Critical angles and minimum yields for planar channeling

Abstract

Local regions on the surface of a sample of ZnO: Zn phosphor powder were deteriorated by low energy heavy ions to a depth of a few hundred Angstrom units. These regions behave as ‘thin films’ in which a negligible small amount of light is produced when an energetic projectile passes through it. The sample was then scanned across energetic ion beams. The scintillation response diminished when the beam impinged onto a film. The decrease, ΔL, in light intensity is the amount of light produced in a phosphor region whose thickness is equivalent to the film thickness. For ¹H and ⁴He the luminescent efficiency, ΔL/ΔE (the ratio of the light produced to the observed energy loss), is approximately independent of energy indicating that the scintillation response depends primarily on the inelastic projectile-electron collisions rather than the elastic projectile target atom encounters.

At a given velocity, a plot of ΔL versus the atomic number of the projectile exhibits oscillatory structure for which a tentative explanation is suggested.