This transformation is accomplished by the emission of particles such as electrons (known as beta decay) or alpha particles.While the moment in time at which a particular nucleus decays is random, a collection of atoms of a radioactive nuclide decays exponentially at a rate described by a parameter known as the half-life, usually given in units of years when discussing dating techniques.Various methods exist differing in accuracy, cost and applicable time scale.
In addition, the initial element and the decay product should not be produced or depleted in significant amounts by other reactions.
The procedures used to isolate and analyze the reaction products must be straightforward and reliable.
Although decay can be accelerated by radioactive bombardment, such bombardment tends to leave evidence of its occurrence.
Therefore, in any material containing a radioactive nuclide, the proportion of the original nuclide to its decay product(s) changes in a predictable way as the original nuclide decays.
Poor vacuum permits gaseous atoms to intercept ionised atoms which are meant to be measured.
The resolution of the receptor is also a factor, but modern equipment is greatly improved on previous editions.
This predictability allows the relative abundances of related nuclides to be used as a clock that measures the time from the incorporation of the original nuclide(s) into a material to the present.
The processes that form specific materials are often conveniently selective as to what elements they incorporate during their formation.
Precision is enhanced if measurements are taken on different samples taken from the same rock body but at different locations.
Alternatively, if several different minerals can be dated from the same sample and are assumed to be formed by the same event and were in equilibrium with the reservoir when they formed, they should form an isochron.
Mass spectrometers are liable to interferences and inaccuracies.