Overview
We introduce a kaleidoscopic scintillator to improve light collection and 3D event localization performance using a single-photon camera.
A kaleidoscopic scintillator consists of a pyramid-shaped scintillator with specular surfaces on all its sides except for the base. A gamma-ray incident on the scintillator causes a scintillation event. The event is approximated as a point source of light. Light is emitted from the event uniformly in all directions and propagates out of the scintillator. Light arrives at the camera either directly from the event or after reflecting off the scintillator's specular surfaces. The event and its mirror reflections are captured in an image containing defocus blur.
We model the image of an event as a Gaussian mixture model (GMM). The spatial relationship between the event and mirror reflections is determined by the scintillators's geometry and embedded in the GMM. Each component of the GMM corresponds to the event or a mirror reflection. All components are constrained by the event's location and scintillator geometry. We estimate the event's location using the EM algorithm.
Due to the scintillator's finite mirrors and the presence of defocus blur, light from a mirror reflection may be truncated along lines corresponding to the mirror's edges. A mirror reflection may be partially truncated or completely missing from an image. The algorithm determines the number of mirror reflections present in an image during its initialization.
Experiments
We validate our image formation model and event localization algorithm on experimentally captured images of gamma-ray events.
Simulations
Simulations show an improvement in 3D localization performance over previous camera-based methods.
