Abstract
The rate of spontaneous emission of radiation by a loosely bound composite system is calculated from quantum electrodynamics correct through terms of relative order ${\ensuremath{\alpha}}^{2}{Z}^{2}$. Recent criticisms by Feinberg and Sucher of the semiclassical method of deriving the higher-order radiation coupling terms are discussed. It is proved that the Breit interaction remains valid in the presence of radiation emission and that the semiclassical and quantum-electrodynamic methods of deriving the higher-order coupling terms always yield the same results to relative order ${\ensuremath{\alpha}}^{2}{Z}^{2}$. We discuss in particular relativistic corrections to allowed and spin-forbidden electric dipole transitions and the $1s2s^{3}S_{1}\ensuremath{-}1{s}^{2}^{1}S_{0}$ magnetic dipole transition.
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