Energy and Angular Dependence of the Differential Cross Section for Production of Electrons by 50-100 keV Protons in Hydrogen Gas

Abstract

Hydrogen gas in a rotatable scattering chamber was bombarded by 50-, 75-, and 100-keV protons. The resulting secondary electrons were analyzed in both direction and energy by a slit system and a cylindrical electrostatic analyzer and counted by an electron multiplier tube with suitable electronics. Relative values of the differential cross section for ejection of secondary electrons were measured for 4- to 300-eV electrons at angles of 23\ifmmode^\circ\else\textdegree\fi{}, 45\ifmmode^\circ\else\textdegree\fi{}, 67.5\ifmmode^\circ\else\textdegree\fi{}, 90\ifmmode^\circ\else\textdegree\fi{}, 112.5\ifmmode^\circ\else\textdegree\fi{}, 135\ifmmode^\circ\else\textdegree\fi{}, and 152\ifmmode^\circ\else\textdegree\fi{} from the proton direction. Absolute values for the differential cross sections were obtained by integration of the 50-keV results over all angles and energies and normalizing to the total ionization cross section measured by Schwirzke. As a function of electron energy, at a fixed angle, the differential cross sections show a broad peak at 4 to 8 eV with a monotonic decrease at higher electron energies. As a function of angle, for fixed electron energy, most of the differential cross sections are largest at 23\ifmmode^\circ\else\textdegree\fi{}, drop off rapidly to about 100\ifmmode^\circ\else\textdegree\fi{}, and are then relatively constant. The differential cross sections have been integrated in various ways to obtain cross sections differential only in energy and in angle, total cross sections for ionization, average energies of the ejected electrons, and the stopping cross section due to ionization. Comparisons are made with other experimental results and with Born approximation calculations.