Year
2007
Abstract
A hybrid K-edge/X-ray fluorescence densitometer (HKED) combines information from two highpurity germanium detector systems to determine the actinide content of a liquid sample. In this study, only spectra from the X-ray fluorescence subsystem of a hybrid densitometer are considered. A method for fitting germanium X-ray escape peaks (GXEPs) in hybrid X-ray fluorescence spectra is described. The relative prominence of the GXEPs that correspond to 103-, 122-, and 136-keV gamma rays was measured in the laboratory. Each gamma-ray peak was found to be accompanied by a germanium K-alpha-1 escape peak approximately one one-thousandth the area of the fullenergy peak. This may seem like a small effect, but the GXEPs for uranium K-beta X-rays appear in the vicinity of neptunium K-alpha X-rays. For samples with high concentrations of uranium and high uranium/neptunium ratios, GXEPs in the vicinity of neptunium K-alpha X-rays would artificially increase the reported neptunium concentration. Failure to account for the presence of GXEPs would cause the neptunium concentration to be overestimated by 10 percent or more in samples with uranium/neptunium ratios greater than 100. A feature that compensates for the effect of GXEPs on the neptunium concentration was included in the Los Alamos National Laboratory (LANL) HKED analytical code. The effectiveness of this feature was evaluated during the analysis of several uranium-neptunium samples, and the results are discussed.