Isotopes of chromium

Naturally occurring chromium (₂₄Cr) is composed of four stable isotopes; ⁵⁰Cr, ⁵²Cr, ⁵³Cr, and ⁵⁴Cr with ⁵²Cr being the most abundant (83.789% natural abundance). ⁵⁰Cr is suspected of decaying by β⁺β⁺ to ⁵⁰Ti with a half-life of (more than) 1.8×10¹⁷ years. Twenty-two radioisotopes, all of which are entirely synthetic, have been characterized with the most stable being ⁵¹Cr with a half-life of 27.7 days. All of the remaining radioactive isotopes have half-lives that are less than 24 hours and the majority of these have half-lives that are less than 1 minute, the least stable being ⁶⁶Cr with a half-life of 10 milliseconds. This element also has 2 meta states, ^45mCr, the more stable one, and ^59mCr, the least stable isotope or isomer.

Main isotopes of chromium (₂₄Cr)

Iso­tope Decay abun­dance half-life (t1/2) mode pro­duct ^50Cr 4.345% stable ^51Cr syn 27.7025 d ε ^51V γ – ^52Cr 83.789% stable ^53Cr 9.501% stable ^54Cr 2.365% stable
Standard atomic weight Ar, standard(Cr)	51.9961(6)[1]

⁵³Cr is the radiogenic decay product of ⁵³Mn. Chromium isotopic contents are typically combined with manganese isotopic contents and have found application in isotope geology. Mn-Cr isotope ratios reinforce the evidence from ²⁶Al and ¹⁰⁷Pd for the early history of the solar system. Variations in ⁵³Cr/⁵²Cr and Mn/Cr ratios from several meteorites indicate an initial ⁵³Mn/⁵⁵Mn ratio that suggests Mn-Cr isotope systematics must result from in-situ decay of ⁵³Mn in differentiated planetary bodies. Hence ⁵³Cr provides additional evidence for nucleosynthetic processes immediately before coalescence of the solar system. The same isotope is preferentially involved in certain leaching reactions, thereby allowing its abundance in seawater sediments to be used as a proxy for atmospheric oxygen concentrations.[2]

The isotopes of chromium range from ⁴²Cr to ⁶⁷Cr. The primary decay mode before the most abundant stable isotope, ⁵²Cr, is electron capture and the primary mode after is beta decay.

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 [n 6]	Spin and parity [n 7][n 4]	Natural abundance (mole fraction)
	Excitation energy[n 4]							Normal proportion	Range of variation
^42Cr	24	18	42.00643(32)#	14(3) ms [13(+4-2) ms]	β^+ (>99.9%)	^42V	0+
					2p (<.1%)	^40Ti
^43Cr	24	19	42.99771(24)#	21.6(7) ms	β^+ (71%)	^43V	(3/2+)
					β^+, p (23%)	^42Ti
					β^+, 2p (6%)	^41Sc
					β^+, α (<.1%)	^39Sc
^44Cr	24	20	43.98555(5)#	54(4) ms [53(+4-3) ms]	β^+ (93%)	^44V	0+
					β^+, p (7%)	^43Ti
^45Cr	24	21	44.97964(54)	50(6) ms	β^+ (73%)	^45V	7/2−#
					β^+, p (27%)	^44Ti
^45mCr	50(100)# keV			1# ms	IT	^45Cr	3/2+#
					β^+	^45V
^46Cr	24	22	45.968359(21)	0.26(6) s	β^+	^46V	0+
^47Cr	24	23	46.962900(15)	500(15) ms	β^+	^47V	3/2−
^48Cr	24	24	47.954032(8)	21.56(3) h	β^+	^48V	0+
^49Cr	24	25	48.9513357(26)	42.3(1) min	β^+	^49V	5/2−
^50Cr	24	26	49.9460442(11)	Observationally Stable[n 8]			0+	0.04345(13)	0.04294–0.04345
^51Cr	24	27	50.9447674(11)	27.7025(24) d	EC	^51V	7/2−
^52Cr	24	28	51.9405075(8)	Stable			0+	0.83789(18)	0.83762–0.83790
^53Cr	24	29	52.9406494(8)	Stable			3/2−	0.09501(17)	0.09501–0.09553
^54Cr	24	30	53.9388804(8)	Stable			0+	0.02365(7)	0.02365–0.02391
^55Cr	24	31	54.9408397(8)	3.497(3) min	β^−	^55Mn	3/2−
^56Cr	24	32	55.9406531(20)	5.94(10) min	β^−	^56Mn	0+
^57Cr	24	33	56.943613(2)	21.1(10) s	β^−	^57Mn	(3/2−)
^58Cr	24	34	57.94435(22)	7.0(3) s	β^−	^58Mn	0+
^59Cr	24	35	58.94859(26)	460(50) ms	β^−	^59Mn	5/2−#
^59mCr	503.0(17) keV			96(20) µs			(9/2+)
^60Cr	24	36	59.95008(23)	560(60) ms	β^−	^60Mn	0+
^61Cr	24	37	60.95472(27)	261(15) ms	β^− (>99.9%)	^61Mn	5/2−#
					β^−, n (<.1%)	^60Mn
^62Cr	24	38	61.95661(36)	199(9) ms	β^− (>99.9%)	^62Mn	0+
					β^−, n	^61Mn
^63Cr	24	39	62.96186(32)#	129(2) ms	β^−	^63Mn	(1/2−)#
					β^−, n	^62Mn
^64Cr	24	40	63.96441(43)#	43(1) ms	β^−	^64Mn	0+
^65Cr	24	41	64.97016(54)#	27(3) ms	β^−	^65Mn	(1/2−)#
^66Cr	24	42	65.97338(64)#	10(6) ms	β^−	^66Mn	0+
^67Cr	24	43	66.97955(75)#	10# ms [>300 ns]	β^−	^67Mn	1/2−#

1. ^mCr – 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
   IT:	Isomeric transition
   p:	Proton emission

6. Bold symbol as daughter – Daughter product is stable.
7. ( ) spin value – Indicates spin with weak assignment arguments.
8. Suspected of decaying by double electron capture to ⁵⁰Ti with a half-life of no less than 1.3×10¹⁸ a

Chromium-51

Radioisotopic tracer. Used in medicine.

References

1. Meija, Juris; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305.
2. R. Frei; C. Gaucher; S. W. Poulton; D. E. Canfield (2009). "Fluctuations in Precambrian atmospheric oxygenation recorded by chromium isotopes". Nature. 461 (7261): 250–3. Bibcode:2009Natur.461..250F. doi:10.1038/nature08266. PMID 19741707. S2CID 4373201.

• 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.

External links

• Chromium isotopes data from The Berkeley Laboratory Isotopes Project's