrator

VIDEO: “RNEPFallout” Dailymotion | Youtube

“This animation depicts a proposed weapon with a one megaton yield. The funding for this weapon was cut in 2005 defense appropriations. However, the United States still has a B61-11 nuclear ‘bunker buster’ in its arsenal which has a 400 kiloton yield, which could still cause hundreds of thousands of deaths and spread radiation to other countries.”

“The Bush Administration has again requested funding from Congress to research a new type of nuclear bomb. The Robust Nuclear Earth Penetrator (RNEP) is a nuclear weapon that would burrow a few meters into rock or concrete before exploding and thus generating a powerful underground shock wave. Its hypothetical targets are deeply buried command bunkers or underground storage sites containing chemical or biological agents.”

Fusion reaction – animation

Dailymotion: Nuclear fusion

“Nuclear fusion is the joining (or fusing) of the nuclei of two atoms to form a single heavier atom. At extremely high temperatures – in the range of tens of millions of degrees – the nuclei of isotopes of hydrogen (and some other light elements) can readily combine to form heavier elements and in the process release considerable energy.

For fusion to occur, the electrostatic repulsion between the atoms must be overcome. Creating these conditions is one of the major problems in triggering a fusion reaction.”

Animation: Fission reaction

Dailymotion: Fission reaction (“Fission”)

“In nuclear fission, a heavy atomic nucleus, such as that of uranium or plutonium, will break up into two lighter nuclei. In the fission process, a large quantity of energy is released, radioactive products are formed, and several neutrons are emitted.

The released neutrons can also induce fission in a nearby nucleus of fissionable material and release more neutrons that can repeat the sequence, causing a chain reaction.”


Animation: 3-D model of Fat Man

Dailymotion: Fat Man was used in the bombing of Nagasaki (“Fatman_vr”)

“The initial design for the plutonium bomb was also based on using a simple gun design (known as the “Thin Man”) like the uranium bomb. As the plutonium was produced in the nuclear reactors at Hanford, Washington, it was discovered that the plutonium was not as pure as the initial samples from Lawrence’s Radiation Laboratory. The plutonium contained amounts of plutonium 240, an isotope with a rapid spontaneous fission rate. This necessitated that a different type of bomb be designed. A gun-type bomb would not be fast enough to work. Before the bomb could be assembled, a few stray neutrons would have been emitted from the spontaneous fissions, and these would start a premature chain reaction, leading to a great reduction in the energy released.

Seth Neddermeyer, a scientist at Los Alamos, developed the idea of using explosive charges to compress a sphere of plutonium very rapidly to a density sufficient to make it go critical and produce a nuclear explosion.”

Animation: 3-D model of Little Boy

Dailymotion: Little Boy the bomb that was used in the bombing of Hiroshima (“Littleboy_vr”)

“In essence, the Little Boy design consisted of a gun that fired one mass of uranium 235 at another mass of uranium 235, thus creating a supercritical mass. A crucial requirement was that the pieces be brought together in a time shorter than the time between spontaneous fissions. Once the two pieces of uranium are brought together, the initiator introduces a burst of neutrons and the chain reaction begins, continuing until the energy released becomes so great that the bomb simply blows itself apart.”

Image from the video

The only secret about nuclear weapons is that there is no secret

When journalist Howard Morland wrote an article explaining how an “H-Bomb” is made, the US Government took him to court. The plates were seized to prevent publication, because US officials claimed American security would be jeopardized if classified details on such an explosive topic were revealed. But Morland won his case without even going to the Supreme Court by showing that all the vital information was available in the Encyclopedia Americana — in an item written by Dr. Edward Teller, the “Father of the H-Bomb”. This picture, taken on the steps of the Supreme Court, shows Morland holding a cut-away model of an H-bomb, with its plutonium trigger (the small black globe at the top). Morland believes that the only secret about nuclear weapons is that there are no secrets. He thinks it is a greater threat to global security to suppose there are secrets when there aren’t, than to discuss how the bombs are actually made, because such false beliefs contribute to a false sense of security and an atmosphere of complacency.

Photo by Robert Del Tredici from his book entitled
At Work In The Fields Of The Bomb (Harper and Row, 1987)

How To Make an H-Bomb (or Thermonuclear bomb)

Howard Morland wrote a magazine article explaining how an “H-Bomb” — or “thermonuclear bomb” — is made, using only publicly available information. In the photo, he is standing on the steps of the US Supreme Court holding a cut-away model of the H-bomb.

An H-bomb is a three-stage weapon: fission, fusion, and then fission again. The first stage, called the “trigger” (the black ball at the top), is a small plutonium bomb similar to the one dropped on Nagasaki in 1945. The energy release at this stage is mainly due to nuclear fission — because the atoms of plutonium are split. Tritium is often added to the centre of the plutonium core to “boost” the fission explosion with some additional fusion energy. Boosted or not, however, the only importance of this first-stage explosion is to irradiate and heat the material in the central column to 100 million degrees celsius so that a much more powerful fusion reaction can be started there.

The second stage explosion is due to nuclear fusion in the central column. The main fusion reaction involves concentrated deuterium and tritium (both heavy isotopes of hydrogen) — which become spontaneously available when neutrons from the first stage explosion bombard a solid material called “lithium deuteride” located in the central column. When this hydrogen-rich mix is heated to 100 million degrees, the deuterium and tritium atoms “fuse” together, releasing enormous amounts of energy. This is the “H” or “thermonuclear” part of the bomb.

Then comes the third stage. The fusion reaction gives off an incredible burst of extremely powerful neutrons — so powerful that they can split or “fission” atoms of uranium-238 (called “depleted uranium”) — which is impossible at lower energy levels. This third stage more than doubles the power of the explosion, and produces most of the radioactive fallout from the weapon.

Unlike fission bombs, which rely only on nuclear fission, and which can achieve explosions equivalent to thousands of tons of TNT (“kilotons”), the power of an H-bomb or thermonuclear weapon has no practical limit — it can be made as powerful as you want, by adding more deuterium/tritium to the second stage. Most H-bombs are measured in “megatons” (equivalent to the explosive power of MILLIONS of tons of TNT — hundreds of times, or even a thousand times more powerful than a fission bomb).

American nuclear arsenal

This field full of ceramic cones represents, in miniature, the 25 000 warheads of the american nuclear arsenal. Plutonium is the principal nuclear explosive in most of these warheads. One of the greatest risks in using plutonium as a civilian nuclear fuel is the relative ease with which some of it could be stolen. Plutonium can be used — by anyone who gets their hands on it — to make nuclear weapons.

Photo by Robert Del Tredici from his book entitled At Work In The Fields Of The Bomb (Harper and Row, 1987)

Glass ball model of plutonium

This glass ball, 3.2 inches across, is the exact size of the plutonium core in the bomb that exploded over Nagasaki on August 9 1945 with a force equivalent to 22 thousand tons of TNT.

Photo by Robert Del Tredici
from his book entitled
At Work In The Fields Of The Bomb
(Harper and Row, 1987) (Canadian Coalition for Nuclear Responsibility)


This is a simple diagram illustrating an example of nuclear fission. A U-235 nucleus captures and absorbs a neutron, turning the nucleus into a U-236 atom. The U-236 atom experiences fission into Ba-141, Kr-92, three neutrons, and energy.

Fastfission, public domain


Caption: When neutrons are bombarded against uanium-235, the uranium-235 nucleus absorbs a neutron to be a uranium-236 and it splits into two fragments of almost equal masses with emitting some neutrons simultaneously and evolving a huge amount of energy larger than 200 MeV. This is nothing but one of the examples of fission of uranium-235. It does not always split into Ba and Kr but usually into two fragments with almost equal masses. The number of emitted neutrons is also not always constant but it distributes over one to several. Then the emitted energy is not always constant but is almost 200 MeV.

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The US Government’s Usage of Atomic Bombs — Domestic — WTC

By Ed Ward, MD

In 1993, Joe Vialls exposes some facts about single explosions that were very similar to the 2001 WTC bombing. [..] URL: Caption: Rare picture of damage from 6.3 tons of explosive from BLU-82

Another crater 22 feet wide and 5 feet deep is noted in the article Bali Micro Nuke – Lack of Radiation Confuses Experts. Within 48 hours the Bali government found traces of C4 explosive. Next came the revised explanation of explosives on top of gas containers. After that failed to explain noted facts, the next theory was explosives with napalm. The final explanation from London quoted a reliable source that an IRA style bomb mixture was used. Still, there were significant problems with the story as the IRA had detonated 1,000 pounds of the mixture and there was no crater produced. The US bomb, BLU-82 – used for clearing helicopter landing zones in the jungles of Vietnam – contains 6.3 tons of high grade military explosive with an aluminum additive for increased heat, but does not create a crater. The 1/4 inch steel encased explosive is parachuted to its target and detonated 1 to 2 feet above ground. Approximately 40 people close enough to be vaporized simply vanished without a trace. Insights on Israel’s .01 kt Dimona nuke are also related in this article. According to the information presented, the bomb uses highly enriched Plutonium 239, 99.78% pure, and only emits alpha radiation which is invisible to most Geiger counters.

Israel’s nuclear arsenal

Dimona nuclear reactor – Vanunu exposes

VIDEO: Dimona. Vanunu gave the a detailed account about the 60 photos he secretly took of the nuclear facility. URL:


‘Vanunu gave the “Sunday Times” a detailed description – 60 photos he secretly shot. We took that information and from that it was possible to learn about the nuclear compound. We took all 60 photos from different parts of the compound, composed it with the information Vanunu gave, processed through computerized simulation, to give a never before seen 3D tour of Israel’s nuclear facilities.

Let us watch.

Only from space can you take pictures of Israel’s top secret site. No plane is allowed within this airspace. Only one man’s testimony – Mordechai Vanunu – revealed what is going on within this row of buildings surrounded by palms, “The row of institutes” as it is referred to. This is Institute No. 1, Dimona’s symbol, the 20 meters high, nuclear reactor’s dome.
Until now only seen from afar, Vanunu took us inside, into the reactor.
A heavy water reactor built in the 50s by the French, declared capacity of 24 MW.

And this is Vanunu’s first revealed secret:

The reactor’s capacity is three – possibly even five times larger than assumed until now.

This reactor produces 40 kg of plutonium a year, enough to build 10 atom bombs.

Adjacent to the reactor is Institute No. 3. In here, the fuel rods powering the reactor are produced together with lithium 6, another ingredient of the bomb.

This is Institute No. 5, here the fuel rods are coated with aluminium.
Institute No. 6 is the power station of the compound.

The lab is in Institute No. 8 and inside is another secret Vanunu revealed:
this is where Israel produces enriched uranium. Like plutonium, it can serve as fissionable material for the bomb. The uranium is produced through gas centrifuges, just like the Iranians are now trying to produce.

By the size of the building, it appears that the amount of uranium produced here is insignificant.

Enriched uranium is also produced in Institute No. 9 using laser – an Israeli unique patent.

Institute No. 10 produces depleted uranium, an important component in the production of armor piercing shells.

Institute No. 4 handles the radioactive waste, prior to being disposed. And this long two story building, with no windows, is Dimona’s big secret – Institute No. 2.

Beneath the two innocent looking floors, hidden underground, are six additional floors.

Vanunu showed the world what no satellite could see. Here Israel set up a plutonium separationf facility, with one goal – manufacturing atomic bombs.
In the 60s, American inspectors visited the first floor. They saw the restaurant and the offices. A special wall was constructed, hiding the elevators leading to the underground levels.

Back outside, trucks bring in the processed uranium rods. Through the large doors, a crane grasps the rods and lowers them to the big workspace, 4 floors below.

The rods are dipped in nitrous acid tanks, cooked for about 30 hours, and then a system of pipes draws the water containing the uranium and plutonium.

Through a chemical process, the materials are separated and then baked in an oven, producing a small 130 gram plutonium ball, 1.7 kg a week. 4 kg and it’s a bomb. Just like this model shot by Vanunu.

The process can be viewed from level 2. A balcony was built for distinguished guests. Nicknamed Golda’s Balcony.

And that’s the control room as shot by Vanunu. Only 150 employees are authorized to enter it. Visits are limited to the prime minister, the minister of defense, and a small group of confidants. Equipped with a hidden camera, Vanunu walked about Institute No. 2 and took pictures of the different sections. Not only plutonium is produced here, at level 4, Vanunu revealed the production of tritium used in the production of thermo-nuclear bombs, which are more powerful than ordinary atom bombs.

Two other essential materials for the bomb are produced here: lithium and deuterium. All these ingredients are taken to level 5, to Unit MD2 – Metal Department 2, where they are assembled into a bomb.

One level down is a recreation room, where Vanunu shot what experts identified as a model of an Israeli thermo-nuclear bomb, 10 times more powerful than the bomb dropped on Hiroshima.

Experts that analyzed Vanunu’s testimony, determined that by the 80s, Israel had produced 100-200 atom bombs.

This ranks Israel as the 6th or even 5th nuclear power in the world.
This presentation was based solely on data delivered by Vanunu to the “Sunday Times”. ‘


Still from the video

Closeup of the Dimona nuclear plant


The Dimona Reactor Dome. (Courtesy of Mordechai Vanunu).


Mockup of a Dimona bomb. (Photo courtesy of Mordechai Vanunu)

Two Mordechai Vanunu photos.


Control room of the Machon 2 plutonium separation plant. (Photo courtesy of Mordechai Vanunu)


Revealed: the secrets of Israel’s nuclear arsenal URL: Caption: On 5 October 1986, the British newspaper The Sunday Times ran Mordechai Vanunu’s story on its front page under the headline: “Revealed: the secrets of Israel’s nuclear arsenal”

Sunday October 5, 1986: Headline: Revealed – the secrets of Israel’s nuclear arsenal/ Atomic technician Mordechai Vanunu reveals secret weapons production

THE SECRETS of a subterranean factory engaged in the manufacture of Israeli nuclear weapons have been uncovered by The Sunday Times Insight team.

Hidden beneath the Negev desert, the factory has been producing atomic warheads for the last 20 years. Now it has almost certainly begun manufacturing thermo-nuclear weapons, with yields big enough to destroy entire cities.

Information about Israel’s capacity to manufacture the bomb come from the testimony of Mordechai Vanunu, a 31-year-old Israeli who worked as a nuclear technician for nearly 10 years in Machon 2 – a top secret, underground bunker built to provide the vital components necessary for weapons production at Dimona, the Israeli nuclear research establishment.

Vanunu’s evidence has surprised nuclear weapons experts who were approached by Insight to verify its accuracy because it shows that Israel does not just have the atom bomb – which has been long suspected – but that it has become a major nuclear power.

Vanunu’s testimony and pictures, which have been scrutinised by nuclear experts on both sides of the Atlantic, show that Israel has developed the sophisticated and highly classified techniques needed to build up a formidable nuclear arsenal. They confirm that:

Israel now ranks as the world’s sixth most powerful nuclear power, afterAmerica, the Soviet Union, Britain France and China – with an arsenal far greater than than those other countries, such as India, Pakistan and South Africa, which have also been suspected of developing nuclear weapons.

It has possessed its secret weapons factory for more than two decades, hiding its plutonium extraction processes from spy satellites and independent inspections during the 1960s by burying it beneath an innocuous, little used building.

The plant is equipped with French plutonium extracting technology, which transformed Dimona from a civilian research establishment to a bomb production facility. Plutonium production rates amount to 40 kilograms a year, enough to build 10 bombs. In the past six years Israel has added further equipment to make components for thermo-nuclear devices.

The 26 megawatt reactor, also built by the French, has been expanded and is probably now operating at 150 megawatts to allow it to extract more plutonium. An ingenious cooling system disguises the output.

The nuclear scientists consulted by The Sunday Times are convinced by Vanunu’s evidence. They calculate that at least 100 and as many as 200 nuclear weapons of varying destructive power have been assembled – 10 times the previously estimated strength of Israel’s nuclear arsenal.

One of the pictures Vanunu took URL: Caption: This is a photo of a plutonium separation plant’s control room, with equipment recognizable by nuclear scientists as part of a nuclear weapons production facility. Dimona Nuclear Weapons Facility Machon 2, Negrev Desert, Israel (courtesy M. Vanunu)

Israeli nuclear ‘power’ exposed

Sunday, 16 March, 2003, 01:47 GMT by Olenka Frankiel URL: Caption: Israel has enforced Vanunu’s silence for 16 years

Mordechai Vanunu, Israel’s nuclear whistleblower, was jailed in 1986 for publishing photographs of Israel’s nuclear bomb factory at Dimona. Olenka Frenkiel reveals the extent of Israel’s nuclear gagging.

Vanunu has spent 17 years in jail, 11 of which were in a minute solitary confinement cell – and he has just had his appeal for parole denied.

He will stay in jail until 2004, when his term is expected to end.

Caption: Revelations hit the press in October 1986 Image: URL:

Sunday Times journalist Peter Hounam heard rumours in 1986 that an Israeli whistleblower was offering proof of what the world had long suspected.

Vanunu was that whistleblower.

His revelations confirmed that Israel was building advanced nuclear weapons

After the Sunday Times published this scoop, Vanunu was lured to Italy and kidnapped by Mossad agents and illegally smuggled back to Israel.

He was tried in secret and convicted of treason and spying.

Security chief exposed

In court, at his parole hearing, Avigdor Feldman, Vanunu’s lawyer, argued that his client had no more secrets and should be freed.

But the prosecutor had a new argument: the imminent war with Iraq.

After the hearing Mr Feldman told Correspondent: “The prosecutor said that if Vanunu were released, the Americans would probably leave Iraq and go after Israel and Israel’s nuclear weapons – which I found extremely ridiculous.”

The real force blocking Vanunu’s release is a man who was known only as “Y”.

In 2001, “Y” was exposed as Yehiyel Horev and it is said that the only thing he fears is publicity.

Mr Horev is the head of Israel’s most powerful intelligence service, dealing with nuclear and military secrets. URL: Caption: Yehiyel Horev unmasked, here, for the first time

His accountability has only been to the many prime ministers he has watched come and go in the 16 years he has built his power base.

He has been likened to the head of the FBI, J Edgar Hoover – an autocrat out of control.

Ronen Bergman, security correspondent for one of Israel’s leading newspapers – Yediot Ahronoth – says: “Horev is a grave danger to Israeli democracy.

“He operates with no law, no real scrutiny and no monitoring by the Israeli parliament.

“Horev was afraid that veterans of the Israeli intelligence and the Israeli nuclear effort would try to maintain their footprint in the history of Israel and tell their story.

“He wanted to frighten them.”

Acting with impunity

Israel never confirms or denies claims that it has nuclear, chemical and biological weapons.

The country positions itself outside international treaties, which would make it subject to inspection.

Uzi Even

Uzi Even – Dimona should be shut down

For 40 years, most Israelis have been content with this policy – known as “nuclear ambiguity”.

But there are some in Israel who argue this policy has had its day.

They say the costs of such secrecy to Israeli democracy are too great.

Uzi Even, was a young scientist working, in the 60s, at Dimona – Israel’s nuclear reactor – as did Vanunu.

Today, Mr Even says it should be shut down.

Forty-year-old reactors tend to have accidents and he believes that Dimona, which is beyond the reach of the Israeli parliament, needs to be brought into a system of accountability and public scrutiny.

Mr Even explained: “You should have an outside watchdog.

“The secrecy more or less created an extra- territorial area in Israel where standard procedures of safety monitoring are not implemented.

“So worker safety, environmental questions and industrial safety procedures, are not covered, and there are thousands of people working there.”

Enforced silence

Nothing illustrates this better than the sensitive issue of Dimona’s cancer victims.

In an Israeli documentary in 2002, Dimona workers said accidents had been routine.

They spoke of explosions, fires and liquid and toxic gas leaks that they had to clean, often without protection. URL: Caption: Accidents were ‘routine’ at Dimona

The authorities denied they had worked with radioactive materials.

They have refused to compensate them or their families for their years of loyal service.

Because of the strict secrecy rules they were even unable to fight for their rights.

When Correspondent approached one of the workers, who was dying of cancer, he refused to be interviewed – but with some regret.

Unaware he was being filmed, he said: “I wanted to talk to you but I have been silenced.

“They came from intelligence and told me not to talk.

“They said I would be like Vanunu.”

Vanunu has another year in jail.

When his sentence is finished he hopes to emigrate to America.

But Mr Horev has clearly let it be known he never intends to let Vanunu leave Israel. URL: Caption: Completed Dimona complex as seen by US Corona satellite on November 11, 1968

Caption: Mordechai Vanunu’s photograph of a Negev Nuclear Research Center glove box containing nuclear materials in a model bomb assembly, one of about 60 photographs he later gave to the British press. URL:

The Third Temple’s Holy Of Holies: Israel’s Nuclear Weapons

by Warner D. Farr, LTC, U.S. Army September 1999


This paper is a history of the Israeli nuclear weapons program drawn from a review of unclassified sources. Israel began its search for nuclear weapons at the inception of the state in 1948. As payment for Israeli participation in the Suez Crisis of 1956, France provided nuclear expertise and constructed a reactor complex for Israel at Dimona capable of large-scale plutonium production and reprocessing. The United States discovered the facility by 1958 and it was a subject of continual discussions between American presidents and Israeli prime ministers. Israel used delay and deception to at first keep the United States at bay, and later used the nuclear option as a bargaining chip for a consistent American conventional arms supply. After French disengagement in the early 1960s, Israel progressed on its own, including through several covert operations, to project completion. Before the 1967 Six-Day War, they felt their nuclear facility threatened and reportedly assembled several nuclear devices. By the 1973 Yom Kippur War Israel had a number of sophisticated nuclear bombs, deployed them, and considered using them. The Arabs may have limited their war aims because of their knowledge of the Israeli nuclear weapons. Israel has most probably conducted several nuclear bomb tests. They have continued to modernize and vertically proliferate and are now one of the world’s larger nuclear powers. Using “bomb in the basement” nuclear opacity, Israel has been able to use its arsenal as a deterrent to the Arab world while not technically violating American nonproliferation requirements.

Mini-nukes and micro-nukes

According to brave activist, Howard Morland, in his article The Holocaust Bomb: a Question of Time, second generation atomic bombs got their start in 1950 and came to fruition in 1956 with Eisenhower’s announcement of a 95% clean bomb. In 1958 the Mk-41C was tested for a 9.3 Megaton yield, 4.8% of the energy was from fission with 95.2% from fusion. Less radioactive (more fusion and less fission energy) or semi-clean H-bombs were known then and were used for testing purposes only. The more powerful, mostly fission bombs were deployed for usage in a cognitive effort to produce maximum destruction on ‘enemies’ for generations and no forethought of the worldwide consequences. Among various other types of hydrogen bomb warheads, the W54 nuke was developed in 1961. The W54 was a micro-nuke that weighed 51 pounds and could be fired from a slightly modified ordinary bazooka. Different versions of the W54 ranged from .01 kt to 1 kt yield. Between the mid 1950’s and the mid 70’s both types (large yield dirty and small yield clean), of 2nd generation H-bombs were refined.

Focused nuclear explosions were envisioned in 1959 as a possible concept for propulsion of the spacecraft Orion. The mere directing of the yield was obviously known prior to 1959. Samuel Cohen has stated that a low yield neutron bomb may be tailored to direct yield and proposed the concept more than 35 years ago. An underground detonation causes shaping of the direction of yield as well.


Nine nuclear and chemical weapons sites in Israel––according to this Hezbollah video

VIDEO: Nine Israeli Nuclear And Chemical Sites مواقع المفاعلات النووية الإسرائيلية  ArchiveOrg


Medium Atomic Demolition Munitions (MADM)

Caption: scientists displaying the warhead (left) and packing container for the Medium Atomic Demolition Munition (MADM), a low-yield (1- to 15-kiloton) nuclear land mine designed to be deployed behind enemy lines and destroy tunnels, bridges, dams, and disrupt enemy troop movements. The entire unit (including warhead) weighed less than 400 pounds and was deployed from 1965 to 1986.

Another view of the MADM, showing (from left) the packing container, warhead, code-decoder unit, and firing unit.

The carrying case for the W54 Special Atomic Demolition Munition (SADM). The SADM had a yield of 0.01, or 0.02-1 kiloton and was operationally deployed between 1964 and 1988. The entire unit weighed less than 163 pounds (74 kilograms).

Images: Credit: Department of Defense (courtesy Natural Resources Defense Council) (Brookings)

BBC documentary on Vanunu – Israel’s Terror WMD Facilities

Youtube: “Vanunu told the world that Israel had developed between one hundred to two hundred atomic bombs, and had gone on to develop neutron bombs and thermonuclear weapons – enough to destroy the entire Middle East, and nobody has done anything about it since.”

“Today proliferation experts report Israel has the sixth largest nuclear arsenal with small tactical nuclear weapons, nuclear land mines as well as medium range nuclear missiles launchable from air land and sea …”

Israel and the Schiphol plane crash

Dirty and clean weapons

“Dirty” and “Clean” Weapons

Whether to make a fission-fusion weapon into a fission-fusion-fission weapon is one of the most basic design issues. A fission-fusion weapon uses an inert (or non-fissionable) tamper and will obtain most of its yield from the fusion reaction directly. A fission-fusion-fission weapon will obtain at least half of its yield (and often far more) from the fusion neutron induced fission of a fissionable tamper.

The basic advantage of a fission-fusion-fission weapon is that energy is extracted from a tamper which is otherwise deadweight as far as energy production in concerned. The tamper has to be there, so a lighter weapon for a given yield (or a more powerful weapon for the same weight) can be obtained without varying any other design factors. Since it is possible to do this at virtually no added cost or other penalty, compared to an inert material like lead, by using natural or depleted uranium or thorium there is basically no reason not to do it if the designer is simply interested in making big explosions.

Fission of course produces radioactive debris – fallout. Fallout can be reduced by using a material that does not become highly radioactive when bombarded by neutrons (like lead or tungsten). This requires a heavier and more expensive weapon to produce a given yield, but is also considerably reduces the short and long term contamination associated with that yield.

This is not to say that the weapon is “clean” in any commonsense meaning of the term. Neutrons escaping the weapon can still produce biohazardous carbon-14 through nitrogen capture in the air. The primary and spark plug may still contribute 10-20% fission, which for a multi-megaton weapon may still be a megaton or more of fission. Significant contamination may also occur from the “inert” tamper radioisotopes, and even from the unburned tritium produced in the fusion stage. Reducing these contributions to the lowest possible level is the realm of “minimum residual radiation” designs discussed further below.

During the fifties interest in both the US and USSR was given to developing basic design that had both clean and dirty variants. The basic design tried to minimize the essential fission yield by using a small fission primary, and spark plug sizes carefully chosen to meet ignition requirements for each stage, without being excessive (note that although only part of the spark plug will fission to ignite the fusion stage, the essentially complete fission of the remainder by fusion neutrons is inevitable). These weapons appear to have all been three-stage weapons to allow multi-megaton yields (even in the clean version) with a relatively small primary. The dirty version might simply replace the inert tamper of the tertiary with a fissionable one to boost yield.

The three-stage Bassoon and Bassoon Prime devices tested in Redwing Zuni (27 May 1956, 3.5 Mt, 15% fission) and Redwing Tewa (20 July 1956, 5 Mt, 87% fission) are US tests of this concept. Clearly though, the second test was not simply a copy of the first with a different tamper. The fusion yield dropped from 3 Mt to 0.65 Mt, and the device weight increased from 5500 kg to 7149 kg between the two tests. The inference can be made that the tertiary in the first used a large volume of relatively expensive (but light) Li-6D in a thin tamper, which was replaced by a heavier, cheaper tertiary using less fusion fuel, but a very thick fissionable tamper to capture as many neutrons as possible.

The 50 Mt three stage Tsar Bomba (King of Bombs) tested by the Soviet Union on 30 October 1961 was the largest and cleanest bomb ever tested, with 97% of its yield coming from fusion (fission yield approximately 1.5 Mt). Assuming a primary of 250 kt (to keep the fissile content relatively low for safety reasons), we might postulate secondary and tertiary stages of 3.5 Mt and 46 Mt respectively. This fusion stages would require 1700 kg of Li6D (at 50% fusion efficiency), and something like 250 kt of fission for reliable ignition. If the initial spark plug firings were 25% efficient, later fission would release another 750 kt – placing the total at 1.25 Mt (close enough to the claimed parameters to match within the limits of accuracy).

This was a design though for a 100-150 Mt weapon! A lead tamper was used in the tested device, which could have been replaced with U-238 for the dirty version (thankfully never tested!).

Minimum Residual Radiation (MRR or “Clean”) Designs

It has been pointed out elsewhere in this FAQ that ordinary fission-fusion- fission bombs (nominally 50% fission yield) are so dirty that they merit consideration as radiological weapons. Simply using a non-fissile tamper to reduce the fission yield to 5% or so helps considerably, but certainly does not result in an especially clean weapon by itself. If minimization of fallout and other sources of residual radiation is desired then considerably more effort needs to be put into design.

Minimum residual radiation designs are especially important for “peaceful nuclear explosions” (PNEs). If a nuclear explosive is to be useful for any civilian purpose, all sources of residual radiation must be reduced to the absolute lowest levels technologically possible. This means elimination of neutron activation of bomb components, of materials outside the bomb, and reducing the fissile content to the smallest possible level. It may also be desirable to minimize the use of relatively hazardous materials like plutonium.

The problems of minimizing fissile yield and eliminating neutron activation are the most important. Clearly any MRR, even a small one, must be primarily a fusion device. The “clean” devices tested in the fifties and early sixties were primarily high yield strategic three-stage systems. For most uses (even military ones) these weapons are not suitable. Developing smaller yields with a low fissile content requires considerable design sophistication – small light primaries so that the low yields still produce useful radiation fluxes and high-burnup secondary designs to give a good fusion output.

Minimizing neutron activation form the abundant fusion neutrons is a serious problem since many materials inside and outside the bomb can produce hazardous activation products. The best way of avoiding this is too prevent the neutrons from getting far from the secondary. This requires using an efficient clean neutron absorber, i.e. boron-10. Ideally this should be incorporated directly into the fuel or as a lining of the fuel capsule to prevent activation of the tamper. Boron shielding of the bomb case, and the primary may be useful also.

It may be feasible to eliminate the fissile spark plug of a MRR secondary by using a centrally located deuterium-tritium spark plug similar to the way ICF capsules are ignited. Fusion bombs unavoidably produce tritium as a by- product, which can be a nuisance in PNEs.

Despite efforts to minimize radiation releases, PNEs have largely been discredited as a cost-saving civilian technology. Generally speaking, MRR devices still produce excessive radiation levels by civilian standards making their use impractical.

MRRs may have military utility as a tactical weapon, since residual contamination is slight. Such weapons are more costly and have lower performance of course.

This leads to another reason why PNEs have lost their attractiveness – there is no way to make a PNE device unsuitable for weapons use. “Peaceful” use of nuclear explosives inherently provides opportunity to develop weapons technology. As the saying goes, “the only difference between a PNE and a bomb is the tail fins”. – Nuclear Weapons Frequently Asked Questions Version 2.04: 20 February 1999 COPYRIGHT CAREY SUBLETTE

Low Yield Weapons

This represents one extreme of the weapon design spectrum – nuclear devices intend to make “small” explosions. Low yield in this context generally means yields much less than the 20 kts of a nominal fission weapon – say, 1-1000 tons. These are, of course, always very large compared to any other types of weapon of remotely similar size. They are small only in comparison to the potential capabilities of nuclear weapons.

The smallest nuclear weapons actually deployed have had yields around 10 tons (like the W54), and have been intended for short range tactical or nuclear demolition use (e.g. blowing up roads and bridges).

A low yield weapon can be made simply by taking an existing weapon and reducing its efficiency in some manner – like reducing the amount of explosive to create a weak implosion. But this likely result in a low-yield the weapon with unnecessarily high mass, volume, and cost.

A weapon designer will probably want to optimize a low yield weapon toward one of two design goals: minimizing its size or minimizing its cost (basically this means minimizing the fissile content of the device). Real weapons typically try to strike a balance between the two extremes.

Minimum Size

A low yield minimum mass or volume weapon would use an efficient fissile material (plutonium or U-233), a low mass implosion system (i.e. a relatively weak one), and a thin beryllium reflector (thickness no more than the core radius). Since volume increases with the cube of the radius, a thick layer of anything (explosive or reflector) surrounding the fissile core will add much more mass than that of the core itself.

Referring to the Reflector Savings Table we can see that for beryllium thicknesses of a few centimeters, the radius of a plutonium core is reduced by 40-60% of the reflector thickness. Since the density difference between these materials is on the order of 10:1, substantial mass savings can be achieved. At some point though increasing the thickness of the reflector begins to add more mass than it saves, this marks the point of minimum total mass for the reflector/core system.

In general, minimum mass and minimum volume designs closely resemble each other. The use of a hollow core adds negligibly to the overall volume.

At the low end of this yield range (tens of tons) simply inducing the delta -> alpha phase transition in a metastable plutonium alloy may provide sufficient reactivity insertion. In this case a classical implosion system is not even necessary, a variety of mechanisms could be used to produce the weak 10-20 kilobar shock required to collapse the crystal structure.

Since the fissile core would be lightly reflected, and weakly compressed, a relatively large amount of fissile material is required: perhaps 10 kg for even a very low yield bomb. The efficiency is of course extremely poor, and the cost relatively high.

The absolute minimum possible mass for a bomb is determined by the smallest critical mass that will produce a significant yield. Since the critical mass for alpha-phase plutonium is 10.5 kg, and an additional 20-25% of mass is needed to make a significant explosion, this implies 13 kg or so. A thin beryllium reflector will reduce this, but the necessary high explosive and packaging will add mass, so the true absolute minimum probably lies in the range of 10-15 kg.

The W54 warhead used in the Davy Crockett had a minimum mass of about 23 kg, and had yields ranging from 10 tons up to 1 kt in various mods (probably achieved by varying the fissile content). The warhead was basically egg-shaped with the minor axis of 27.3 cm and a major axis of 40 cm. The W-54 probably represents a near minimum diameter for a spherical implosion device (the U.S. has conducted tests of a 25.4 cm implosion system however).

The test devices for this design fired in Hardtack Phase II (shots Hamilton and Humboldt on 15 October and 29 October 1958) weighed only 16 kg, impressively close to the minimum mass estimated above. These devices were 28 cm by 30 cm, Humboldt used PBX-9404 as the explosive. – Nuclear Weapons Frequently Asked Questions Version 2.04: 20 February 1999 COPYRIGHT CAREY SUBLETTE

Davy Crockett weapon – From Wikipedia: Davy Crockett


Caption: The Davy Crockett (shown here at the Aberdeen Proving Ground in Maryland in March 1961) was the smallest and lightest nuclear weapon ever deployed by the U.S. military. It was designed for use in Europe against Soviet troop formations.

The M-28 or M-29 Davy Crockett Weapon System(s) was a tactical nuclear recoilless gun for firing the M388 nuclear projectile that was deployed by the United States during the Cold War. Named after American soldier, congressman and folk hero Davy Crockett, it was one of the smallest nuclear weapon systems ever built. [..]

Img: URL: Caption: A Davy Crockett casing preserved in the United States Army Ordnance Museum

The M-388 round used a version of the W54 warhead, a very small sub-kiloton fission device. The Mk-54 weighed about 51 lb (23 kg), with a selectable yield equivalent to 10 or 20 tons of TNT (very close to the minimum practical size and yield for a fission warhead). The complete round weighed 76 lb (34.5 kg). It was 31 in. (78.7 cm) long with a diameter of 11 in. (28 cm) at its widest point; a subcaliber piston at the back of the shell was inserted into the launcher’s barrel for firing

The World’s Smallest Nuke

VIDEO: The World’s Smallest Nuke  Dailymotion

W54 – From Wikipedia: W54

The W54 was the smallest nuclear warhead deployed by the United States. It was a very compact implosion-type nuclear weapon design, designed for tactical use and had a very low yield for a nuclear weapon. [..]

Img: URL: Caption:The W54 nuclear warhead was used in the man-portable M-388 Davy Crockett projectile. The unusually small size of the warhead is apparent

There were four distinct models of the basic W54 design used, each with different yield, but the same basic design. These were:

  • Mk-54 (Davy Crockett) — 10 or 20 ton yield, Davy Crockett artillery warhead
  • Mk-54 (SADM) — variable yield 10 ton to 1 kiloton, Special Atomic Demolition Munition device
  • W-54 — 250 ton yield, warhead for AIM-26 Falcon air to air missile
  • W72 — 600 ton yield, rebuilt W-54 (Falcon warhead) for AGM-62 Walleye

All four variants share the same basic core: a nuclear system which is 10.75 inches diameter (270 mm), about 15.7 inches long (400 mm), and weighs around or slightly over 50 pounds (23 kg). [..]

Though small compared to most other nuclear weapons, whose yields are usually measured in the thousands of tons of TNT (kilotons), in human terms they are still extremely large. By comparison, the smallest yield version of the W54 (10 tons) is two to four times as powerful as the 1995 Oklahoma City bombing, making the 250 ton version 50 to 100 times as powerful. [..]

The W54 style warhead was known to be used on the M-388 Davy Crockett, a tactical nuclear recoilless rifle projectile that was deployed by the United States during the Cold War.

The W54 is small enough to be deployed as a SADM (Special Atomic Demolition Munition) or so called “Backpack Nuke”. It was the closest thing the U.S. is known to have to developed to a so-called “suitcase bomb”.

Img: URL: Caption: The W54 would have fit into the Special Atomic Demolition Munition (“Backpack Nuke”) casing

The W54 was tested for use in a U.S. Navy SEALs project that was demonstrated as feasible in the mid-to-late 1960s, designed to attack a harbor or other strategic location that could be accessed from the sea. The SEALs version would be delivered into water by parachute along with a two man team, then floated to the target, set in place and armed by hand.

Thermonuclear devices – Wikipedia Nuclear Weapon Design

Two-stage thermonuclear weapons are essentially a chain of fission-boosted fusion weapons [..] usually with only two stages in the chain. The second stage, called the “secondary,” is imploded by x-ray energy from the first stage, called the “primary.” This radiation implosion is much more effective than the high-explosive implosion of the primary. Consequently, the secondary can be many times more powerful than the primary, without being bigger. The secondary can be designed to maximize fusion energy release, but in most designs fusion is employed only to drive or enhance fission, as it is in the primary. More stages could be added, but the result would be a multi-megaton weapon too powerful to serve any plausible purpose. [..]

The term thermonuclear refers to the high temperatures required to initiate fusion. It ignores the equally important factor of pressure, which was considered secret at the time the term became current. [..]

Pure fission or fusion-boosted fission weapons can be made to yield hundreds of kilotons, at great expense in fissile material and tritium, but by far the most efficient way to increase nuclear weapon yield beyond ten or so kilotons is to tack on a second independent stage, called a secondary.

In the 1940s, bomb designers at Los Alamos thought the secondary would be a canister of deuterium in liquified or hydride form. [..] Mathematical simulations showed it wouldn’t work, even with large amounts of prohibitively expensive tritium added in.

The entire fusion fuel canister would need to be enveloped by fission energy, to both compress and heat it, as with the booster charge in a boosted primary. The design breakthrough came in January 1951, when Edward Teller and Stanisław Ulam invented radiation implosion. [..]

In radiation implosion, the burst of X-ray energy coming from an exploding primary is captured and contained within an opaque-walled radiation channel which surrounds the nuclear energy components of the secondary. The radiation quickly turns the plastic foam that had been filling the channel into a plasma which is mostly transparent to X-rays, and the radiation is absorbed in the outermost layers of the pusher/tamper surrounding the secondary, which ablates and applies a massive force [..] causing the fusion fuel capsule to implode much like the pit of the primary. As the secondary implodes a fissile “spark plug” at its center ignites and provides heat which enables the fusion fuel to ignite as well. The fission and fusion chain reactions exchange neutrons with each other and boost the efficiency of both reactions. The greater implosive force, enhanced efficiency of the fissile “spark plug” due to boosting via fusion neutrons, and the fusion explosion itself provides significantly greater explosive yield from the secondary despite often not being much larger than the primary.

Clean bombs – From Wikipedia: Nuclear Weapon Design

[..] In response to the public alarm over fallout, an effort was made to design a clean multi-megaton weapon, relying almost entirely on fusion. Since the energy produced by fission is essentially free, using the vital tamper as a source of extra energy, the clean bomb needed to be much larger for the same yield. For the only time, a third stage, called the tertiary, was added, using the secondary as its primary. The device was called Bassoon. It was tested as the Zuni shot of Operation Redwing, at Bikini on May 28, 1956. With all the uranium in Bassoon replaced with a substitute material such as lead, its yield was 3.5 megatons, 85% fusion and only 15% fission. The records for devices that produced the highest proportion of their yield via fusion only reactions, known in the public domain are, the Redwing Navajo test at 95% Fusion, The Hardtack Poplar test at 95.2% & the 97% Tsar bomba.

Tsar Bomba – from Wikipedia: Tsar Bomba

Tsar Bomba (Russian: Царь-бомба) is the nickname for the AN602 hydrogen bomb, the most powerful nuclear weapon ever detonated. Also known as Kuz`kina Mat` (Russian: Кузькина мать, Kuzma’s mother).

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Developed by the Soviet Union, the bomb was originally designed to have a yield of about 100 megatons of TNT (420 PJ); however, the bomb yield was reduced to 50 megatons—one quarter of the estimated yield of the 1883 eruption of Krakatoa—in order to reduce nuclear fallout. This attempt was successful, as it was one of the cleanest (relative to its yield) atomic bombs ever detonated. Only one bomb of this type was ever built and it was tested on October 30, 1961, in the Novaya Zemlya archipelago. [..]

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The tsar was a three-stage Teller–Ulam design hydrogen bomb with a yield of 50 megatons (Mt). This is equivalent to 1,400 times the combined power of the two nuclear explosives used in World War II (Little Boy (13–18 kilotons) and Fat Man (21 kilotons), the bombs that destroyed Hiroshima and Nagasaki), or 10 times the combined power of all the explosives used in WWII. A three-stage H-bomb uses a fission bomb primary to compress a thermonuclear secondary, as in most H-bombs, and then uses energy from the resulting explosion to compress a much larger additional thermonuclear stage. However, there is evidence that the Tsar Bomba had a number of third stages rather than a single very large one.

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The initial three-stage design was capable of approximately 100 Mt, but would have caused too much radioactive fallout. To limit fallout, the third stage and possibly the second stage had a lead tamper instead of a uranium-238 fusion tamper (which greatly amplifies the reaction by fissioning uranium atoms with fast neutrons from fusion reaction). This eliminated fast fission by the fusion-stage neutrons, so that approximately 97% of the total energy resulted from fusion alone (as such, it was one of the “cleanest” nuclear bombs ever created, generating a very low amount of fallout relative to its yield). There was a strong incentive for this modification since most of the fallout from a test of the bomb would fall on populated Soviet territory.

Img: URL: URL: Caption: The Tsar Bomba mushroom cloud

Tsar Bomb – The King of the bombs URL: Caption: Tsar Bomba – King of the Bombs. On October 23, 1961, Soviet pilot A. E. Durnovtsev guides his Tu-95 Bomber towards the Arctic Sea above Novaya Zemlya Island. This day will make atomic history, not as an advancement in nuclear science, but rather as a statement of intimidation by the Soviet Union to the United States in those tense days now known as The Cold War.

The bomber is carrying a secret cargo that will soon make the world take notice of Russia as a serious nuclear threat to the survial of mankind. For on this day a nuclear weapon rides into history as the largest thermonuclear bomb ever constructed and detonated named, “Tsar Bomba…King of the Bombs.”

Teller-Ulam design – from Wikipedia: Teller-Ulam design

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The Teller–Ulam design is the nuclear weapon design concept used in most of the world’s nuclear weapons. [..] It is named for its two chief contributors, Edward Teller and Stanisław Ulam, who developed it in 1951 for the United States. It was first used in multi-megaton-range thermonuclear weapons. As it is also the most efficient design concept for small nuclear weapons, today virtually all the nuclear weapons deployed by the five major nuclear-armed nations use the Teller–Ulam design.

Its essential features, which officially remained secret for nearly three decades, are: 1) separation of stages into a triggering “primary” explosive and a much more powerful “secondary” explosive, 2) compression of the secondary by X-rays coming from nuclear fission in the primary, a process called the “radiation implosion” of the secondary, and 3) heating of the secondary, after cold compression, by a second fission explosion inside the secondary.

The radiation implosion mechanism is a heat engine exploiting the temperature difference between the hot radiation channel, surrounding the secondary, and the relatively cool interior of the secondary. This temperature difference is briefly maintained by a massive heat barrier called the “pusher”. The pusher is also an implosion tamper, increasing and prolonging the compression of the secondary, and, if made of uranium, which it usually is, it undergoes fission by capturing the neutrons produced by fusion. In most Teller–Ulam weapons, fission of the pusher dominates the explosion and produces radioactive fission product fallout. [..] URL:

The basic principle of the Teller–Ulam configuration is the idea that different parts of a thermonuclear weapon can be chained together in “stages”, with the detonation of each stage providing the energy to ignite the next stage. At a bare minimum, this implies a primary section which consists of a fission bomb (a “trigger”), and a secondary section which consists of fusion fuel. Because of the staged design, it is thought that a tertiary section, again of fusion fuel, could be added as well, based on the same principle of the secondary. The energy released by the primary compresses the secondary through the concept of “radiation implosion”, at which point it is heated and undergoes nuclear fusion. [..]



A simplified summary of the above explanation would be:

1. An implosion assembly type of fission bomb is exploded. This is the primary stage. If a small amount of deuterium/tritium gas is placed inside the primary’s core, it will be compressed during the explosion and a nuclear fusion reaction will occur; the released neutrons from this fusion reaction will induce further fission in the plutonium-239 or uranium-235 used in the primary stage. The use of fusion fuel to enhance the efficiency of a fission reaction is called boosting. Without boosting, a large portion of the fissile material will remain unreacted; the Little Boy and Fat Man bombs had an efficiency of only 1.4% and 14%, respectively, because they were unboosted.

2. Energy released in the primary stage is transferred to the secondary (or fusion) stage. The exact mechanism whereby this happens is unknown. This energy compresses the fusion fuel and sparkplug; the compressed sparkplug becomes critical and undergoes a fission chain reaction, further heating the compressed fusion fuel to a high enough temperature to induce fusion, and also supplying neutrons that react with lithium to create tritium for fusion. Generally, increasing the kinetic energy of gas molecules contained in a limited volume will increase both temperature and pressure (see gas laws).

3. The fusion fuel of the secondary stage may be surrounded by depleted uranium or natural uranium, whose U-238 is not fissile and cannot sustain a chain reaction, but which is fissionable when bombarded by the high-energy neutrons released by fusion in the secondary stage.

Actual designs of thermonuclear weapons may vary. For example, they may or may not use a boosted primary stage, use different types of fusion fuel, and may surround the fusion fuel with beryllium (or another neutron reflecting material) instead of depleted uranium to prevent further fission from occurring. [..]

Fusion, unlike fission, is relatively “clean”—it releases energy but no harmful radioactive products or large amounts of nuclear fallout. The fission reactions though, especially the last fission reaction, release a tremendous amount of fission products and fallout. If the last fission stage is omitted, by replacing the uranium tamper with one made of lead, for example, the overall explosive force is reduced by approximately half but the amount of fallout is relatively low. [..]

Tamper-pusher ablation

The tamper-pusher ablation proposed mechanism is that the primary compression mechanism for the thermonuclear secondary is that the outer layers of the tamper-pusher, or heavy metal casing around the thermonuclear fuel, are heated so much by the X-ray flux from the primary that they ablate away, exploding outwards at such high speed that the rest of the tamper recoils inwards at a tremendous velocity, crushing the fusion fuel and the spark plug. uRL:

Nuclear reactions

Nuclear fission splits heavier atoms to form lighter atoms. Nuclear fusion bonds together lighter atoms to form heavier atoms. Both reactions generate roughly a million times more energy than comparable chemical reactions, making nuclear bombs a million times more powerful than non-nuclear bombs. [..]


When a free neutron hits the nucleus of a fissionable atom like uranium-235 ( 235U), the uranium splits into two smaller atoms called fission fragments, plus more neutrons. Fission can be self-sustaining because it produces more neutrons of the speed required to cause new fissions.

The uranium atom can split any one of dozens of different ways, as long as the atomic weights add up to 236 (uranium plus the extra neutron). The following equation shows one possible split, namely into strontium-95 ( 95Sr), xenon-139 (139Xe), and two neutrons (n), plus energy:

235U + n = 95Sr + 139Xe + 2n + 180MeV

The immediate energy release per atom is 180 million electron volts (MeV), i.e. 74 TJ/kg, of which 90% is kinetic energy (or motion) of the fission fragments, flying away from each other mutually repelled by the positive charge of their protons (38 for strontium, 54 for xenon). Thus their initial kinetic energy is 67 TJ/kg, hence their initial speed is 12,000 kilometers per second, but their high electric charge causes many inelastic collisions with nearby nuclei. The fragments remain trapped inside the bomb’s uranium pit until their motion is converted into x-ray heat, a process which takes about a millionth of a second (a microsecond).

This x-ray energy produces the blast and fire which are normally the purpose of a nuclear explosion.

After the fission products slow down, they remain radioactive. Being new elements with too many neutrons, they eventually become stable by means of beta decay, converting neutrons into protons by throwing off electrons and gamma rays. Each fission product nucleus decays between one and six times, average three times, producing a variety of isotopes of different elements, some stable, some highly radioactive, and others radioactive with half-lives up to 200,000 years. In reactors, the radioactive products are the nuclear waste in spent fuel. In bombs, they become radioactive fallout, both local and global.

Meanwhile, inside the exploding bomb, the free neutrons released by fission strike nearby U-235 nuclei causing them to fission in an exponentially growing chain reaction (1, 2, 4, 8, 16, etc.). Starting from one, the number of fissions can theoretically double a hundred times in a microsecond, which could consume all uranium up to hundreds of tons by the hundredth link in the chain. In practice, bombs do not contain that much uranium, and, anyway, just a few kilograms undergo fission before the uranium blows itself apart. [..]

Materials which can sustain a chain reaction are called fissile. The two fissile materials used in nuclear weapons are: U-235, also known as highly enriched uranium (HEU), oralloy (Oy) meaning Oak Ridge Alloy, or 25 (the last digits of the atomic number, which is 92 for uranium, and the atomic weight, here 235, respectively); and Pu-239, also known as plutonium, or 49 (from 94 and 239). [..]
Fusion is unlikely to be self-sustaining because it does not produce the heat and pressure necessary for more fusion. It produces neutrons which run away with the energy. In weapons, the most important fusion reaction is called the D-T reaction. Using the heat and pressure of fission, hydrogen-2, or deuterium (


D), fuses with hydrogen-3, or tritium (3T), to form helium-4 (4He) plus one neutron (n) and energy:

2D + 3T = 4He + n + 17.6 MeV

Notice that the total energy output, 17.6 MeV, is one tenth of that with fission, but the ingredients are only one-fiftieth as massive, so the energy output per unit mass is greater. However, in this fusion reaction 80% of the energy, or 14 MeV, is in the motion of the neutron which, having no electric charge and being almost as massive as the hydrogen nuclei that created it, can escape the scene without leaving its energy behind to help sustain the reaction – or to generate x-rays for blast and fire.

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The only practical way to capture most of the fusion energy is to trap the neutrons inside a massive bottle of heavy material such as lead, uranium, or plutonium. If the 14 MeV neutron is captured by uranium (either type: 235 or 238) or plutonium, the result is fission and the release of 180 MeV of fission energy, multiplying the energy output tenfold.

Fission is thus necessary to start fusion, helps to sustain fusion, and captures and multiplies the energy released in fusion neutrons. [..]

Tritium production

A third important nuclear reaction is the one that creates tritium, essential to the type of fusion used in weapons and, incidentally, the most expensive ingredient in any nuclear weapon. Tritium, or hydrogen-3, is made by bombarding lithium-6 ( 6Li) with a neutron (n) to produce helium-4 ( 4He) plus tritium ( 3T) and energy:

6Li + n = 4He + 3T + 5 MeV

A nuclear reactor is necessary to provide the neutrons. The industrial-scale conversion of lithium-6 to tritium is very similar to the conversion of uranium-238 into plutonium-239. [..]

However, an exploding nuclear bomb is a nuclear reactor. The above reaction can take place simultaneously throughout the secondary of a two-stage thermonuclear weapon, producing tritium in place as the device explodes.

Of the three basic types of nuclear weapon, the first, pure fission, uses the first of the three nuclear reactions above. The second, fusion-boosted fission, uses the first two. The third, two-stage thermonuclear, uses all three.

Bunker busters URL: Caption: Photo courtesy Air Force GBU-28 Bunker Buster

Description: URL: Caption: Photo courtesy Air Force F-111 & GBU-28 “Bunker Buster”


Description: URL: Caption: The finished bomb, known as the GBU-28 or the BLU-113, is 19 feet (5.8 meters) long, 14.5 inches (36.8 cm) in diameter and weighs 4,400 pounds (1,996 kg).

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Photos courtesy U.S. Department of Defense
An F-117 Nighthawk engages its target and drops a bunker buster during a testing mission at Hill Air Force Base, Utah. URL: Caption:
Photos courtesy U.S. Department of Defense
An F-117 Nighthawk engages its target and drops a bunker buster during a testing mission at Hill Air Force Base, Utah. URL: Caption: Photo courtesy U.S. Department of Defense
An F-15E Strike Eagle pilot and a weapons system officer inspect a GBU-28 laser-guided bomb. URL: Caption: Photo courtesy U.S. Department of Defense
Air-to-air view of GBU-28 hard target bomb on an F-15E Eagle

IMG: URL: Caption: graphic source: 28nov04

MY COMMENT: These bombs were used to penetrate the World Trade Centers. They created the necessary entry holes for the planes. The bombs were attached to the underbelly of the planes and were fired just before the planes hit the towers. There were smart fuses to time their firing for exactly the right moment so that it would look like the planes crashed into the towers and made the entry holes. These bunker buster bombs were necessary because without them, it is highly likely that the planes would have either bounced off the perimeter walls of the towers or would have only partially penetrated the towers. Likewise, the Pentagon plane also carried this bunker buster bomb. This accounts for its very neat entry into the Pentagon.

The bunker buster bombs probably contained depleted uranium. This accounts for the white flash that came from the flames and sparks of melting metal seen in pictures. This is incorrectly attributed to thermite. Depleted uranium burns in a similar way to magnesium giving off an intense white flash.

In pictures taken of the World Trade Center planes, there is a bulging in the underbelly that looks like the outline of a missile.

Just before one of the planes hits the tower, there is a bright orange fireball at its nose-end just as it is about to make contact with the tower. This is the fireball of the bunker buster exploding as it hits the perimeter wall of the tower. The missile could be fired in a very precise manner because it was equipped with a smart fuse.

Hard Target Smart Fuse (HTSF)

The Hard Target Smart Fuze enables precision bombs with penetrating warheads to detonate at a desired point inside buried or reinforced concrete targets such as underground bunkers and command centers. Detonation occurs after a sensor tells the fuse that the weapon has passed through a pre-programmed number of hard layers or voids in the target.

One of the newest weapons in the Air Force’s arsenal of hard target penetrating bombs is the AFRL Munitions Directorate-developed Advanced Unitary Penetrator (AUP), equipped with the Hard Target Smart Fuze. [..] The HTSF, designated the FMU-157/B, is an active decision-making accelerometer-based fuzing system capable of counting layers and voids (floors), as well as calculating distance traveled. When the weapon reaches the pre-determined floor it tells the bomb to explode. The HTSF is compatible with a variety of penetrating warheads.

The Hard-Target Smart Fuze [HTSF], developed at the Wright lab, is a microcontroller-based, in line fuze designed to be physically and electrically compatible with GBU-10, GBU-15, GBU-24, GBU-27, GBU-28, AGM-130, and general purpose MK-80 series weapons. The HTSF was designed for current and future penetrator weapons to define the fuze function point as either a desired distance within a desired void or a depth of burial beneath a hard layer. It operates in one of three modes: hard-layer detection, void detection, and path-length integration. It also has an adjustable backup time delay that is set in 1-msec increments with a maximum delay of 250 msec. The HTSF uses a void sensing technique to count layers within a structure to initiate fuze function, a depth of burial mode that causes the fuze to function a preset distance after it senses a hard layer, and an integral time delay backup.

Mark 83 – strategic nuclear bomb designed to be carried by aircraft


TIFF from: Img: Caption:


  • Yield: Low Kt to 1.2 Kt
  • Fusing: Retarded Airburst, and Contact Laydown.
  • Number Produced: 650
  • Weight: 2,400 lbs.
  • Dimensions: 18″ x 145″

The Mark 83 is the current high-yield strategic TN bomb. 650 were produced between June, 1983 and 1991. In 1997, all were in service.

The B61 (Mark-61) bomb URL: Caption: B61 about to be loaded

The B61, which exists in several mods, is actually a family of weapons based on a single basic weapon and physics package design. The physics package of the B61 has been adapted to yield several other warheads – the W-80, W-81 (now retired and dismantled), W-84 (now retired and in the inactive stockpile), and the W-85 (which was retired, and then readapted to yield another B61 variant). See W-80 page for pictures of the actual warhead.

Two stage radiation implosion weapon.

Light weight, intermediate yield bomb with variable yield options (“dial-a-yield” or DAY), and flexible fuzing and delivery options. Designed for high-speed external carriage and low altitude delivery. Modular weapon system design.

Contains two neutron generators (supplied by General Electric).

Spin stabilized by rocket. 24 ft. Nylon/Kevlar-29 ribbon parachute ejected by gas generator. Allows rapid deceleration from supersonic velocity (only 2 seconds required to decelerate to 35 mph). Tested at up to Mach 1.2.

The lowest yield option for the B61 (the same for all tactical mods) is 300 tons which probably represents the basic unboosted yield of the fission primary. URL:

The B61 has four major sections:

  • Nose Subassembly: contains a dual-channel radar airburst fuze and two piezoelectric crystal impact fuzes, and shock mitigating material for laydown delivery.
  • Center Warhead Subassembly: “hard case” containing the actual thermonuclear warhead, sealed and desiccated with polyurethane spacers to support warhead and provide shock isolation. Also contains thermal batteries, safeties, and firing circuits.
  • Rear Subassembly: Preflight arming controls, fuzing option switches, safe separation setting dials, and spin rockets for free fall weapon stabilization.
  • Tail Subassembly: consists of bomb fins, afterbody structure, parachute with associated deployment and release mechanisms. Complete parachute assembly weighs 115 lb. URL: Caption: B61 bomb in various stages of assembly. The nuclear component is the smaller silver cylinder behind the nose cone.

Primary consists of beryllium reflected plutonium (the derivative W80-0 contains supergrade plutonium)

  • Deuterium-tritium boosted
  • Primary also contains aluminum and uranium
  • Contains oralloy (highly enriched uranium), either in primary or as secondary tampe
  • Lithium-6 (95% enrichment) deuteride fusion fuel URL: Caption: Internal nuclear components of the B61 bomb.

The B61 (Mk-61) Bomb

Weight 695-716 lbs
Length (body) 10 ft 10.75 in (130.75 in)
Length (incl. fins) 11 ft 9.5 in (141.5 in)
Body Diameter 13.4 in
Tail Fin Span 22.5 in
Number In Service 600 (tactical), 750 (strategic)
Available Yields (Kt) 0.3 / 1.5 / 60 / 170
Type Tactical
Available Yields (Kt) 0.3 / 1.5 / 10 / 45
Type Tactical
Available Yields (Kt) 10 / ? / 340
Type Strategic
Available Yields (Kt) 0.3 / 5 / 10 / 80
Type Tactical
Available Yields (Kt) 0.3? / ? / 340
Type Tactical/Strategic

Flash of ordnance

IMG1: IMG2: URL: Caption: The small-diameter bomb is a 250-pound class munition, providing the warfighter with a four-fold increase in weapons per aircraft station. It can penetrate more than 13 feet into a target and can be accurate from up to 70 miles away.

My comment: Look at the ordnance flash. Colors seen in this flash are white, yellow and orange. These colors reflect the high temperatures of the fireballs. The materials that burn in an explosion have high temperatures at which they vaporize. The white color is the highest temperature, next yellow, then orange and lastly red. [Include temperature chart of burning materials or steel] This flash looks like the one seen when the planes crashed into the Twin Towers and the Pentagon. On these occasions, the flashes were seen just as the planes hit or were about to hit the buildings.

Fission Weapons

Fission Weapons – from Federation of American Scientists

An ordinary “atomic” bomb of the kinds used in World War II uses the process of nuclear fission to release the binding energy in certain nuclei. The energy release is rapid and, because of the large amounts of energy locked in nuclei, violent. The principal materials used for fission weapons are U-235 and Pu-239, which are termed fissile because they can be split into two roughly equal-mass fragments when struck by a neutron of even low energies. When a large enough mass of either material is assembled, a self-sustaining chain reaction results after the first fission is produced.

The minimum mass of fissile material that can sustain a nuclear chain reaction is called a critical mass and depends on the density, shape, and type of fissile material, as well as the effectiveness of any surrounding material (called a reflector or tamper) at reflecting neutrons back into the fissioning mass. Critical masses in spherical geometry for weapon-grade materials are as follows:

Uranium-235 Plutonium-239
Bare sphere: 56 kg 11 kg
Thick Tamper: 15 kg 5 kg

The critical mass of compressed fissile material decreases as the inverse square of the density achieved. Since critical mass decreases rapidly as density increases, the implosion technique can make do with substantially less nuclear material than the gun-assembly method. The “Fat Man” atomic bomb that destroyed Nagasaki in 1945 used 6.2 kilograms of plutonium and produced an explosive yield of 21-23 kilotons [a 1987 reassessment of the Japanese bombings placed the yield at 21 Kt]. Until January 1994, the Department of Energy (DOE) estimated that 8 kilograms would typically be needed to make a small nuclear weapon. Subsequently, however, DOE reduced the estimate of the amount of plutonium needed to 4 kilograms. Some US scientists believe that 1 kilogram of plutonium will suffice.

If any more material is added to a critical mass a condition of supercriticality results. The chain reaction in a supercritical mass increases rapidly in intensity until the heat generated by the nuclear reactions causes the mass to expand so greatly that the assembly is no longer critical.

Fission weapons require a system to assemble a supercritical mass from a sub-critical mass in a very short time. Two classic assembly systems have been used, gun and implosion. In the simpler gun-type device, two subcritical masses are brought together by using a mechanism similar to an artillery gun to shoot one mass (the projectile) at the other mass (the target). The Hiroshima weapon was gun-assembled and used 235 U as a fuel. Gun-assembled weapons using highly enriched uranium are considered the easiest of all nuclear devices to construct and the most foolproof.

Implosion-Device – from Federation of American Scientists

Because of the short time interval between spontaneous neutron emissions (and, therefore, the large number of background neutrons) found in plutonium because of the decay by spontaneous fission of the isotope Pu-240, Manhattan Project scientists devised the implosion method of assembly in which high explosives are arranged to form an imploding shock wave which compresses the fissile material to supercriticality.

The core of fissile material that is formed into a super-critical mass by chemical high explosives (HE) or propellants. When the high explosive is detonated, an inwardly directed implosion wave is produced. This wave compresses the sphere of fissionable material. The decrease in surface to volume ratio of this compressed mass plus its increased density is then such as to make the mass supercritical. The HE is exploded by detonators timed electronically by a fuzing system, which may use altitude sensors or other means of control.

The nuclear chain-reaction is normally started by an initiator that injects a burst of neutrons into the fissile core at an appropriate moment. The timing of the initiation of the chain reaction is important and must be carefully designed for the weapon to have a predictable yield. A neutron generator emits a burst of neutrons to initiate the chain reaction at the proper moment —- near the point of maximum compression in an implosion design or of full assembly in the gun-barrel design.

A surrounding tamper may help keep the nuclear material assembled for a longer time before it blows itself apart, thus increasing the yield. The tamper often doubles as a neutron reflector.

Implosion systems can be built using either Pu-239 or U-235 but the gun assembly only works for uranium. Implosion weapons are more difficult to build than gun weapons, but they are also more efficient, requiring less SNM and producing larger yields. Iraq attempted to build an implosion bomb using U-235. In contrast, North Korea chose to use 239 Pu produced in a nuclear reactor.

other mass (the target). The Hiroshima weapon was gun-assembled and used 235 U as a fuel. Gun-assembled weapons using highly enriched uranium are considered the easiest of all nuclear devices to construct and the most foolproof.

Fusion Weapons – From Federation of American Scientists

A more powerful but more complex weapon uses the fusion of heavy isotopes of hydrogen, deuterium, and tritium to release large numbers of neutrons when the fusile (sometimes termed “fusionable”) material is compressed by the energy released by a fission device called a primary. Fusion (or ‘‘thermonuclear’ weapons derive a significant amount of their total energy from fusion reactions. The intense temperatures and pressures generated by a fission explosion overcome the strong electrical repulsion that would otherwise keep the positively charged nuclei of the fusion fuel from reacting. The fusion part of the weapon is called a secondary.In general, the x-rays from a fission primary heat and compress material surrounding a secondary fusion stage.

It is inconvenient to carry deuterium and tritium as gases in a thermonuclear weapon, and certainly impractical to carry them as liquefied gases, which requires high pressures and cryogenic temperatures. Instead, one can make a “dry” device in which 6Li is combined with deuterium to form the compound 6Li D (lithium-6 deuteride). Neutrons from a fission “primary” device bombard the 6 Li in the compound, liberating tritium, which quickly fuses with the nearby deuterium. The a particles, being electrically charged and at high temperatures, contribute directly to forming the nuclear fireball. The neutrons can bombard additional 6Li nuclei or cause the remaining uranium and plutonium in the weapon to undergo fission. This two-stage thermonuclear weapon has explosive yields far greater than can be achieved with one point safe designs of pure fission weapons, and thermonuclear fusion stages can be ignited in sequence to deliver any desired yield. Such bombs, in theory, can be designed with arbitrarily large yields: the Soviet Union once tested a device with a yield of about 59 megatons.

In a relatively crude sense, 6 Li can be thought of as consisting of an alpha particle ( 4He) and a deuteron ( 2H) bound together. When bombarded by neutrons, 6 Li disintegrates into a triton ( 3 H) and an alpha:

6 Li + Neutron = 3 H + 3 He + Energy.

This is the key to its importance in nuclear weapons physics. The nuclear fusion reaction which ignites most readily is

2 H + 3 H = 4 He + n + 17.6 MeV,

or, phrased in other terms, deuterium plus tritium produces 4He plus a neutron plus 17.6 MeV of free energy:

D + T = 4 He + n + 17.6 MeV.

Lithium-7 also contributes to the production of tritium in a thermonuclear secondary, albeit at a lower rate than 6Li. The fusion reactions derived from tritium produced from 7 Li contributed many unexpected neutrons (and hence far more energy release than planned) to the final stage of the infamous 1953 Castle/BRAVO atmospheric test, nearly doubling its expected yield.

Underground Nuclear Weapons Testing – From FAS (illustrate with your own diagrams of WTC) – THESE ARE THE STEPS THE PERPS TOOK TO DEMOLISH THE WTC TWIN TOWERS)

The following description of a vertical drill-hole test breaks down the operation into seven individual steps:

Step1. Site Selection and Drilling.

There are two subsets of site selection as it applies to nuclear tests, namely: selection of an existing drill hole for a specific event, and selection of a new drill site from the Nuclear Test Zone for a specific event because the stockpile does not contain a suitable site. The goal of siting is to optimize the various parameters so that operational feasibility and successful containment of yields of interest to device designers can be attained at a suitably low cost.

Many factors are considered. Some of these are: (1) scheduling of field resources; (2) event schedules; (3) shock sensitivity of a given experiment and possible interactions with other experiments; (4) depth range required for a suitable device emplacement; (5) geologic structure; (6) geologic material properties; (7) depth of standing water; (8) potential drilling problems; (9) adjacent expended sites, craters, chimneys, subsurface collapses; (10) adjacent open emplacement holes or unplugged post-shot or exploratory holes; and (11) non-test program constraints such as groundwater concerns, roads, and power lines (Olsen, 1993).

When drilling is required after a test location is chosen by the sponsoring national laboratory, a drilling program outlining the requirements of the specific hole is completed. The event site is surveyed, staked, and checked for cultural and biological resources. When all environmental clearances are completed, the site is graded and leveled, and a drilling-fluid sump is constructed to contain drilling fluid and cuttings. A drill rig, usually with its own power and utilities, is moved onto the site. Water is brought in by truck, or piped in, and mixed with drilling compounds to fill the sump. The hole is then drilled using standard NTS big-hole drilling techniques. A normal hole is from 1 to 3 meters (m) (48 to 120 inches [in.]) diameter and from 213 to 762 meters (m) (600 to 2,500 feet [ft]) deep. During drilling, samples of drill cuttings are collected at 3-m (10-ft) intervals, and rock cores are taken as required. After drilling is complete,geophysical logs are run into the hole to evaluate the condition of the hole and gain a more thorough understanding of the geology. The drill site is then secured by filling the sump and installing specially designed covers over the hole.

Step 2. Event-Site Engineering and Construction.

When a hole is selected as a location for a nuclear test, the area around the hole is surveyed and staked according to the criteria set forth by the sponsoring national laboratory. The cultural and biological surveys are then rerun to determine if the status of the area has changed. The hole is also uncovered, and selected geophysical logs are refed in the hole to reconfirm its condition.

Once it is assured that the environmental clearances are complete, an area is cleared and leveled for the surface ground-zero equipment; another area close by the selected site is cleared and leveled for the recording trailer park. This is a typical earthmoving operation; native materials are used to top the pads or, if active material is unstable, decomposed granite fill is used. The on-site construction is temporary and is abandoned after the event is complete. Concrete pads are poured around the surface ground-zero to provide a stable platform for downhole operations and to provide a base for the assembly towers. Equipment is moved in to emplace the nuclear device in the hole, record the data produced, and provide radiological and seismic monitoring of the site. An extensive grounding system is used to establish baseline instrumentation grounds, which might include a pit containing salt water. The equipment to be left in position during the explosion is protected with an aluminum-foil hexcell-shaped shock-mounting material or dense foam. A circle of radiation detectors is placed back from the surface ground-zero to detect and assess any releases from the experiment. Finally, a perimeter fence is erected, and access is controlled both into and out of the event site.

Step 3. Device Delivery and Assembly.

For safety reasons, the nuclear device is delivered to the NTS unassembled. The device is assembled and inserted into a container at the Device Assembly Facility in Area 6 or in the Area 27 Assembly/Staging Facilities. The Device Assembly Facility is discussed at the end of this section. The device, now encased in the container, is delivered to the event site accompanied by armored convoy. It is then attached to the diagnostics canister in preparation for emplacement into the hole. Checks are run, and alignment is assured. Heavy security is maintained during all operations that involve the nuclear device.

Step 4. Diagnostic Assembly.

A diagnostic canister is assembled off site and transported to the test site. A typical diagnostic canister might be 2 m (8 ft) in diameter and 30 m (120 ft) long and contain all the instrumentation required to receive data at the time of the explosion (real time). The diagnostic canister might contain lead and other materials as shielding for the detectors. Upon arrival at the event site, the diagnostic canister is installed in the assembly tower to be mated with the device on site. Instrumentation cables are connected to the experiments and the recording trailer park. Slack in the cables allows the diagnostic canister to be lowered into the hole.

Step 5. Emplacement of the Experiment.

The nuclear explosive and special measurement devices are moved to the hole and lowered to the detonation position; all required diagnostic materials and instrumentation cables are also lowered into the hole at this time. Downhole operations are conducted according to a defined checklist and are monitored by independent inspectors. The whole assembly is placed on a set of fracture-safe beams that span the opening. Any auxiliary equipment is then lowered into the hole, and the area is secured. Emplacement equipment is removed from the area, and test runs are conducted on the downhole experiment.

The hole is stemmed to prevent radioactive materials from escaping during or after the experiment. Stemming materials used to backfill the hole are generally placed in alternating layers, according to the containment specification. Alternate layers of 1-centimeter (cm) (3/8–in.) pea gravel are combined with fine material to provide a barrier equal to or better than the undisturbed material. Sand, gypsum, grout, cold tar, or epoxy plugs are also placed in the hole to provide impenetrable zones. In these zones, the instrument cables are sealed to prevent a radioactive gas path to the surface. Once completed, the area is cleared of unnecessary equipment. A report is compiled for the Containment Evaluation Panel to show that the as-built condition reflects the containment design plan.

Step 6. Test Execution.

After the Containment Evaluation Panel accepts the as-built design of containment and all preliminary tests are successful, the nuclear device is ready for detonation. Security operations begin two days before the test to assure that all nonevent-related personnel are evacuated prior to the test for security and personal safety. The explosive is armed. Radiation monitors are activated, and aircraft with tracking capability circle the site in case gas and debris unexpectedly vent to the surface. Weather forecasts and fallout pattern predictions are reviewed. Then, detonation occurs.

When an underground nuclear device is detonated, the energy release almost instantaneously produces extremely high temperatures and pressure that vaporizes the nuclear device and the surrounding rock. Within a fraction of a second after detonation, a generally spherical cavity is formed at the emplacement position. As the hot gases cool, a lining of molten rock puddles at the cavity bottom.

After a period of minutes to hours, as the gases in the cavity cool, the pressure subsides and the weight of the overburden causes the cavity roof to collapse, producing a vertical, rubble-filled column known as a rubble chimney.

The rubble chimney commonly extends to the ground surface, forming a subsidence crater. Numerous subsidence craters are present at the test site. Subsidence craters generally are bowl-shaped depressions with a diameter ranging from about 60 to 600 m (200 to 2,000 ft) and a depth ranging from a few meters up to 60 m (200 ft), depending on the depth of burial and the explosive energy yield. Some deeply buried explosions of low yield form cavities that do not collapse to the surface and, consequently, do not create subsidence craters. Past underground nuclear tests in Yucca Flat and on Pahute Mesa have fractured the ground surface above the explosions, causing displacement of the surface along preexisting faults adjacent to explosion sites.

After the test is conducted, the event site remains secure until it can be assured that the event has been contained. After a suitable time, a reentry crew is dispatched to the site. Data are retrieved, and the condition of equipment is noted. After all is assured to be secure, normal NTS operations resume. The event site is roped off, outlining an exclusion zone where there is danger of potential cratering.

Step 7. Post-shot Operations.

After the temperature of the cavity has cooled, a post-shot hole is usually drilled into the point of the explosion in order to retrieve samples of the debris. These samples are highly radioactive, but provide important information on the test. The post-shot hole is as small in diameter as possible and is drilled at an angle to allow the drill rig to be positioned safely away from surface ground-zero. After drilling and sampling operations are complete, the drill rig and tools are decontaminated. Residual radiation is cleaned up at the site, and the hole is plugged back to the surface. This generally completes the event operation, and the site is turned back to the DOE.


Plutonium manufacture and Fabrication – from Nuclear Weapon Archive

All plutonium originates in nuclear reactors and is produced by the capture of extra neutrons by uranium-238 to form U-239, which then undergoes a series of decays to form Pu-239:

U-238 + n -> U-239 -> Np-239 -> Pu-239

Some of this plutonium gets consumed by fission before it is removed from the reactor, and some of it gets transmuted to heavier isotopes of plutonium by capturing more neutrons:

Pu-239 + n -> Pu-240

The isotopic composition of plutonium is affected by how long it stays in the reactor. Short exposures produce plutonium with very little Pu-240 and with very little plutonium being consumed by fission. Long exposures produce high Pu-240 concentrations, and a substantial portion of the plutonium produced is consumed by fission.

The isotopic composition matters with regard to manufacturing weapons for two reasons.

  • First (and least important) is that Pu-240 is less fissile then Pu-239, so somewhat more plutonium is needed to make up the required amount for the weapon,
  • Second (and more important) is that Pu-240 decays through spontaneous fission, producing a substantial flux of neutrons.

In the earliest years of weapon design the emission of neutrons was a problem in making a reliable efficient weapon because of the problem of predetonation. A high neutron flux makes it difficult or impossible to compress a bomb core containing several kilograms of plutonium to supercriticality before the bomb disassembled with a greatly reduced yield. The advent of composite cores containing highly enriched U-235 and plutonium (in the late 1940s) greatly reduced this difficulty though since the option of using a relatively small amount of plutonium in a mostly uranium core became available. The later development of fusion boosted weapons (in the mid 1950s) eliminated it entirely since the fusion boosting effect ensures efficient weapons, even with low initial fission yields.

Plutonium can be obtained from special purpose plutonium production reactors, or as a by-product of commercial power or research reactors. The plutonium produced by special purpose production reactors has a relatively low Pu-240 content (20% and is called “reactor grade”.

Essentially all of the plutonium currently in weapons throughout the world was produced in special purpose plutonium production reactors. Initially each of the five declared nuclear powers began producing plutonium for weapons on a large scale many years before they developed significant numbers of commercial power reactors. Special purpose reactors were required for weapons production because there was no other sources of plutonium available.

These special purpose reactors produce “weapon grade” plutonium, as opposed to grades with higher Pu-240 concentrations, for two reasons:

1. Economics: the only reason the reactor exists is to produce plutonium. Burning plutonium up in fission, or transmuting it to less fissile Pu-240 reduces output and increases cost (up to a point, this must be balanced against the cost of processing fuel with low plutonium concentrations).

2. Handling problems: although neutron emissions do not create serious problems in weapon design, it can produce problems with weapons manufacture and handling. Neutron emissions create occupational exposures to plutonium for those assembling weapons, or handling weapons already assembled. In fact weapons that are kept in close proximity to people (like the W80-0) may even require special “supergrade” low neutron emission plutonium for this reason. URL: Caption: Plutonium processing glove boxes.

The actual fabrication and processing of plutonium is done manually in glove boxes like these at Los Alamos, which means there is negligible shielding between the operator and the neutron-emitting plutonium.

The actual fabrication and processing of plutonium is done manually in glove boxes like these, which means there is negligible shielding between the operator and the neutron-emitting plutonium. If higher Pu-240 plutonium were used in weapons, then either remote control processing cells would have to be used, or the number of hours that each worker could spend at these tasks would have to be sharply reduced. Either of these would drive up the cost of weapon processing considerably. It is for this reason, as well as historical and policy reasons, that explain why reactor grade plutonium is not used in U.S. weapon. It is not due to any inherent inability to do so (contrary to some statements made by the nuclear power industry). URL: Caption: Another example of a typical plutonium processing operation.

High-Purity Plutonium Ring URL: Caption: A ring of weapons-grade 99.96% pure electrorefined plutonium, enough for one bomb core. The ring weighs 5.3 kg, is ca. 11 cm in diameter and its shape helps with criticality safety.

This ring of electrorefined plutonium metal has a purity of more than 99.96 per cent. It is typical of the rings that were prepared at Los Alamos and shipped to Rocky Flats for weapon fabrication before the latter facility was shut down, and U.S. weapon manufacture halted. The ring weighs 5.3 kilograms, enough for one bomb core, and is approximately 11 centimeters in diameter. The ring shape is important for criticality safety. There is enough plutonium in this ring to make a modern strategic nuclear weapon. URL: Caption:
Plutonium-gallium alloy ingot reclaimed from weapon pit (LLNL).

Plutonium pictures URL: Caption: Various images of plutonium metal. URL: Caption: Various images of plutonium metal. URL: Caption: Various images of plutonium metal. URL: Caption: A sample of 0.89 g of highly pure plutonium (99.99%). This sample, a standard for analysis, was
manufactured at Los Alamos, in a oxygen-free environment, and sealed under vacuum in a glass ampoule.

[image] URL: Caption:
Pu(IV) colors change with different ligands. URL: Caption: Colors of the different oxidation states of plutonium, in 1 M HClO4. URL: Caption:
A hemisphere of purified, but gallium-stabilized, delta-phase plutonium metal. URL: Caption:
Buttons of refined plutonium metal.

Uranium enrichment

Gas centrifuge process URL: Caption:
Principle of a gas centrifuge process for uranium enrichment

Process to separate isotopes in which heavy atoms are split from the lighter atoms by centrifugal forces. The separation factor depends on the mass difference of the isotopes to be separated. The process is suitable for the separation of uranium isotopes, the achievable separation factor amounts to 1.25. Uranium enrichment plants applying this process are operated in Gronau/Wesphalia (Germany) and by URENCO at Capenhurst (UK).

What’s a uranium centrifuge?

By Marshall Brain

Uran­ium is an element that is similar to iron. Like iron, you dig uranium ore out of the ground and then process it to extract the pure uranium from the ore. When you finish processing uranium ore, what you have is uranium oxide. Uranium oxide contains two types (or isotopes) of uranium: U-235 and U-238. U-235 is what you need if you want to make a bomb or fuel a nuclear power plant. But the uranium oxide from the mine is about 99 percent U-238. So you need to somehow separate the U-235 from the U-238 and increase the amount of U-235. The process of concentrating the U-235 is called enrichment, and centrifuges are a central part of the process. URL: Caption:
Photo courtesy Oak Ridge National Laboratory
Uranium centrifuge cascades

U-235 weighs slightly less than U-238. By exploiting this weight difference, you can separate the U-235 and the U-238. The first step is to react the uranium with hydrofluoric acid, an extremely powerful acid. After several steps, you create the gas uranium hexafluoride.

Now that the uranium is in a gaseous form, it is easier to work with. You can put the gas into a centrifuge and spin it up. The centrifuge creates a force thousands of times more powerful than the force of gravity. Because the U-238 atoms are slightly heavier than the U-235 atoms, they tend to move out toward the walls of the centrifuge. The U-235 atoms tend to stay more toward the center of the centrifuge.

Although it is only a slight difference in concentrations, when you extract the gas from the center of the centrifuge, it has slightly more U-235 than it did before. You place this slightly concentrated gas in another centrifuge and do the same thing. If you do this thousands of times, you can create a gas that is highly enriched in U-235. At a uranium enrichment plant, thousands of centrifuges are chained together in long cascades.

At the end of a long chain of centrifuges, you have uranium hexafluoride gas containing a high concentration of U-235 atoms.

The creation of the centrifuges is a huge technological challenge. The centrifuges must spin very quickly — in the range of 100,000 rpm. To spin this fast, the centrifuges must have:

  • very light, yet strong, rotors
  • well-balanced rotors
  • high-speed bearings, usually magnetic to reduce friction

Meeting all three of these requirements has been out of reach for most countries. The recent development of inexpensive, high-precision computer-controlled machining equipment has made things somewhat easier. This is why more countries are learning to enrich uranium in recent years.

Now you need to turn the uranium hexafluoride gas back into uranium metal. You do this by adding calcium. The calcium reacts with the fluoride to create a salt, and the pure uranium metal is left behind. With this highly concentrated U-235 metal, you can either make a nuclear bomb or power a nuclear reactor.

Uranium pictures URL: Caption: Uranium URL: Caption: Yellowcake is a concentrated mixture of uranium oxides that is further refined to extract pure uranium. URL: Caption: Cascades of gas centrifuges are used to enrich uranium ore to concentrate its fissionable isotopes. URL: Caption: Uranium in its oxidation states III, IV, V, VI

[image] URL: Caption: Uraninite, also known as Pitchblende, is the most common ore mined to extract uranium.

Israel: Plutonium Production

The Risk Report

Volume 2 Number 4 (July-August 1996)

Israel makes plutonium for atomic bombs at Dimona, a secret nuclear complex in the Negev Desert. The French-supplied reactor there has produced plutonium free from international controls since 1963. The quality of the plutonium created by the Dimona reactor is ideal for making atomic bombs.

The size of the reactor at Dimona is listed by the International Atomic Energy Agency [IAEA] as 26 megawatts (thermal). However, experts believe it is much more powerful than that. Mordechai Vanunu, an Israeli technician who worked at Dimona for eight years, reported that the reactor had been scaled up twice before he arrived at the site in 1977. The first scale-up was from 26MWt to 70MWt; the second was to some higher level.

The first scale-up was planned when Dimona was built. Israel convinced France to make the reactor’s critical components–including its cooling circuit–three times larger than needed for a facility of its nominal size, and three times larger than originally agreed upon. This modification permitted a scale-up to 70MWt without the addition of extra cooling circuits, which would have attracted outside attention. Further evidence of a scale-up came in late 1968, when Israel diverted 200 metric tons of Belgian uranium on the high seas–a quantity considerably greater than a 26-megawatt reactor would have required. Israel probably needed the additional uranium for the first scale-up, which appears to have occurred in 1970.

Vanunu also said that Dimona had been producing 40 kilograms of plutonium per year for some time before he arrived in 1977. If the reactor at Dimona was unusually efficient (i.e., producing more than 1 gram of plutonium per megawatt day) and ran for as many as 300 days per year, the 40 kilograms could have been produced with a peak power of sightly more than 100MWt. If the reactor were less efficient, and operated for fewer days per year, the peak power would have to approach 150MWt.

Plutonium extraction

To be used in weapons, plutonium must be extracted chemically from irradiated nuclear reactor fuel. A French firm, St. Gobain Techniques, supplied Israel with a chemical extraction plant at Dimona. The plant’s first trial runs were in late 1965. By 1968, Israel had extracted enough plutonium for an atomic bomb.

The Dimona reactor, if operated continuously, could have created as much as 870 kilograms of plutonium through 1994. This figure assumes that the reactor started operating at 26MWt in 1963, was scaled up to 70MWt in 1970, and was scaled up again in 1977 to a level at which it could produce about 40kg of plutonium per year. Vanunu reported that the extraction plant where he worked produced 1.17 kilograms of plutonium per week for 34 weeks per year, a total of 40 kilograms annually. At this rate, 320 kilograms of plutonium would have been produced during the eight years Vanunu worked at Dimona. If the reactor experienced shutdowns, or was operated at a lower power, this figure could be significantly smaller.

Future plutonium production at Dimona is uncertain, primarily because of the reactor’s age. The United States has urged Israel to cap its nuclear program and cease plutonium production at Dimona, but Israel has not agreed to do so.

Size of Israel’s arsenal

The above figures for plutonium production indicate that Israel could have up to 175 bombs’ worth of plutonium in its nuclear arsenal today. This figure assumes roughly 5 kilograms of plutonium are needed per bomb, including processing losses. (Vanunu reported in 1986 that Israel was using about 4.4kg of plutonium per bomb, an amount slightly greater than the reflected fast critical mass of plutonium-239.)

It is impossible to estimate the exact size of Israel’s arsenal without knowing Dimona’s true operating history and the characteristics of Israeli nuclear weapon designs. For example, Israel has produced enriched uranium, which could be used to make additional weapons. Israel has also made a number of “boosted” weapons using tritium, also produced at Dimona. Tritium can be produced by irradiating lithium-6 targets in the Dimona reactor.

Dimona reactor:

Reactor: IRR-II
Type: Heavy water
Power: 26-megawatt (thermal) scaled up to 70MWt or more
Start-up: 1963
Safeguards: None
Plutonium created through 1994: Up to 870 kilograms

FROM: Wisconsin Project on Nuclear Arms Control Copyright © 2003 – 2011