Isotopes of chromium

Isotopes of chromium (24Cr)
Main isotopes Decay
abun­dance half-life (t1/2) mode pro­duct
50Cr 4.34% stable
51Cr synth 27.7025 d ε 51V
γ
52Cr 83.8% stable
53Cr 9.50% stable
54Cr 2.37% stable
Standard atomic weight Ar°(Cr)
  • 51.9961±0.0006
  • 51.996±0.001 (abridged)

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, 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. This element also has two meta states, 45mCr, the more stable one, and 59mCr, the least stable isotope or isomer.

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.

The 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
Z N Isotopic mass (Da)
Half-life
Decay
mode

Daughter
isotope

Spin and
parity
Natural abundance (mole fraction)
Excitation energy 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 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−#
68Cr 24 44 67.98316(54)# 10# ms
(>620 ns)
β? 68Mn 0+
β, n? 67Mn
β, 2n? 66Mn
69Cr 24 45 68.98966(54)# 6# ms
(>620 ns)
β? 69Mn 7/2+#
β, n? 68Mn
β, 2n? 67Mn
70Cr 24 46 69.99395(64)# 6# ms
(>620 ns)
β? 70Mn 0+
β, n? 69Mn
β, 2n? 68Mn
This table header & footer:
  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. ^ a b c # – 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
  9. ^ a b c d e f g h i Decay mode shown is energetically allowed, but has not been experimentally observed to occur in this nuclide.

Chromium-51

Chromium-51 is a synthetic radioactive isotope of chromium having a half-life of 27.7 days and decaying by electron capture with emission of gamma rays (0.32 MeV); 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 Cr-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.

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