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

|-id=Berkelium-233 | rowspan=2|233Bk | rowspan=2 style="text-align:right" | 97 | rowspan=2 style="text-align:right" | 136 | rowspan=2|233.05665(25)# | rowspan=2 style="text-align:center" | 2015 | rowspan=2| | α (82%) | 229Am | rowspan=2|3/2−# |- | β+? (18%) | 233Cm |-id=Berkelium-234 | rowspan=2|234Bk | rowspan=2 style="text-align:right" | 97 | rowspan=2 style="text-align:right" | 137 | rowspan=2|234.05732(16)# | rowspan=2 style="text-align:center" | 2016 | rowspan=2| | α (>80%) | 230Am | rowspan=2|3−# |- | β+ (<20%) | 234Cm |-id=Berkelium-235 | rowspan=2|235Bk | rowspan=2 style="text-align:right" | 97 | rowspan=2 style="text-align:right" | 138 | rowspan=2|235.05665(43)# | rowspan=2 style="text-align:center" | 2026 | rowspan=2|1# min | α | 231Am | rowspan=2|3/2−# |- | β+ | 235Cm |-id=Berkelium-236 | rowspan=2|236Bk | rowspan=2 style="text-align:right" | 97 | rowspan=2 style="text-align:right" | 139 | rowspan=2|236.05748(39)# | rowspan=2 style="text-align:center" | 2017 | rowspan=2| | β+ (99.96%) | 236Cm | rowspan=2|4+# |- | β+, SF (0.04%) | (various) |-id=Berkelium-238 | rowspan=2|238Bk | rowspan=2 style="text-align:right" | 97 | rowspan=2 style="text-align:right" | 141 | rowspan=2|238.05820(28)# | rowspan=2 style="text-align:center" | 1994 | rowspan=2| | β+ (99.95%) | 238Cm | rowspan=2| 1# |- | β+, SF (0.048%) | (various) |-id=Berkelium-239 | 239Bk | style="text-align:right" | 97 | style="text-align:right" | 142 | 239.05824(22)# | style="text-align:center" | (2010)Populated, but no properties measured, not included in discovery database | 100# s | β+ | 239Cm | (7/2+) |-id=Berkelium-240 | rowspan=3|240Bk | rowspan=3 style="text-align:right" | 97 | rowspan=3 style="text-align:right" | 143 | rowspan=3|240.05976(16)# | rowspan=3 style="text-align:center" | 1980 | rowspan=3| | β+? | 240Cm | rowspan=3|7−# |- | α? | 236Am |- | β+, SF (0.0013%) | (various) |-id=Berkelium-241 | 241Bk | style="text-align:right" | 97 | style="text-align:right" | 144 | 241.06010(18)# | style="text-align:center" | 2003 | | β+ | 241Cm | (7/2+) |-id=Berkelium-242 | rowspan=2|242Bk | rowspan=2 style="text-align:right" | 97 | rowspan=2 style="text-align:right" | 145 | rowspan=2|242.06200(14)# | rowspan=2 style="text-align:center" | 1972 | rowspan=2| | β+ | 242Cm | rowspan=2|3+# |- | β+, SF (<3×10−5%) | (various) |-id=Berkelium-242m | style="text-indent:1em" | 242mBk | colspan="3" style="text-indent:2em" | 2000(200)# keV | style="text-align:center" | 1979 | | SF | (various) | |-id=Berkelium-243 | rowspan=2|243Bk | rowspan=2 style="text-align:right" | 97 | rowspan=2 style="text-align:right" | 146 | rowspan=2|243.063006(5) | rowspan=2 style="text-align:center" | 1950 | rowspan=2| | β+ (99.85%) | 243Cm | rowspan=2|3/2− |- | α (0.15%) | 239Am |-id=Berkelium-244 | rowspan=2|244Bk | rowspan=2 style="text-align:right" | 97 | rowspan=2 style="text-align:right" | 147 | rowspan=2|244.065179(15) | rowspan=2 style="text-align:center" | 1972 | rowspan=2| | β+ (99.994%)NUBASE2020 question-marks this decay, but it has been observed directly, see e.g. the IAEA Chart of Nuclides. | 244Cm | rowspan=2|4− |- | α (0.006%) | 240Am |-id=Berkelium-244m | style="text-indent:1em" | 244mBk | colspan="3" style="text-indent:2em" | 1500(500)# keV | style="text-align:center" | 2014 | | SF | (various) | |-id=Berkelium-245 | rowspan=2|245Bk | rowspan=2 style="text-align:right" | 97 | rowspan=2 style="text-align:right" | 148 | rowspan=2|245.0663598(19) | rowspan=2 style="text-align:center" | 1951 | rowspan=2| | EC (99.88%) | 245Cm | rowspan=2|3/2− |- | α (0.12%) | 241Am |-id=Berkelium-246 | 246Bk | style="text-align:right" | 97 | style="text-align:right" | 149 | 246.06867(6) | style="text-align:center" | 1954 | | β+ | 246Cm | 2(−) |-id=Berkelium-247 | rowspan=2|247Bk | rowspan=2 style="text-align:right" | 97 | rowspan=2 style="text-align:right" | 150 | rowspan=2|247.070306(6) | rowspan=2 style="text-align:center" | 1965 | rowspan=2| | α | 243Am | rowspan=2|3/2− |- | SF? | (various) |-id=Berkelium-248 | rowspan=3|248Bk | rowspan=3 style="text-align:right" | 97 | rowspan=3 style="text-align:right" | 151 | rowspan=3|248.07314(5) | rowspan=3 style="text-align:center" | 1956 | rowspan=3|>9 y | α? | 244Am | rowspan=3|6+# |- | EC? | 248Cm |- | β−? | 248Cf |-id=Berkelium-248m | rowspan=2 style="text-indent:1em" | 248mBk | rowspan=2 colspan="3" style="text-indent:2em" | −20(50) keV | rowspan=2 style="text-align:center" | 1965 | rowspan=2| 23.7(2) h | β− (70%) | 248Cf | rowspan=2|1(−) |- | EC (30%) | 248Cm |-id=Berkelium-249 | rowspan=3|249BkMost common isotope | rowspan=3 style="text-align:right" | 97 | rowspan=3 style="text-align:right" | 152 | rowspan=3|249.0749831(13) | rowspan=3 style="text-align:center" | 1954 | rowspan=3| | β− | 249Cf | rowspan=3|7/2+ |- | α (0.00145%) | 245Am |- | SF (4.7×10−8%) | (various) |-id=Berkelium-249m | style="text-indent:1em" | 249mBk | colspan="3" style="text-indent:2em" | 8.777(14) keV | style="text-align:center" | (1960)Only published in a conference proceeding and not a refereed journal | | IT | 249Bk | 3/2− |-id=Berkelium-250 | 250Bk | style="text-align:right" | 97 | style="text-align:right" | 153 | 250.078317(3) | style="text-align:center" | 1954 | | β− | 250Cf | 2− |-id=Berkelium-250m1 | style="text-indent:1em" | 250m1Bk | colspan="3" style="text-indent:2em" | 35.59(10) keV | style="text-align:center" | 1966 | | IT | 250Bk | 4+ |-id=Berkelium-250m2 | style="text-indent:1em" | 250m2Bk | colspan="3" style="text-indent:2em" | 85.6(16) keV | style="text-align:center" | 1966 | | IT | 250Bk | 7+ |-id=Berkelium-251 | 251Bk | style="text-align:right" | 97 | style="text-align:right" | 154 | 251.080761(12) | style="text-align:center" | 1967 | | β− | 251Cf | (3/2−) |-id=Berkelium-251m | style="text-indent:1em" | 251mBk | colspan="3" style="text-indent:2em" | 35.5(13) keV | style="text-align:center" | (1966) Half-life not measured, not included in discovery database | | IT | 251Bk | (7/2+) |-id=Berkelium-252 | 252Bk | style="text-align:right" | 97 | style="text-align:right" | 155 | 252.08431(22)# | style="text-align:center" | (1992) | | β− | 252Cf | |-id=Berkelium-253 | 253Bk | style="text-align:right" | 97 | style="text-align:right" | 156 | 253.08688(39)# | style="text-align:center" | (1992) | 60# min | β−? | 253Cf | 3/2-#

Actinides vs fission products

References

Isotope masses from:

Half-life, spin, and isomer data selected from the following sources.