Actinides and fission products by half-life
Actinides[1] by decay chain Half-life
range (a)
Fission products by yield[2]
4n 4n+1 4n+2 4n+3
4.5–7% 0.04–1.25% <0.001%
228Ra 4–6 155Euþ
244Cm 241Puƒ 250Cf 227Ac 10–29 90Sr 85Kr 113mCdþ
232Uƒ 238Pu 243Cmƒ 29–97 137Cs 151Smþ 121mSn
249Cfƒ 242mAmƒ 141–351

No fission products
have a half-life
in the range of
100–210k years…

241Am 251Cfƒ[3] 430–900
226Ra 247Bk 1.3k–1.6k
240Pu 229Th 246Cm 243Am 4.7k–7.4k
245Cmƒ 250Cm 8.3k–8.5k
239Puƒ 24.1k
230Th 231Pa 32k–76k
236Npƒ 233Uƒ 234U 150k–250k 99Tc 126Sn
248Cm 242Pu 327k–375k 79Se
1.53M 93Zr
237Np 2.1M–6.5M 135Cs 107Pd
236U 247Cmƒ 15M–24M 129I
244Pu 80M

...nor beyond 15.7M[4]

232Th 238U 235Uƒ№ 0.7G–14G

Legend for superscript symbols
₡  has thermal neutron capture cross section in the range of 8–50 barns
ƒ  fissile
metastable isomer
№  naturally occurring radioactive material (NORM)
þ  neutron poison (thermal neutron capture cross section greater than 3k barns)
†  range 4a–97a: Medium-lived fission product
‡  over 200ka: Long-lived fission product

Curium (Cm) is an artificial element, and thus a standard atomic mass cannot be given. Like all artificial elements, it has no stable isotopes. The first isotope synthesized was 242Cm in 1944.

Trace quantities are found in nature from neutron capture by uranium atoms.[5]

There are 21 known radioisotopes with atomic masses ranging from 232Cm to 252Cm. There are also four known nuclear isomers (243mCm, 244mCm, 245mCm, and 249mCm). The longest-lived isotope is 247Cm, with a half-life of 15.6 million years - several orders of magnitude longer than the half-life of all known nuclei of elements beyond curium in the periodic table. The longest-lived isomer is 244mCm with a half-life of 34 milliseconds.


isotopic mass
half-life decay
mode(s)[6][n 1]
isotopes[n 2]
excitation energy
232Cm 96 136 1? min 0+
233Cm 96 137 233.05077(8) 1# min β+ 233Am 3/2+#
α 229Pu
234Cm 96 138 234.05016(2) 51(12) s β+ 234Am 0+
α 230Pu
235Cm 96 139 235.05143(22)# 5# min β+ 235Am 5/2+#
α 231Pu
236Cm 96 140 236.05141(22)# 10# min β+ 236Am 0+
α 232Pu
237Cm 96 141 237.05290(22)# 20# min β+ 237Am 5/2+#
α 233Pu
238Cm 96 142 238.05303(4) 2.4(1) h EC (90%) 238Am 0+
α (10%) 234Pu
239Cm 96 143 239.05496(11)# ~2.9 h β+ (99.9%) 239Am (7/2-)
α (.1%) 235Pu
240Cm 96 144 240.0555295(25) 27(1) d α (99.5%) 236Pu 0+
EC (.5%) 240Am
SF (3.9×10−6%) (various)
241Cm 96 145 241.0576530(23) 32.8(2) d EC (99%) 241Am 1/2+
α (1%) 237Pu
242Cm[n 3] 96 146 242.0588358(20) 162.8(2) d α 238Pu 0+
SF (6.33×10−6%) (various)
CD (10−14%)[n 4] 208Pb
β+β+ (rare) 242Pu
243Cm 96 147 243.0613891(22) 29.1(1) a α (99.71%) 239Pu 5/2+
EC (.29%) 243Am
SF (5.3×10−9%) (various)
243mCm 87.4(1) keV 1.08(3) µs 1/2+
244Cm[n 3] 96 148 244.0627526(20) 18.10(2) a α 240Pu 0+
SF (1.34×10−4%) (various)
244mCm 1040.188(12) keV 34(2) ms IT 244Cm 6+
245Cm 96 149 245.0654912(22) 8.5(1)×103 a α 241Pu 7/2+
SF (6.1×10−7%) (various)
245mCm 355.90(10) keV 290(20) ns 1/2+
246Cm 96 150 246.0672237(22) 4.76(4)×103 a α (99.97%) 242Pu 0+
SF (.0261%) (various)
247Cm 96 151 247.070354(5) 1.56(5)×107 a α 243Pu 9/2-
248Cm 96 152 248.072349(5) 3.48(6)×105 a α (91.74%) 244Pu 0+
SF (8.26%) (various)
β-β- (rare) 248Cf
249Cm 96 153 249.075953(5) 64.15(3) min β- 249Bk 1/2(+)
249mCm 48.758(17) keV 23 µs (7/2+)
250Cm 96 154 250.078357(12) 8,300# a SF (80%)[n 5] (various) 0+
α (11%) 246Pu
β- (9%) 250Bk
251Cm 96 155 251.082285(24) 16.8(2) min β- 251Bk (1/2+)
252Cm 96 156 252.08487(32)# <1 d β- 252Bk 0+


  • Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
  • Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.


  • Isotope masses from:
  • Isotopic compositions and standard atomic masses from:
  • Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.

Isotopes of americium Isotopes of curium Isotopes of berkelium
Table of nuclides
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