The application of high-resolution gamma spectrometry to the in-line determination of uranium and plutonium concentrations in solution

Measurements using high resolution gamma spectrometry have been made on aqueous solutions contained in stainless steel flow cells to determine the statistical counting errors and concentration or detection limits for the assay of plutonium and uranium nitrates. Measurements have also been made to determine the gamma-ray attenuation effect of uranyl nitrate at concentrations of up to 350 gU/l for the energy range of 122 to 500 keV. The results have shown that the isotopic mass abundance of reactor grade plutonium (3.6% Pu-241) can be determined with a precision of about +- 1% after correction for the Pu-242 content. These data can be used to determine the counting efficiency with a similar precision for the energy range of 125 to 414 keV. The lower concentration limits for the determination of plutonium in 11 ml solution, based on the counting statistics for a counting time of 5 mins, are about 1g Pu/l and 0.05 g Pu/l for an accuracy of +- 1% and +- 5% respectively. The concentration limit for the analysis of natural uranium using the 186 keV gamma-ray of U-235 is about 30 g U/l in the absence of other gamma emitters and for an accuracy of +- 5% with a counting time of 5 mins. (author)