Energy and Angular Distributions of Electrons Ejected from Various Gases by 50 keV Protons

Abstract

Measurements have been made of the energy and angular distributions of electrons ejected from H2, N2, 02, CO2, CH4, H20, and Ar by 50 keV protons. The angular range extends from 0 to 100* and the electron energy from 5 to 150 eV. The relative values of the distribution functions for the different gases have been established by determining the relative gas number densities in the gas jet used for the target. Finally, by using previously obtained cross sections for helium, the distributions have been normalized to give absolute differential cross sections. The measurements were made with an apparatus which uses the principle of the 30* parallel plate electro- static analyzer for energy analysis of the electrons at a number of angles simultaneously (2, 3). The number of electrons scattered into each angle and energy coordinate from the intersection of the proton beam and a fine jet of target gas was found by taking the difference between two measurements. In the first measure- ment the beam passed through the jet and through background gas which consisted almost entirely of target gas at a pressure proportional to the rate of inflow through the jet. In the second measurement the background gas pressure was raised by admitting target gas through a standard leak valve, so that the difference between the two measurements represented the electrons ejected from the jet only. The effec- tiveness of capillary arrays has been demonstrated by, for example, Steckelmacher et al. (4). This is sup- ported by calculations (2) that in our apparatus 90% of the target gas is contained within a 2-mm-diameter region at the distance from the capillary at which the beam traverses. We believe that this technique pre-