(e,2e) measurements using a magnetic angle changer

Abstract

While measurements of triple differential cross sections (TDCS) for electron impact ionization have been performed for almost 40 years, the angular range of available data has generally been restricted due to physical constraints of the apparatus. We have overcome these constraints by incorporating a magnetic angle changer (MAC) into a conventional (e,2e) spectrometer. Use of a MAC in an (e,2e) experiment allows access to regions where as yet unobserved physical effects occur. One such example is where the scattered and ejected electrons emerge at the same angle, a region where the Coulomb repulsion between the two should be largest. This ‘post-collision interaction’ (PCI) is thought to play an important role in low energy electron impact ionization. We discuss recently published data for TDCS of the inner valence shell 3s ionization of argon measured over the backward scattering direction. We also present new data for outer shell 3p ionization of argon over the full angular range in the scattering plane, including the region where scattered/ejected electrons emerge at the same angle. To our knowledge, this is the first reported TDCS over the complete 360° angular range using a conventional (e,2e) spectrometer.