(e,2e) investigation of atomic hydrogen and helium close to threshold

Abstract
For the first time triple differential cross sections of the electron impact ionization of atomic hydrogen close to threshold have been measured. The angular correlation of the outgoing electrons have been determined at 4 eV excess energy and are compared with results obtained with helium. A method is proposed allowing to measure the range of the threshold law. The data are analyzed using a partial-wave method. Although the asymptotic states of the two processes are the samethe charge of the ion is Z=1 in both casesthe triple differential cross sections are drastically different.