Ionization of U, UO, and UO2 by Electron Impact

Abstract

The first ionization potential of uranium and the first appearance potentials of UO and UO2 by electron impact have been measured in a mass spectrometer, using the retarding potential difference (RPD) method. Small modifications of the RPD source are described. Crucibles of zirconium diboride were found to be preferable to tantalum crucibles for vaporization of uranium metal. Correction is made to the uranium appearance potential for thermally excited low-lying levels of the uranium atom, and for the several possible ionization paths. The ionization potential for uranium is 6.11±0.05 eV; for UO and UO2 the appearance potentials are 5.72±0.06 eV and 5.5±0.1 eV. Ionization probability curves were determined for U and UO.