Isotopes elements used radioactive dating
Some techniques place the sample in a nuclear reactor first to excite the isotopes present, then measure these isotopes using a mass spectrometer (such as in the argon-argon scheme).
These are released as radioactive particles (there are many types).
For an element to be useful for geochronology (measuring geological time), the isotope must be reasonably abundant and produce daughter isotopes at a good rate.
Either a whole rock or a single mineral grain can be dated.
This technique uses the same minerals and rocks as for K-Ar dating but restricts measurements to the argon isotopic system which is not so affected by metamorphic and alteration events. The decay of 147Sm to 143Nd for dating rocks began in the mid-1970s and was widespread by the early 1980s.
It is useful for dating very old igneous and metamorphic rocks and also meteorites and other cosmic fragments.