Some optimum conditions for proton induced ultrasoft x-ray production

The proton beam from an AN700 van de Graaff accelerator has been used to bombard solid targets of C, TiB2, SiC, SiN, Al and Au in the energy range 250-700 keV. A study of target surface contamination, the nature of the angular dependence in the x-ray emission and the dependence of the x-ray yield on proton energy has been undertaken. Our findings suggest that the optimum target angle is 30 degrees with respect to the incident proton direction and the detector angle 90 degrees to the target surface. In a vacuum of 10(-5) Torr (approximately 1.33 mPa) and at proton currents of 50-100 muA, a carbon deposit can be expected to build up with time on the target surface to reduce the characteristic x-ray intensity from the target. In the comparison between the energy dependent yields of CK and AlK x-rays, we find a slightly smaller dependence on energy than that predicted by the empirical cross section formula of Paul (1984) although the latter is not expected to be valid down to Z = 6.