Chlorine-36 (³⁶Cl) is an isotope of chlorine.

Chlorine Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...

has two

stable isotope Stable nuclides are Isotope, isotopes of a chemical element whose Nucleon, nucleons are in a configuration that does not permit them the surplus energy required to produce a radioactive emission. The Atomic nucleus, nuclei of such isotopes are no ...

s and one naturally occurring

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is conside ...

isotope, the cosmogenic isotope ³⁶Cl. Its half-life is 301,300 ± 1,500 years. ³⁶Cl decays primarily (98%) by beta-minus decay to ³⁶ Ar, and the balance to ³⁶ S. Trace amounts of

³⁶Cl exist in the environment, in a ratio of about to 1 with respect to the stable chlorine isotopes. This ³⁶Cl/Cl ratio is sometimes abbreviated as R³⁶Cl. This corresponds to a concentration of approximately . ³⁶Cl is produced in the atmosphere by spallation of ³⁶ Ar by interactions with

cosmic ray Cosmic rays or astroparticles are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the ...

proton A proton is a stable subatomic particle, symbol , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...

s. In the top meter of the

lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time ...

, ³⁶Cl is generated primarily by thermal neutron activation of ³⁵Cl and spallation of ³⁹ K and ⁴⁰ Ca. In the subsurface environment, muon capture by ⁴⁰Ca becomes more important. The production rates are about 4200 atoms ³⁶Cl/yr/mole ³⁹K and 3000 atoms ³⁶Cl/yr/mole ⁴⁰Ca, due to spallation in rocks at sea level. The half-life of this isotope makes it suitable for geologic dating in the range of 60,000 to 1 million years. Its properties make it useful as a proxy data source to characterize cosmic particle bombardment and solar activity of the past. Additionally, large amounts of ³⁶Cl were produced by irradiation of

seawater Seawater, or sea water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/L, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has approximat ...

during atmospheric and underwater test detonations of

nuclear weapon A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission or atomic bomb) or a combination of fission and fusion reactions (thermonuclear weapon), producing a nuclear exp ...

s between 1952 and 1958. The residence time of ³⁶Cl in the atmosphere is about 2 years. Thus, as an event marker of 1950s water in

soil Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...

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, including dating ice and sediments.

References

{{reflist, 2 Isotopes of chlorine Environmental isotopes Radionuclides used in radiometric dating

See also

References