N. Murtha¹ , L. Sinclair² , P. Saull³ , A. MacLeod³ , A. McCann⁴

¹Carleton University Canada
²Canadian National Data Centre, Canadian Hazards Information Service
³National Research Council Canada
⁴Canadian National Data Centre, Canadian Hazards Information Service, Natural Resources Canada

Abstract:

Under the Comprehensive-Nuclear-Test-Ban-Treaty a State Party can request an on-site inspection to establish whether or not a nuclear explosion has been carried out. Gamma radiation measurements would form a key component of the operation. However, the inspected State Party may declare up to 50 km^2 of restricted-access sites (RAs) each of area up to 4 km^2. We have developed the Silicon photomultiplier-based Compton Telescope for Safety and Security (SCoTSS) gamma imager and survey spectrometer. In a mobile survey along the perimeter of a restricted-access site, SCoTSS can perform a kind of triangulation to work out the distribution of radioactivity inside. This scenario has been enacted experimentally with controlled distribution of 10 GBq of radioactive lanthanum in an L-shaped pattern of area 3,200 m^2 followed by perimeter survey using the SCoTSS imager. We have developed tomographic methods to reconstruct the distribution of radioactivity using the images from multiple points of view. Despite the imager being constrained to locations on the ground over 200 m from the source, it is possible to localize the distribution of the radioactivity. These experimental results and methods will be presented and their potential application to restricted-access sites in on-site inspection will be discussed.