The rate of decay (given the symbol λ) is the fraction of the 'parent' atoms that decay in unit time.For geological purposes, this is taken as one year.The Re-Os isotopic system was first developed in the early 1960s, but recently has been improved for accurate age determinations.
The half-life is the time it takes for half of the parent atoms to decay.
This decay process leads to a more balanced nucleus and when the number of protons and neutrons balance, the atom becomes stable.
This radioactivity can be used for dating, since a radioactive 'parent' element decays into a stable 'daughter' element at a constant rate.
Radiocarbon dating is normally suitable for organic materials less than 50 000 years old because beyond that time the amount of 14C becomes too small to be accurately measured.
This scheme was developed in 1937 but became more useful when mass spectrometers were improved in the late 1950s and early 1960s.
those that form during chemical reactions without breaking down).