In addition, the initial element and the decay product should not be produced or depleted in significant amounts by other reactions.
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.
All ordinary matter is made up of combinations of chemical elements, each with its own atomic number, indicating the number of protons in the atomic nucleus.
If a material that selectively rejects the daughter nuclide is heated, any daughter nuclides that have been accumulated over time will be lost through diffusion, setting the isotopic "clock" to zero.
The temperature at which this happens is known as the "blocking temperature" and is specific to a particular material.After one half-life has elapsed, one half of the atoms of the substance in question will have decayed.Many radioactive substances decay from one nuclide into a final, stable decay product (or "daughter") through a series of steps known as a decay chain.In the ideal case, the material will incorporate a parent nuclide and reject the daughter nuclide.In this case, the only daughter nuclides to be found through examination of a sample must have been created since the sample was formed.Although decay can be accelerated by radioactive bombardment, such bombardment tends to leave evidence of its occurrence.