A new method has been developed that achieves plutonium isotopic analysis precisions of better than 2% in counting times of only a few minutes, using only the 59- to 208-keV energy region of a spectrum. This breakthrough was achieved by developing a unique but highly accurate method for delineating the overall ''intrinsic'' efficiency curve, including the plutonium K-shell absorption discontinuity at 121 keV. Consequently, the measured 129- and 148-keV peak intensities can now be used to reliably determine the relative abundances of 239Pu and 241Pu. The intense 94- to 104-keV region is also analyzed, providing accurate data for the other isotopes of interest. 5 refs., 3 figs., 2 tabs.

The MGA (Multiple Group Analysis) code which we developed several years ago required two detectors when analyzing high SU Pu content samples. The isotopic information, which was obtained from the 300-keV regions, can now be obtained equally well from the low-energy region (50 to 208 keV). This breakthrough was achieved by developing a unique and highly accurate method for delineating the overall ''intrinsic'' efficiency curve, including the plutonium K-shell absorption edge discontinuity. Consequently, the intense 129- and 148-keV peak intensities can now be used reliably in place of the peaks in the 300-keV regions to determine the relative abundances of STZPu and SU Pu. The 203/208- and 148/152-keV pairs, and all of the intense 94- to 104-keV peaks, are included in the analysis to provide accurate data for the other isotopes of interest.

Techniques have been developed which permit rapid, high-precision analyses of uranium and plutonium by multiple-filament thermal ionization mass spectrometry utilizing a commercial multicollector instrument. The salient feature of the method is volatilization of the entire sample while simultaneously integrating the signal from each isotope, thus virtually eliminating the effects of isotope fractionation in the evaporation process. The method permits the analysis of samples much smaller than required for conventional techniques using Faraday collectors and is expected to have application in the analysis of many elements in addition to uranium and plutonium. Run-to-run reproducibilities of

Thermal ionization mass spectrometry (TIMS) is accepted widely as the benchmark method for precise and accurate isotopic determination of plutonium. TIMS is one of the few analytical methods capable of determining Pu in bioassay samples at the level required for detecting a 50 yr committed dose of 100 mRem resulting from an inhalation exposure to highly insoluble forms of Pu. Typically, Pu is measured in bioassay samples by radiochemical separation, electrodeposition onto a planchet, and radiometric determination by alpha spectrometry. If, based on the alpha spectrometry results, a sample is deemed to need a more sensitive analysis (i.e. suspected uptake, borderline alpha spectrometry positive for Pu uptake, etc.), then the sample is prepared for analysis by TIMS. Part of the development process for establishing a program to determine Pu in bioassay samples by TIMS at the Savannah River Site involved a careful evaluation of the Pu blank value in the reagents used for sample preparation and in urine blanks. This exercise allowed for the evaluation of the newly developed radiochemical separation procedure, the resin bead loading procedure, and the detection limits of the thermal ionization mass spectrometer.