Plutonium-241 (241 Pu or Pu-241) is an isotope of plutonium formed when plutonium-240 captures a neutron. Like some other plutonium isotopes (especially 239Pu), 241Pu is fissile, with a neutron absorptioncross section about one-third greater than that of 239Pu, and a similar probability of fissioning on neutron absorption, around 73%. In the non-fission case, neutron capture produces plutonium-242. In general, isotopes with an odd number of neutrons are both more likely to absorb a neutron and more likely to undergo fission on neutron absorption than isotopes with an even number of neutrons.
Decay properties
Process of successive neutron capture from 239Pu through 245Cm, including 241Pu.
Plutonium-241 is a beta emitter with a half-life of 14.3 years, corresponding to a decay of about 5% of 241Pu nuclei over a one-year period. This decay has a Q-value of 20.78±0.17 keV and a mean of 5.227±0.043 keV, and does not emit gamma rays.[1] The longer spent nuclear fuel waits before reprocessing, the more 241Pu decays to americium-241, which is nonfissile (although fissionable by fast neutrons) and an alpha emitter with a half-life of 432 years; 241Am is a major contributor to the radioactivity of nuclear waste on a scale of hundreds or thousands of years.[citation needed] In its fully ionized state, the beta-decay half-life of 241Pu94+ decreases to 4.2 days, and only bound-state beta decay is possible.[2]
Plutonium-241 also has a rare alpha decay branch to uranium-237, occurring in about 0.002% of decays. With a Q-value of 5.055±0.005 MeV, it can emit Auger electrons and associated X-rays, unlike the beta-decay process.[1]
In a thermal reactor, 241Am captures a neutron to become americium-242, which quickly becomes curium-242 (or, 17.3% of the time, 242Pu) via beta decay. Both 242Cm and 242Pu are much less likely to absorb a neutron, and even less likely to fission; however, 242Cm is short-lived (half-life 160 days) and almost always undergoes alpha decay to 238Pu rather than capturing another neutron. In short, 241Am needs to absorb two neutrons before again becoming a fissile isotope.
^Plus radium (element 88). While actually a sub-actinide, it immediately precedes actinium (89) and follows a three-element gap of instability after polonium (84) where no nuclides have half-lives of at least four years (the longest-lived nuclide in the gap is radon-222 with a half life of less than four days). Radium's longest lived isotope, at 1,600 years, thus merits the element's inclusion here.
^Milsted, J.; Friedman, A. M.; Stevens, C. M. (1965). "The alpha half-life of berkelium-247; a new long-lived isomer of berkelium-248". Nuclear Physics. 71 (2): 299. Bibcode:1965NucPh..71..299M. doi:10.1016/0029-5582(65)90719-4. "The isotopic analyses disclosed a species of mass 248 in constant abundance in three samples analysed over a period of about 10 months. This was ascribed to an isomer of Bk248 with a half-life greater than 9 [years]. No growth of Cf248 was detected, and a lower limit for the β− half-life can be set at about 104 [years]. No alpha activity attributable to the new isomer has been detected; the alpha half-life is probably greater than 300 [years]."
^This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".
^Excluding those "classically stable" nuclides with half-lives significantly in excess of 232Th; e.g., while 113mCd has a half-life of only fourteen years, that of 113Cd is eight quadrillion years.
