For instance, carbon-14 has a half-life of 5,730 years.After an organism has been dead for 60,000 years, so little carbon-14 is left that accurate dating cannot be established.Another possibility is spontaneous fission into two or more nuclides.
This predictability allows the relative abundances of related nuclides to be used as a clock to measure the time from the incorporation of the original nuclides into a material to the present.
The basic equation of radiometric dating requires that neither the parent nuclide nor the daughter product can enter or leave the material after its formation.
As the mineral cools, the crystal structure begins to form and diffusion of isotopes is less easy.
At a certain temperature, the crystal structure has formed sufficiently to prevent diffusion of isotopes.
The temperature at which this happens is known as the closure temperature or blocking temperature and is specific to a particular material and isotopic system.
These temperatures are experimentally determined in the lab by artificially resetting sample minerals using a high-temperature furnace.In these cases, usually the half-life of interest in radiometric dating is the longest one in the chain, which is the rate-limiting factor in the ultimate transformation of the radioactive nuclide into its stable daughter.Isotopic systems that have been exploited for radiometric dating have half-lives ranging from only about 10 years (e.g., tritium) to over 100 billion years (e.g., samarium-147).Finally, correlation between different isotopic dating methods may be required to confirm the age of a sample.For example, the age of the Amitsoq gneisses from western Greenland was determined to be Accurate radiometric dating generally requires that the parent has a long enough half-life that it will be present in significant amounts at the time of measurement (except as described below under "Dating with short-lived extinct radionuclides"), the half-life of the parent is accurately known, and enough of the daughter product is produced to be accurately measured and distinguished from the initial amount of the daughter present in the material.For most radioactive nuclides, the half-life depends solely on nuclear properties and is essentially a constant.