Experimental Confirmation of the Specification of a HEU Disc Standard Source Used in Holdup*

The Safeguards Laboratory of the Oak Ridge National Laboratory (ORNL) possesses an encapsulated highly enriched uranium metal disc used in the calibration of holdup instruments. This disc has been extensively used over a number of years and is well documented. Because this disc is so significant for many instrument calibrations, ORNL has used current methods and evolving quality techniques to perform additional measurements intended to verify the source content (enrichment and mass) and empirically confirm the attenuation correction factors that were previously calculated from the source specification data. In particular, we use gamma-ray transmission techniques to determine the thickness and attenuation factor of the encapsulation and the areal density of the uranium metal. Our motivation is to describe a practical approach that can be readily adopted or adapted by others to test the characteristics of their own reference materials as part of a comprehensive quality program.