Spatial unfolding of an extended La-140 source within a 0.5 km-wide exclusion zone using Compton gamma imaging measurements

Results from applying an advanced spatial-unfolding technique to outdoor-trial data acquired with a Silicon photomultiplier-based Compton Telescope for Safety and Security (SCoTSS) gamma imager during perimeter survey of a distributed La-140 source lying within a 500 m x 500 m exclusion zone are presented. A synthetic-data version of the experiment was also modelled using Monte Carlo simulations and reconstructed. For both experimental and synthetic data the method faithfully reproduces the shape of the activity distribution, and for synthetic data the total activity is reproduced as well. However, for the experimental data the method underestimates the total activity by a factor of six. This can be accounted for by environmental snow and soil conditions not included in the detector response functions. This application of the Compton gamma imager survey-data inversion method demonstrates its applicability under austere conditions wherein extreme weather and transportation constraints severely impacted the quality of the data collected. The trial shows that the method has widespread applicability in the radiological and nuclear safety and security field, particularly for scenarios in which a threat material or contaminated area lies within a no-entry or no-fly zone.