Isotopes of cobalt

Naturally occurring cobalt, Co, consists of a single stable isotope, ⁵⁹Co (thus, cobalt is a mononuclidic element). Twenty-eight radioisotopes have been characterized; the most stable are ⁶⁰Co with a half-life of 5.2714 years, ⁵⁷Co (271.811 days), ⁵⁶Co (77.236 days), and ⁵⁸Co (70.844 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 8.853 h.

Isotopes of cobalt (₂₇Co)

Main isotopes[1] Decay abun­dance half-life (t1/2) mode pro­duct 56Co synth 77.236 d β+ 56Fe 57Co synth 271.811 d ε 57Fe 58Co synth 70.844 d β+ 58Fe 59Co 100% stable 60Co trace 5.2714 y β−100% 60Ni
Standard atomic weight Ar°(Co)
	58.933194±0.000003[2] 58.933±0.001 (abridged)[3]
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The isotopes of cobalt range in atomic weight from ⁵⁰Co to ⁷⁸Co. The main decay mode for isotopes with atomic mass less than that of the stable isotope, ⁵⁹Co, is electron capture and the main mode of decay for those of greater than 59 atomic mass units is beta decay. The main decay products before ⁵⁹Co are iron isotopes and the main products after are nickel isotopes.

Radioisotopes can be produced by various nuclear reactions. For example, ⁵⁷Co is produced by cyclotron irradiation of iron. The main reaction is the (d,n) reaction ⁵⁶Fe + ²H → n + ⁵⁷Co.^[4]

List of isotopes

Nuclide [n 1]	Z	N	Isotopic mass (Da)[5] [n 2][n 3]	Half-life[1] [n 4]	Decay mode[1] [n 5]	Daughter isotope [n 6]	Spin and parity[1] [n 7][n 4]	Isotopic abundance
	Excitation energy[n 4]
50Co	27	23	49.98112(14)	38.8(2) ms	β+, p (70.5%)	49Mn	(6+)
					β+ (29.5%)	50Fe
					β+, 2p?	48Mn
51Co	27	24	50.970647(52)	68.8(19) ms	β+ (96.2%)	51Fe	7/2−
					β+, p (<3.8%)	50Mn
52Co	27	25	51.9631302(57)	111.7(21) ms	β+	52Fe	6+
					β+, p?	51Mn
52mCo	376(9) keV			102(5) ms	β+	52Fe	2+
					IT?	52Co
					β+, p?	51Mn
53Co	27	26	52.9542033(19)	244.6(28) ms	β+	53Fe	7/2−#
53mCo	3174.3(9) keV			250(10) ms	β+? (~98.5%)	53Fe	(19/2−)
					p (~1.5%)	52Fe
54Co	27	27	53.94845908(38)	193.27(6) ms	β+	54Fe	0+
54mCo	197.57(10) keV			1.48(2) min	β+	54Fe	7+
55Co	27	28	54.94199642(43)	17.53(3) h	β+	55Fe	7/2−
56Co	27	29	55.93983803(51)	77.236(26) d	β+	56Fe	4+
57Co	27	30	56.93628982(55)	271.811(32) d	EC	57Fe	7/2−
58Co	27	31	57.9357513(12)	70.844(20) d	EC (85.21%)	58Fe	2+
					β+ (14.79%)	58Fe
58m1Co	24.95(6) keV			8.853(23) h	IT	58Co	5+
					EC (0.00120%)	58Fe
58m2Co	53.15(7) keV			10.5(3) μs	IT	58Co	4+
59Co	27	32	58.93319352(43)	Stable			7/2−	1.0000
60Co	27	33	59.93381554(43)	5.2714(6) y	β−	60Ni	5+
60mCo	58.59(1) keV			10.467(6) min	IT (99.75%)	60Co	2+
					β− (0.25%)	60Ni
61Co	27	34	60.93247603(90)	1.649(5) h	β−	61Ni	7/2−
62Co	27	35	61.934058(20)	1.54(10) min	β−	62Ni	(2)+
62mCo	22(5) keV			13.86(9) min	β− (>99.5%)	62Ni	(5)+
					IT (<0.5%)	62Co
63Co	27	36	62.933600(20)	26.9(4) s	β−	63Ni	7/2−
64Co	27	37	63.935810(21)	300(30) ms	β−	64Ni	1+
64mCo	107(20) keV			300# ms	β−?	64Ni	5+#
					IT?	64Co
65Co	27	38	64.9364621(22)	1.16(3) s	β−	65Ni	(7/2)−
66Co	27	39	65.939443(15)	194(17) ms	β−	66Ni	(1+)
					β−, n?	65Ni
66m1Co	175.1(3) keV			824(22) ns	IT	66Co	(3+)
66m2Co	642(5) keV			>100 μs	IT	66Co	(8−)
67Co	27	40	66.9406096(69)	329(28) ms	β−	67Ni	(7/2−)
					β−, n?	66Ni
67mCo	491.55(11) keV			496(33) ms	IT (>80%)	67Co	(1/2−)
					β−	67Ni
68Co	27	41	67.9445594(41)	200(20) ms	β−	68Ni	(7−)
					β−, n?	67Ni
68m1Co[n 8]	150(150)# keV			1.6(3) s	β−	68Ni	(2−)
					β−, n (>2.6%)	67Ni
68m2Co	195(150)# keV			101(10) ns	IT	68Co	(1)
69Co	27	42	68.945909(92)	180(20) ms	β−	69Ni	(7/2−)
					β−, n?	68Ni
69mCo[n 8]	170(90) keV			750(250) ms	β−	69Ni	1/2−#
70Co	27	43	69.950053(12)	508(7) ms	β−	70Ni	(1+)
					β−, n?	69Ni
					β−, 2n?	68Ni
70mCo[n 8]	200(200)# keV			112(7) ms	β−	70Ni	(7−)
					IT?	70Co
					β−, n?	69Ni
					β−, 2n?	68Ni
71Co	27	44	70.95237(50)	80(3) ms	β− (97%)	71Ni	(7/2−)
					β−, n (3%)	70Ni
72Co	27	45	71.95674(32)#	51.5(3) ms	β− (<96%)	72Ni	(6−,7−)
					β−, n (>4%)	71Ni
					β−, 2n?	70Ni
72mCo[n 8]	200(200)# keV			47.8(5) ms	β−	72Ni	(0+,1+)
73Co	27	46	72.95924(32)#	42.0(8) ms	β− (94%)	73Ni	(7/2−)
					β−, n (6%)	72Ni
					β−, 2n?	71Ni
74Co	27	47	73.96399(43)#	31.3(13) ms	β− (82%)	74Ni	7−#
					β−, n (18%)	73Ni
					β−, 2n?	72Ni
75Co	27	48	74.96719(43)#	26.5(12) ms	β− (>84%)	75Ni	7/2−#
					β−, n (<16%)	74Ni
					β−, 2n?	73Ni
76Co	27	49	75.97245(54)#	23(6) ms	β−	76Ni	(8−)
					β−, n?	75Ni
					β−, 2n?	74Ni
76m1Co[n 8]	100(100)# keV			16(4) ms	β−	76Ni	(1−)
76m2Co	740(100)# keV			2.99(27) μs	IT	76Co	(3+)
77Co	27	50	76.97648(64)#	15(6) ms	β−	77Ni	7/2−#
					β−, n?	76Ni
					β−, 2n?	75Ni
					β−, 3n?	74Ni
78Co	27	51	77.983 55(75)#	11# ms [>410 ns]	β−?	78Ni
This table header & footer: view

1. ^mCo – 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. # – 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
   n:	Neutron emission
   p:	Proton emission

6. Bold symbol as daughter – Daughter product is stable.
7. ( ) spin value – Indicates spin with weak assignment arguments.
8. Order of ground state and isomer is uncertain.

Stellar nucleosynthesis of cobalt-56

One of the terminal nuclear reactions in stars prior to supernova produces ⁵⁶Ni. Following its production, ⁵⁶Ni decays to ⁵⁶Co, and then ⁵⁶Co subsequently decays to ⁵⁶Fe. These decay reactions power the luminosity displayed in light decay curves. Both the light decay and radioactive decay curves are expected to be exponential. Therefore, the light decay curve should give an indication of the nuclear reactions powering it. This has been confirmed by observation of bolometric light decay curves for SN 1987A. Between 600 and 800 days after SN1987A occurred, the bolometric light curve decreased at an exponential rate with half-life values from τ_1/2 = 68.6 days to τ_1/2 = 69.6 days.^[6] The rate at which the luminosity decreased closely matched the exponential decay of ⁵⁶Co with a half-life of τ_1/2 = 77.233 days.

Use of cobalt radioisotopes in medicine

Cobalt-57 (⁵⁷Co or Co-57) is used in medical tests; it is used as a radiolabel for vitamin B₁₂ uptake. It is useful for the Schilling test.^[7]

Cobalt-60 (⁶⁰Co or Co-60) is used in radiotherapy. It produces two gamma rays with energies of 1.17 MeV and 1.33 MeV. The ⁶⁰Co source is about 2 cm in diameter and as a result produces a geometric penumbra, making the edge of the radiation field fuzzy. The metal has the unfortunate habit of producing fine dust, causing problems with radiation protection. The ⁶⁰Co source is useful for about 5 years but even after this point is still very radioactive, and so cobalt machines have fallen from favor in the Western world where Linacs are common.

Industrial uses for radioactive isotopes

Cobalt-60 (⁶⁰Co) is useful as a gamma ray source because it can be produced in predictable quantities, and for its high radioactivity simply by exposing natural cobalt to neutrons in a reactor.^[8] The uses for industrial cobalt include:

• Sterilization of medical supplies and medical waste
• Radiation treatment of foods for sterilization (cold pasteurization)^[9]
• Industrial radiography (e.g., weld integrity radiographs)
• Density measurements (e.g., concrete density measurements)
• Tank fill height switches

⁵⁷Co is used as a source in Mössbauer spectroscopy of iron-containing samples. Electron capture by ⁵⁷Co forms an excited state of the ⁵⁷Fe nucleus, which in turn decays to the ground state with the emission of a gamma ray. Measurement of the gamma-ray spectrum provides information about the chemical state of the iron atom in the sample.

References

1. Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3): 030001. doi:10.1088/1674-1137/abddae.
2. "Standard Atomic Weights: Cobalt". CIAAW. 2017.
3. Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
4. Diaz, L. E. "Cobalt-57: Production". JPNM Physics Isotopes. University of Harvard. Archived from the original on 2000-10-31. Retrieved 2013-11-15.
5. Wang, Meng; Huang, W.J.; Kondev, F.G.; Audi, G.; Naimi, S. (2021). "The AME 2020 atomic mass evaluation (II). Tables, graphs and references*". Chinese Physics C. 45 (3): 030003. doi:10.1088/1674-1137/abddaf.
6. Bouchet, P.; Danziger, I.J.; Lucy, L.B. (September 1991). "Bolometric Light Curve of SN 1987A: Results from Day 616 to 1316 After Outburst". The Astronomical Journal. 102 (3): 1135–1146. doi:10.1086/115939 – via Astrophysics Data System.
7. Diaz, L. E. "Cobalt-57: Uses". JPNM Physics Isotopes. University of Harvard. Archived from the original on 2011-06-11. Retrieved 2010-09-13.
8. "Properties of Cobalt-60". Radioactive Isotopes. Retrieved 2022-12-09.
9. "Beneficial Uses of Cobalt-60". INTERNATIONAL IRRADIATION ASSOCIATION. Retrieved 2022-12-09.

• Isotope masses from:
  • Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
• Half-life, spin, and isomer data selected from the following sources.
  • Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
  • National Nuclear Data Center. "NuDat 2.x database". Brookhaven National Laboratory.
  • Holden, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.). CRC Handbook of Chemistry and Physics (85th ed.). Boca Raton, Florida: CRC Press. ISBN 978-0-8493-0485-9.