An Improved Electrostatic Electron Selector

A cylindrical electrostatic electron selector is described which provides a 10 −7 ampere beam of electrons whose energy may be varied from 0 to 50 ev and whose energy spread is less than 100 mv. Space-charge problems involved in the construction of the device were overcome by the use of grids for focusing electrodes with exterior electron traps, and a non-reflecting surface for electrons made from a network of tiny tubes. The selector is provided with an energy analyzer. When used to determine the appearance potential curve of argon, the selector resolved the 2P 3/2 and 2P 1/2 states separated by 0.18 ev, and indicated the formation of Formula: see text at an energy of 0.8 ev below the threshold for A + .