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.

Main isotopes of curium (₉₆Cm)

Iso­tope Decay abun­dance half-life (t1/2) mode pro­duct ^242Cm syn 160 d α ^238Pu SF – ^243Cm syn 29.1 y α ^239Pu ε ^243Am SF – ^244Cm syn 18.1 y α ^240Pu SF – ^245Cm syn 8500 y α ^241Pu SF – ^246Cm syn 4730 y α ^242Pu SF – ^247Cm syn 1.56×10^7 y α ^243Pu ^248Cm syn 3.40×10^5 y α ^244Pu SF – ^250Cm syn 9000 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 a half-life of 15.6 million years – several orders of magnitude longer than the half-life of all known nuclei of elements beyond curium in the periodic table. 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)	27(10) 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	96	139	235.05143(22)#	300(+250−100) s	β^+	^235Am	5/2+#
					α	^231Pu
^236Cm	96	140	236.05141(22)#	6.8(0.8) min	β^+ (82%)	^236Am	0+
					α (18%)	^232Pu
^237Cm	96	141	237.05290(22)#	20# min	β^+	^237Am	5/2+#
					α	^233Pu
^238Cm	96	142	238.05303(4)	2.4(1) h	EC (90%)	^238Am	0+
					α (10%)	^234Pu
^239Cm	96	143	239.05496(11)#	2.5(0.4) h	β^+ (99.9%)	^239Am	(7/2−)
					α (.1%)	^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	^238Pu	0+
					SF (6.33×10^−6%)	(various)
					CD (10^−14%)[n 8]	^208Pb ^34Si
					β^+β^+ (rare)	^242Pu
^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)×10^3 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)×10^3 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)×10^7 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)×10^5 y	α (91.74%)	^244Pu	0+
					SF (8.26%)	(various)
					β^−β^− (rare)	^248Cf
^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 9]	(various)	0+
					α (18%)	^246Pu
					β^− (8%)	^250Bk
^251Cm	96	155	251.082285(24)	16.8(2) min	β^−	^251Bk	(1/2+)

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. Heaviest known nuclide to undergo cluster decay
9. 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[1] by decay chain				Half-life range (a)	Fission products of ^235U by yield[2]
4n	4n+1	4n+2	4n+3
						4.5–7%	0.04–1.25%	<0.001%
^228Ra^№				4–6 a	†		^155Eu^þ
^244Cm^ƒ	^241Pu^ƒ	^250Cf	^227Ac^№	10–29 a		^90Sr	^85Kr	^113mCd^þ
^232U^ƒ		^238Pu^ƒ	^243Cm^ƒ	29–97 a		^137Cs	^151Sm^þ	^121mSn
^248Bk[3]	^249Cf^ƒ	^242mAm^ƒ		141–351 a	No fission products have a half-life in the range of 100–210 ka ...
	^241Am^ƒ		^251Cf^ƒ[4]	430–900 a
		^226Ra^№	^247Bk	1.3–1.6 ka
^240Pu	^229Th	^246Cm^ƒ	^243Am^ƒ	4.7–7.4 ka
	^245Cm^ƒ	^250Cm		8.3–8.5 ka
			^239Pu^ƒ	24.1 ka
		^230Th^№	^231Pa^№	32–76 ka
^236Np^ƒ	^233U^ƒ	^234U^№		150–250 ka	‡	^99Tc^₡	^126Sn
^248Cm		^242Pu		327–375 ka			^79Se^₡
				1.53 Ma		^93Zr
	^237Np^ƒ			2.1–6.5 Ma		^135Cs^₡	^107Pd
^236U			^247Cm^ƒ	15–24 Ma			^129I^₡
^244Pu				80 Ma	... nor beyond 15.7 Ma[5]
^232Th^№		^238U^№	^235U^ƒ№	0.7–14.1 Ga
Legend for superscript symbols ₡  has thermal neutron capture cross section in the range of 8–50 barns ƒ  fissile m  metastable isomer №  primarily a naturally occurring radioactive material (NORM) þ  neutron poison (thermal neutron capture cross section greater than 3k barns) †  range 4–97 a: Medium-lived fission product ‡  over 200 ka: Long-lived fission product

References

1. 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.
2. Specifically from thermal neutron fission of U-235, e.g. in a typical nuclear reactor.
3. 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]."
4. This is the heaviest nuclide with a half-life of at least four years before the "Sea of Instability".
5. 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 nearly 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
• Isotopic compositions and standard atomic masses from:
  • de Laeter, John Robert; Böhlke, John Karl; De Bièvre, Paul; Hidaka, Hiroshi; Peiser, H. Steffen; Rosman, Kevin J. R.; Taylor, Philip D. P. (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683.
  • Wieser, Michael E. (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051. Lay summary.
• 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.