Radioactive dating is a method of dating rocks and minerals using radioactive isotopes.
This method is useful for igneous and metamorphic rocks, which cannot be dated by the stratigraphic correlation method used for sedimentary rocks. Some do not change with time and form stable isotopes (i.e.
The initial step in the dating process is the irradiation of the geological sample in a neutron flux to convert a portion of the the naturally occurring stable isotope K-39 to Ar-39, a radioisotope with a moderate half-life of 269 years.
Another isotope of argon, Ar-40, will also be present in the sample as the decay product of the naturally occurring long-lived radioisotope K-40 with a half life of 1,280,000,000 years.
The technique of comparing the abundance ratio of a radioactive isotope to a reference isotope to determine the age of a material is called radioactive dating.