Dependence of secondary-electron emission on the emergent angle of frozen-chargedH0andH+projectiles penetrating a thin carbon foil

Abstract

The statistical distributions of the number of secondary electrons (SEs) emitted per projectile from a thin carbon foil under irradiation with the frozen-charged ${\mathrm{H}}^{0}$ and ${\mathrm{H}}^{+}$ projectiles of $2.5--3.5\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ have been measured as a function of the emergent angle of projectiles in the range from $0.0\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}2.0\phantom{\rule{0.3em}{0ex}}\mathrm{mrad}$ in every $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{mrad}$ step. The measurement of SEs was carried out in the forward and the backward directions of the incident beam independently. From $0.0\phantom{\rule{0.3em}{0ex}}\mathrm{mrad}$ to $\ensuremath{\sim}1.0\phantom{\rule{0.3em}{0ex}}\mathrm{mrad}$, the SE yields, that is, the mean number of emitted electrons per incident ion, increase with increasing emergent angle and tend to be saturated at larger angles. This is a common trend, regardless of incident energies and charge states of a projectile and also of emitted directions of SEs. Quantitatively, the saturated SE yields at larger angles for the ${\mathrm{H}}^{+}$ penetration are about 40--50 % larger than those at $0.0\phantom{\rule{0.3em}{0ex}}\mathrm{mrad}$. On the other hand, the corresponding relative increase for the ${\mathrm{H}}^{0}$ penetration reaches as high as $\ensuremath{\sim}100%$ or more. The observed proton-hydrogen difference is well reproduced in the calculated energy losses by a Monte Carlo simulation including the impact parameter dependent stopping cross sections in a single collision of a hydrogen or a proton with a carbon atom.