Decay constant
A decay constant is the fixed probability per unit time that a radioactive nucleus will decay.
The decay constant, written with the Greek letter lambda (λ), measures how quickly a radioactive isotope decays. It is the fraction of nuclei that decay per unit of time and is related to the half-life by a simple formula: half-life equals the natural logarithm of 2, about 0.693, divided by the decay constant.
Accurate decay constants are essential for accurate ages. Small errors in a decay constant translate directly into errors in ages. For uranium–lead dating, the decay constants of uranium-238 and uranium-235 are known very precisely, which is one reason lead–lead ages of meteorite inclusions can be quoted to within a few hundred thousand years.
Some decay constants, such as those of rubidium-87 and lutetium-176, have been revised over the years, partly by comparing results from meteorites with uranium–lead ages. Meteorites therefore not only depend on decay constants but also help refine them, because many dating methods can be applied to the same ancient rocks.
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