AES and XPS study of plutonium oxidation

Abstract

The initial oxidation of plutonium metal at 27°C has been studied using AES and XPS. Initially a ’’clean’’ plutonium surface was prepared by prolonged Ar+ bombardment followed by 500°C anneal and Ar+ bombardment cleaning cycles. Changes occurring in the plutonium Auger electron spectra in the energy range of 40–120 eV and the 4f5/2, 4f7/2 (core levels), and valence band XPS peaks were monitored during oxygen exposures of 10 to 1.8×108L. Examination of the 4f7/2 level revealed two oxidation states which are attributed to a suboxide an PuO2. The 4f7/2 binding energies for the two oxidation states and plutonium metal are 426.1, 424.4, and 422.2 eV, respectively. It was observed that oxidation proceeded in two steps. In the first step there was a rapid reaction of oxygen with the formation of a suboxide. In the second stage, the uptake of oxygen leveled off with conversion of the suboxide to PuO2.