Performance of the Skid-Mounted Tomographic Gamma Scanner for Assays of Plutonium Residues at R

The performance of the skid-mounted tomographic gamma scanner (TGS) on Rocky Flats Environmental Technology Site residues containing macroscopic lumps of plutonium has been determined. The TGS/FRAM random error was quantified using the scatter of replicate measurements about the corresponding mean (average) values. FRAM is a gamma-ray spectrum analysis code and is used in conjunction wiht TGS emission spectra to determine the ratio between the total plutonium and the 239Pu within a given container. The bias error was obtained by comparing TGS/FRAM measurements of the total plutonium content of cans to the corresponding values obtained by calorimetric assay (Cal/gamma). The random error, bias error, and total measurement uncertainty (TMU) for MSE residues in cans were found to be approximately 6.3%, 7.3%, and 9.6% respectively. TGS scans of a 133Ba source in 55-gallon drums containing various matrices were analyzed using differnt spatial response maps. If the spatial response maps are accurate to within 1cm then the TMU for a range of matrices, with axial densities up to about 50 g/cm2, is 7.5%. This TMU is a little less than the value extracted for MSE residues because the mass, and because the extracted MSE TMU includes a component due to the uncertainty of Cal/gamma measurements.