Used most often for radioactive dating
Most of the radioactive isotopes used for radioactive dating of rock samples have too many neutrons in the nucleus to be stable.
Recall that an isotope is a particular form of an element.
Radiometric dating is a method of determining the age of an artifact by assuming that on average decay rates have been constant (see below for the flaws in that assumption) and measuring the amount of radioactive decay that has occurred.
Radiometric dating is also used to date archaeological materials, including ancient artifacts.
Radiometric dating methods are used to establish the geological time scale.
A particular isotope of a particular element is called a nuclide. That is, at some point in time, an atom of such a nuclide will spontaneously change into a different nuclide by radioactive decay.
The decay may happen by emission of particles (usually electrons (beta decay), positrons or alpha particles) or by spontaneous nuclear fission, and electron capture.
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