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 ³He²⁺ 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 ${}{ω} {{}{ω}[{{{σ}}ₕ({}{ω})}{4{-}{{σ}}ₚ({}{ω})}]}$ and ratio of the cross sections $R({}{ω}) [{≡}{{{σ}}ₕ({}{ω})}{4{{σ}}ₚ({}{ω})}]$ for the proton and $³He²⁺$-ion impact, where ${{σ}}ₕ({}{ω})$ and ${{σ}}ₚ({}{ω})$ are the x-ray-production cross sections for proton and $³He²⁺$-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 ³He²⁺ impact is clearly found.