Projectile-charge dependence of quasi-free-electron bremsstrahlung

Continuum x rays induced by bombardments of a Be target with 20.14-MeV/amu protons and He2+3 ions have been measured with a Si(Li) detector in the direction of 90°with respect to the incident beam. Differences in the x-ray-production cross sections multiplied by the x-ray energy { [h() 4-p()] } and ratio of the cross sections R () [h() 4p()] for the proton and He2+3-ion impact, where h() and p() are the x-ray-production cross sections for proton and He2+3-ion impact, respectively, were obtained as a function of the x-ray energy. Both the difference and the ratio show peaks in the region where the x-ray energy is equal to the relative kinetic energy between the projectile and the inner-shell electron to be scattered by the projectile. From the comparison with a theory of quasi-free-electron bremsstrahlung based on the impulse approximation, it is found that this peak corresponds to the maximum of the velocity-distribution function of the inner-shell electron. Furthermore, the contribution of the radiative electron-capture process in the case of proton and He2+3 impact is clearly found.