Improvements to the Shielding Algorithm System (SAS) Software for the Analysis of Gamma Ray Spectra


  1. Moats, K.
Corporate Authors
Defence Research and Development Canada, Ottawa Research Centre, Ottawa ON (CAN);Zernam Enterprises Inc., Ottawa ON (CAN)
The objective of the Special Nuclear Material (SNM) detection work being conducted at Defence Research and Development Canada (DRDC) is to develop technologies that improve the ability of the Canadian Armed Forces (CAF) to detect, quantify, and determine the threat level of SNM. The Shielding Algorithm System (SAS) software is one such tool, which uses an improved analysis of gamma ray spectra from radiological sources or SNM to determine the quantity and threat level of the material. The SAS C++ software calculates the shielding factor for several combinations of shielding materials, including self-shielding effects. This algorithm uses a chi-squared minimization routine based on the Minuit code, and had been previously tested using relatively simple scenarios involving only a single isotope. In this work, the software was modified to correctly account for sources containing multiple isotopes, to improve the chi-squared minimization calculations, including a procedure for discarding outlier peaks entered by the user, as well as modelling concentric spherical shell sources. Using the measured spectrum from a 789 g sample of reactor grade plutonium, the bestfit materials and thicknesses were determined by the SAS software, as well as the activity and mass of the source, which was found to be a mixture of Pu-239, Pu-240, Am-241, and U-238. Although the plutonium mass was found to be slightly lower than expected, it was of the same order of magnitude as the actual value. A spect
Radiation detection;special nuclear material;identification;isotope enrichment;gamma-ray;spectrometry;radiation shielding
Report Number
DRDC-RDDC-2017-C315 — Contract Report
Date of publication
01 Jan 2018
Number of Pages
Electronic Document(PDF)

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