Isotopes of chlorine

Chlorine (Cl) has 24 isotopes with mass numbers ranging from ²²Cl to ⁵¹Cl and 2 isomers (^34mCl and ^38mCl). There are two principal stable isotopes, ³⁵Cl (75.78%) and ³⁷Cl (24.22%), found in the relative proportions of 37.89:12.11, respectively, giving chlorine a relative atomic mass of 35.453. 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 ²⁹Cl and ³⁰Cl, with half-lives less than 20 and 30 nanoseconds, respectively—the half-life of ²⁸Cl is unknown.

Relative atomic mass: 35.453(2)

Chlorine-36 (³⁶Cl)

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 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.

Table

nuclide symbol	Atomic Number	N(n)	isotopic mass (u)	half-life	decay mode(s)	daughter isotope(s)	nuclear spin	representative isotopic composition (mole fraction)	range of natural variation (mole fraction)
	excitation energy
28Cl	17	11	28.02851(54)#		p	27S	(1+)#
29Cl	17	12	29.01411(21)#	<20 ns	p	28S	(3/2+)#
30Cl	17	13	30.00477(21)#	<30 ns	p	29S	(3+)#
31Cl	17	14	30.99241(5)	150(25) ms	β+ (99.3%)	31S	3/2+
					β+, p (.7%)	30P
32Cl	17	15	31.985690(7)	298(1) ms	β+ (99.92%)	32S	1+
					β+, α (.054%)	28Si
					β+, p (.026%)	31P
33Cl	17	16	32.9774519(5)	2.511(3) s	β+	33S	3/2+
34Cl	17	17	33.97376282(19)	1.5264(14) s	β+	34S	0+
34mCl	146.36(3) keV			32.00(4) min	β+ (55.4%)	34S	3+
					IT (44.6%)	34Cl
35Cl	17	18	34.96885268(4)	Stable			3/2+	0.7576(10)	0.75644–0.75923
36Cl	17	19	35.96830698(8)	3.01(2)×105 y	β− (98.1%)	36Ar	2+	Trace	approx. 7*10−13
					ε (1.9%)	36S
37Cl	17	20	36.96590259(5)	Stable			3/2+	0.2424(10)	0.24077–0.24356
38Cl	17	21	37.96801043(10)	37.24(5) min	β−	38Ar	2−
38mCl	671.361(8) keV			715(3) ms	IT	38Cl	5−
39Cl	17	22	38.9680082(19)	55.6(2) 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	41.97325(15)	6.8(3) s	β−	42Ar
43Cl	17	26	42.97405(17)	3.07(7) s	β− (>99.9%)	43Ar	3/2+#
					β−, n (<.1%)	42Ar
44Cl	17	27	43.97828(12)	0.56(11) s	β− (92%)	44Ar
					β−, n (8%)	43Ar
45Cl	17	28	44.98029(13)	400(40) ms	β− (76%)	45Ar	3/2+#
					β−, n (24%)	44Ar
46Cl	17	29	45.98421(77)	232(2) ms	β−, n (60%)	45Ar
					β− (40%)	46Ar
47Cl	17	30	46.98871(64)#	101(6) ms	β− (97%)	47Ar	3/2+#
					β−, n (3%)	46Ar
48Cl	17	31	47.99495(75)#	100# ms [>200 ns]	β−	48Ar
49Cl	17	32	49.00032(86)#	50# ms [>200 ns]	β−	49Ar	3/2+#
50Cl	17	33	50.00784(97)#	20# ms	β−	50Ar
51Cl	17	34	51.01449(107)#	2# ms [>200 ns]	β−	51Ar	3/2+#

Notes

• Geologically exceptional samples are known in which the isotopic composition lies outside the reported range. The uncertainty in the atomic mass may exceed the stated value for such specimens.
• Commercially available materials may have been subjected to an undisclosed or inadvertent isotopic fractionation. Substantial deviations from the given mass and composition can occur.
• Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses.
• Uncertainties are given in concise form in parentheses after the corresponding last digits. Uncertainty values denote one standard deviation, except isotopic composition and standard atomic mass from IUPAC, which use expanded uncertainties.

References

• Isotope masses from:
• Isotopic compositions and standard atomic masses from:
• Half-life, spin, and isomer data selected from the following sources. See editing notes on this article's talk page.

External links

• Chlorine isotopes data from The Berkeley Laboratory Isotopes Project's

Isotopes of sulfur	Isotopes of chlorine	Isotopes of argon
Table of nuclides