Higher-order processes in X-ray photoionization and decay

Over the past decade, modern synchrotron radiation sources have provided continuously tunable, intense well-collimated beams of hard X-rays. Our group has exploited such beams, in the energy range 2-100 keV, to study higher-order processes in atomic photoionization and vacancy decay which were hitherto difficult to observe and we review five specific examples of that work here. These topics include high-energy photoionization of helium, nondipolar photoionization, double K-shell ionization, two-photon decays of inner-shell vacancies, and nuclear excitations by electronic transition. (C) 2004 Elsevier Ltd. All rights reserved.