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Plutonium-238 (238 Pu or Pu-238) is a radioactive isotope of plutonium that has a half-life of 87.7 years. Plutonium-238 is a very powerful alpha emitter ; as alpha particles are easily blocked, this makes the plutonium-238 isotope suitable for usage in radioisotope thermoelectric generators (RTGs) and radioisotope heater units .
For instance, 3.6 kg of plutonium-238 undergoes the same number of radioactive decays per second as 1 tonne of plutonium-239. Since the morbidity of the two isotopes in terms of absorbed radioactivity is almost exactly the same, [ 55 ] plutonium-238 is around 275 times more toxic by weight than plutonium-239.
The isotope produces 0.57 watts of thermal power per gram of 238 Pu. [5] Soviet missions have used other isotopes, such as the polonium-210 heat source used in the Lunokhod lunar rovers. [6] [7] With a half-life of 138.376 days, polonium-210 produces more thermal power per unit mass, but is suitable only for shorter duration missions.
U-232 hazards, a result of its highly radioactive decay products such as thallium-208, are significant even at 5 parts per million. Implosion nuclear weapons require U-232 levels below 50 PPM (above which the U-233 is considered "low grade"; cf. "Standard weapon grade plutonium requires a Pu-240 content of no more than 6.5
talk. edit. Plutonium (94 Pu) is an artificial element, except for trace quantities resulting from neutron capture by uranium, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. It was synthesized long before being found in nature, the first isotope synthesized being plutonium-238 in 1940.
Trace amounts of plutonium-238, plutonium-239, plutonium-240, and plutonium-244 can be found in nature. Small traces of plutonium-239, a few parts per trillion , and its decay products are naturally found in some concentrated ores of uranium, [ 52 ] such as the natural nuclear fission reactor in Oklo , Gabon . [ 53 ]
After starting the reactor with existing U-233 or some other fissile material such as U-235 or Pu-239, a breeding cycle similar to but more efficient [57] than that with U-238 and plutonium can be created. The Th-232 absorbs a neutron to become Th-233 which quickly decays to protactinium-233. Protactinium-233 in turn decays with a half-life of ...
For one thing, it may operate at higher burnups and therefore increase the relative abundance of the non-fissile, but fertile, isotopes plutonium-238, plutonium-240, and plutonium-242. [34] Unlike PUREX reprocessing, the IFR's electrolytic reprocessing of spent fuel does not separate out pure plutonium. Instead, it is left mixed with minor ...