| Actinides | Half-life | Fission products | ||||||
|---|---|---|---|---|---|---|---|---|
| 244Cm | 241Pu f | 250Cf | 243Cmf | 10–30 y | 137Cs | 90Sr | 85Kr | |
| 232U f | 238Pu | f is for fissile |
69–90 y | 151Sm nc➔ | ||||
| 4n | 249Cf f | 242Amf | 141–351 | No fission product has half-life 102 to 2×105 years |
||||
| 241Am | 251Cf f | 431–898 | ||||||
| 240Pu | 229Th | 246Cm | 243Am | 5–7 ky | ||||
| 4n | 245Cmf | 250Cm | 239Pu f | 8–24 ky | ||||
| 233U f | 230Th | 231Pa | 32–160 | |||||
| 4n+1 | 234U | 4n+3 | 211–290 | 99Tc | 126Sn | 79Se | ||
| 248Cm | 242Pu | 340–373 | Long-lived fission products | |||||
| 237Np | 4n+2 | 1–2 My | 93Zr | 135Cs nc➔ | ||||
| 236U | 4n+1 | 247Cmf | 6–23 My | 107Pd | 129I | |||
| 244Pu | 80 My | >7% | >5% | >1% | >.1% | |||
| 232Th | 238U | 235U f | 0.7–12 Gy | fission product yield | ||||
Plutonium-244 (244Pu) is an isotope of plutonium that has a halflife of 80 million years. This is longer than any of the other isotopes of plutonium and longer than any actinide except for the three naturally abundant ones uranium-235 (700my), uranium-238, and thorium-232. It is also longer than any other known radioactive isotopes except samarium-146 (103my), potassium-40 (1.25by), and a number of nearly stable isotopes with half-lives much longer than the age of the universe, such as bismuth-209 (19 quintillion years).
More accurate measurements, beginning in the early 1970s, have detected primordial plutonium-244.[1] As the age of the Earth is about 50 half-lives, the amount of plutonium-244 left should be very small. However, since plutonium-244 cannot be easily produced by natural neutron capture in the low neutron activity environment of uranium ores (see below), its presence cannot plausibly be explained by any other means than creation by r-process nucleosynthesis in supernovae. Plutonium-244 is thus the shortest-lived and heaviest primordial isotope yet detected or theoretically predicted.
Unlike plutonium-238, plutonium-239, plutonium-240, plutonium-241, and plutonium-242, plutonium-244 is not produced in quantity by the nuclear fuel cycle, because further neutron capture on plutonium-242 produces plutonium-243 which has a short halflife (5 hours) and quickly beta decays to americium-243 before having much opportunity to further capture neutrons in any but very high neutron flux environments. However a nuclear weapon explosion can produce some plutonium-244 by rapid successive neutron capture.