Isotopes of curium

Isotopes of curium (₉₆Cm)
SF	–
CD	208Pb
ε	243Am
SF	–
SF	–
SF	–
SF	–
SF	–
α	246Pu
β−	250Bk
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Curium (₉₆Cm) is an artificial element with an atomic number of 96. Because it is an artificial element, a standard atomic weight cannot be given, and it has no stable isotopes. The first isotope synthesized was ²⁴²Cm in 1944, which has 146 neutrons.

There are 19 known radioisotopes ranging from ²³³Cm to ²⁵¹Cm. There are also ten known nuclear isomers. The longest-lived isotope is ²⁴⁷Cm, with half-life 15.6 million years – orders of magnitude longer than that of any known isotope beyond curium, and long enough to study as a possible extinct radionuclide that would be produced by the r-process.^[2]^[3] The longest-lived known isomer is ^246mCm with a half-life of 1.12 seconds.

List of isotopes

Nuclide ^{[n 1]}	Z	N	Isotopic mass (Da)^[4] ^{[n 2]}^{[n 3]}	Half-life^[1] ^{[n 4]}	Decay mode^[1] ^{[n 5]}	Daughter isotope	Spin and parity^[1] ^{[n 6]}^{[n 4]}
Nuclide ^{[n 1]}	Excitation energy^{[n 4]}			Half-life^[1] ^{[n 4]}	Decay mode^[1] ^{[n 5]}	Daughter isotope	Spin and parity^[1] ^{[n 6]}^{[n 4]}
²³³Cm	96	137	233.050771(87)	27(10) s	β⁺ (80%)	²³³Am	3/2+#
²³³Cm	96	137	233.050771(87)	27(10) s	α (20%)	²²⁹Pu	3/2+#
²³⁴Cm	96	138	234.050159(18)	52(9) s	β⁺ (71%)	²³⁴Am	0+
					α (27%)	²³⁰Pu
					SF (2%)	(various)
²³⁵Cm	96	139	235.05155(11)#	7(3) min	β⁺ (96%)	²³⁵Am	5/2+#
²³⁵Cm	96	139	235.05155(11)#	7(3) min	α (4%)	²³¹Pu	5/2+#
²³⁶Cm	96	140	236.051372(19)	6.8(8) min	β⁺ (82%)	²³⁶Am	0+
²³⁶Cm	96	140	236.051372(19)	6.8(8) min	α (18%)	²³²Pu	0+
²³⁷Cm	96	141	237.052869(80)	>10# min	α (?%)	²³³Pu	5/2+#
²³⁸Cm	96	142	238.053082(13)	2.2(4) h	EC (96.11%)	²³⁸Am	0+
					α (3.84%)	²³⁴Pu
					SF (0.048%)	(various)
²³⁹Cm	96	143	239.05491(16)	2.5(4) h	β⁺	²³⁹Am	7/2−#
²³⁹Cm	96	143	239.05491(16)	2.5(4) h	α (6.2x10⁻³%)	²³⁵Pu	7/2−#
²⁴⁰Cm	96	144	240.0555282(20)	30.4(37) d	α	²³⁶Pu	0+
²⁴⁰Cm	96	144	240.0555282(20)	30.4(37) d	SF (3.9×10⁻⁶%)	(various)	0+
²⁴¹Cm	96	145	241.0576512(17)	32.8(2) d	EC (99.0%)	²⁴¹Am	1/2+
²⁴¹Cm	96	145	241.0576512(17)	32.8(2) d	α (1.0%)	²³⁷Pu	1/2+
²⁴²Cm	96	146	242.0588342(12)	162.8(2) d	α^{[n 7]}	²³⁸Pu	0+
					SF (6.2×10⁻⁶%)	(various)
					CD (1.1×10⁻¹⁴%)^{[n 8]}	²⁰⁸Pb ³⁴Si
^242mCm	2800(100) keV			180(70) ns
²⁴³Cm	96	147	243.0613873(16)	29.1(1) y	α (99.71%)	²³⁹Pu	5/2+
					EC (0.29%)	²⁴³Am
					SF (5.3×10⁻⁹%)	(various)
^243mCm	87.4(1) keV			1.08(3) μs	IT	²⁴³Cm	1/2+
²⁴⁴Cm	96	148	244.0627506(12)	18.11(3) y	α	²⁴⁰Pu	0+
²⁴⁴Cm	96	148	244.0627506(12)	18.11(3) y	SF (1.37×10⁻⁴%)	(various)	0+
^244m1Cm	1040.181(11) keV			34(2) ms	IT	²⁴⁴Cm	6+
^244m2Cm	1100(900)# keV			>500 ns	SF	(various)
²⁴⁵Cm	96	149	245.0654910(12)	8250(70) y	α	²⁴¹Pu	7/2+
²⁴⁵Cm	96	149	245.0654910(12)	8250(70) y	SF (6.1×10⁻⁷%)	(various)	7/2+
^245mCm	355.92(10) keV			290(20) ns	IT	²⁴⁵Cm	1/2+
²⁴⁶Cm	96	150	246.0672220(16)	4706(40) y	α (99.97%)	²⁴²Pu	0+
²⁴⁶Cm	96	150	246.0672220(16)	4706(40) y	SF (0.02615%)	(various	0+
^246mCm	1179.66(13) keV			1.12(24) s	IT	²⁴⁶Cm	8−
²⁴⁷Cm	96	151	247.0703527(41)	1.56(5)×10⁷ y	α	²⁴³Pu	9/2−
^247m1Cm	227.38(19) keV			26.3(3) μs	IT	²⁴⁷Cm	5/2+
^247m2Cm	404.90(3) keV			100.6(6) ns	IT	²⁴⁷Cm	1/2+
²⁴⁸Cm	96	152	248.0723491(25)	3.48(6)×10⁵ y	α (91.61%)^{[n 9]}	²⁴⁴Pu	0+
²⁴⁸Cm	96	152	248.0723491(25)	3.48(6)×10⁵ y	SF (8.39%)	(various)	0+
^248mCm	1458.1(10) keV			146(18) μs	IT	²⁴⁸Cm	8−#
²⁴⁹Cm	96	153	249.0759540(25)	64.15(3) min	β⁻	²⁴⁹Bk	1/2+
^249mCm	48.76(4) keV			23 μs	α	²⁴⁵Pu	7/2+
²⁵⁰Cm	96	154	250.078358(11)	8300# y	SF (74%)^{[n 10]}	(various)	0+
					α (?%)	²⁴⁶Pu
					β⁻ (?%)	²⁵⁰Bk
²⁵¹Cm	96	155	251.082285(24)	16.8(2) min	β⁻	²⁵¹Bk	(3/2+)
This table header & footer: view

^ ^mCm – Excited nuclear isomer.
^ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
^ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
^ ^a ^b ^c # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
^ Modes of decay:

CD: Cluster decay

EC: Electron capture

SF: Spontaneous fission
^ ( ) spin value – Indicates spin with weak assignment arguments.
^ Theoretically capable of β⁺β⁺ decay to ²⁴²Pu
^ Heaviest known nuclide to undergo cluster decay
^ Theoretically capable of β⁻β⁻ decay to ²⁴⁸Cf
^ The nuclide with the lowest atomic number known to undergo spontaneous fission as the main decay mode

Actinides vs fission products

Actinides and fission products by half-life v t e
Actinides^[5] by decay chain				Half-life range (a)	Fission products of ²³⁵U by yield^[6]
4n	4n + 1	4n + 2	4n + 3	Half-life range (a)	4.5–7%	0.04–1.25%	<0.001%
²²⁸Ra^№				4–6 a		¹⁵⁵Eu^þ
²⁴⁸Bk^[7]				> 9 a
²⁴⁴Cm^ƒ	²⁴¹Pu^ƒ	²⁵⁰Cf	²²⁷Ac^№	10–29 a	⁹⁰Sr	⁸⁵Kr	^113mCd^þ
²³²U^ƒ		²³⁸Pu^ƒ	²⁴³Cm^ƒ	29–97 a	¹³⁷Cs	¹⁵¹Sm^þ	^121mSn
	²⁴⁹Cf^ƒ	^242mAm^ƒ		141–351 a	No fission products have a half-life in the range of 100 a–210 ka ...
	²⁴¹Am^ƒ		²⁵¹Cf^ƒ^[8]	430–900 a
		²²⁶Ra^№	²⁴⁷Bk	1.3–1.6 ka
²⁴⁰Pu	²²⁹Th	²⁴⁶Cm^ƒ	²⁴³Am^ƒ	4.7–7.4 ka
	²⁴⁵Cm^ƒ	²⁵⁰Cm		8.3–8.5 ka
			²³⁹Pu^ƒ	24.1 ka
		²³⁰Th^№	²³¹Pa^№	32–76 ka
²³⁶Np^ƒ	²³³U^ƒ	²³⁴U^№		150–250 ka	⁹⁹Tc^₡	¹²⁶Sn
²⁴⁸Cm		²⁴²Pu		327–375 ka		⁷⁹Se^₡
				1.33 Ma	¹³⁵Cs^₡
	²³⁷Np^ƒ			1.61–6.5 Ma	⁹³Zr	¹⁰⁷Pd
²³⁶U			²⁴⁷Cm^ƒ	15–24 Ma		¹²⁹I^₡
²⁴⁴Pu				80 Ma	... nor beyond 15.7 Ma^[9]
²³²Th^№		²³⁸U^№	²³⁵U^ƒ№	0.7–14.1 Ga	... nor beyond 15.7 Ma^[9]
₡, has thermal neutron capture cross section in the range of 8–50 barns ƒ, fissile №, primarily a naturally occurring radioactive material (NORM) þ, neutron poison (thermal neutron capture cross section greater than 3k barns)

References

^ ^a ^b ^c ^d Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
^ Côté, Benoit; Eichler, Marius; Yagüe López, Andrés; Vassh, Nicole; Mumpower, Matthew R.; Világos, Blanka; Soós, Benjámin; Arcones, Almudena; Sprouse, Trevor M.; Surman, Rebecca; Pignatari, Marco; Pető, Mária K.; Wehmeyer, Benjamin; Rauscher, Thomas; Lugaro, Maria (26 February 2021). "¹²⁹I and ²⁴⁷Cm in meteorites constrain the last astrophysical source of solar r-process elements". Science. 371 (6532): 945–948. arXiv:2006.04833. Bibcode:2021Sci...371..945C. doi:10.1126/science.aba1111. PMID 33632846. S2CID 232050526.
^ Davis, A.M.; McKeegan, K.D. (2014). "Short-Lived Radionuclides and Early Solar System Chronology". Treatise on Geochemistry: 383. doi:10.1016/B978-0-08-095975-7.00113-3. ISBN 9780080983004.
^ Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3): 030003. doi:10.1088/1674-1137/abddaf.
^ 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 uranium-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 [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.

Isotope masses from:
- Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
Half-life, spin, and isomer data selected from the following sources.
- Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
- National Nuclear Data Center. "NuDat 2.x database". Brookhaven National Laboratory.
- Holden, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.). CRC Handbook of Chemistry and Physics (85th ed.). Boca Raton, Florida: CRC Press. ISBN 978-0-8493-0485-9.

[4] Cm – Excited nuclear isomer.

[6] ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.

[TMS-7] # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).

[TNN-8] # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).

[9] Modes of decay:

CD: Cluster decay

EC: Electron capture

SF: Spontaneous fission

[10] ( ) spin value – Indicates spin with weak assignment arguments.

[11] Theoretically capable of β⁺β⁺ decay to ²⁴²Pu

[12] Heaviest known nuclide to undergo cluster decay

[13] Theoretically capable of β⁻β⁻ decay to ²⁴⁸Cf

[14] The nuclide with the lowest atomic number known to undergo spontaneous fission as the main decay mode

[NUBASE2020-1] Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.

[Cm-Côté-2] Côté, Benoit; Eichler, Marius; Yagüe López, Andrés; Vassh, Nicole; Mumpower, Matthew R.; Világos, Blanka; Soós, Benjámin; Arcones, Almudena; Sprouse, Trevor M.; Surman, Rebecca; Pignatari, Marco; Pető, Mária K.; Wehmeyer, Benjamin; Rauscher, Thomas; Lugaro, Maria (26 February 2021). "¹²⁹I and ²⁴⁷Cm in meteorites constrain the last astrophysical source of solar r-process elements". Science. 371 (6532): 945–948. arXiv:2006.04833. Bibcode:2021Sci...371..945C. doi:10.1126/science.aba1111. PMID 33632846. S2CID 232050526.

[Cm-Davis-3] Davis, A.M.; McKeegan, K.D. (2014). "Short-Lived Radionuclides and Early Solar System Chronology". Treatise on Geochemistry: 383. doi:10.1016/B978-0-08-095975-7.00113-3. ISBN 9780080983004.

[AME2020_II-5] Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3): 030003. doi:10.1088/1674-1137/abddaf.

[15] 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.

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

[17] 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]."

[18] This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".

[19] 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.

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