Mapping the Minimum Detectable Activities of Gamma-Ray Sources in a 3-D Scene

Abstract

The ability to formulate maps of minimal detectable activities (MDAs) that describe the sensitivity of an ad hoc measurement that used one or more freely moving radiation detector systems would be significantly beneficial for the conduct and understanding of many radiological search activities. In a real-time scenario with a free-moving detector system, an MDA map can provide useful feedback to the operator about which areas have not been searched as thoroughly as others, thereby allowing the operator to prioritize future actions. Similarly, such a calculation could be used to inform subsequent navigation decisions of autonomous platforms. Here we describe a near realtime MDA mapping approach that can be applied when searching for point sources using detected events in a spectral region of interest while assuming a constant, unknown background rate. We show the application of this MDA mapping method to a real scenario, a survey of the interior of a small building using a handheld detector system. Repeated measurements with no sources and with 137 Cs sources of different strengths yield results consistent with the estimated thresholds and MDA values; namely, that for background-only measurements no sources are seen above threshold anywhere in the scene, while when sources are present they are detected above the thresholds calculated for their locations.

Ongoing advancement of free-moving radiation imaging and mapping

“…Using this information, the MDA estimator determines the activity emitted from each voxel that should result in a pre-specified probability of detection using the PSL algorithm. 23 Beyond the PSL algorithm, LBNL continues to work toward more accurate, more stable, and better quantified SDF algorithms for non point-like distributions of radioactivity. It was recently demonstrated that the ML-EM approach, coupled with regularizer terms (to help induce a more sparse activity map) can render quantitative SDF results in free-moving survey configurations.…”