Active Collimator for the BGO Anti-Compton Shield of the HPGe Clover Detector

An active collimator has been designed to replace the heavy metal collimator of the BGO anti-Compton shield to improve the performance of the hybrid Indian National Gamma Array (INGA) at TIFR, Mumbai. The active collimators of the 24 clover detectors, along with the BGO anti-Compton shields and 18 LaBr3(Ce) detectors, can act as a γ-ray multiplicity filter. This configuration will be beneficial for studying weak band structures decaying by high γ-ray multiplicity events. In addition, the energy deposited in all the detectors can be added to get the sum energy for certain measurements aiming to use the hybrid array for calorimetric application. We have characterized an active collimator coupled with one of the anti-Compton shields and an HPGe clover detector with various radioactive sources. The peak-to-total ratio for the active collimator configuration is similar to the standard design with the heavy metal configuration with the 60Co source. Additionally, we have evaluated the Compton cross-talk between the clover HPGe detector and the anti-Compton shield/active collimator. The total multiplicity distribution for a cascade of eleven γ-rays with an energy range of 702000 keV has been obtained through GEANT4 simulation. The simulation results indicate the possibility of conducting a meaningful study of decay chains with a multiplicity of twelve.