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

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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 known isomer is ^246mCm with a half-life of 1.12 seconds.

List of isotopes

Nuclide [n 1]	Z	N	Isotopic mass (Da)[4] [n 2][n 3]	Half-life[1] [n 4]	Decay mode[1] [n 5]	Daughter isotope	Spin and parity[1] [n 6][n 4]
	Excitation energy[n 4]
233Cm	96	137	233.050771(87)	27(10) s	β+ (80%)	233Am	3/2+#
					α (20%)	229Pu
234Cm	96	138	234.050159(18)	52(9) s	β+ (71%)	234Am	0+
					α (27%)	230Pu
					SF (2%)	(various)
235Cm	96	139	235.05155(11)#	7(3) min	β+ (96%)	235Am	5/2+#
					α (4%)	231Pu
236Cm	96	140	236.051372(19)	6.8(8) min	β+ (82%)	236Am	0+
					α (18%)	232Pu
237Cm	96	141	237.052869(80)	>10# min	α (?%)	233Pu	5/2+#
238Cm	96	142	238.053082(13)	2.2(4) h	EC (96.11%)	238Am	0+
					α (3.84%)	234Pu
					SF (0.048%)	(various)
239Cm	96	143	239.05491(16)	2.5(4) h	β+	239Am	7/2−#
					α (6.2x10−3%)	235Pu
240Cm	96	144	240.0555282(20)	30.4(37) d	α	236Pu	0+
					SF (3.9×10−6%)	(various)
241Cm	96	145	241.0576512(17)	32.8(2) d	EC (99.0%)	241Am	1/2+
					α (1.0%)	237Pu
242Cm	96	146	242.0588342(12)	162.8(2) d	α[n 7]	238Pu	0+
					SF (6.2×10−6%)	(various)
					CD (1.1×10−14%)[n 8]	208Pb 34Si
242mCm	2800(100) keV			180(70) ns
243Cm	96	147	243.0613873(16)	29.1(1) y	α (99.71%)	239Pu	5/2+
					EC (0.29%)	243Am
					SF (5.3×10−9%)	(various)
243mCm	87.4(1) keV			1.08(3) μs	IT	243Cm	1/2+
244Cm	96	148	244.0627506(12)	18.11(3) y	α	240Pu	0+
					SF (1.37×10−4%)	(various)
244m1Cm	1040.181(11) keV			34(2) ms	IT	244Cm	6+
244m2Cm	1100(900)# keV			>500 ns	SF	(various)
245Cm	96	149	245.0654910(12)	8250(70) 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	246.0672220(16)	4706(40) y	α (99.97%)	242Pu	0+
					SF (0.02615%)	(various
246mCm	1179.66(13) keV			1.12(24) s	IT	246Cm	8−
247Cm	96	151	247.0703527(41)	1.56(5)×107 y	α	243Pu	9/2−
247m1Cm	227.38(19) keV			26.3(3) μs	IT	247Cm	5/2+
247m2Cm	404.90(3) keV			100.6(6) ns	IT	247Cm	1/2+
248Cm	96	152	248.0723491(25)	3.48(6)×105 y	α (91.61%)[n 9]	244Pu	0+
					SF (8.39%)	(various)
248mCm	1458.1(10) keV			146(18) μs	IT	248Cm	8−#
249Cm	96	153	249.0759540(25)	64.15(3) min	β−	249Bk	1/2+
249mCm	48.76(4) keV			23 μs	α	245Pu	7/2+
250Cm	96	154	250.078358(11)	8300# y	SF (74%)[n 10]	(various)	0+
					α (?%)	246Pu
					β− (?%)	250Bk
251Cm	96	155	251.082285(24)	16.8(2) min	β−	251Bk	(3/2+)
This table header & footer: view

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. Theoretically capable of β⁺β⁺ decay to ²⁴²Pu
8. Heaviest known nuclide to undergo cluster decay
9. Theoretically capable of β⁻β⁻ decay to ²⁴⁸Cf
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 v t e
Actinides[5] by decay chain				Half-life range (a)	Fission products of 235U by yield[6]
4n	4n + 1	4n + 2	4n + 3		4.5–7%	0.04–1.25%	<0.001%
228Ra№				4–6 a		155Euþ
248Bk[7]				> 9 a
244Cmƒ	241Puƒ	250Cf	227Ac№	10–29 a	90Sr	85Kr	113mCdþ
232Uƒ		238Puƒ	243Cmƒ	29–97 a	137Cs	151Smþ	121mSn
	249Cfƒ	242mAmƒ		141–351 a	No fission products have a half-life in the range of 100 a–210 ka ...
	241Amƒ		251Cfƒ[8]	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₡
				1.33 Ma	135Cs₡
	237Npƒ			1.61–6.5 Ma	93Zr	107Pd
236U			247Cmƒ	15–24 Ma		129I₡
244Pu				80 Ma	... nor beyond 15.7 Ma[9]
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). "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.
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. 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.
5. 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.
6. Specifically from thermal neutron fission of uranium-235, e.g. in a typical nuclear reactor.
7. 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]."
8. This is the heaviest nuclide with a half-life of at least four years before the "sea of instability".
9. 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.

• Isotope masses from:
  • Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
• Half-life, spin, and isomer data selected from the following sources.
  • Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
  • National Nuclear Data Center. "NuDat 2.x database". Brookhaven National Laboratory.
  • Holden, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.). CRC Handbook of Chemistry and Physics (85th ed.). Boca Raton, Florida: CRC Press. ISBN 978-0-8493-0485-9.