Kα1 radiation from heavy, heliumlike ions produced in relativistic collisions

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 Kα1 (1s1/22p3/21,3PJ=1,2→1s1/221SJ=0) radiative decay of heliumlike uranium U90+ 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 1P1→1S0 electric dipole and 3P2→1S0 magnetic quadrupole transitions, both of which contribute to the Kα1 radiation. Detailed computations on the anisotropy of the Kα1 radiation have been carried out for a wide range of projectile energies and are compared to available experimental data