Method for narrowing energy width of e+ and e− beams in a TOF system

Abstract

A method for narrowing the energy width of e+ and e- beams using a 22Na radio-isotope and a W moderator is developed. The method provides a width of about 1 eV for 10-20 eV beams, and is applied to inelastic scattering measurements on the Schumann-Runge excitation of an O2 molecule by e+ and e- impact. The ratio of the excitation cross section in O2 by e+ impact to that by e- is about 1.2 for impact energies in the range 13-22 eV.