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␣ 1 ͑1s 1/2 2p 3/2 1,3 P J=1,2 → 1s 1/2 2 1 S J=0 ͒ radiative decay of heliumlike uranium 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

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... th previous experiments and calculations based on a "oneparticle" model. We show that the unexpected isotropy essentially results from the mutual cancellation of the angular distributions of the 1 P 1 → 1 S 0 electric dipole and 3 P 2 → 1 S 0 magnetic quadrupole transitions, both of which contribute to the K␣ 1 radiation. Detailed computations on the anisotropy of the K␣ 1 radiation have been carried out for a wide range of projectile energies and are compared to available experimental data.