Detection of plutonium hydride using X-ray photoelectron spectroscopy

Abstract

Methods to distinguish trivalent plutonium hydride from trivalent plutonium oxide with X-ray photoelectron Spectroscopy (XPS) were investigated. Spectra were recorded for a black surface hydride film that was prepared on clean plutonium metal by hydrogen exposure. The hydride cannot be differentiated from the trivalent oxide by measurements of the Pu4 f binding energy alone, since the Pu4 f 7 2 binding energies of PuH 2 and Pu 2O 3 are 425.0 and 424.8 eV, respectively. The peak width (FWHM) ofPuH 2 (3.6eV) was found to be broader than the peak width of Pu 2O 3 (2.6 eV). Data for chemical state plots were recorded. Although the energy shift of the Pu (83 eV) Auger peak for hydride and oxide was small, its chemical state information is helpful in distinguishing between oxide and hydride compounds. Additional information useful in distinguishing hydride from oxide can be obtained from the peak position of the Pu4 f 7 2 and from a calculation of the surface oxygen concentration. If no oxygen is present and plutonium is in the Pu(III) state, the presence of hydride can be inferred (in the absence of other elemental impurities). Hydride is also detectable when significant oxygen contamination is present. Data on the effect of oxygen on the Pu(0) state, metallic plutonium, showed that the metallic state can easily be detected at oxygen concentrations less than 40 at.%. Thus, in the absence of the metallic state and when the oxygen concentration is less than 40 at.%, hydride is implicated as the surface component. The detection of hydride in the presence of oxygen contamination was confirmed by examination of a hydrided surface that was subsequently oxidized. After sputter etching through the outer oxide layer, the spectral information indicated that hydride was present on the surface.