Performance and Inter-Comparison of Novel 4Π-Optimized Compton Imagers

Compton imagers determine the location of a gamma-emitting radioactive source by tracking the interactions of a gamma ray within a position-sensitive spectroscopic gamma detector. The Compton imaging technology is naturally capable of delineating multiple and extended sources as well as localizing point sources. With their graphic output of source location probability contours overlaid on a photograph, Compton imagers are finding application in astronomy, medical imaging, environmental remediation, nuclear nonproliferation and national security. Over the past several years this group has been developing the Silicon photomultiplier-based Compton Telescope for Safety and Security (SCoTSS) imager using a traditional two-plane design with a forward "scatter" plane and a rear "absorber’ plane [1]. At the 2019 IEEE NSS MIC conference we described adapted SCoTSS designs optimized for 4π imaging including cubic, spherical and cruciform geometries and discussed their performance determined from GEANT4 simulations [2]. In this submission we present the results of studies performed on the realized instruments in a laboratory setting, quantifying and comparing their point source response and their imaging uniformity over large fractions the 4π incident angle space. These results, using real data, permit verification of the performance expectations for the various design principles of the detectors.