Doppler shift of continuum x rays from heavy-ion collisions

The continuum K x-ray spectrum from 200-MeV Kr + Zr has been found to undergo a Doppler shift with an effective Doppler velocity equal to (0.92±0.03)vci, where vci is equal to the center-of-mass velocity of the intermediate Kr + Zr molecule, corresponding to the incident projectile velocity. If the x rays are indeed generated by quasimolecular processes, the expected Doppler velocity is 0.90vci, taking into account the slowing down of the projectile in the target. The anisotropy of the continuum spectrum in the c.m. system is derived.