Plutonium-238

Plutonium-238 (also known as Pu-238 or ²³⁸Pu) is a radioactive isotope of plutonium that has a half-life of 87.7 years.

Plutonium-238 is a very powerful alpha emitter and – unlike other isotopes of plutonium – it does not emit significant amounts of other, more penetrating and thus more problematic radiation. This makes the plutonium-238 isotope suitable for usage in radioisotope thermoelectric generators (RTGs) and radioisotope heater units – one gram of plutonium-238 generates approximately 0.5 watts of thermal power.

History

Plutonium-238 was the first isotope of plutonium to be discovered. It was synthesized by Glenn Seaborg and associates in 1941 by bombarding uranium-238 with deuterons, creating neptunium-238, which then decays to form plutonium-238. Plutonium-238 decays to uranium-234 and then further along the radium series to lead-206.

Production

Reactor-grade plutonium from spent nuclear fuel contains various isotopes of plutonium. Pu-238 makes up only one or two percent, but it may be responsible for much of the short-term decay heat because of its short half-life relative to other plutonium isotopes. Reactor-grade plutonium is not useful for producing Pu-238 for RTGs because difficult isotopic separation would be needed.