Regular Article

Gamma ray transport simulations using SGaRD code

CEA DAM Ile-de-France, Bruyères-le-Châtel, 91297 Arpajon cedex, France

^⁎ e-mail: philippe.humbert@cea.fr

Received: 18 November 2016
Received in final form: 7 February 2017
Accepted: 15 February 2017
Published online: 21 March 2017

Abstract

SGaRD (Spectroscopy, Gamma rays, Rapid, Deterministic) code is used for the fast calculation of the gamma-ray spectrum, produced by a spherical shielded source and measured by a detector. The photon source lines originate from the radioactive decay of the unstable isotopes. The leakage spectrum is separated in two parts: the uncollided component is transported by ray tracing, and the scattered component is calculated using a multigroup discrete ordinates method. The pulse height spectrum is then simulated by folding the leakage spectrum with the detector response function, which is precalculated for each considered detector type. An application to the simulation of the gamma spectrum produced by a natural uranium ball coated with plexiglass and measured using a NaI detector is presented. The SGaRD code is also used to infer the dimensions of a one-dimensional model of a shielded gamma ray source. The method is based on the simulation of the uncollided leakage current of discrete gamma lines that are produced by nuclear decay. The material thicknesses are computed with SGaRD using a fast ray-tracing algorithm embedded in a nonlinear multidimensional iterative optimization procedure that minimizes the error metric between calculated and measured signatures.