Multiple minima in ground-state photoionization: Interchannel coupling at high Z

The photoionization of the 7s subshell of Ra has been investigated using a 20-channel relativistic random-phase-approximation calculation. The results show that in addition to the "natural" Cooper minimum, there are two others induced by interchannel coupling with the 6p and 5d photoionization channels. This result has important consequences for photoelectron angular distributions as well as excited-state photoionization for high-Z atoms. © 1986 The American Physical Society.