Study of the emission intensities of doubly ionized uranium (U iii) in a hollow-cathode discharge

Abstract

The emission intensities of doubly ionized uranium, produced in a hollow-cathode discharge, are studied by using mixtures of helium and other rare gases as fill gases. The U iii emission intensities, obtained with optimized mixtures, are found to increase when the ionization potential of the heavier gas decreases. An explanation of this behavior is presented. The strongest emission intensities are observed with a helium–xenon 100:1 mixture at a total pressure of 600 Pa. In this case the enhancement, relative to a pure-neon fill gas, becomes more substantial for U iii transitions originating from relatively high energy levels. When helium was mixed with neon, no enhancement was observed. A hybrid Penning charge-transfer reaction is suggested as a possible excitation mechanism.