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.[1]
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.
|-| rowspan=2|42Cr| rowspan=2 style="text-align:right" | 24| rowspan=2 style="text-align:right" | 18| rowspan=2|42.00643(32)#| rowspan=2|14(3) ms
[13(+4-2) ms]| β+ (>99.9%)| 42V| rowspan=2|0+| rowspan=2|| rowspan=2||-| 2p (<.1%)| 40Ti|-| rowspan=4|43Cr| rowspan=4 style="text-align:right" | 24| rowspan=4 style="text-align:right" | 19| rowspan=4|42.99771(24)#| rowspan=4|21.6(7) ms| β+ (71%)| 43V| rowspan=4|(3/2+)| rowspan=4|| rowspan=4||-| β+, p (23%)| 42Ti|-| β+, 2p (6%)| 41Sc|-| β+, α (<.1%)| 39Sc|-| rowspan=2|44Cr| rowspan=2 style="text-align:right" | 24| rowspan=2 style="text-align:right" | 20| rowspan=2|43.98555(5)#| rowspan=2|54(4) ms
[53(+4-3) ms]| β+ (93%)| 44V| rowspan=2|0+| rowspan=2|| rowspan=2||-| β+, p (7%)| 43Ti|-| rowspan=2|45Cr| rowspan=2 style="text-align:right" | 24| rowspan=2 style="text-align:right" | 21| rowspan=2|44.97964(54)| rowspan=2|50(6) ms| β+ (73%)| 45V| rowspan=2|7/2−#| rowspan=2|| rowspan=2||-| β+, p (27%)| 44Ti|-| rowspan=2 style="text-indent:1em" | 45mCr| rowspan=2 colspan="3" style="text-indent:2em" | 50(100)# keV| rowspan=2|1# ms| IT| 45Cr| rowspan=2|3/2+#| rowspan=2|| rowspan=2||-| β+| 45V|-| 46Cr| style="text-align:right" | 24| style="text-align:right" | 22| 45.968359(21)| 0.26(6) s| β+| 46V| 0+|||-| 47Cr| style="text-align:right" | 24| style="text-align:right" | 23| 46.962900(15)| 500(15) ms| β+| 47V| 3/2−|||-| 48Cr| style="text-align:right" | 24| style="text-align:right" | 24| 47.954032(8)| 21.56(3) h| β+| 48V| 0+|||-| 49Cr| style="text-align:right" | 24| style="text-align:right" | 25| 48.9513357(26)| 42.3(1) min| β+| 49V| 5/2−|||-| 50Cr| style="text-align:right" | 24| style="text-align:right" | 26| 49.9460442(11)| colspan=3 align=center|Observationally Stable[2] | 0+| 0.04345(13)| 0.04294–0.04345|-| 51Cr| style="text-align:right" | 24| style="text-align:right" | 27| 50.9447674(11)| 27.7025(24) d| EC| 51V| 7/2−|||-| 52Cr| style="text-align:right" | 24| style="text-align:right" | 28| 51.9405075(8)| colspan=3 align=center|Stable| 0+| 0.83789(18)| 0.83762–0.83790|-| 53Cr| style="text-align:right" | 24| style="text-align:right" | 29| 52.9406494(8)| colspan=3 align=center|Stable| 3/2−| 0.09501(17)| 0.09501–0.09553|-| 54Cr| style="text-align:right" | 24| style="text-align:right" | 30| 53.9388804(8)| colspan=3 align=center|Stable| 0+| 0.02365(7)| 0.02365–0.02391|-| 55Cr| style="text-align:right" | 24| style="text-align:right" | 31| 54.9408397(8)| 3.497(3) min| β-| 55Mn| 3/2−|||-| 56Cr| style="text-align:right" | 24| style="text-align:right" | 32| 55.9406531(20)| 5.94(10) min| β-| 56Mn| 0+|||-| 57Cr| style="text-align:right" | 24| style="text-align:right" | 33| 56.943613(2)| 21.1(10) s| β-| 57Mn| (3/2−)|||-| 58Cr| style="text-align:right" | 24| style="text-align:right" | 34| 57.94435(22)| 7.0(3) s| β-| 58Mn| 0+|||-| 59Cr| style="text-align:right" | 24| style="text-align:right" | 35| 58.94859(26)| 460(50) ms| β-| 59Mn| 5/2−#|||-| style="text-indent:1em" | 59mCr| colspan="3" style="text-indent:2em" | 503.0(17) keV| 96(20) μs||| (9/2+)|||-| 60Cr| style="text-align:right" | 24| style="text-align:right" | 36| 59.95008(23)| 560(60) ms| β-| 60Mn| 0+|||-| rowspan=2|61Cr| rowspan=2 style="text-align:right" | 24| rowspan=2 style="text-align:right" | 37| rowspan=2|60.95472(27)| rowspan=2|261(15) ms| β- (>99.9%)| 61Mn| rowspan=2|5/2−#| rowspan=2|| rowspan=2||-| β-, n (<.1%)| 60Mn|-| rowspan=2|62Cr| rowspan=2 style="text-align:right" | 24| rowspan=2 style="text-align:right" | 38| rowspan=2|61.95661(36)| rowspan=2|199(9) ms| β- (>99.9%)| 62Mn| rowspan=2|0+| rowspan=2|| rowspan=2||-| β-, n| 61Mn|-| rowspan=2|63Cr| rowspan=2 style="text-align:right" | 24| rowspan=2 style="text-align:right" | 39| rowspan=2|62.96186(32)#| rowspan=2|129(2) ms| β-| 63Mn| rowspan=2|(1/2−)#| rowspan=2|| rowspan=2||-| β-, n| 62Mn|-| 64Cr| style="text-align:right" | 24| style="text-align:right" | 40| 63.96441(43)#| 43(1) ms| β-| 64Mn| 0+|||-| 65Cr| style="text-align:right" | 24| style="text-align:right" | 41| 64.97016(54)#| 27(3) ms| β-| 65Mn| (1/2−)#|||-| 66Cr| style="text-align:right" | 24| style="text-align:right" | 42| 65.97338(64)#| 10(6) ms| β-| 66Mn| 0+| | |-| 67Cr| style="text-align:right" | 24| style="text-align:right" | 43| 66.97955(75)#| 10# ms
[>300 ns]| β-| 67Mn| 1/2−#|||-| rowspan=3|68Cr[3] | rowspan=3 style="text-align:right" | 24| rowspan=3 style="text-align:right" | 44| rowspan=3|67.98316(54)#| rowspan=3|10# ms
(>620 ns)| β−?[4] | 68Mn| rowspan=3|0+| rowspan=3|| rowspan=3||-| β−, n?[4] | 67Mn|-| β−, 2n?[4] | 66Mn|-| rowspan=3|69Cr[5] | rowspan=3 style="text-align:right" | 24| rowspan=3 style="text-align:right" | 45| rowspan=3|68.98966(54)#| rowspan=3|6# ms
(>620 ns)| β−?[4] | 69Mn| rowspan=3|7/2+#| rowspan=3|| rowspan=3||-| β−, n?[4] | 68Mn|-| β−, 2n?[4] | 67Mn|-| rowspan=3|70Cr[5] | rowspan=3 style="text-align:right" | 24| rowspan=3 style="text-align:right" | 46| rowspan=3|69.99395(64)#| rowspan=3|6# ms
(>620 ns)| β−?[4] | 70Mn| rowspan=3|0+| rowspan=3|| rowspan=3||-| β−, n?[4] | 69Mn|-| β−, 2n?[4] | 68Mn
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.[6]