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). Twenty-two radioisotopes, all synthetic, have been characterized, the most stable being ⁵¹Cr with a half-life of 27.70 days. All of the remaining radioactive isotopes have half-lives less than a day and for the majority of these less than a minute. This element also has two very short-lived meta states: ^45mCr and ^59mCr.

Isotopes of chromium (₂₄Cr)

Main isotopes[1] Decay abun­dance half-life (t1/2) mode pro­duct 50Cr 4.34% stable 51Cr synth 27.7015 d ε 51V 52Cr 83.8% stable 53Cr 9.50% stable 54Cr 2.37% stable
Standard atomic weight Ar°(Cr)
	51.9961±0.0006[2] 51.996±0.001 (abridged)[3]
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⁵³Cr is the radiogenic decay product of ⁵³Mn. Chromium and manganese are found together sufficiently for measurement of both to find 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 a non-zero initial ⁵³Mn/⁵⁵Mn ratio, implying that Cr isotopic variation 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.

Chromium isotope ratios also allow its abundance in seawater sediments to be used as a proxy for atmospheric oxygen concentrations, as rates of certain leaching reactions exhibit variation.^[4]

The known isotopes of chromium range from ⁴²Cr to ⁷⁰Cr. 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)[5] [n 2][n 3]	Half-life[1] [n 4]	Decay mode[1] [n 5]	Daughter isotope [n 6]	Spin and parity[1] [n 7][n 4]	Natural abundance (mole fraction)
	Excitation energy[n 4]							Normal proportion[1]	Range of variation
42Cr	24	18	42.00758(32)#	13.3(10) ms	β+ (94.4%)	42V	0+
					β+, p (5.6%)	41Ti
43Cr	24	19	42.99789(22)#	21.1(3) ms	β+, p (79.3%)	42Ti	(3/2+)
					β+, 2p (11.6%)	41Sc
					β+ (8.97%)	43V
					β+, 3p (0.13%)	40Ca
44Cr	24	20	43.985591(55)	42.8(6) ms	β+ (88%)	44V	0+
					β+, p (12%)	43Ti
45Cr	24	21	44.979050(38)	60.9(4) ms	β+ (65.6%)	45V	7/2−#
					β+, p (34.4%)	44Ti
45mCr[n 8]	107(1) keV			>80 μs	IT	45Cr	(3/2)
46Cr	24	22	45.968361(12)	224.3(13) ms	β+	46V	0+
47Cr	24	23	46.9628950(56)	461.6(15) ms	β+	47V	3/2−
48Cr	24	24	47.9540294(78)	21.56(3) h	β+	48V	0+
49Cr	24	25	48.9513337(24)	42.3(1) min	β+	49V	5/2−
50Cr	24	26	49.94604221(10)	Observationally Stable[n 9]			0+	0.04345(13)
51Cr	24	27	50.94476539(18)	27.7015(11) d	EC	51V	7/2−
52Cr	24	28	51.94050471(12)	Stable			0+	0.83789(18)
53Cr	24	29	52.94064630(12)	Stable			3/2−	0.09501(17)
54Cr	24	30	53.93887736(14)	Stable			0+	0.02365(7)
55Cr	24	31	54.94083664(25)	3.497(3) min	β−	55Mn	3/2−
56Cr	24	32	55.94064898(62)	5.94(10) min	β−	56Mn	0+
57Cr	24	33	56.9436121(20)	21.1(10) s	β−	57Mn	(3/2)−
58Cr	24	34	57.9441845(32)	7.0(3) s	β−	58Mn	0+
59Cr	24	35	58.94834543(72)	1.05(9) s	β−	59Mn	(1/2−)
59mCr	502.7(11) keV			96(20) μs	IT	59Cr	(9/2+)
60Cr	24	36	59.9496417(12)	490(10) ms	β−	60Mn	0+
61Cr	24	37	60.9543781(20)	243(9) ms	β−	61Mn	(5/2−)
62Cr	24	38	61.9561429(37)	206(12) ms	β−	62Mn	0+
63Cr	24	39	62.961161(78)	129(2) ms	β−	63Mn	1/2−#
64Cr	24	40	63.96389(32)	43(1) ms	β−	64Mn	0+
65Cr	24	41	64.96961(22)#	27.5(21) ms	β−	65Mn	1/2−#
66Cr	24	42	65.97301(32)#	23.8(18) ms	β−	66Mn	0+
67Cr	24	43	66.97931(43)#	11# ms [>300 ns]			1/2−#
68Cr	24	44	67.98316(54)#	10# ms [>620 ns]			0+
69Cr	24	45	68.98966(54)#	6# ms [>620 ns]			7/2+#
70Cr	24	46	69.99395(64)#	6# ms [>620 ns]			0+
This table header & footer: view

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. Order of ground state and isomer is uncertain.
9. Suspected of decaying by double β⁺ decay to ⁵⁰Ti with a half-life of no less than 1.3×10¹⁸ years

Chromium-51

Chromium-51 is a synthetic radioactive isotope of chromium having a half-life of 27.70 days and decaying by electron capture and emitting a 320-keV gamma ray; it is used to label red blood cells for measurement of mass or volume, survival time, and sequestration studies, for the diagnosis of gastrointestinal bleeding, and to label platelets to study their survival. It has a role as a radioactive label. Chromium-51 has been used as a radioactive label for decades. It is used as a diagnostic radiopharmaceutical agent in nephrology to determine glomerular filtration rate, and in hematology to determine red blood cell volume or mass, study the red blood cell survival time and evaluate blood loss.^[6]

See also

Daughter products other than chromium

• Isotopes of manganese
• Isotopes of vanadium
• Isotopes of titanium
• Isotopes of scandium