Isotopes of curium

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

Isotopes of curium (96Cm)
Main isotopes[1] Decay
abun­dance half-life (t1/2) mode pro­duct
242Cm synth 162.8 d α 238Pu
SF –
CD 208Pb
243Cm synth 29.1 y α 239Pu
ε 243Am
SF –
244Cm synth 18.11 y α 240Pu
SF –
245Cm synth 8250 y α 241Pu
SF –
246Cm synth 4760 y α 242Pu
SF –
247Cm synth 1.56×107 y α 243Pu
248Cm synth 3.480×105 y α 244Pu
SF –
250Cm synth 8300 y SF –
α 246Pu
β− 250Bk

There are 19 known radioisotopes ranging from 233Cm to 251Cm. There are also ten known nuclear isomers. The longest-lived isotope is 247Cm, with half-life 15.6 million years – orders of magnitude longer than that of any known isotope beyond curium, and long enough to study as a possible extinct radionuclide that would be produced by the r-process.[2][3] The longest-lived isomer is 246mCm with a half-life of 1.12 seconds.

List of isotopes
Nuclide
[n 1]		 Z N Isotopic mass (Da)
[n 2][n 3]		 Half-life
[n 4]		 Decay
mode
[n 5]		 Daughter
isotope
 Spin and
parity
[n 6][n 4]
Excitation energy[n 4]
233Cm 96 137 233.05077(8) 23+13
−6 s		 β+ (80%) 233Am 3/2+#
α (20%) 229Pu
234Cm 96 138 234.05016(2) 52(9) s β+ (71%) 234Am 0+
α (27%) 230Pu
SF (2%) (various)
235Cm[4] 96 139 235.05143(22)# 300+250
−100 s		 β+ (99.0%) 235Am (5/2+)
α (1.0%) 231Pu
236Cm 96 140 236.05141(22)# 6.8(8) min β+ (82%) 236Am 0+
α (18%) 232Pu
SF (<0.1%)[5] (various)
237Cm[6][4] 96 141 237.05290(22)# >660 s β+ 237Am (5/2+)
α (<1%) 233Pu
238Cm[6] 96 142 238.05303(4) 2.2(4) h EC (~94%) 238Am 0+
α (~6%) 234Pu
239Cm[1] 96 143 239.05496(11)# 2.5(4) h β+ 239Am (7/2−)
α (6.2x10−3%) 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 7] 96 146 242.0588358(20) 162.8(2) d α[n 8] 238Pu 0+
SF (6.33×10−6%) (various)
CD (10−14%)[n 9] 208Pb
34Si
242mCm 2800(100) keV 180(70) ns
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 IT 243Cm 1/2+
244Cm[n 7] 96 148 244.0627526(20) 18.10(2) y α 240Pu 0+
SF (1.34×10−4%) (various)
244m1Cm 1040.188(12) keV 34(2) ms IT 244Cm 6+
244m2Cm 1100(900)# keV >500 ns SF (various)
245Cm 96 149 245.0654912(22) 8.5(1)×103 y α 241Pu 7/2+
SF (6.1×10−7%) (various)
245mCm 355.92(10) keV 290(20) ns IT 245Cm 1/2+
246Cm 96 150 246.0672237(22) 4.76(4)×103 y α (99.97%) 242Pu 0+
SF (.0261%) (various)
246mCm 1179.66(13) keV 1.12(0.24) s IT 246Cm 8−
247Cm 96 151 247.070354(5) 1.56(5)×107 y α 243Pu 9/2−
247m1Cm 227.38(19) keV 26.3(0.3) μs IT 247Cm 5/2+
247m2Cm 404.90(3) keV 100.6(0.6) ns IT 247Cm 1/2+
248Cm 96 152 248.072349(5) 3.48(6)×105 y α (91.74%) 244Pu 0+
SF (8.26%) (various)
248mCm 1458.1(1) keV 146(18) μs IT 248Cm (8−)
249Cm 96 153 249.075953(5) 64.15(3) min β− 249Bk 1/2(+)
249mCm 48.758(17) keV 23 μs α 245Pu (7/2+)
250Cm 96 154 250.078357(12) 8300# y SF (74%)[n 10] (various) 0+
α (18%) 246Pu
β− (8%) 250Bk
251Cm 96 155 251.082285(24) 16.8(2) min β− 251Bk (1/2+)
This table header & footer:
  1. mCm – 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. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
  5. Modes of decay:
    CD:Cluster decay
    EC:Electron capture
    SF:Spontaneous fission
  6. ( ) spin value – Indicates spin with weak assignment arguments.
  7. Most common isotopes
  8. Theoretically capable of β+β+ decay to 242Pu[1]
  9. Heaviest known nuclide to undergo cluster decay
  10. The nuclide with the lowest atomic number known to undergo spontaneous fission as the main decay mode

Actinides vs fission products
Actinides and fission products by half-life
Actinides[7] by decay chain Half-life
range (a)		 Fission products of 235U by yield[8]
4n 4n + 1 4n + 2 4n + 3 4.5–7% 0.04–1.25% <0.001%
228Ra№ 4–6 a 155Euþ
244Cmƒ 241Puƒ 250Cf 227Ac№ 10–29 a 90Sr 85Kr 113mCdþ
232Uƒ 238Puƒ 243Cmƒ 29–97 a 137Cs 151Smþ 121mSn
248Bk[9] 249Cfƒ 242mAmƒ 141–351 a

No fission products have a half-life
in the range of 100 a–210 ka ...

241Amƒ 251Cfƒ[10] 430–900 a
226Ra№ 247Bk 1.3–1.6 ka
240Pu 229Th 246Cmƒ 243Amƒ 4.7–7.4 ka
245Cmƒ 250Cm 8.3–8.5 ka
239Puƒ 24.1 ka
230Th№ 231Pa№ 32–76 ka
236Npƒ 233Uƒ 234U№ 150–250 ka 99Tc₡ 126Sn
248Cm 242Pu 327–375 ka 79Se₡
1.53 Ma 93Zr
237Npƒ 2.1–6.5 Ma 135Cs₡ 107Pd
236U 247Cmƒ 15–24 Ma 129I₡
244Pu 80 Ma

... nor beyond 15.7 Ma[11]

232Th№ 238U№ 235Uƒ№ 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)

References
  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. Côté, Benoit; Eichler, Marius; Yagüe López, Andrés; Vassh, Nicole; Mumpower, Matthew R.; Világos, Blanka; Soós, Benjámin; Arcones, Almudena; Sprouse, Trevor M.; Surman, Rebecca; Pignatari, Marco; Pető, Mária K.; Wehmeyer, Benjamin; Rauscher, Thomas; Lugaro, Maria (26 February 2021). "129 I and 247 Cm in meteorites constrain the last astrophysical source of solar r-process elements". Science. 371 (6532): 945–948. arXiv:2006.04833. Bibcode:2021Sci...371..945C. doi:10.1126/science.aba1111. PMID 33632846. S2CID 232050526.
  3. Davis, A.M.; McKeegan, K.D. (2014). "Short-Lived Radionuclides and Early Solar System Chronology". Treatise on Geochemistry: 383. doi:10.1016/B978-0-08-095975-7.00113-3. ISBN 9780080983004.
  4. Khuyagbaatar, J.; Heßberger, F. P.; Hofmann, S.; Ackermann, D.; Burkhard, H. G.; Heinz, S.; Kindler, B.; Kojouharov, I.; Lommel, B.; Mann, R.; Maurer, J.; Nishio, K. (12 October 2020). "α decay of Fm 243 143 and Fm 245 145 , and of their daughter nuclei". Physical Review C. 102 (4): 044312. doi:10.1103/PhysRevC.102.044312. ISSN 2469-9985. S2CID 241259726. Retrieved 24 June 2023.
  5. Khuyagbaatar, J.; Heßberger, F. P.; Hofmann, S.; Ackermann, D.; Comas, V. S.; Heinz, S.; Heredia, J. A.; Kindler, B.; Kojouharov, I.; Lommel, B.; Mann, R.; Nishio, K.; Yakushev, A. (1 October 2010). "The new isotope 236Cm and new data on 233Cm and 237, 238, 240Cf" (PDF). The European Physical Journal A. 46 (1): 59–67. Bibcode:2010EPJA...46...59K. doi:10.1140/epja/i2010-11026-9. ISSN 1434-601X. S2CID 122809010. Retrieved 24 June 2023.
  6. Asai, M.; Tsukada, K.; Ichikawa, S.; Sakama, M.; Haba, H.; Nishinaka, I.; Nagame, Y.; Goto, S.; Kojima, Y.; Oura, Y.; Shibata, M. (20 June 2006). "α decay of 238Cm and the new isotope 237Cm". Physical Review C. 73 (6): 067301. doi:10.1103/PhysRevC.73.067301. Retrieved 24 June 2023.
  7. 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.
  8. Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor.
  9. 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]."
  10. This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".
  11. 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.
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