Density effect in relativistic K-shell ionization

Abstract

Using a grazing emission method, we have made measurements of 22.6-GeV electron impact ionization cross sections at the front and back faces of ∼ 70-µm thick Al and Cu foils. These give, respectively, the cross sections without and with a density effect predicted by Fermi. For Cu, the back cross section ratio at 22.6 and 5.1 GeV (previously measured) is 1.00±0.04, confirming the predicted energy independence of this cross section. The absolute cross sections agree overall with theoretical calculations.