Nuclear weapons supercritical mass

In a nuclear weapon, the fissile material is initially subcritical. The challenge is to produce a supercritical mass so rapidly that the chain reaction takes place uniformly throughout the metal. Supercriticality can be achieved by shooting two subcritical blocks toward each other (as was done in the bomb that fell on Hiroshima) or by implosion of a single subcritical mass (the technique used in the bomb that destroyed Nagasaki). A strong neutron emitter, typically polonium, helps to initiate the chain reaction. 

Implosion method Explosives are also used in nuclear weapons to generate the implosion required to bring the two halves of the radioactive device together. The implosion is achieved with the help of secondary explosives which surround the material and rapidly compress the mass to a supercritical state on their detonation. This encompasses two major assemblies (i) com-... 

The type of nuclear explosion produced by a nuclear weapon cannot occur in a nuclear reactor. The concentration of fissionable materials in a reactor is not sufficient to form a supercritical mass. 

An actual nuclear explosion, of the type prodnced by a nn-clear weapon, carmot occnr in a nnclear reactor because the concentration of the fissionable materials is not sufficient to form a supercritical mass. 

A critical mass of a fissionable material is the amount needed to provide a high enough internal neutron flux to sustain the chain reaction (production of enough neutrons to cause the continuous fission of further material). A sample with less than a critical mass is stUl radioactive, but cannot sustain a chain reaction. 56. An actual nuclear explosion, of the type produced by a nuclear weapon, carmot occur in a nuclear reactor because the concentration of the fissionable materials is not sufficient to form a supercritical mass. 

IMPLOSION DEVICE IMPLOSION WEAPON. A type of nuclear weapon whose design features a spherical device that contains a quantity of fissionable material slightly helow critical mass at ordinary pressure. At detonation, the device undergoes implosion,having its volume suddenly reduced hy compression brought about by chemical explosives. The compression takes the fissionable material to a supercritical mass, and a nuclear explosion ensues. Plutonium is often used as the fissile material in such a design. Fat Man, the bomb dropped on Nagasaki, is an example of an implosion device. 

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