NONDESTRUCTIVE DETERMINATION OF URANIUM ENRICHMENT USING LOW ENERGY X AND GAMMA RAYS

An accurate nondestructive technique has been developed to determine uranium enrichment using low-energy X and gamma rays. By comparing the 89.9 keV thorium X ray from 235U decay with a 92-keV gamma ray doublet from a \"°U daughter, uranium enrichment can be accurately computed. An intense thorium X ray is emitted at 93.3 keV, so it is necessary to accurately resolve this X ray from the 92-keV doublet. Resolution has been accomplished in the present work by using either a spectrum stripping (STRIP) technique available on most new multichannel analyzers or by using the peak-fitting program GRPANL which is presently used for plutonium isotopic determinations. Because the gamma ray and X ray used for the determination are close in energy, the self-absorption corrections are minimized. Results from 13 enrichment samples show an average difference between accepted and measured values of less than 0.3% over an enrichment range from 0.27% to 60.0%. Features of this method that are of interest from a safeguards inspection viewpoint are: (1) gamma-ray spectra were obtained using a high-resolution portable coaxial Ge detector; (2) the 92-keV gamma-ray doublet is much more intense than the 1001-keV gamma ray usually used for enrichment calculations, so one can obtain a statistically adequate spectrum in much less time; (3) the method works well in samples of unknown matrix content.