Physics:Isotopes of curium

Main isotopes of Chemistry:curium (₉₆Cm)
SF	–
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.^[1]^[2] It is followed by ²⁴⁸Cm, which has a half-life of 348,000 years. 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 (u) ^{[n 2]}^{[n 3]}	Half-life ^{[n 4]}	Decay mode ^{[n 5]}	Daughter isotope	Spin and parity ^{[n 6]}^{[n 4]}
Nuclide ^{[n 1]}	Excitation energy^{[n 4]}			Half-life ^{[n 4]}	Decay mode ^{[n 5]}	Daughter isotope	Spin and parity ^{[n 6]}^{[n 4]}
²³³Cm	96	137	233.05077(9)	2010	27(10) s	β⁺ (80%)	²³³Am	3/2+#
²³³Cm	96	137	233.05077(9)	2010	27(10) s	α (20%)	²²⁹Pu	3/2+#
²³⁴Cm	96	138	234.050159(18)	2016	52(9) s	β⁺ (71%)	²³⁴Am	0+
						α (27%)	²³⁰Pu
						SF (2%)	(various)
²³⁵Cm	96	139	235.05155(11)#	2020	7(3) min	β⁺? (96%)	²³⁵Am	5/2+#
²³⁵Cm	96	139	235.05155(11)#	2020	7(3) min	α (4%)	²³¹Pu	5/2+#
²³⁶Cm	96	140	236.051372(19)	2010	6.8(8) min	β⁺ (82%)	²³⁶Am	0+
²³⁶Cm	96	140	236.051372(19)	2010	6.8(8) min	α (18%)	²³²Pu	0+
²³⁷Cm	96	141	237.05287(8)	2002	>10# min	α (?%)	²³³Pu	5/2+#
²³⁸Cm	96	142	238.053082(13)	1994	2.2(4) h	EC? (96.11%)	²³⁸Am	0+
						α (3.84%)	²³⁴Pu
						SF (0.048%)	(various)
²³⁹Cm	96	143	239.05491(16)	2008	2.5(4) h	β⁺	²³⁹Am	7/2−#
²³⁹Cm	96	143	239.05491(16)	2008	2.5(4) h	α (6.2x10⁻³%)	²³⁵Pu	7/2−#
²⁴⁰Cm	96	144	240.0555282(20)	1949	30.4(37) d	α	²³⁶Pu	0+
²⁴⁰Cm	96	144	240.0555282(20)	1949	30.4(37) d	SF (3.9×10⁻⁶%)	(various)	0+
²⁴¹Cm	96	145	241.0576512(17)	1952	32.8(2) d	EC (99.0%)	²⁴¹Am	1/2+
²⁴¹Cm	96	145	241.0576512(17)	1952	32.8(2) d	α (1.0%)	²³⁷Pu	1/2+
²⁴²Cm	96	146	242.0588342(12)	1949	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			1971	180(70) ns	SF?	(various)
^242mCm	2800(100) keV			1971	180(70) ns	IT?	²⁴²Cm
²⁴³Cm	96	147	243.0613873(16)	1950	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			1975	1.08(3) μs	IT	²⁴³Cm	1/2+
²⁴⁴Cm	96	148	244.0627506(12)	1950	18.11(3) y	α	²⁴⁰Pu	0+
²⁴⁴Cm	96	148	244.0627506(12)	1950	18.11(3) y	SF (1.37×10⁻⁴%)	(various)	0+
^244m1Cm	1040.181(11) keV			1963	34(2) ms	IT	²⁴⁴Cm	6+
^244m2Cm	1100(900)# xkeV			(1969)^{[n 9]}	>500 ns	SF	(various)
²⁴⁵Cm	96	149	245.0654910(12)	1954	8250(70) y	α	²⁴¹Pu	7/2+
²⁴⁵Cm	96	149	245.0654910(12)	1954	8250(70) y	SF (6.1×10⁻⁷%)	(various)	7/2+
^245mCm	355.92(10) keV			1975	290(20) ns	IT	²⁴⁵Cm	1/2+
²⁴⁶Cm	96	150	246.0672220(16)	1954	4706(40) y	α (99.97%)	²⁴²Pu	0+
²⁴⁶Cm	96	150	246.0672220(16)	1954	4706(40) y	SF (0.02615%)	(various)	0+
^246mCm	1179.66(13) keV			2008	1.12(24) s	IT	²⁴⁶Cm	8−
²⁴⁷Cm	96	151	247.070353(4)	1954	1.56(5)×10⁷ y	α^{[n 10]}	²⁴³Pu	9/2−
^247m1Cm	227.38(19) keV			1968	26.3(3) μs	IT	²⁴⁷Cm	5/2+
^247m2Cm	404.90(3) keV			2003	100.6(6) ns	IT	²⁴⁷Cm	1/2+
²⁴⁸Cm	96	152	248.0723491(25)	1956	3.48(6)×10⁵ y	α (91.61%)^{[n 11]}	²⁴⁴Pu	0+
²⁴⁸Cm	96	152	248.0723491(25)	1956	3.48(6)×10⁵ y	SF (8.39%)	(various)	0+
^248mCm	1458.1(10) keV			2019	146(18) μs	IT	²⁴⁸Cm	8−#
²⁴⁹Cm	96	153	249.0759540(25)	1956	64.15(3) min	β⁻	²⁴⁹Bk	1/2+
^249mCm	48.76(4) keV			(1966)^{[n 12]}	23 μs			7/2+
²⁵⁰Cm	96	154	250.078358(11)	1966	8300# y^{[n 13]}	SF^{[n 14]}	(various)	0+
						α (?%)	²⁴⁶Pu
						β⁻ (?%)	²⁵⁰Bk
²⁵¹Cm	96	155	251.082285(24)	1978	16.8(2) min	β⁻	²⁵¹Bk	(3/2+)

↑ ^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).
↑ ^4.0 ^4.1 ^4.2 # – 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
↑ Only published in a conference proceeding and not a refereed journal
↑ Theoretically capable of β⁻ decay to ²⁴⁷Bk or SF
↑ Theoretically capable of β⁻β⁻ decay to ²⁴⁸Cf
↑ Only quoted from a private communication and not a refereed journal
↑ Only SF has been observed with a half-life 11,300 years; the value given theoretically estimates alpha- and beta-decay branches, which is quite uncertain.^[3]
↑ The nuclide with the lowest atomic number known (almost surely) to undergo spontaneous fission as the main decay mode

Actinides vs fission products

Actinides and fission products by half-life v · d · e
Actinides^[4] by decay chain				Half-life range (y)	Fission products of ²³⁵U by yield<ref>Specifically from thermal neutron fission of U-235, e.g. in a typical nuclear reactor.</ref>
4n	4n+1	4n+2	4n+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^[5]	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^[6]	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^[7]
²³²Th^№		²³⁸U^№	²³⁵U^ƒ№	0.7 G – 14.1 G	... nor beyond 15.7 M years^[7]
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

References

↑ Côté, Benoit; Eichler, Marius; Yagüe López, Andrés; Vassh, Nicole; Mumpower, Matthew R.; Világos, Blanka; Soós, Benjámin; Arcones, Almudena et al. (26 February 2021). "¹²⁹I and ²⁴⁷Cm in meteorites constrain the last astrophysical source of solar r-process elements". Science 371 (6532): 945–948. doi:10.1126/science.aba1111. PMID 33632846. Bibcode: 2021Sci...371..945C.
↑ 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.
↑ "Adopted Levels for ²⁵⁰Cm". NNDC Chart of Nuclides. https://www.nndc.bnl.gov/ensnds/250/Cm/adopted.pdf.
↑ 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. doi:10.1016/0029-5582(65)90719-4. Bibcode: 1965NucPh..71..299M.
"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.

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, doi:10.1016/j.nuclphysa.2003.11.001, Bibcode: 2003NuPhA.729....3A, https://hal.archives-ouvertes.fr/in2p3-00020241/document
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, doi:10.1016/j.nuclphysa.2003.11.001, Bibcode: 2003NuPhA.729....3A, https://hal.archives-ouvertes.fr/in2p3-00020241/document
- National Nuclear Data Center. "NuDat 2.x database". Brookhaven National Laboratory. http://www.nndc.bnl.gov/nudat2/.
- Lide, David R., ed (2004). "11. Table of the Isotopes". CRC Handbook of Chemistry and Physics (85th ed.). Boca Raton, Florida: CRC Press. ISBN 978-0-8493-0485-9.

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[3] Cm – Excited nuclear isomer.

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

[TMS-5] # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).

[TNN-6] 4.0 ^4.1 ^4.2 # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).

[7] Modes of decay:

CD: Cluster decay

EC: Electron capture

SF: Spontaneous fission

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

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

[10] Heaviest known nuclide to undergo cluster decay

[11] Only published in a conference proceeding and not a refereed journal

[12] Theoretically capable of β⁻ decay to ²⁴⁷Bk or SF

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

[14] Only quoted from a private communication and not a refereed journal

[16] Only SF has been observed with a half-life 11,300 years; the value given theoretically estimates alpha- and beta-decay branches, which is quite uncertain.^[3]

[17] The nuclide with the lowest atomic number known (almost surely) to undergo spontaneous fission as the main decay mode

[Cm-Côté-1] Côté, Benoit; Eichler, Marius; Yagüe López, Andrés; Vassh, Nicole; Mumpower, Matthew R.; Világos, Blanka; Soós, Benjámin; Arcones, Almudena et al. (26 February 2021). "¹²⁹I and ²⁴⁷Cm in meteorites constrain the last astrophysical source of solar r-process elements". Science 371 (6532): 945–948. doi:10.1126/science.aba1111. PMID 33632846. Bibcode: 2021Sci...371..945C.

[Cm-Davis-2] 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.

[15] "Adopted Levels for ²⁵⁰Cm". NNDC Chart of Nuclides. https://www.nndc.bnl.gov/ensnds/250/Cm/adopted.pdf.

[18] 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.

[19] 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. doi:10.1016/0029-5582(65)90719-4. Bibcode: 1965NucPh..71..299M.
"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."

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

[21] 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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