Nuclear safeguards progress report, July--December 1975

Abstract

The gamma-ray energy region from 120 to 350 keV was investigated using a 1-cc planar Ge(Li) detector. Plutonium isotopic ratios are presented for 0.25 g NBS Standard Reference Material. The results show the feasibility of obtaining /sup 240/Pu and /sup 241/Am isotopic ratios to better than 5 percent of the chemical value by using gamma-ray spectrometers having 600-eV resolution at 122 keV. A single exponential equation has been used to predict the equilibrium of a 1-in. x 3-in. calorimeter (Mound Laboratory Model 100). The formulas necessary for this prediction are presented with some preliminary results. This technique has proved to be successful in significantly reducing the time required to calorimetrically analyze a sample. The installation of the X,Y,Z transporter on a test frame and the computer programs necessary to test it were completed. Tests were performed to determine the sensitivity, thermal resistance, heat distribution error, and reproducibility of the APAS calorimeter. Two computer programs were written to facilitate the handling of inventory verification data. Seventy-nine samples were analyzed using calorimetric assay techniques. The results of the isotopic ratio determinations are presented. The overall uncertainty in the plutonium measurements is less than 1 percent. Gamma-ray spectroscopic techniques were used to measure the isotopic ratios for five ZPPR fuel pins. The data were analyzed using two gaussian fitting programs. The resulting plutonium values determined using gamma-ray isotopic ratios in calorimetric assay are 0.43 percent and 1.2 percent higher than those using chemical isotopic ratios. The contribution from the uncertainty in the gamma-ray isotopic ratios to the overall uncertainty in calorimetric assay is about 0.7 percent.