Isotopes of chlorine

Chlorine (17Cl) has 25 isotopes, ranging from 28Cl to 52Cl, and two isomers, 34mCl and 38mCl. There are two stable isotopes, 35Cl (75.77%) and 37Cl (24.23%), giving chlorine a standard atomic weight of 35.45. The longest-lived radioactive isotope is 36Cl, which has a half-life of 301,000 years. All other isotopes have half-lives under 1 hour, many less than one second. The shortest-lived are proton-unbound 29Cl and 30Cl, with half-lives less than 10 picoseconds and 30 nanoseconds, respectively; the half-life of 28Cl is unknown.

Isotopes of chlorine (17Cl)
Main isotopes[1] Decay
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°(Cl)
  • [35.446, 35.457]
  • 35.45±0.01 (abridged)[2][3]

List of isotopes
Nuclide[4]
[n 1]		 Z N Isotopic mass (Da)[5]
[n 2][n 3]		 Half-life
[n 4]		 Decay
mode
[n 5]		 Daughter
isotope
[n 6]		 Spin and
parity
[n 7][n 4]		 Natural abundance (mole fraction)
Excitation energy Normal proportion Range of variation
28Cl[6] 17 11 28.02954(64)# p 27S 1+#
29Cl[6] 17 12 29.01413(20) <10 ps p 28S (1/2+)
30Cl[6] 17 13 30.00477(21)# <30 ns p 29S 3+#
31Cl 17 14 30.992448(4) 190(1) ms β+ (97.6%) 31S 3/2+
β+, p (2.4%) 30P
32Cl 17 15 31.9856846(6) 298(1) ms β+ (99.92%) 32S 1+
β+, α (.054%) 28Si
β+, p (.026%) 31P
33Cl 17 16 32.9774520(4) 2.5038(22) s β+ 33S 3/2+
34Cl 17 17 33.97376249(5) 1.5266(4) s β+ 34S 0+
34mCl 146.360(27) keV 31.99(3) min β+ (55.4%) 34S 3+
IT (44.6%) 34Cl
35Cl 17 18 34.96885269(4) Stable 3/2+ 0.7576(10) 0.75644–0.75923
36Cl[n 8] 17 19 35.96830682(4) 3.013(15)×105 y β− (98.1%) 36Ar 2+ Trace[n 9] approx. 7×10−13
β+ (1.9%) 36S
37Cl 17 20 36.96590258(6) Stable 3/2+ 0.2424(10) 0.24077–0.24356
38Cl 17 21 37.96801042(11) 37.24(5) min β− 38Ar 2−
38mCl 671.365(8) keV 715(3) ms IT 38Cl 5−
39Cl 17 22 38.9680082(19) 56.2(6) min β− 39Ar 3/2+
40Cl 17 23 39.97042(3) 1.35(2) min β− 40Ar 2−
41Cl 17 24 40.97068(7) 38.4(8) s β− 41Ar (1/2+,3/2+)
42Cl 17 25 41.97334(6) 6.8(3) s β− 42Ar
43Cl 17 26 42.97406(7) 3.13(9) s β− (>99.9%) 43Ar (3/2+)
β−, n (<.1%) 42Ar
44Cl 17 27 43.97812(15) 0.56(11) s β− (92%) 44Ar (2-)
β−, n (8%) 43Ar
45Cl 17 28 44.98039(15) 513(36) ms[7] β− (76%) 45Ar (3/2+)
β−, n (24%) 44Ar
46Cl 17 29 45.98512(22) 232(2) ms β−, n (60%) 45Ar 2-#
β− (40%) 46Ar
47Cl 17 30 46.98950(43)# 101(6) ms β− (97%) 47Ar 3/2+#
β−, n (3%) 46Ar
48Cl 17 31 47.99541(54)# 100# ms [>200 ns] β− 48Ar
49Cl 17 32 49.00101(64)# 50# ms [>200 ns] β− 49Ar 3/2+#
50Cl 17 33 50.00831(64)# 20# ms β− 50Ar
51Cl 17 34 51.01534(75)# 2# ms [>200 ns] β− 51Ar 3/2+#
52Cl[8] 17 35 β− 52Ar
This table header & footer:
  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. # – 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
    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

Chlorine-36
Main article: 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 36
Cl by neutron capture is an inevitable consequence of using natural isotope mixtures of chlorine (i.e. Those containing 35
Cl). This produces a long lived radioactive product which has to be stored or disposed off. Isotope separation to produce pure 37
Cl can vastly reduce 36
Cl production, but a small amount might still be produced by (n,2n) reactions involving fast neutrons.

Chlorine-37
Main article: Chlorine-37

Stable chlorine-37 makes up about 24.23% of the naturally occurring chlorine on earth. Variation occurs as chloride mineral deposits have a slightly elevated chlorine-37 balance over the average found in sea water and halite deposits.

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: Chlorine". CIAAW. 2009.
  3. Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; et al. (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. Half-life, decay mode, nuclear spin, and isotopic composition is sourced in:
    Audi, G.; Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S. (2017). "The NUBASE2016 evaluation of nuclear properties" (PDF). Chinese Physics C. 41 (3): 030001. Bibcode:2017ChPhC..41c0001A. doi:10.1088/1674-1137/41/3/030001.
  5. Wang, M.; Audi, G.; Kondev, F. G.; Huang, W. J.; Naimi, S.; Xu, X. (2017). "The AME2016 atomic mass evaluation (II). Tables, graphs, and references" (PDF). Chinese Physics C. 41 (3): 030003-1–030003-442. doi:10.1088/1674-1137/41/3/030003.
  6. Mukha, I.; et al. (2018). "Deep excursion beyond the proton dripline. I. Argon and chlorine isotope chains". Physical Review C. 98 (6): 064308–1–064308–13. arXiv:1803.10951. Bibcode:2018PhRvC..98f4308M. doi:10.1103/PhysRevC.98.064308. S2CID 119384311.
  7. Bhattacharya, Soumik; Tripathi, Vandana; Tabor, S. L.; Volya, A.; Bender, P. C.; Benetti, C.; Carpenter, M. P.; Carroll, J. J.; Chester, A.; Chiara, C. J.; Childers, K.; Clark, B. R.; Crider, B. P.; Harke, J. T.; Jain, R.; Liddick, S. N.; Lubna, R. S.; Luitel, S.; Longfellow, B.; Mogannam, M. J.; Ogunbeku, T. H.; Perello, J.; Richard, A. L.; Rubino, E.; Saha, S.; Shehu, O. A.; Unz, R.; Xiao, Y.; Zhu, Yiyi (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.
  8. Neufcourt, L.; Cao, Y.; Nazarewicz, W.; Olsen, E.; Viens, F. (2019). "Neutron drip line in the Ca region from Bayesian model averaging". Physical Review Letters. 122 (6): 062502–1–062502–6. arXiv:1901.07632. Bibcode:2019PhRvL.122f2502N. doi:10.1103/PhysRevLett.122.062502. PMID 30822058. S2CID 73508148.
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