Dating in the 1940s
In many cases, the daughter nuclide itself is radioactive, resulting in a decay chain, eventually ending with the formation of a stable (nonradioactive) daughter nuclide; each step in such a chain is characterized by a distinct half-life.
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).
For most radioactive nuclides, the half-life depends solely on nuclear properties and is essentially a constant.
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This transformation may be accomplished in a number of different ways, including alpha decay (emission of alpha particles) and beta decay (electron emission, positron emission, or electron capture).
Another possibility is spontaneous fission into two or more nuclides.
An original 1940s fashion pin-up, Bette Davis works a blue gown in this seductive shot, taken in 1943, perfectly paired with a full red lip.