A bomb which works in the principle of a fast nuclear chain reaction is referred to as the atomic bomb. It contains two subcritical masses or fissionable material U-235 or Pu-239.
(Subcritical Mass: If the mass of the fissionable material is less than its critical mass, nuclear fission wouldn’t occur, this system is then said to be subcritical.)
It has a mass of trinitrotoluene in a separate pocket. When TNT is detonated, it drives one mass of U-235 into the other. A supercritical mass of the fissionable material is obtained. As a result of the instantaneous chain reaction, the bomb explodes with the release of tremendous heat energy. The temperature developed in an atomic bomb believed to be 10 million degree centigrade.
Besides, many radio nuclei and heat and deadly gamma ray is released. This play havoc with life and environment. If the bomb explodes near the ground, it raises storm of dust into the air, the radioactive materials adhering to dust is known as fall out. It spreads over wide radius and as a lingering source of radioactive hazard for long periods.
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