Retardation andKX-Ray Relative Intensities

Abstract

The matrix elements for electric dipole transitions with retardation have been numerically evaluated for transitions between the $1s$ and higher discrete states of a single Dirac electron in a Coulomb field. The results are used to calculate the relative intensities of the principal $K$ x-ray lines in elements of high atomic number. Comparison of the retarded and nonretarded matrix elements confirms the earlier result for lead that the effect of retardation is significant in heavy elements only when the total angular momentum of the electron changes. Comparison with the experiments of Beckman indicate that this conclusion is correct, and that in the $K{\alpha }_2$ to $K{\alpha }_1$ intensity ratio the effect of retardation is more significant than screening effects.