Mechanism
A cobalt bomb could be made by placing a quantity of ordinary cobalt metal (59Co) inside a nuclear bomb. When the bomb explodes, the neutrons produced by the explosion would transmute the cobalt to the radioactive isotope cobalt-60 (60Co), which would be vaporized by the explosion. The cobalt would then condense and fall back to Earth with the dust and debris from the explosion, contaminating the ground.
The deposited Cobalt-60 would have a half-life of 5.27 years, decaying into 60Ni. The Nickel nucleus is activated, and emits two gamma rays with energies of 1.17 and 1.33 MeV, hence the overall nuclear equation of the reaction is:
59
27Co + n → 60
27Co → 60
28Ni + e− + gamma rays.
Nickel-60 is a stable isotope and undergoes no further decays after emitting the gamma rays.
The 5.27 year half life of the 60Co is long enough to allow it to settle out before significant decay has occurred. The half-life is long enough for it to be impractical to wait in shelters for it to decay, yet short enough that intense radiation is produced. Many isotopes are more radioactive (gold-198, tantalum-182, zinc-65, sodium-24, and many more), but they would decay faster, possibly allowing some population to survive in shelters.
In a fission bomb, it has been suggested, the weapon's tamper could be made of cobalt. In a fusion bomb the radiation case around the weapon, normally made of uranium 238, could be made of cobalt. These changes would reduce the explosive power (yield) of the weapon somewhat.
Read more about this topic: Cobalt Bomb
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