Isotopes of chlorine

Main isotopes of Chemistry:chlorine (17Cl) | Iso­tope | Decay

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| abun­dance | half-life (t1/2) | mode | pro­duct
35Cl  | 76%  | stable
36Cl  | trace | 3.01×105 y | β− | 36Ar
ε | 36S
37Cl  | 24%  | stable
Standard atomic weight Ar, standard(Cl)|

* [35.446, 35.457][1]
* Conventional: 35.45

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Chlorine (17Cl) has two stable isotopes, 35Cl (75.8%) and 37Cl (24.2%), giving chlorine a standard atomic weight of 35.45. Artificical radioisotopes are known ranging from 28Cl to 52Cl, and there are also two isomers, 34mCl and 38mCl. The longest-lived radioactive isotope is 36Cl, which has a half-life of 301,000 years. All other isotopes and isomers have half-lives under an hour, and most under 10 seconds.

## Contents

* 1 List of isotopes
* 2 Stable isotope analysis
* 3 Chlorine-36
* 4 Chlorine-37
* 5 See also
* 6 References

## List of isotopes

Nuclide
[n 1] | Z | N | Isotopic mass (u)
[n 2][n 3] | Half-life
[n 4] | Decay
mode
[n 5] | Daughter
isotope
[n 6] | Spin and
parity
[n 7][n 4] | Physics:Natural abundance (mole fraction)

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Excitation energy  | Normal proportion  | Range of variation
28Cl[2] | 17  | 11  | 28.03035(54)#  | 2018 |  | p | 27S  | 1+#  |  |
29Cl  | 17  | 12  | 29.01505(20)#  | 2015 | 5.4(19) zs  | p  | 28S  | (1/2+)  |  |
30Cl  | 17  | 13  | 30.005018(26)  | 2018 | <50 ns[2] | p  | 29S  | 3+#  |  |
31Cl  | 17  | 14  | 30.9924481(37)  | 1977 | 190(1) ms  | β+ (97.6%)  | 31S  | 3/2+  |  |
β+, p (2.4%)  | 30P
32Cl  | 17  | 15  | 31.98568461(60)  | 1953 | 298(1) ms  | β+ (99.92%)  | 32S | 1+  |  |
β+, α (0.054%)  | 28Si
β+, p (0.026%)  | 31P
33Cl  | 17  | 16  | 32.97745199(42)  | 1940 | 2.5038(22) s  | β+ | 33S | 3/2+  |  |
34Cl  | 17  | 17  | 33.973762490(52)  | 1934 | 1.5267(4) s  | β+ | 34S | 0+  |  |
34mCl  | 146.360(27) keV  | 1953 | 31.99(3) min  | β+ (55.4%)  | 34S | 3+  |  |
IT (44.6%)  | 34Cl
35Cl  | 17  | 18  | 34.968852694(38)  | 1919 | Stable | 3/2+  | 0.758(2)  |
36Cl[n 8] | 17  | 19  | 35.968306822(38)  | 1941 | 3.013(15)×105 y  | β− (98.1%)  | 36Ar | 2+  | 7×10−13[3][4][n 9] |
β+ (1.9%)  | 36S
37Cl | 17  | 20  | 36.965902573(55)  | 1919 | Stable | 3/2+  | 0.242(2)  |
38Cl  | 17  | 21  | 37.96801041(11)  | 1940 | 37.230(14) min  | β− | 38Ar | 2−  |  |
38mCl  | 671.365(8) keV  | 1962 | 715(3) ms  | IT  | 38Cl  | 5−  |  |
39Cl  | 17  | 22  | 38.9680082(19)  | 1949 | 56.2(6) min  | β− | 39Ar  | 3/2+  |  |
40Cl  | 17  | 23  | 39.970415(34)  | 1956 | 1.35(3) min  | β− | 40Ar | 2−  |  |
41Cl  | 17  | 24  | 40.970685(74)  | 1971 | 38.4(8) s  | β− | 41Ar  | (1/2+)  |  |
42Cl  | 17  | 25  | 41.973342(64)  | 1971 | 6.8(3) s  | β− | 42Ar  | (2−)  |  |
β−, n?  | 41Ar
43Cl  | 17  | 26  | 42.974064(66)  | 1976 | 3.13(9) s  | β− | 43Ar  | (3/2+)  |  |
β−, n?  | 42Ar
44Cl  | 17  | 27  | 43.978015(92)  | 1979 | 0.56(11) s  | β− (>92%)  | 44Ar  | (2-)  |  |
β−, n? (<8%)  | 43Ar
45Cl  | 17  | 28  | 44.98039(15)  | 1979 | 513(36) ms[5] | β− (76%)  | 45Ar  | (3/2+)  |  |
β−, n (24%)  | 44Ar
46Cl  | 17  | 29  | 45.98525(10)  | 1989 | 232(2) ms  | β−, n (60%)  | 45Ar  | 2-#  |  |
β− (40%)  | 46Ar
β−, 2n?  | 44Ar
47Cl  | 17  | 30  | 46.98972(22)#  | 1989 | 101(5) ms  | β− (>97%)  | 47Ar  | 3/2+#  |  |
β−, n (<3%)  | 46Ar
β−, 2n?  | 45Ar
48Cl  | 17  | 31  | 47.99541(54)#  | 1989 | 30# ms
[>200 ns]  | β−?  | 48Ar  |  |  |
β−, n?  | 47Ar
β−, 2n?  | 46Ar
49Cl  | 17  | 32  | 49.00079(43)#  | 1989 | 35# ms
[>200 ns]  | β−?  | 49Ar  | 3/2+#  |  |
β−, n?  | 48Ar
β−, 2n?  | 47Ar
50Cl  | 17  | 33  | 50.00827(43)#  | 2009 | 10# ms
[>620 ns]  | β− | 50Ar  |  |  |
β−, n?  | 49Ar
β−, 2n?  | 48Ar
51Cl  | 17  | 34  | 51.01534(75)#  | 2009 | 5# ms
[>200 ns]  | β−?  | 51Ar  | 3/2+#  |  |
β−, n?  | 50Ar
β−, 2n?  | 49Ar
52Cl  | 17  | 35  | 52.02400(75)#  | 2018 | 2# ms
[>400 ns]  | β−?  | 52Ar  |  |  |
β−, n?  | 51Ar
β−, 2n?  | 50Ar

1. ↑ mCl - 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. ↑ 4.0 4.1 # - Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
5. ↑ Modes of decay:  IT: | Isomeric transition

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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. ↑ Used in radiodating water
9. ↑ Cosmogenic nuclide

## Stable isotope analysis

The representative terrestrial abundance of chlorine contains about is 24.2% of 37Cl, with a normal range of 23.9–24.5% of chlorine atoms.[6] When measuring deviations in isotopic composition, the usual reference point is "Standard Mean Ocean Chloride" (SMOC), although a NIST Standard Reference Material (975a) also exists. SMOC is known to have a 37Cl/35Cl ratio of 0.319627 ± 0.000199 (24.221% ± 0.0015% chlorine-37)[7] and to have an atomic weight of 35.4525.

There is known variation in the isotopic abundance of chlorine. This heavier isotope tends to be more prevalent in chloride minerals than in aqueous solutions such as seawater, although the isotopic composition of organochlorine compounds can vary in either direction from the SMOC standard in the range of several parts per thousand.[6]

## Chlorine-36

Main article: Physics:Chlorine-36

Trace amounts of radioactive 36Cl exist in the environment, in a ratio of about 7×10−13 to 1 with stable isotopes. 36Cl is produced in the atmosphere by spallation of 36Ar by interactions with cosmic ray protons. In the subsurface environment, 36Cl is generated primarily as a result of neutron capture by 35Cl or muon capture by 40Ca. 36Cl decays to either 36S (1.9%) or to 36Ar (98.1%), with a combined half-life of 308,000 years. The half-life of this hydrophilic nonreactive isotope makes it suitable for geologic dating in the range of 60,000 to 1 million years. Additionally, large amounts of 36Cl were produced by neutron irradiation of seawater during atmospheric detonations of nuclear weapons between 1952 and 1958. The residence time of 36Cl in the atmosphere is about 1 week. Thus, as an event marker of 1950s water in soil and ground water, 36Cl is also useful for dating waters less than 50 years before the present. 36Cl has seen use in other areas of the geological sciences, forecasts, and elements. In chloride-based molten salt reactors the production of 36Cl by neutron capture is an inevitable consequence of using natural isotope mixtures of chlorine (i.e. Those containing 35Cl). This produces a long lived radioactive product which has to be stored or disposed of. Isotope separation to produce pure 37Cl can vastly reduce 36Cl production, but a small amount might still be produced by (n,2n) reactions involving fast neutrons.

## Chlorine-37

Main article: Physics:Chlorine-37

Besides being a component of natural stable chlorine, the chief notability of this isotope is its use to detect solar neutrinos through inverse electron capture (producing the gas 37Ar). This was used in the first detection at the Homestake experiment. Subsequently gallium-71 was found more suitable for this purpose, and used in GALLEX/GNO and SAGE.

## See also

Daughter products other than chlorine

* Isotopes of argon
* Isotopes of sulfur
* Isotopes of phosphorus
* Isotopes of silicon

## References

1. ↑ Meija, Juris; Coplen, Tyler B.; Berglund, Michael; Brand, Willi A.; De Bièvre, Paul; Gröning, Manfred; Holden, Norman E.; Irrgeher, Johanna et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry 88 (3): 265–91. doi:10.1515/pac-2015-0305.
2. ↑ 2.0 2.1 Mukha, I. (2018). "Deep excursion beyond the proton dripline. I. Argon and chlorine isotope chains". Physical Review C 98 (6): 064308–1–064308–13. doi:10.1103/PhysRevC.98.064308. Bibcode: 2018PhRvC..98f4308M.
3. ↑ M. Zreda (1991). "Cosmogenic chlorine-36 production rates in terrestrial rocks". Earth and Planetary Science Letters 105 (1–3): 94–109. doi:10.1016/0012-821X(91)90123-Y. Bibcode: 1991E&PSL.105...94Z.
4. ↑ M. Sheppard and M. Herod (2012). "Variation in background concentrations and specific activities of 36Cl, 129I and U/Th-series radionuclides in surface waters". Journal of Environmental Radioactivity 106: 27–34. doi:10.1016/j.jenvrad.2011.10.015. PMID 22304997.
5. ↑ Bhattacharya, Soumik; Tripathi, Vandana; Tabor, S. L.; Volya, A.; Bender, P. C.; Benetti, C.; Carpenter, M. P.; Carroll, J. J. et al. (2023-08-18). "β− decay of neutron-rich 45Cl located at the magic number N=28". Physical Review C (American Physical Society (APS)) 108 (2). doi:10.1103/physrevc.108.024312. ISSN 2469-9985. https://www.academia.edu/download/111135528/fulltext.pdf.
6. ↑ 6.0 6.1 Cite error: Invalid `<ref>` tag; no text was provided for refs named `CIAAWchlorine`
7. ↑ Chlorine-bearing species and the 37Cl/35Cl isotope ratio ... \- Figure 8. This is the only source I find giving the actual composition of SMOC (as the isotope ratio). There surely should be a better one.

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