Gamma-ray isotopic analysis of plutonium within highly attenuating shipping containers

Isotopic measurements of items stored in shielded shipping containers presents a challenge to standard, nondestructive high-resolution gamma spectroscopy analysis. For example, some plutonium oxide material that will be shipped from Rocky Flats will be packaged in a combination of containers that places more than 12 mm of lead and 25 mm of steel between the material and the detector. This shielding effectively eliminates gamma rays below approximately 300 keV. Spectra were taken through simulated containers and analyzed using FRAM version 4.0 and a parameter set developed for use with highly attenuated items. The results indicate that 10% precision in measured {sup 240}Pu content should be achievable with 2-hour measurements