Mach-shock electron distributions from solids

A solid target material can be considered as a homogeneous, isotropic dispersive electron plasma with the nuclear charges as a positive background. The response of the plasma to a penetrating charged particle with a high enough velocity manifests itself as a wake of electron density fluctuations behind the projectile. The wake shows the characteristic features of Mach shock waves. A method for detecting the electron wake in solid-state materials by measuring the angular distribution of emitted electrons of low energy is proposed. These show as distinct max. at certain angles. The emission angle, Theta em, increases with bombarding energy, and follows the Mach relation cos Theta em = vs/v0, where vs is the Mach shock-wave velocity and v0 is the projectile velocity. 14 ref.--R.B.