Dense silvery radioactive metallic transuranic element, belongs to the actinoids. Pu-244 is the most stable isotope with a half-life of 7.6*10^7 years. Thirteen isotopes are known. Pu-239 is the most important, it undergoes nuclear fission with slow neutrons and is hence important to nuclear weapons and reactors. Plutonium production is monitored down to the gram to prevent military misuse. First produced by Gleen T. Seaborg, Edwin M. McMillan, J.W. Kennedy and A.C. Wahl in 1940.
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