Kα1radiation from heavy, heliumlike ions produced in relativistic collisions

Abstract

Bound-state transitions in few-electron, heavy ions following radiative electron capture are studied within the framework of the density matrix theory and the multiconfiguration Dirac-Fock approach. Special attention is paid to the $K{\ensuremath{\alpha}}_{1}$ $(1{s}_{1∕2}2{p}_{3∕2}\phantom{\rule{0.2em}{0ex}}^{1,3}P_{J=1,2}\ensuremath{\rightarrow}1{s}_{1∕2}^{2}\phantom{\rule{0.2em}{0ex}}^{1}S_{J=0})$ radiative decay of heliumlike uranium ${\mathrm{U}}^{90+}$ projectiles. This decay has recently been observed at the GSI facility in Darmstadt, giving rise to a surprisingly isotropic angular distribution, which is inconsistent with previous experiments and calculations based on a ``one-particle'' model. We show that the unexpected isotropy essentially results from the mutual cancellation of the angular distributions of the $^{1}P_{1}\ensuremath{\rightarrow}^{1}S_{0}$ electric dipole and $^{3}P_{2}\ensuremath{\rightarrow}^{1}S_{0}$ magnetic quadrupole transitions, both of which contribute to the $K{\ensuremath{\alpha}}_{1}$ radiation. Detailed computations on the anisotropy of the $K{\ensuremath{\alpha}}_{1}$ radiation have been carried out for a wide range of projectile energies and are compared to available experimental data.