For most radioactive nuclides, the half-life depends solely on nuclear properties and is essentially a constant.It is not affected by external factors such as temperature, pressure, chemical environment, or presence of a magnetic or electric field.A particular isotope of a particular element is called a nuclide. That is, at some point in time, an atom of such a nuclide will undergo radioactive decay and spontaneously transform into a different nuclide.
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.
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).
Among the best-known techniques are radiocarbon dating, potassium–argon dating and uranium–lead dating.