What is radioactive dating and what isotopes are used
Radioactive decay is a natural process and comes from the atomic nucleus becoming unstable and releasing bits and pieces.
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.
All rely on the fact that certain elements (particularly uranium and potassium) contain a number of different isotopes whose half-life is exactly known and therefore the relative concentrations of these isotopes within a rock or mineral can measure the age.
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).
Others place mineral grains under a special microscope, firing a laser beam at the grains which ionises the mineral and releases the isotopes.
Another way of expressing this is the half-life period (given the symbol T).
The half-life is the time it takes for half of the parent atoms to decay.