A high sensitivity 4π view gamma imager with a monolithic 3D position-sensitive detector

Imaging is an effective way to survey gamma radiation hotspots in nuclear safety, public health and homeland security applications. The existing gamma imagers either equip a collimator, which limits the imaging field of view (FOV) and sensitivity, or work without a collimator but require a high performance detector with sophisticated data processing and image reconstruction methods, e.g. the Compton camera. In this work, we demonstrate the feasibility of a high sensitivity 4 pi view gamma imager design concept. Based on the photon event density distribution inside a monolithic 3D position-sensitive detector, the imager reconstructs the 4 pi view of the surrounding gamma hotspots that the detector is exposed to. Monte Carlo simulations and experiments were conducted for several configurations of surrounding sparse gamma point sources in the energy range from 0.1 to 1.5 MeV. The results show that the reconstructed 4 pi view image can identify multiple gamma hotspots, with the hotspots' positioning accuracy and resolution dependent on the detector's intrinsic resolution and the statistics of the acquired data. We conclude that the proposed design can be used for surveying gamma hotspots in nuclear security applications.