Naturally occurring cobalt, Co, consists of a single stable isotope, Co (thus, cobalt is a mononuclidic element). Twenty-eight radioisotopes have been characterized; the most stable are Co with a half-life of 5.2714 years, Co (271.81 days), Co (77.24 days), and Co (70.84 days). All other isotopes have half-lives of less than 18 hours and most of these have half-lives of less than 1 second. This element also has 19 meta states, of which the most stable is 58m1Co with a half-life of 8.85 hours.

The isotopes of cobalt range in atomic weight from Co to Co. The main decay mode for isotopes with atomic mass less than that of the stable isotope, Co, is electron capture to iron isotopes, and the main mode of decay for those with greater mass is beta decay to nickel isotopes.

List of isotopes

|-id=Cobalt-50 | rowspan=3|Co | rowspan=3 style="text-align:right" | 27 | rowspan=3 style="text-align:right" | 23 | rowspan=3|49.98112(14) | rowspan=3 style="text-align:center" | 1987 | rowspan=3|38.8(2) ms | β, p (70.5%) | Mn | rowspan=3|(6+) | rowspan=3| |- | β (29.5%) | Fe |- | β, 2p? | Cr |-id=Cobalt-51 | rowspan=2|Co | rowspan=2 style="text-align:right" | 27 | rowspan=2 style="text-align:right" | 24 | rowspan=2|50.970647(52) | rowspan=2 style="text-align:center" | 1987 | rowspan=2|68.8(19) ms | β (96.2%) | Fe | rowspan=2|7/2− | rowspan=2| |- | β, p (<3.8%) | Mn |-id=Cobalt-52 | rowspan=2|Co | rowspan=2 style="text-align:right" | 27 | rowspan=2 style="text-align:right" | 25 | rowspan=2|51.9631302(57) | rowspan=2 style="text-align:center" | 1987 | rowspan=2|111.7(21) ms | β | Fe | rowspan=2|6+ | rowspan=2| |- | β, p? | Mn |-id=Cobalt-52m | rowspan=3 style="text-indent:1em" | Co | rowspan=3 colspan="3" style="text-indent:2em" | 376(9) keV | rowspan=3 style="text-align:center" | 2017 | rowspan=3|102(5) ms | β | Fe | rowspan=3|2+ | rowspan=3| |- | IT? | Co |- | β, p? | Mn |-id=Cobalt-53 | Co | style="text-align:right" | 27 | style="text-align:right" | 26 | 52.9542033(19) | style="text-align:center" | 1970 | 244.6(28) ms | β | Fe | 7/2−# | |-id=Cobalt-53m | rowspan=2 style="text-indent:1em" | Co | rowspan=2 colspan="3" style="text-indent:2em" | 3174.3(9) keV | rowspan=2 style="text-align:center" | 1970 | rowspan=2|250(10) ms | β? (~98.5%) | Fe | rowspan=2|(19/2−) | rowspan=2| |- | p (~1.5%) | Fe |-id=Cobalt-54 | Co | style="text-align:right" | 27 | style="text-align:right" | 27 | 53.94845908(38) | style="text-align:center" | 1952 | 193.27(6) ms | β | Fe | 0+ | |-id=Cobalt-54m | style="text-indent:1em" | Co | colspan="3" style="text-indent:2em" | 197.57(10) keV | style="text-align:center" | 1967 | 1.48(2) min | β | Fe | 7+ | |-id=Cobalt-55 | Co | style="text-align:right" | 27 | style="text-align:right" | 28 | 54.94199642(43) | style="text-align:center" | 1938 | 17.53(3) h | β | Fe | 7/2− | |-id=Cobalt-56 | Co | style="text-align:right" | 27 | style="text-align:right" | 29 | 55.93983803(51) | style="text-align:center" | 1941 | 77.236(26) d | β | Fe | 4+ | |-id=Cobalt-57 | Co | style="text-align:right" | 27 | style="text-align:right" | 30 | 56.93628982(55) | style="text-align:center" | 1941 | 271.811(32) d | EC | Fe | 7/2− | |-id=Cobalt-58 | rowspan=2|Co | rowspan=2 style="text-align:right" | 27 | rowspan=2 style="text-align:right" | 31 | rowspan=2|57.9357513(12) | rowspan=2 style="text-align:center" | 1941 | rowspan=2|70.844(20) d | EC (85.21%) | Fe | rowspan=2|2+ | rowspan=2| |- | β (14.79%) | Fe |-id=Cobalt-58m1 | rowspan=2 style="text-indent:1em" | Co | rowspan=2 colspan="3" style="text-indent:2em" | 24.95(6) keV | rowspan=2 style="text-align:center" | 1950 | rowspan=2|8.853(23) h | IT (99.9988%) | Co | rowspan=2|5+ | rowspan=2| |- | EC (0.00120%) | Fe |-id=Cobalt-58m2 | style="text-indent:1em" | Co | colspan="3" style="text-indent:2em" | 53.15(7) keV | style="text-align:center" | 1964 | 10.5(3) μs | IT | Co | 4+ | |-id=Cobalt-59 | Co | style="text-align:right" | 27 | style="text-align:right" | 32 | 58.93319352(43) | style="text-align:center" | 1923 | colspan="3" style="text-align:center;"|Stable | 7/2− | 1.0000 |-id=Cobalt-60m | Co | style="text-align:right" | 27 | style="text-align:right" | 33 | 59.93381554(43) | style="text-align:center" | 1941 | 5.2714(6) y | β | Ni | 5+ | trace |-id=Cobalt-60m | rowspan=2 style="text-indent:1em" | Co | rowspan=2 colspan="3" style="text-indent:2em" | 58.59(1) keV | rowspan=2 style="text-align:center" | 1941 | rowspan=2|10.467(6) min | IT (99.75%) | Co | rowspan=2|2+ | rowspan=2| |- | β (0.25%) | Ni |-id=Cobalt-61 | Co | style="text-align:right" | 27 | style="text-align:right" | 34 | 60.93247603(90) | style="text-align:center" | 1947 | 1.649(5) h | β | Ni | 7/2− | |-id=Cobalt-62 | Co | style="text-align:right" | 27 | style="text-align:right" | 35 | 61.934058(20) | style="text-align:center" | 1949 | 1.54(10) min | β | Ni | (2)+ | |-id=Cobalt-62m | rowspan=2 style="text-indent:1em" | Co | rowspan=2 colspan="3" style="text-indent:2em" | 22(5) keV | rowspan=2 style="text-align:center" | 1949 | rowspan=2|13.86(9) min | β (>99.5%) | Ni | rowspan=2|(5)+ | rowspan=2| |- | IT (<0.5%) | Co |-id=Cobalt-63 | Co | style="text-align:right" | 27 | style="text-align:right" | 36 | 62.933600(20) | style="text-align:center" | 1960 | 26.9(4) s | β | Ni | 7/2− | |-id=Cobalt-64 | Co | style="text-align:right" | 27 | style="text-align:right" | 37 | 63.935810(21) | style="text-align:center" | 1969 | 300(30) ms | β | Ni | 1+ | |-id=Cobalt-64m | rowspan=2 style="text-indent:1em" | Co | rowspan=2 colspan="3" style="text-indent:2em" | 107(20) keV | rowspan=2 style="text-align:center" | 2010 | rowspan=2|300# ms | β? | Ni | rowspan=2|5+# | rowspan=2| |- | IT? | Co |-id=Cobalt-65 | Co | style="text-align:right" | 27 | style="text-align:right" | 38 | 64.9364621(22) | style="text-align:center" | 1978 | 1.16(3) s | β | Ni | (7/2)− | |-id=Cobalt-66 | rowspan=2|Co | rowspan=2 style="text-align:right" | 27 | rowspan=2 style="text-align:right" | 39 | rowspan=2|65.939443(15) | rowspan=2 style="text-align:center" | 1985 | rowspan=2|194(17) ms | β | Ni | rowspan=2|(1+) | rowspan=2| |- | β, n? | Ni |-id=Cobalt-66m1 | style="text-indent:1em" | Co | colspan="3" style="text-indent:2em" | 175.1(3) keV | style="text-align:center" | 1998 | 824(22) ns | IT | 66Co | (3+) | |-id=Cobalt-66m2 | style="text-indent:1em" | Co | colspan="3" style="text-indent:2em" | 642(5) keV | style="text-align:center" | 1998 | >100 μs | IT | 66Co | (8−) | |-id=Cobalt-67 | rowspan=2|Co | rowspan=2 style="text-align:right" | 27 | rowspan=2 style="text-align:right" | 40 | rowspan=2|66.9406096(69) | rowspan=2 style="text-align:center" | 1985 | rowspan=2|329(28) ms | β | Ni | rowspan=2|(7/2−) | rowspan=2| |- | β, n? | Ni |-id=Cobalt-67m | rowspan=2 style="text-indent:1em" | Co | rowspan=2 colspan="3" style="text-indent:2em" | 491.55(11) keV | rowspan=2 style="text-align:center" | 2008 | rowspan=2|496(33) ms | IT (>80%) | 67Co | rowspan=2|(1/2−) | rowspan=2| |- | β | 67Ni |-id=Cobalt-68 | rowspan=2|Co | rowspan=2 style="text-align:right" | 27 | rowspan=2 style="text-align:right" | 41 | rowspan=2|67.9445594(41) | rowspan=2 style="text-align:center" | 1985 | rowspan=2|200(20) ms | β | Ni | rowspan=2|(7−) | rowspan=2| |- | β, n? | Ni |-id=Cobalt-68m1 | rowspan=2 style="text-indent:1em" | CoOrder of ground state and isomer is uncertain. | rowspan=2 colspan="3" style="text-indent:2em" | 150(150)# keV | rowspan=2 style="text-align:center" | 2000 | rowspan=2|1.6(3) s | β | Ni | rowspan=2|(2−) | rowspan=2| |- | β, n (>2.6%) | Ni |-id=Cobalt-68m2 | style="text-indent:1em" | Co | colspan="3" style="text-indent:2em" | 195(150)# keV | style="text-align:center" | 2010 | 101(10) ns | IT | 68Co | (1) | |-id=Cobalt-69 | rowspan=2|Co | rowspan=2 style="text-align:right" | 27 | rowspan=2 style="text-align:right" | 42 | rowspan=2|68.945909(92) | rowspan=2 style="text-align:center" | 1985 | rowspan=2|180(20) ms | β | Ni | rowspan=2|(7/2−) | rowspan=2| |- | β, n? | Ni |-id=Cobalt-69m | style="text-indent:1em" | Co | colspan="3" style="text-indent:2em" | 170(90) keV | style="text-align:center" | 2015 | 750(250) ms | β | Ni | 1/2−# | |-id=Cobalt-70 | rowspan=3|Co | rowspan=3 style="text-align:right" | 27 | rowspan=3 style="text-align:right" | 43 | rowspan=3|69.950053(12) | rowspan=3 style="text-align:center" | 1985 | rowspan=3|508(7) ms | β | Ni | rowspan=3|(1+) | rowspan=3| |- | β, n? | Ni |- | β, 2n? | Ni |-id=Cobalt-70m | rowspan=4 style="text-indent:1em" | Co | rowspan=4 colspan="3" style="text-indent:2em" | 200(200)# keV | rowspan=4 style="text-align:center" | 2000 | rowspan=4|112(7) ms | β | Ni | rowspan=4|(7−) | rowspan=4| |- | IT? | Co |- | β, n? | Ni |- | β, 2n? | Ni |-id=Cobalt-71 | rowspan=2|Co | rowspan=2 style="text-align:right" | 27 | rowspan=2 style="text-align:right" | 44 | rowspan=2|70.95237(50) | rowspan=2 style="text-align:center" | 1992 | rowspan=2|80(3) ms | β (97%) | Ni | rowspan=2|(7/2−) | rowspan=2| |- | β, n (3%) | Ni |-id=Cobalt-72 | rowspan=3|Co | rowspan=3 style="text-align:right" | 27 | rowspan=3 style="text-align:right" | 45 | rowspan=3|71.95674(32)# | rowspan=3 style="text-align:center" | 1992 | rowspan=3|51.5(3) ms | β (<96%) | Ni | rowspan=3|(6−,7−) | rowspan=3| |- | β, n (>4%) | Ni |- | β, 2n? | Ni |-id=Cobalt-72m | style="text-indent:1em" | Co | colspan="3" style="text-indent:2em" | 200(200)# keV | style="text-align:center" | 2016 | 47.8(5) ms | β | Ni | (0+,1+) | |-id=Cobalt-73 | rowspan=3|Co | rowspan=3 style="text-align:right" | 27 | rowspan=3 style="text-align:right" | 46 | rowspan=3|72.95924(32)# | rowspan=3 style="text-align:center" | 1995 | rowspan=3|42.0(8) ms | β (94%) | Ni | rowspan=3|(7/2−) | rowspan=3| |- | β, n (6%) | Ni |- | β, 2n? | Ni |-id=Cobalt-74 | rowspan=3|Co | rowspan=3 style="text-align:right" | 27 | rowspan=3 style="text-align:right" | 47 | rowspan=3|73.96399(43)# | rowspan=3 style="text-align:center" | 1995 | rowspan=3|31.3(13) ms | β (82%) | Ni | rowspan=3|7−# | rowspan=3| |- | β, n (18%) | Ni |- | β, 2n? | Ni |-id=Cobalt-75 | rowspan=3|Co | rowspan=3 style="text-align:right" | 27 | rowspan=3 style="text-align:right" | 48 | rowspan=3|74.96719(43)# | rowspan=3 style="text-align:center" | 1995 | rowspan=3|26.5(12) ms | β (>84%) | Ni | rowspan=3|7/2−# | rowspan=3| |- | β, n (<16%) | Ni |- | β, 2n? | Ni |-id=Cobalt-75m | style="text-indent:1em" | Co | colspan="3" style="text-indent:2em" | 1914(2) keV | style="text-align:center" | 2021 | 13(6) μs | IT | Co | (1/2)− | |-id=Cobalt-76 | rowspan=3|Co | rowspan=3 style="text-align:right" | 27 | rowspan=3 style="text-align:right" | 49 | rowspan=3|75.97245(54)# | rowspan=3 style="text-align:center" | 2010 | rowspan=3|23(6) ms | β | Ni | rowspan=3|(8−) | rowspan=3| |- | β, n? | Ni |- | β, 2n? | Ni |-id=Cobalt-76m1 | style="text-indent:1em" | Co | colspan="3" style="text-indent:2em" | 100(100)# keV | style="text-align:center" | 2015 | 16(4) ms | β | Ni | (1−) | |-id=Cobalt-76m2 | style="text-indent:1em" | Co | colspan="3" style="text-indent:2em" | 740(100)# keV | style="text-align:center" | 2015 | 2.99(27) μs | IT | Co | (3+) | |-id=Cobalt-77 | rowspan=4|Co | rowspan=4 style="text-align:right" | 27 | rowspan=4 style="text-align:right" | 50 | rowspan=4|76.97648(64)# | rowspan=4 style="text-align:center" | 2014 | rowspan=4|15(6) ms | β | Ni | rowspan=4|7/2−# | rowspan=4| |- | β, n? | Ni |- | β, 2n? | Ni |- | β, 3n? | Ni |-id=Cobalt-78 | Co | style="text-align:right" | 27 | style="text-align:right" | 51 | 77.983 55(75)# | style="text-align:center" | 2017 | 11# ms[>410 ns] | β? | Ni

|-id=Cobalt-79 | 79Co | style="text-align:right" | 27 | style="text-align:right" | 52 | | style="text-align:center" | 2026

|-id=Cobalt-80 | 80Co | style="text-align:right" | 27 | style="text-align:right" | 53 | | style="text-align:center" | 2026

Stellar nucleosynthesis of cobalt-56