Plutonium-241

Plutonium-241, ²⁴¹Pu
General
Symbol	241Pu
Names	plutonium-241, Pu-241
Protons	94
Neutrons	147
Nuclide data
Natural abundance	0 (Artificial)
Half-life	14 years
Decay products	241Am
Isotope mass	241.057 u
Decay modes
Decay mode	Decay energy (MeV)
β−	0.0208 [1]
	Isotopes of plutonium ; Complete table of nuclides

Plutonium-241 (²⁴¹Pu, Pu-241) is an isotope of plutonium formed when plutonium-240 captures a neutron. Like ²³⁹Pu but unlike ²⁴⁰Pu, ²⁴¹Pu is fissile, with a neutron absorption cross section about 1/3 greater than 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.

Actinides and fission products by half-life
Actinides[2] by decay chain				Half-life range (y)	Fission products of ²³⁵U by yield[3]
4n	4n+1	4n+2	4n+3		Fission products of ²³⁵U by yield[3]
4n	4n+1	4n+2	4n+3			4.5–7%	0.04–1.25%	<0.001%
²²⁸Ra^№				4–6	†		¹⁵⁵Eu^þ
²⁴⁴Cm^ƒ	²⁴¹Pu^ƒ	²⁵⁰Cf	²²⁷Ac^№	10–29		⁹⁰Sr	⁸⁵Kr	^113mCd^þ
²³²U^ƒ		²³⁸Pu^ƒ	²⁴³Cm^ƒ	29–97		¹³⁷Cs	¹⁵¹Sm^þ	^121mSn
²⁴⁸Bk[4]	²⁴⁹Cf^ƒ	^242mAm^ƒ		141–351	No fission products have a half-life in the range of 100–210 k years ...
	²⁴¹Am^ƒ		²⁵¹Cf^ƒ[5]	430–900
		²²⁶Ra^№	²⁴⁷Bk	1.3 k – 1.6 k
²⁴⁰Pu	²²⁹Th	²⁴⁶Cm^ƒ	²⁴³Am^ƒ	4.7 k – 7.4 k
	²⁴⁵Cm^ƒ	²⁵⁰Cm		8.3 k – 8.5 k
			²³⁹Pu^ƒ	24.1 k
		²³⁰Th^№	²³¹Pa^№	32 k – 76 k
²³⁶Np^ƒ	²³³U^ƒ	²³⁴U^№		150 k – 250 k	‡	⁹⁹Tc^₡	¹²⁶Sn
²⁴⁸Cm		²⁴²Pu		327 k – 375 k			⁷⁹Se^₡
				1.53 M		⁹³Zr
	²³⁷Np^ƒ			2.1 M – 6.5 M		¹³⁵Cs^₡	¹⁰⁷Pd
²³⁶U			²⁴⁷Cm^ƒ	15 M – 24 M			¹²⁹I^₡
²⁴⁴Pu				80 M	... nor beyond 15.7 M years[6]
²³²Th^№		²³⁸U^№	²³⁵U^ƒ№	0.7 G – 14.1 G	... nor beyond 15.7 M years[6]
Legend for superscript symbols ₡ has thermal neutron capture cross section in the range of 8–50 barns ƒ fissile m metastable isomer № primarily a naturally occurring radioactive material (NORM) þ neutron poison (thermal neutron capture cross section greater than 3k barns) † range 4–97 y: Medium-lived fission product ‡ over 200,000 y: Long-lived fission product

Decay to americium

²⁴¹Pu has a half-life of 14 years, corresponding to a decay of about 5% of ²⁴¹Pu nuclei over a one-year period. 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 halflife of 432 years; ²⁴¹Am is a major contributor to the radioactivity of nuclear waste on a scale of hundreds or thousands of years.

Americium has lower valence and lower electronegativity than plutonium, neptunium or uranium, so in most nuclear reprocessing, Am tends to fractionate not with U, Np, or Pu, but with the alkaline fission products: lanthanides, strontium, caesium, barium, yttrium, and 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.

References

Table de Radionucleides Pu-241, Laboratoire National Henri Becquerel
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.
Specifically from thermal neutron fission of U-235, e.g. in a typical nuclear reactor.
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 y. No growth of Cf²⁴⁸ was detected, and a lower limit for the β⁻ half-life can be set at about 10⁴ y. No alpha activity attributable to the new isomer has been detected; the alpha half-life is probably greater than 300 y."
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 nearly eight quadrillion years.

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[1] Table de Radionucleides Pu-241, Laboratoire National Henri Becquerel

[2] 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.

[3] Specifically from thermal neutron fission of U-235, e.g. in a typical nuclear reactor.

[4] 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 y. No growth of Cf²⁴⁸ was detected, and a lower limit for the β⁻ half-life can be set at about 10⁴ y. No alpha activity attributable to the new isomer has been detected; the alpha half-life is probably greater than 300 y."

[5] This is the heaviest nuclide with a half-life of at least four years before the "Sea of Instability".

[6] 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 nearly eight quadrillion years.