The production and provisional certification of an equal atom plutonium isotopic standard

NBL performed a study to determine the effects of sample preparation, filament loading and sample burn temperature on CRM 128 isotopic analysis. Sample preparation was studied through dissolution of one unit of CRM 128 in 1 N HNO3 and isotopic analysis of aliqots (1) with no pretreatment, (2) following ion exchange and (3) following H2O2 equilibration and ion exchange. Results indicated no statistically significant difference between any of the three groups of aliquots. Initial filament loading studies attempted to reproduce a value of 100 ng of plutonium per filament. However, due to slight differences in solution concentrations a mean value of 85 ng +.15-20% was actually observed. These variations in sample size caused a significant difference, on the order of +.0.03% at the 95% confidence interval, in the measured 242Pu/239Pu ratio