Doubly differential cross sections of secondary electrons ejected from gases by electron impact: 50-300 eV on helium

Abstract

Doubly differential cross sections of secondary electrons ejected from He by electron impact have been measured utilizing a crossed-beam method. The incident energies used were 50, 100, 200, and 300 eV. The energy and angular range of the secondary electrons measured were from half of the difference between incident energy and ionization energy to 1.0 eV and from 6\ifmmode^\circ\else\textdegree\fi{} to 156\ifmmode^\circ\else\textdegree\fi{}, respectively, with an emphasis on the measurements of low-energy secondary electrons. The present results have been placed on an absolute scale by using the ionization cross section at 100 eV. The results indicate a strong forward peak for lowenergy ( 5 eV) secondaries at angles less than 30\ifmmode^\circ\else\textdegree\fi{}. There is good agreement among the measurements of the high-energy secondary electrons but considerable differences exist in the measurements of the low-energy secondary electrons.