Isotopes of berkelium

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 nineteen known radioisotopes, from ²³³Bk to ²⁵³Bk (except ²³⁵Bk and 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.

Isotopes of berkelium (₉₇Bk)

Main isotopes Decay Isotope abun­dance half-life (t1/2) mode pro­duct ^245Bk synth 4.94 d ε ^245Cm α ^241Am ^246Bk synth 1.80 d β^+ ^246Cm α ^242Am ^247Bk synth 1380 y α ^243Am ^248Bk synth >9 y α ^244Am ^249Bk synth 327.2 d β^− ^249Cf α ^245Am SF –

view talk edit

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

List of isotopes

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

1. ^mBk – Excited nuclear isomer.
2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
4. Modes of decay:

   EC:	Electron capture
   SF:	Spontaneous fission

5. ( ) spin value – Indicates spin with weak assignment arguments.
6. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
7. NUBASE2020 question-marks this decay, but it has been observed directly, see e.g. the IAEA Chart of Nuclides.
8. Order of ground state and isomer is uncertain.
9. Most common isotope

Actinides vs fission products

Actinides and fission products by half-life v t e
Actinides by decay chain				Half-life range (a)	Fission products of ^235U by yield
4n (Thorium)	4n + 1 (Neptunium)	4n + 2 (Radium)	4n + 3 (Actinium)		4.5–7%	0.04–1.25%	<0.001%
^228Ra^№				4–6 a		^155Eu^þ
^248Bk				> 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	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
^232Th^№		^238U^№	^235U^ƒ№	0.7–14.1 Ga
₡,  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)