Isotopes of curium

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Actinides and fission products by half-life
Actinides[1] by decay chain Half-life
range (y)		 Fission products of 235U 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
248Bk[3] 249Cfƒ 242mAmƒ 141–351

No fission products
have a half-life
in the range of
100–210 k years ...
241Amƒ 251Cfƒ[4] 430–900
226Ra№ 247Bk 1.3 k – 1.6 k
240Pu 229Th№ 246Cm 243Amƒ 4.7 k – 7.4 k
245Cmƒ 250Cm 8.3 k – 8.5 k
239Puƒ№ 24.1 k
230Th№ 231Pa№ 32 k – 76 k
236Npƒ 233Uƒ№ 234U№ 150 k – 250 k ‡ 99Tc₡ 126Sn
248Cm 242Pu 327 k – 375 k 79Se₡
1.53 M 93Zr
237Np№ 2.1 M – 6.5 M 135Cs₡ 107Pd
236U№ 247Cmƒ 15 M – 24 M 129I₡
244Pu№ 80 M

... nor beyond 15.7 M years[5]
232Th№ 238U№ 235Uƒ№ 0.7 G – 14.1 G

Legend for superscript symbols
₡  has thermal neutron capture cross section in the range of 8–50 barns
ƒ  fissile
m  metastable isomer
№  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

Curium (Cm) is an artificial element with an atomic number of 96. Because it is an artificial element, a standard atomic mass cannot be given, and it has no stable isotopes. The first isotope synthesized was 242Cm in 1944, which has 146 neutrons. All of the isotopes are radioactive.

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.

Table

nuclide
symbol		 Z(p) N(n)  
isotopic mass (u)
 		 half-life decay
mode(s)[6][n 1]		 daughter
isotope(s)[n 2]		 nuclear
spin
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
34Si
β+β+ (rare) 242Pu
243Cm 96 147 243.0613891(22) 29.1(1) y 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) y 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 y 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 y α (99.97%) 242Pu 0+
SF (.0261%) (various)
247Cm 96 151 247.070354(5) 1.56(5)×107 y α 243Pu 9/2−
248Cm 96 152 248.072349(5) 3.48(6)×105 y 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# y 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+
  1. ↑ Abbreviations:
    CD: Cluster decay
    EC: Electron capture
    IT: Isomeric transition
    SF: Spontaneous fission
  2. ↑ Bold for stable isotopes
  3. ↑ 3.0 3.1 Most common isotopes
  4. ↑ Heaviest known nuclide to undergo cluster decay
  5. ↑ Lightest nuclide to undergo spontaneous fission as the main decay mode

Notes

  • 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.

References

  1. ↑ 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 isotopes have half-lives of at least four years (the longest-lived isotope 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.
  2. ↑ Specifically from thermal neutron fission of U-235, e.g. in a typical nuclear reactor.
  3. ↑ Lua error in package.lua at line 80: module 'strict' not found.
    "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."
  4. ↑ This is the heaviest isotope with a half-life of at least four years before the "Sea of Instability".
  5. ↑ Excluding those "classically stable" isotopes 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.
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  • Isotope masses from:
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  • Isotopic compositions and standard atomic masses from:
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  • Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.
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Isotopes of americium Isotopes of curium Isotopes of berkelium
Table of nuclides
Isotopes of the chemical elements
1
H		 2
He
3
Li		 4
Be		 5
B		 6
C		 7
N		 8
O		 9
F		 10
Ne
11
Na		 12
Mg		 13
Al		 14
Si		 15
P		 16
S		 17
Cl		 18
Ar
19
K		 20
Ca		 21
Sc		 22
Ti		 23
V		 24
Cr		 25
Mn		 26
Fe		 27
Co		 28
Ni		 29
Cu		 30
Zn		 31
Ga		 32
Ge		 33
As		 34
Se		 35
Br		 36
Kr
37
Rb		 38
Sr		 39
Y		 40
Zr		 41
Nb		 42
Mo		 43
Tc		 44
Ru		 45
Rh		 46
Pd		 47
Ag		 48
Cd		 49
In		 50
Sn		 51
Sb		 52
Te		 53
I		 54
Xe
55
Cs		 56
Ba		 1 asterisk 72
Hf		 73
Ta		 74
W		 75
Re		 76
Os		 77
Ir		 78
Pt		 79
Au		 80
Hg		 81
Tl		 82
Pb		 83
Bi		 84
Po		 85
At		 86
Rn
87
Fr		 88
Ra		 2 asterisks 104
Rf		 105
Db		 106
Sg		 107
Bh		 108
Hs		 109
Mt		 110
Ds		 111
Rg		 112
Cn		 113
Uut		 114
Fl		 115
Uup		 116
Lv		 117
Uus		 118
Uuo
1 asterisk 57
La		 58
Ce		 59
Pr		 60
Nd		 61
Pm		 62
Sm		 63
Eu		 64
Gd		 65
Tb		 66
Dy		 67
Ho		 68
Er		 69
Tm		 70
Yb		 71
Lu
2 asterisks 89
Ac		 90
Th		 91
Pa		 92
U		 93
Np		 94
Pu		 95
Am		 96
Cm		 97
Bk		 98
Cf		 99
Es		 100
Fm		 101
Md		 102
No		 103
Lr
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