RELATIVISTIC EFFECT OF ATOMIC RADIATIVE PROCESSES

We present a theoretical study of the relativistic effect of atomic ra diative processes. In order to avoid any entanglement of the atomic sc reening effect, we elucidate the relativistic effect of the atomic rad iative processes by examining t,he radiative processes of the hydrogen like atomic ion system. We discover a type of ''zero'' at which the el ectric dipole matrix element vanishes for nkappa --> epsilonkappa' tra nsitions with \kappa\ = \kappa'\ owing to the relativistic retardation effect. Such ''zero'' serves as a precursor of a transition of the ph otoionization cross section from nonrelativistic behavior to relativis tic behavior.