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[n 10]	245Pu	7/2+
250Cm	96	154	250.078358(11)	8300# y	SF (74%)[n 11]	(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:

   EC:	Electron capture
   CD:	Cluster decay
   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. Decay mode is uncertain due to disagreements between theoretical predictions and reported experimental data.
11. 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)