ABSTRACT

This paper describes a comparison of two gamma-ray efficiency determination methods – CANBERRA’s LabSOCS (Laboratory SOurceless Calibration Software) vs. source-based efficiency calibrations – for common nuclear power plant sample types. These included process, RadCon, radwaste and effluent sample types in a variety of sample container geometries. These included point sources, paper and charcoal filters, cylindrical gas and liquid containers and both gas and liquid Marinelli beakers.

LabSOCS geometry modeling which included sample fixtures, sample containers, sample matrices, sample-todetector spacing and internal detector dimensions and materials have been developed using the Geometry Composer feature of CANBERRA’s Genie™ 2000 Version 2.0 and Gamma Analysis Version 2.0A software packages for 48 common nuclear power plant sample types. A total of 16 different sample container types at five source-to-detector spacings were included in the LabSOCS analysis. Sample matrices were limited to simulated water (epoxy) and simulated air (polystyrene), as well as the point source, paper filter and charcoal cartridge filters. Customized templates were created to accurately define inner and outer wall contours, materials and density values of each container.

A coaxial Intrinsic Germanium (IGe) detector, which was characterized by CANBERRA and calibrated using commercially available sources, was used in this study. The CANBERRA LabSOCS system Version 4.0 was used to generate source-based gamma-ray efficiency calibrations for this detector. The source-based detector efficiencies for the 898.02 and 1836.01 keV lines of ⁸⁸Y and the 1173.22 and 1332.49 keV lines of ⁶⁰Co were corrected for cascade summing by performing a Peak-to-Total Calibration (PTC) and applying the resultant cascade summing correction factors. The uncertainties were then calculated for each efficiency value for each standard.

The LabSOCS efficiencies were compared to the source-based efficiencies for each geometry by calculating the efficiency ratios and ratio uncertainties for each gamma-ray energy for each standard source. The results indicate agreement at the 95% confidence level for an energy range of 59.5 to 1838.01 keV for all geometries.