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Isotopes of curium
Artificial nuclides with atomic number of 96 but with different mass numbers

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.

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. The longest-lived known isomer is 246mCm with a half-life of 1.12 seconds.

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List of isotopes

Nuclide3ZNIsotopic mass (Da)456Half-life78Decaymode910DaughterisotopeSpin andparity111213
Excitation energy14
233Cm96137233.050771(87)27(10) sβ+ (80%)233Am3/2+#
α (20%)229Pu
234Cm96138234.050159(18)52(9) sβ+ (71%)234Am0+
α (27%)230Pu
SF (2%)(various)
235Cm96139235.05155(11)#7(3) minβ+ (96%)235Am5/2+#
α (4%)231Pu
236Cm96140236.051372(19)6.8(8) minβ+ (82%)236Am0+
α (18%)232Pu
237Cm96141237.052869(80)>10# minα (?%)233Pu5/2+#
238Cm96142238.053082(13)2.2(4) hEC (96.11%)238Am0+
α (3.84%)234Pu
SF (0.048%)(various)
239Cm96143239.05491(16)2.5(4) hβ+239Am7/2−#
α (6.2x10−3%)235Pu
240Cm96144240.0555282(20)30.4(37) dα236Pu0+
SF (3.9×10−6%)(various)
241Cm96145241.0576512(17)32.8(2) dEC (99.0%)241Am1/2+
α (1.0%)237Pu
242Cm96146242.0588342(12)162.8(2) dα15238Pu0+
SF (6.2×10−6%)(various)
CD (1.1×10−14%)16208Pb34Si
242mCm2800(100) keV180(70) ns
243Cm96147243.0613873(16)29.1(1) yα (99.71%)239Pu5/2+
EC (0.29%)243Am
SF (5.3×10−9%)(various)
243mCm87.4(1) keV1.08(3) μsIT243Cm1/2+
244Cm96148244.0627506(12)18.11(3) yα240Pu0+
SF (1.37×10−4%)(various)
244m1Cm1040.181(11) keV34(2) msIT244Cm6+
244m2Cm1100(900)# keV>500 nsSF(various)
245Cm96149245.0654910(12)8250(70) yα241Pu7/2+
SF (6.1×10−7%)(various)
245mCm355.92(10) keV290(20) nsIT245Cm1/2+
246Cm96150246.0672220(16)4706(40) yα (99.97%)242Pu0+
SF (0.02615%)(various
246mCm1179.66(13) keV1.12(24) sIT246Cm8−
247Cm96151247.0703527(41)1.56(5)×107 yα243Pu9/2−
247m1Cm227.38(19) keV26.3(3) μsIT247Cm5/2+
247m2Cm404.90(3) keV100.6(6) nsIT247Cm1/2+
248Cm96152248.0723491(25)3.48(6)×105 yα (91.61%)17244Pu0+
SF (8.39%)(various)
248mCm1458.1(10) keV146(18) μsIT248Cm8−#
249Cm96153249.0759540(25)64.15(3) minβ−249Bk1/2+
249mCm48.76(4) keV23 μsα245Pu7/2+
250Cm96154250.078358(11)8300# ySF (74%)18(various)0+
α (?%)246Pu
β− (?%)250Bk
251Cm96155251.082285(24)16.8(2) minβ−251Bk(3/2+)
This table header & footer:
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Actinides vs fission products

Actinides and fission products by half-life
  • v
  • t
  • e
Actinides19 by decay chainHalf-life range (a)Fission products of 235U by yield20
4n4n + 14n + 24n + 34.5–7%0.04–1.25%<0.001%
228Ra№4–6 a155Euþ
248Bk21> 9 a
244Cmƒ241Puƒ250Cf227Ac№10–29 a90Sr85Kr113mCdþ
232238Puƒ243Cmƒ29–97 a137Cs151Smþ121mSn
249Cfƒ242mAmƒ141–351 a

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

241Amƒ251Cfƒ22430–900 a
226Ra№247Bk1.3–1.6 ka
240Pu229Th246Cmƒ243Amƒ4.7–7.4 ka
245Cmƒ250Cm8.3–8.5 ka
239Puƒ24.1 ka
230Th№231Pa№32–76 ka
236Npƒ233234U№150–250 ka99Tc₡126Sn
248Cm242Pu327–375 ka79Se₡
1.33 Ma135Cs₡
237Npƒ1.61–6.5 Ma93Zr107Pd
236U247Cmƒ15–24 Ma129I₡
244Pu80 Ma

... nor beyond 15.7 Ma23

232Th№238U№235Uƒ№0.7–14.1 Ga

References

  1. 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). "129I and 247Cm 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. /wiki/Almudena_Arcones

  2. 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. 9780080983004

  3. mCm – Excited nuclear isomer. /wiki/Nuclear_isomer

  4. Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3): 030003. doi:10.1088/1674-1137/abddaf. /wiki/Doi_(identifier)

  5. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.

  6. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).

  7. 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. https://www-nds.iaea.org/amdc/ame2020/NUBASE2020.pdf

  8. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).

  9. 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. https://www-nds.iaea.org/amdc/ame2020/NUBASE2020.pdf

  10. Modes of decay: EC:Electron captureCD:Cluster decaySF:Spontaneous fission /wiki/Electron_capture

  11. 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. https://www-nds.iaea.org/amdc/ame2020/NUBASE2020.pdf

  12. ( ) spin value – Indicates spin with weak assignment arguments.

  13. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).

  14. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).

  15. Theoretically capable of β+β+ decay to 242Pu

  16. Heaviest known nuclide to undergo cluster decay /wiki/Cluster_decay

  17. Theoretically capable of β−β− decay to 248Cf

  18. The nuclide with the lowest atomic number known to undergo spontaneous fission as the main decay mode /wiki/Atomic_number

  19. 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. /wiki/Polonium

  20. Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor. /wiki/Thermal_neutron

  21. 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]." /wiki/Bibcode_(identifier)

  22. This is the heaviest nuclide with a half-life of at least four years before the "sea of instability". /wiki/Sea_of_instability

  23. 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. /wiki/Primordial_nuclide