Quasifree-electron bremsstrahlung induced by the projectile field

Continuum x rays from targets of Be, C, and Al bombarded with 6--40-MeV protons were observed with a Si (Li) detector. In addition to the secondary-electron bremsstrahlung (SEB), the spectra show another component, of which the high-energy limit is given by the relative kinetic energy between the projectile and orbital electrons of the target atom and by the Doppler effect. The component can well be explained in terms of the bremsstrahlung produced by the quasifree scattering of orbital electrons in the field of the projectile. The effect of the binding energy of the orbital electrons on this bremsstrahlung spectrum has been studied. From the comparison of the experimental results with theoretical predictions based on the plane-wave Born approximation and the binary-encounter approximation, the importance of the effect of secondary-electron escape from the target material on the SEB at high-projectile energies was pointed out