Optimal design for a μBq/kg gamma spectrometer based on Monte Carlo simulation.

In response to the urgent requirement of material screening in rare event experiments, a new ARray of GermaniUm γ-ray Spectrometer (ARGUS) is planned to be established in China Jinping Underground Laboratory (CJPL). The spectrometer was optimized with Monte Carlo simulation using Geant4. Five HPGe detectors were combined in ARGUS for higher efficiency. Two shielding systems, one with liquid nitrogen, the other with lead plus copper were evaluated. With the combination of multiple detectors, low activity materials and the optimized design of shielding systems, the decision threshold at the level of 10μBq/kg for U/Th decay chain could be achieved.