# Isotopes of chromium

Naturally occurring chromium ($_{24}$Cr) is composed of four stable isotopes; $^{50}$Cr, $^{52}$Cr, $^{53}$Cr, and $^{54}$Cr with $^{52}$Cr being the most abundant (83.789% natural abundance). $^{50}$Cr is suspected of decaying by β$^+$β$^+$ to $^{50}$Ti with a half-life of (more than) 1.8×10$^{17}$ years. Twenty-two radioisotopes, all of which are entirely synthetic, have been characterized, the most stable being $^{51}$Cr 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, $^{45m}$Cr, the more stable one, and $^{59m}$Cr, the least stable isotope or isomer.
$^{53}$Cr is the radiogenic decay product of $^{53}$Mn. 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 $^{26}$Al and $^{107}$Pd for the early history of the Solar System. Variations in $^{53}$Cr/$^{52}$Cr and Mn/Cr ratios from several meteorites indicate an initial $^{53}$Mn/$^{55}$Mn ratio that suggests Mn-Cr isotope systematics must result from in-situ decay of $^{53}$Mn in differentiated planetary bodies. Hence $^{53}$Cr 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 $^{42}$Cr to $^{70}$Cr. The primary decay mode before the most abundant stable isotope, $^{52}$Cr, 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) | Natural abundance (mole fraction) |
| Nuclide | Excitation energy | Excitation energy | Excitation energy | Half-life | Decay mode | Daughter isotope | Spin and parity | Normal proportion | Range of variation |
| $^{42}$Cr | 24 | 18 | 42.00758(32)# | 13.3(10) ms | β$^+$ (94.4%) | $^{42}$V | 0+ | | |
| $^{42}$Cr | 24 | 18 | 42.00758(32)# | 13.3(10) ms | β$^+$, p (5.6%) | $^{41}$Ti | 0+ | | |
| $^{43}$Cr | 24 | 19 | 42.99789(22)# | 21.1(3) ms | β$^+$, p (79.3%) | $^{42}$Ti | (3/2+) | | |
| $^{43}$Cr | 24 | 19 | 42.99789(22)# | 21.1(3) ms | β$^+$, 2p (11.6%) | $^{41}$Sc | (3/2+) | | |
| $^{43}$Cr | 24 | 19 | 42.99789(22)# | 21.1(3) ms | β$^+$ (8.97%) | $^{43}$V | (3/2+) | | |
| $^{43}$Cr | 24 | 19 | 42.99789(22)# | 21.1(3) ms | β$^+$, 3p (0.13%) | $^{40}$Ca | (3/2+) | | |
| $^{44}$Cr | 24 | 20 | 43.985591(55) | 42.8(6) ms | β$^+$ (88%) | $^{44}$V | 0+ | | |
| $^{44}$Cr | 24 | 20 | 43.985591(55) | 42.8(6) ms | β$^+$, p (12%) | $^{43}$Ti | 0+ | | |
| $^{45}$Cr | 24 | 21 | 44.979050(38) | 60.9(4) ms | β$^+$ (65.6%) | $^{45}$V | 7/2−# | | |
| $^{45}$Cr | 24 | 21 | 44.979050(38) | 60.9(4) ms | β$^+$, p (34.4%) | $^{44}$Ti | 7/2−# | | |
| $^{45m}$Cr | 107(1) keV | 107(1) keV | 107(1) keV | >80 μs | IT | $^{45}$Cr | (3/2) | | |
| $^{46}$Cr | 24 | 22 | 45.968361(12) | 224.3(13) ms | β$^+$ | $^{46}$V | 0+ | | |
| $^{47}$Cr | 24 | 23 | 46.9628950(56) | 461.6(15) ms | β$^+$ | $^{47}$V | 3/2− | | |
| $^{48}$Cr | 24 | 24 | 47.9540294(78) | 21.56(3) h | β$^+$ | $^{48}$V | 0+ | | |
| $^{49}$Cr | 24 | 25 | 48.9513337(24) | 42.3(1) min | β$^+$ | $^{49}$V | 5/2− | | |
| $^{50}$Cr | 24 | 26 | 49.94604221(10) | Observationally Stable | Observationally Stable | Observationally Stable | 0+ | 0.04345(13) | |
| $^{51}$Cr | 24 | 27 | 50.94476539(18) | 27.7015(11) d | EC | $^{51}$V | 7/2− | | |
| $^{52}$Cr | 24 | 28 | 51.94050471(12) | Stable | Stable | Stable | 0+ | 0.83789(18) | |
| $^{53}$Cr | 24 | 29 | 52.94064630(12) | Stable | Stable | Stable | 3/2− | 0.09501(17) | |
| $^{54}$Cr | 24 | 30 | 53.93887736(14) | Stable | Stable | Stable | 0+ | 0.02365(7) | |
| $^{55}$Cr | 24 | 31 | 54.94083664(25) | 3.497(3) min | β$^−$ | $^{55}$Mn | 3/2− | | |
| $^{56}$Cr | 24 | 32 | 55.94064898(62) | 5.94(10) min | β$^−$ | $^{56}$Mn | 0+ | | |
| $^{57}$Cr | 24 | 33 | 56.9436121(20) | 21.1(10) s | β$^−$ | $^{57}$Mn | (3/2)− | | |
| $^{58}$Cr | 24 | 34 | 57.9441845(32) | 7.0(3) s | β$^−$ | $^{58}$Mn | 0+ | | |
| $^{59}$Cr | 24 | 35 | 58.94834543(72) | 1.05(9) s | β$^−$ | $^{59}$Mn | (1/2−) | | |
| $^{59m}$Cr | 502.7(11) keV | 502.7(11) keV | 502.7(11) keV | 96(20) μs | IT | $^{59}$Cr | (9/2+) | | |
| $^{60}$Cr | 24 | 36 | 59.9496417(12) | 490(10) ms | β$^−$ | $^{60}$Mn | 0+ | | |
| $^{61}$Cr | 24 | 37 | 60.9543781(20) | 243(9) ms | β$^−$ | $^{61}$Mn | (5/2−) | | |
| $^{62}$Cr | 24 | 38 | 61.9561429(37) | 206(12) ms | β$^−$ | $^{62}$Mn | 0+ | | |
| $^{63}$Cr | 24 | 39 | 62.961161(78) | 129(2) ms | β$^−$ | $^{63}$Mn | 1/2−# | | |
| $^{64}$Cr | 24 | 40 | 63.96389(32) | 43(1) ms | β$^−$ | $^{64}$Mn | 0+ | | |
| $^{65}$Cr | 24 | 41 | 64.96961(22)# | 27.5(21) ms | β$^−$ | $^{65}$Mn | 1/2−# | | |
| $^{66}$Cr | 24 | 42 | 65.97301(32)# | 23.8(18) ms | β$^−$ | $^{66}$Mn | 0+ | | |
| $^{67}$Cr | 24 | 43 | 66.97931(43)# | 11# ms [>300 ns] | | | 1/2−# | | |
| $^{68}$Cr | 24 | 44 | 67.98316(54)# | 10# ms [>620 ns] | | | 0+ | | |
| $^{69}$Cr | 24 | 45 | 68.98966(54)# | 6# ms [>620 ns] | | | 7/2+# | | |
| $^{70}$Cr | 24 | 46 | 69.99395(64)# | 6# ms [>620 ns] | | | 0+ | | |
| This table header & footer: view ||||||||||
* ↑ $^m$Cr – Excited nuclear isomer.
* ↑ ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
* ↑ # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
* 1 2 3 # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
* ↑ Modes of decay: EC:Electron capture IT:Isomeric transition p:Proton emission
* ↑ Bold symbol as daughter – Daughter product is stable.
* ↑ ( ) spin value – Indicates spin with weak assignment arguments.
* ↑ Order of ground state and isomer is uncertain.
* ↑ Suspected of decaying by double β$^+$ decay to $^{50}$Ti with a half-life of no less than 1.3×10$^{18}$ years

## 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.