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18.   Atomic Lifetimes

The radiative lifetime τk of an atomic level k is related to the sum of transition probabilities to all levels i lower in energy than k:
$\tau_k=\left(\sum_i \, A_{ki}\right)^{-1}\quad.$ (27)

The branching ratio of a particular transition, say to state i ′, is defined as
equation 28 (28)

If only one branch (i ′) exists (or if all other branches may be neglected), one obtains Aki ′ τk = 1, and
$\tau_k=1/A_{ki\prime}\quad.$ (29)

Precision lifetime measurement techniques are discussed in Atomic, Molecular, & Optical Physics Handbook, Chaps. 17 and 18, ed. by G.W.F. Drake (AIP, Woodbury, NY, 1996).


19.   Regularities and Scaling

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