Noun
English Wikipedia has an article on:chlorine-36Wikipedia
chlorine-36 (uncountable)
(physics) A long-lived radioactive isotope of chlorine, 17Cl, having seventeen protons and nineteen neutrons, and a half-life of 3x10 years; it can be used to date samples of groundwater
Chlorine-36 dating method Large amounts of otherwise rare 36 Cl (half-life ~300ky) were produced by irradiation of seawater during atmospheric detonations of nuclear weapons between 1952 and 1958. Source: Internet