Angular Distribution Studies for the Time-Reversed Photoionization Process in Hydrogenlike Uranium: The Identification of Spin-Flip Transitions

Abstract

The $K$-shell photoelectric effect for a hydrogenlike ${\mathrm{U}}^{91+}$ ion is studied by its time-reversed process occurring in relativistic collisions between bare uranium ions and low- $Z$ target atoms. In the time-reversed situation, an electron is captured into the $1s$ ground state with the simultaneous emission of a photon. We present an angular differential study of these transitions for laboratory observation angles between nearly 0\ifmmode^\circ\else\textdegree\fi{} and 150\ifmmode^\circ\else\textdegree\fi{}. Our observation of photon emission close to 0\ifmmode^\circ\else\textdegree\fi{} allowed us to identify spin-flip contributions to the photoionization process and to determine their relative strength.