Who discovered that plutonium was fissile, and when?

Glenn Seaborg, Emilo Segrè, and Joseph Kennedy (no, not that Kennedy!) discovered that Element 94 was fissile shortly after its first production in 1941. This wasn't published openly for quite some time -- 1946, if I recall correctly. read more

The idea that Element 93 and Element 94 might have fissile isotopes [3] seems to have been widespread shortly after the discovery of fission. Nuclear physicists around the world would have been aware of this. To my mind, the remarkable achievement is Seaborg's development of the techniques for separating plutonium from spent fuel. read more

Plutonium recovered from spent reactor fuel poses little proliferation hazard, because of excessive contamination with non-fissile plutonium-240 and plutonium-242. Separation of the isotopes is not feasible. read more