Abstract
We recently developed a fieldable large-area, coded-aperture, gamma imager (the Large Area Imager - LAI). The instrument was developed to detect weak radiation sources in a fluctuating natural background. Ideally, the efficacy of the instrument is determined using receiver-operator statistics generated from measurement data in terms of probability of detection versus probability of false alarm. However, due to the impracticality of hiding many sources in public areas, it is difficult to measure the data required to generate receiver-operator characteristic (ROC) curves. Instead, we develop a high statistics "model source" from measurements of a real point source and then inject the model source into data collected from the world at large where, presumably, no source exists. In this paper we have applied this "source injection" technique to evaluate the performance of the LAI. We plotted ROC curves obtained for different source locations from the imager and for different source strengths when the source is injected at 50 m from the imager. The result shows that this prototype instrument provides excellent performance for a 1-mCi source at a distance of 50 m from the imager in a single pass at 25 mph.
