Year
2006
Abstract
A combination of calorimetry and high resolution gamma spectrometry is one of the preferred non-destructive quantitative analysis methods for plutonium accountability measurements. The accuracy and precision obtained in these measurements are evaluated in the New Brunswick Laboratory (NBL) Calorimetric Exchange (CALEX) Program using plutonium oxide standards with well-characterized values for the plutonium mass, plutonium isotopes abundance and 241Am abundance. The CALEX program participants make repeated measurements of the standards at frequent intervals and submit the results to NBL for evaluation of accuracy and precision. The measurement results for plutonium mass, plutonium isotopes abundance, 241Am abundance, effective specific power, and power are compared to the corresponding characterized values and evaluated. The characterized values are corrected for radioactive decay to the measurement dates. Half-life values recommended by DOE in 2002 are used in the decay calculations. Prior to 2002, half-life values contained in the ASTM standard C 1458-00 were used. Small differences exist between these two sets. For example, the DOE value for 241Pu half-life is 14.290 ± 0.006 years whereas the ASTM value is 14.348 ± 0.022 years. In addition to DOE and ASTM there are other sources (e.g., IUPAC) for half-lives. Radioactive decay calculations were performed using all these sets of published values to assess the effects of variations in half-lives on the decay-corrected reference values for mass, effective specific power, power and isotope abundance. The results and conclusions of these calculations will be discussed with specific reference to their impact on the evaluation of calorimetric measurement results.