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.

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. It is followed by 248Cm, which has a half-life of 348,000 years. The longest-lived known isomer is 246mCm with a half-life of 1.12 seconds.

List of isotopes

Nuclide	Z	N	Isotopic mass (Da)	Discovery year	Half-life	Decay mode	Daughter isotope	Spin and parity
Excitation energy
233Cm	96	137	233.05077(9)		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	237.05287(8)		>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	238Pu	0+
SF (6.2×10−6%)	(various)
CD (1.1×10−14%)	208Pb 34Si
242mCm	2800(100) keV		180(70) ns	SF?	(various)
IT?	242Cm
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)# xkeV	(1969)	>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	247.070353(4)		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%)	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	(1966)	23 μs			7/2+
250Cm	96	154	250.078358(11)		8300# y	SF	(various)	0+
α (?%)	246Pu
β− (?%)	250Bk
251Cm	96	155	251.082285(24)		16.8(2) min	β−	251Bk	(3/2+)
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Actinides vs fission products

Actinides and fission products by half-life vte
Actinides by decay chain	Half-life range (a)	Fission products of 235U by yield
4n (Thorium)	4n + 1 (Neptunium)	4n + 2 (Radium)	4n + 3 (Actinium)	4.5–7%	0.04–1.25%	<0.001%
228Ra№				4–6 a		155Euþ
248Bk				> 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	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
232Th№		238U№	235Uƒ№	0.7–14.1 Ga
₡, has thermal neutron capture cross section in the range of 8–50 barnsƒ, fissile№, primarily a naturally occurring radioactive material (NORM)þ, neutron poison (thermal neutron capture cross section greater than 3k barns)

Isotope masses from: Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), , Nuclear Physics A, 729: 3–128, Bibcode:, doi:
Half-life, spin, and isomer data selected from the following sources. Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), , Nuclear Physics A, 729: 3–128, Bibcode:, doi: National Nuclear Data Center. . 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.