Isotopes of chromium

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Naturally occurring chromium (Cr) 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) 1.8x1017 years. Twenty-two radioisotopes, all 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, 45Crm, the more stable one, and 59Crm, 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.[1]

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.

Standard atomic mass: 51.9961(6) u

Table[edit]

nuclide
symbol
Z(p) N(n)  
isotopic mass (u)
 
half-life decay
mode(s)[2][n 1]
daughter
isotope(s)[n 2]
nuclear
spin
representative
isotopic
composition
(mole fraction)
range of natural
variation
(mole fraction)
excitation energy
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 3] 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. ^ Abbreviations:
    EC: Electron capture
    IT: Isomeric transition
  2. ^ Bold for stable isotopes
  3. ^ Suspected of decaying by β+β+ decay to 50Ti with a half-life of no less than 1.3×1018 a

Notes[edit]

  • Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
  • Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC which use expanded uncertainties.
  • Nuclide masses are given by IUPAP Commission on Symbols, Units, Nomenclature, Atomic Masses and Fundamental Constants (SUNAMCO)
  • Isotope abundances are given by IUPAC Commission on Isotopic Abundances and Atomic Weights

References[edit]

  1. ^ 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. 
  2. ^ http://www.nucleonica.net/unc.aspx

External links[edit]


Isotopes of vanadium Isotopes of chromium Isotopes of manganese
Table of nuclides