Isotopes of chlorine

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.

List of isotopes

|-id=Chlorine-28 | ²⁸Cl | style="text-align:right" | 17 | style="text-align:right" | 11 | 28.03035(54)# | | p | ²⁷S | 1+# | | |-id=Chlorine-29 | ²⁹Cl | style="text-align:right" | 17 | style="text-align:right" | 12 | 29.01505(20)# | 5.4(19)&nbsp;zs | p | ²⁸S | (1/2+) | | |-id=Chlorine-30 | ³⁰Cl | style="text-align:right" | 17 | style="text-align:right" | 13 | 30.005018(26) | <50&nbsp;ns | p | ²⁹S | 3+# | | |-id=Chlorine-31 | rowspan=2|³¹Cl | rowspan=2 style="text-align:right" | 17 | rowspan=2 style="text-align:right" | 14 | rowspan=2|30.9924481(37) | rowspan=2|190(1)&nbsp;ms | β⁺ (97.6%) | ³¹S | rowspan=2|3/2+ | rowspan=2| | rowspan=2| |- | β⁺, p (2.4%) | ³⁰P |-id=Chlorine-32 | rowspan=3|³²Cl | rowspan=3 style="text-align:right" | 17 | rowspan=3 style="text-align:right" | 15 | rowspan=3|31.98568461(60) | rowspan=3|298(1)&nbsp;ms | β⁺ (99.92%) | ³²S | rowspan=3|1+ | rowspan=3| | rowspan=3| |- | β⁺, α (0.054%) |²⁸Si |- | β⁺, p (0.026%) | ³¹P |-id=Chlorine-33 | ³³Cl | style="text-align:right" | 17 | style="text-align:right" | 16 | 32.97745199(42) | 2.5038(22)&nbsp;s | β⁺ | ³³S | 3/2+ | | |-id=Chlorine-34 | ³⁴Cl | style="text-align:right" | 17 | style="text-align:right" | 17 | 33.973762490(52) | 1.5267(4)&nbsp;s | β⁺ | ³⁴S | 0+ | | |-id=Chlorine-34m | rowspan=2 style="text-indent:1em" | ^34mCl | rowspan=2 colspan="3" style="text-indent:2em" | 146.360(27)&nbsp;keV | rowspan=2|31.99(3)&nbsp;min | β⁺ (55.4%) | ³⁴S | rowspan=2|3+ | rowspan=2| | rowspan=2| |- | IT (44.6%) | ³⁴Cl |-id=Chlorine-35 | ³⁵Cl | style="text-align:right" | 17 | style="text-align:right" | 18 | 34.968852694(38) | colspan=3 align=center|Stable | 3/2+ | 0.758(2) | |- | rowspan=2|³⁶Cl | rowspan=2 style="text-align:right" | 17 | rowspan=2 style="text-align:right" | 19 | rowspan=2|35.968306822(38) | rowspan=2|3.013(15)×10⁵&nbsp;y | β^− (98.1%) | ³⁶Ar | rowspan=2|2+ | rowspan=2| | rowspan=2| |- | β⁺ (1.9%) | ³⁶S |- | ³⁷Cl | style="text-align:right" | 17 | style="text-align:right" | 20 | 36.965902573(55) | colspan=3 align=center|Stable | 3/2+ | 0.242(2) | |-id=Chlorine-38 | ³⁸Cl | style="text-align:right" | 17 | style="text-align:right" | 21 | 37.96801041(11) | 37.230(14)&nbsp;min | β^− | ³⁸Ar | 2− | | |-id=Chlorine-38m | style="text-indent:1em" | ^38mCl | colspan="3" style="text-indent:2em" | 671.365(8)&nbsp;keV | 715(3)&nbsp;ms | IT | ³⁸Cl | 5− | | |-id=Chlorine-39 | ³⁹Cl | style="text-align:right" | 17 | style="text-align:right" | 22 | 38.9680082(19) | 56.2(6)&nbsp;min | β^− | ³⁹Ar | 3/2+ | | |-id=Chlorine-40 | ⁴⁰Cl | style="text-align:right" | 17 | style="text-align:right" | 23 | 39.970415(34) | 1.35(3)&nbsp;min | β^− | ⁴⁰Ar | 2− | | |-id=Chlorine-41 | ⁴¹Cl | style="text-align:right" | 17 | style="text-align:right" | 24 | 40.970685(74) | 38.4(8)&nbsp;s | β^− | ⁴¹Ar | (1/2+) | | |-id=Chlorine-42 | rowspan=2|⁴²Cl | rowspan=2 style="text-align:right" | 17 | rowspan=2 style="text-align:right" | 25 | rowspan=2|41.973342(64) | rowspan=2|6.8(3)&nbsp;s | β^− | ⁴²Ar | rowspan=2|(2−) | rowspan=2| | rowspan=2| |- | β^−, n? | ⁴¹Ar |-id=Chlorine-43 | rowspan=2|⁴³Cl | rowspan=2 style="text-align:right" | 17 | rowspan=2 style="text-align:right" | 26 | rowspan=2|42.974064(66) | rowspan=2|3.13(9)&nbsp;s | β^− | ⁴³Ar | rowspan=2|(3/2+) | rowspan=2| | rowspan=2| |- | β^−, n? | ⁴²Ar |-id=Chlorine-44 | rowspan=2|⁴⁴Cl | rowspan=2 style="text-align:right" | 17 | rowspan=2 style="text-align:right" | 27 | rowspan=2|43.978015(92) | rowspan=2|0.56(11)&nbsp;s | β^− (>92%) | ⁴⁴Ar | rowspan=2|(2-) | rowspan=2| | rowspan=2| |- | β^−, n? (<8%) | ⁴³Ar |-id=Chlorine-45 | rowspan=2|⁴⁵Cl | rowspan=2 style="text-align:right" | 17 | rowspan=2 style="text-align:right" | 28 | rowspan=2|44.98039(15) | rowspan=2|513(36)&nbsp;ms | β^− (76%) | ⁴⁵Ar | rowspan=2|(3/2+) | rowspan=2| | rowspan=2| |- | β^−, n (24%) | ⁴⁴Ar |-id=Chlorine-46 | rowspan=3|⁴⁶Cl | rowspan=3 style="text-align:right" | 17 | rowspan=3 style="text-align:right" | 29 | rowspan=3|45.98525(10) | rowspan=3|232(2)&nbsp;ms | β^−, n (60%) | ⁴⁵Ar | rowspan=3|2-# | rowspan=3| | rowspan=3| |- | β^− (40%) | ⁴⁶Ar |- | β^−, 2n? | ⁴⁴Ar |-id=Chlorine-47 | rowspan=3|⁴⁷Cl | rowspan=3 style="text-align:right" | 17 | rowspan=3 style="text-align:right" | 30 | rowspan=3|46.98972(22)# | rowspan=3|101(5)&nbsp;ms | β^− (>97%) | ⁴⁷Ar | rowspan=3|3/2+# | rowspan=3| | rowspan=3| |- | β^−, n (<3%) | ⁴⁶Ar |- | β^−, 2n? | ⁴⁵Ar |-id=Chlorine-48 | rowspan=3|⁴⁸Cl | rowspan=3 style="text-align:right" | 17 | rowspan=3 style="text-align:right" | 31 | rowspan=3|47.99541(54)# | rowspan=3|30#&nbsp;ms<br />[>200&nbsp;ns] | β^−? | ⁴⁸Ar | rowspan=3| | rowspan=3| | rowspan=3| |- | β^−, n? | ⁴⁷Ar |- | β^−, 2n? | ⁴⁶Ar |-id=Chlorine-49 | rowspan=3|⁴⁹Cl | rowspan=3 style="text-align:right" | 17 | rowspan=3 style="text-align:right" | 32 | rowspan=3|49.00079(43)# | rowspan=3|35#&nbsp;ms<br />[>200&nbsp;ns] | β^−? | ⁴⁹Ar | rowspan=3|3/2+# | rowspan=3| | rowspan=3| |- | β^−, n? | ⁴⁸Ar |- | β^−, 2n? | ⁴⁷Ar |-id=Chlorine-50 | rowspan=3|⁵⁰Cl | rowspan=3 style="text-align:right" | 17 | rowspan=3 style="text-align:right" | 33 | rowspan=3|50.00827(43)# | rowspan=3|10#&nbsp;ms<br />[>620&nbsp;ns] | β^− | ⁵⁰Ar | rowspan=3| | rowspan=3| | rowspan=3| |- | β^−, n? | ⁴⁹Ar |- | β^−, 2n? | ⁴⁸Ar |-id=Chlorine-51 | rowspan=3|⁵¹Cl | rowspan=3 style="text-align:right" | 17 | rowspan=3 style="text-align:right" | 34 | rowspan=3|51.01534(75)# | rowspan=3|5#&nbsp;ms<br />[>200&nbsp;ns] | β^−? | ⁵¹Ar | rowspan=3|3/2+# | rowspan=3| | rowspan=3| |- | β^−, n? | ⁵⁰Ar |- | β^−, 2n? | ⁴⁹Ar |-id=Chlorine-52 | rowspan=3|⁵²Cl | rowspan=3 style="text-align:right" | 17 | rowspan=3 style="text-align:right" | 35 | rowspan=3|52.02400(75)# | rowspan=3|2#&nbsp;ms<br />[>400&nbsp;ns] | β^−? | ⁵²Ar | rowspan=3| | rowspan=3| | rowspan=3| |- | β^−, n? | ⁵¹Ar |- | β^−, 2n? | ⁵⁰Ar

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. 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) 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.

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

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