Plutonium-241

Template:Short description Template:Template other Plutonium-241 (Template:SimpleNuclide 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 absorption cross 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

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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 and a mean of , and does not emit gamma rays. 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. 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.

Plutonium-241 also has a rare alpha decay branch to uranium-237, occurring in about 0.002% of decays. With a Q-value of , it can emit Auger electrons and associated X-rays, unlike the beta-decay process.

Role in nuclear fuel

Americium has lower valence and lower electronegativity than plutonium, neptunium or uranium, so in most nuclear reprocessing, americium tends to fractionate with the alkaline fission products – lanthanides, strontium, caesium, barium, yttrium – rather than with other actinides. Americium is therefore not recycled into nuclear fuel unless special efforts are made.

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.

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