EVALUATION OF SOFT-X-RAY YIELD OF AL FROM 27.557-MEV NEUTRAL PARTICLES

Extreme ultraviolet (XUV) emission from Al bombarded by 50-MeV H-0 par ticles has been reported by James, Sauers, and Arakawa. However, the c ontribution to the observed signal from scattered electrons has not be en evaluated, and the origin of XUV light was not determined since onl y broadband filters were used. We have therefore measured the XUV emis sion for 15 keV electrons incident on an Al target using a grazing inc idence spectrometer. We find the emission is composed primarily of Al L(23) soft x rays and determine a yield of 0.021 photons/electron. Thi s value is large compared with previous work with high-Z materials, an d our yield values are 100 times higher than standard theories which d o not consider secondary electrons. We show that L-shell emission in l ow-Z materials is due primarily to ionizations from secondary electron s created near the surface. Since the number of secondary electrons cr eated by an energetic particle is roughly proportional to the energy d eposited by the particle, relative x-ray yields from energetic protons and electrons can be determined from a knowledge of stopping powers. Using stopping power calculations, we estimate that the Al L(23) soft x-ray yield from 27.542-MeV proton bombardment is 0.027 photons/proton . A 27.557-MeV H-0 particle is essentially equivalent to a 27.542-MeV proton and a 15-keV electron; thus, the yield of Al L(23) soft x rays from 27.557-MeV H-0 particle bombardment is 0.048 photons/particle.