Photoionization of the outer shells of radon and radium: Relativistic random-phase approximation for high-Z atoms

Photoionization cross sections, branching ratios, and photoelectron angular distributions have been calculated for Ra (Z=88) 7s, 6p, 6s, 5d, and 5p, and Rn (Z=86) 6p, 6s, 5d, and 5p subshells within the framework of the relativistic random-phase approximation, including coupling between all of the relativistic channels arising from these subshells, in an effort to elucidate the interplay between relativistic and interchannel interactions at high Z where no experiments are extant. The results show that, aside from inducing structure in subshell cross sections, relativistic plus interchannel effects dominate the photoelectron angular-distribution asymmetry parameter and the branching ratio between spin-orbit doublets largely through the relativistic splitting of Cooper minima. This qualitatively confirms effects predicted by simple central-field calculations. Detailed explanations of the reasons for each of the structures are presented.