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Content: The metal exhibits six allotropic modifications having various crystalline structures. The densities of these vary from 16.00 to 19.86 g/cm3. The most important isotope of plutonium is 239Pu, with a half-life of 24,200 years. Because of its short half-life, there are only extremely tiny trace amounts of plutonium naturally in uraniumores. It is produced in extensive quantities in nuclear reactors from natural uranium: 238U(n, gamma) --> 239U--(beta) --> 239Np--(beta) --> 239Pu. Fifteen isotopes of plutonium are known. Applications
Plutonium is a key fissilecomponent in modern nuclear weapons; care must be taken to avoid accumulation of amounts of plutonium which approach critical mass, the amount of plutonium which will self-generate a nuclear reaction. Despite not being confined by external pressure as is required for a nuclear weapon, it will nevertheless heat itself and break whatever confining environment it is in.