![]() DU is 1.7 times denser than lead and, when turned into metal and used to make shells, it penetrates heavy steel and concrete with relative ease. Much like natural uranium, depleted uranium is both toxic and radioactive and, because of its long half-life (4.5 billion years), it is practically indestructible. These weapons do not require weapons-grade materials and even the relatively common materials used in radiological medical equipment would be enough to cause catastrophic results and an extensive loss of life.įigure 2 A reporter using a radiation detector examines an Iraqi tank destroyed by depleted uranium bullets.ĭepleted uranium (DU) is the byproduct of the reprocessing of spent nuclear fuel that has been enriched for use in nuclear reactors or weapons- essentially pure uranium-238. These may include conventional weapons which, upon explosion, spread radioactive, biological, or toxic materials and may be delivered as an aerosol or simply by wrapping the materials around dynamite. The term “dirty bomb” usually refers to any device that generates a significant amount of radioactive waste without actually undergoing a fission reaction. Two examples are dirty bombs and depleted uranium warheads. In addition to the A-bomb, which is a result of fission reactions, radioactive materials can be used in conventional bombs and warheads. The Little Boy was a gun-type the Fat Man was of the implosive design. The rapid increase in pressure compresses the fissile mass, preventing neutrons from escaping through the void and reducing the critical mass necessary to initiate the fission reaction (Figure 1b).The implosion device is very difficult to build, as the implosion has to be highly symmetrical. An alternative method (called implosion method) is to detonate a conventional explosive that surrounds the fissionable material. The tamper (also called neutron reflector) reduces the number of neutrons that can escape and prevents the bomb’s premature explosion (Figure 1a). A heavy material, called a tamper, surrounds the fissile mass. The simplest mechanism for assembling a supercritical mass is to shoot one piece of the material against another in a gun tube. This is accomplished by bringing two or more subcritical masses together. To make detonation possible, the mass of the fissile material must become critical. b) In the implosion method (bottom), a conventional explosive compresses a fissile material (plutonium-239) releasing more neutrons and starting the fission. Plutonium, on the other hand, requires waste-reprocessing facilities that, unlike the uranium enrichment plants, cannot be easily hidden.įigure 1 Construction of A-Bombs a) In the gun method (top), a conventional propellant is used to shoot a subcritical mass of fissile material (uranium-235) into another subcritical mass, making the combined mass supercritical. It is far easier for countries to develop secret weapons using enriched uranium fuel the necessary facilities can be disguised as ordinary chemical plants, and they do not produce signatures that can be readily identified. Construction of a plutonium bomb is more difficult, however, as a byproduct of plutonium processing operation, Plutonium-240 is highly unstable and cause predetonation which reduces the effectiveness of the bomb. The critical mass necessary to construct a bomb using Pu-239 is only the size of a baseball. Building weapons with HEU is, however, easier, as no reprocessing facility to separate plutonium from spent reactor fuel is needed. For this reason, plutonium is favored over highly enriched uranium (HEU). Naturally occurring uranium has only 0.7% of the fissile uranium-235 isotope and must be enriched to a minimum 90% before it qualifies as weapons-grade. Plutonium has a very small critical mass, whereas uranium must be enriched substantially before it can serve as a weapons-grade material. In an atomic bomb, a mass of fissile material greater than the critical mass must be assembled and held together for about a millionth of a second to permit the chain reaction to propagate and the bomb to explode. The minimum amount of fissile material (of a given shape) required for maintaining a chain reaction is known as the critical mass. This mass is dependent upon the size, shape, and purity of the isotopes being used. A large enough mass of these materials is needed to ensure that enough neutrons are generated to compensate for the loss through the void. Too many neutrons leak out through the large empty volume surrounding nuclei. A small mass of pure fissile material, such as uranium-235 or plutonium-239, would not sustain a chain reaction. ![]()
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