Impact-parameter dependence ofK-vacancy production in Cu-Ni collisions

We have measured the impact-parameter ($b$) dependent probabilities ($P$) for the production of Ni (and Cu) $K$ x rays in the bombardment of thin nickel foils by 50- and 65.5-MeV Cu beams. The shape of $P\left(b\right)\mathrm{}$ is found to be independent of nickel-foil thickness ($t$) and of the presence of a pre-exciting carbon layer, but the magnitude scale of both $P\left(b\right)\mathrm{}$ and of the total $K$-x-ray cross section is quite dependent upon $t$ and on the presence of the carbon. The data suggest that $2p\sigma$ vacancies are being produced via $2p\pi -2p\sigma$ rotational coupling preceded by preparation of the necessary projectile $2p$ vacancies in both single- and multiple-collision processes. The shape of $P\left(b\right)\mathrm{}$ is only qualitatively similar to that expected for the rotational-coupling process, however.