Angular Distribution of Fast Protons from Singly and Doubly Ionizing Collisions with He

Abstract

Angular distributions of 3-9-MeV protons scattered in singly and doubly ionizing collisions with He have been measured. A sharp shoulder is seen at 0.55 mrad, a feature attributed to binary encounters between the projectile protons and quasifree target electrons. The ratio of double to single ionization of He is found to be nearly independent of scattering angle between 0.25 and 0.55 mrad and to have a value near 2%, substantially lower than the ratio found in photoionization producing fast ejected electrons with the same energies.