Absolute Total and Partial Cross-Sections for Ionization of Ba and Eu Atoms by Electron Impact

Abstract

Experimental apparatus and procedure for measurements of absolute total (apparent and counting) and relative partial cross sections for ionization of atoms by electron impact are described in some detail, and results on Ba and Eu atom are reported. A crossed electron-atom beam ion source combined with a 60° sector mass analyzer has been used to measure the partial cross sections. For the measurement of the absolute total cross sections, another type of crossed electron-atom beam arrangement combined with a time-of-flight (TOF) velocity measurements of target atoms has been used. The absolute cross sections have been determined with experimental accuracy of ±23%, and have been used to calibrate the partial cross-sections. The results of Ba atom agree well with previously reported results. The Eu + cross section curve shows remarkable peak structure near the 4 f ionization thresholds, probably attributed to the resonance excitation of 4 f 6 6 s 2 n l aoutoionization states via temporal negative-ion formation.