Isotopes of berkelium

Isotopes of berkelium (₉₇Bk)
α	241Am
α	242Am
α	245Am
SF	–

Berkelium (₉₇Bk) is an artificial element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was ²⁴³Bk in 1949. There are twenty known radioisotopes, from ²³³Bk to ²⁵³Bk (except ²³⁷Bk), and seven nuclear isomers. The longest-lived isotope known is ²⁴⁷Bk with a half-life of 1,380 years; however ²⁴⁸Bk, which has not been observed to decay, may live longer.

The isotope commonly used in study, though, is ²⁴⁹Bk, as is it the only berkelium isotope that can be usefully extracted from reactor actinides and accumulated in weighable quantities.

List of isotopes

Nuclide ^{[n 1]}	Z	N	Isotopic mass (Da)^[3] ^{[n 2]}^{[n 3]}	Discovery year	Half-life^[1]	Decay mode^[1] ^{[n 4]}	Daughter isotope	Spin and parity^[1] ^{[n 5]}^{[n 6]}
Nuclide ^{[n 1]}	Excitation energy^{[n 6]}			Discovery year	Half-life^[1]	Decay mode^[1] ^{[n 4]}	Daughter isotope	Spin and parity^[1] ^{[n 5]}^{[n 6]}
²³³Bk	97	136	233.05665(25)#	2015	40(30) s	α (82%)	²²⁹Am	3/2−#
²³³Bk	97	136	233.05665(25)#	2015	40(30) s	β⁺? (18%)	²³³Cm	3/2−#
²³⁴Bk	97	137	234.05732(16)#	2016	20(5) s	α (>80%)	²³⁰Am	3−#
²³⁴Bk	97	137	234.05732(16)#	2016	20(5) s	β⁺ (<20%)	²³⁴Cm	3−#
²³⁵Bk^[4]	97	138	235.05665(43)#	2026	1# min	α	²³¹Am	3/2−#
²³⁵Bk^[4]	97	138	235.05665(43)#	2026	1# min	β⁺	²³⁵Cm	3/2−#
²³⁶Bk	97	139	236.05748(39)#	2017	26(10) s	β⁺ (99.96%)	²³⁶Cm	4+#
²³⁶Bk	97	139	236.05748(39)#	2017	26(10) s	β⁺, SF (0.04%)	(various)	4+#
²³⁸Bk	97	141	238.05820(28)#	1994	2.40(8) min	β⁺ (99.95%)	²³⁸Cm	1#
²³⁸Bk	97	141	238.05820(28)#	1994	2.40(8) min	β⁺, SF (0.048%)	(various)	1#
²³⁹Bk	97	142	239.05824(22)#	(2010)^{[n 7]}	100# s	β⁺	²³⁹Cm	(7/2+)
²⁴⁰Bk	97	143	240.05976(16)#	1980	4.8(8) min	β⁺?	²⁴⁰Cm	7−#
						α?	²³⁶Am
						β⁺, SF (0.0013%)	(various)
²⁴¹Bk	97	144	241.06010(18)#	2003	4.6(4) min	β⁺	²⁴¹Cm	(7/2+)
²⁴²Bk	97	145	242.06200(14)#	1972	7.0(13) min	β⁺	²⁴²Cm	3+#
²⁴²Bk	97	145	242.06200(14)#	1972	7.0(13) min	β⁺, SF (<3×10⁻⁵%)	(various)	3+#
^242mBk	2000(200)# keV			1979	600(100) ns	SF	(various)
²⁴³Bk	97	146	243.063006(5)	1950	4.6(2) h	β⁺ (99.85%)	²⁴³Cm	3/2−
²⁴³Bk	97	146	243.063006(5)	1950	4.6(2) h	α (0.15%)	²³⁹Am	3/2−
²⁴⁴Bk	97	147	244.065179(15)	1972	5.02(3) h	β⁺ (99.994%)^{[n 8]}	²⁴⁴Cm	4−
²⁴⁴Bk	97	147	244.065179(15)	1972	5.02(3) h	α (0.006%)	²⁴⁰Am	4−
^244mBk	1500(500)# keV			2014	820(60) ns	SF	(various)
²⁴⁵Bk	97	148	245.0663598(19)	1951	4.95(3) d	EC (99.88%)	²⁴⁵Cm	3/2−
²⁴⁵Bk	97	148	245.0663598(19)	1951	4.95(3) d	α (0.12%)	²⁴¹Am	3/2−
²⁴⁶Bk	97	149	246.06867(6)	1954	1.80(2) d	β⁺	²⁴⁶Cm	2(−)
²⁴⁷Bk	97	150	247.070306(6)	1965	1.38(25)×10³ y	α	²⁴³Am	3/2−
²⁴⁷Bk	97	150	247.070306(6)	1965	1.38(25)×10³ y	SF?	(various)	3/2−
²⁴⁸Bk	97	151	248.07314(5)	1956	>9 y	α?	²⁴⁴Am	6+#
						EC?	²⁴⁸Cm
						β⁻?	²⁴⁸Cf
^248mBk^{[n 9]}	−20(50) keV			1965	23.7(2) h	β⁻ (70%)	²⁴⁸Cf	1(−)
^248mBk^{[n 9]}	−20(50) keV			1965	23.7(2) h	EC (30%)	²⁴⁸Cm	1(−)
²⁴⁹Bk^{[n 10]}	97	152	249.0749831(13)	1954	327.2(3) d	β⁻	²⁴⁹Cf	7/2+
						α (0.00145%)	²⁴⁵Am
						SF (4.7×10⁻⁸%)	(various)
^249mBk	8.777(14) keV			(1960)^{[n 11]}	300 μs	IT	²⁴⁹Bk	3/2−
²⁵⁰Bk	97	153	250.078317(3)	1954	3.212(5) h	β⁻	²⁵⁰Cf	2−
^250m1Bk	35.59(10) keV			1966	29(1) μs	IT	²⁵⁰Bk	4+
^250m2Bk	85.6(16) keV			1966	213(8) μs	IT	²⁵⁰Bk	7+
²⁵¹Bk	97	154	251.080761(12)	1967	55.6(11) min	β⁻	²⁵¹Cf	(3/2−)
^251mBk	35.5(13) keV			(1966)^{[n 12]}	58(4) μs	IT	²⁵¹Bk	(7/2+)
²⁵²Bk	97	155	252.08431(22)#	(1992)	1.8(5) min	β⁻	²⁵²Cf
²⁵³Bk	97	156	253.08688(39)#	(1992)	60# min	β⁻?	²⁵³Cf	3/2-#
This table header & footer:

^ ^mBk – 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).
^ Modes of decay:

EC: Electron capture

SF: Spontaneous fission
^ ( ) spin value – Indicates spin with weak assignment arguments.
^ ^a ^b # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
^ Populated, but not properties measured, not included in discovery database
^ NUBASE2020 question-marks this decay, but it has been observed directly, see e.g. the IAEA Chart of Nuclides.
^ Order of ground state and isomer is uncertain.
^ Most common isotope
^ Only published in a conference proceeding and not a refereed journal
^ Half-life not measured, not included in discovery database

Actinides vs fission products

Actinides and fission products by half-life
Actinides^[5] by decay chain				Half-life range (a)	Fission products of ²³⁵U by yield^[6]
4n (Thorium)	4n + 1 (Neptunium)	4n + 2 (Radium)	4n + 3 (Actinium)	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.
^ 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.
^ 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.
^ Wang, J. G.; Li, Z. C.; Zhang, Z. Y.; et al. (2026). "Decay properties of new isotopes ²³⁵Bk and ²³¹Am". Physics Letters B. 875 (140365). doi:10.1016/j.physletb.2026.140365.
^ 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 3.0 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.

[3] Bk – Excited nuclear isomer.

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

[TMS-6] # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).

[7] Modes of decay:

EC: Electron capture

SF: Spontaneous fission

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

[TNN-9] # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).

[11] Populated, but not properties measured, not included in discovery database

[12] NUBASE2020 question-marks this decay, but it has been observed directly, see e.g. the IAEA Chart of Nuclides.

[OGI-13] Order of ground state and isomer is uncertain.

[14] Most common isotope

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

[16] Half-life not measured, not included in discovery database

[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.

[2] 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.

[AME2020_II-4] 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.

[235Bk-231Am-10] Wang, J. G.; Li, Z. C.; Zhang, Z. Y.; et al. (2026). "Decay properties of new isotopes ²³⁵Bk and ²³¹Am". Physics Letters B. 875 (140365). doi:10.1016/j.physletb.2026.140365.

[17] 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.

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

[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. 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]."

[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 eight quadrillion years.

[1]

[2]

[n 1]

[3]

[n 2]

[n 3]

[n 4]

[n 5]

[n 6]

[4]

[n 7]

[n 8]

[n 9]

[n 10]

[n 11]

[n 12]

[5]

[6]

[7]

[8]

[9]

EC:	Electron capture
SF:	Spontaneous fission