Monte Carlo investigation of a high-efficiency, two-plane Compton camera for long-range localization of radioactive materials

Compton cameras have become an instrument of interest for long-range localization of radioactive materials in nuclear-nonproliferation applications. In this work, a specialized simulation tool was developed for the optimization of a Compton camera through realistic Monte Carlo simulations. This tool can be used for Compton cameras with different geometries. The MCNPX-PoliMi code was used to simulate Compton scatters and photoelectric absorptions in the camera's detectors. The imaging capability is derived from the physics of Compton scattering and the full-energy information obtained in photoelectric absorptions. The simulated system is a 1 × 1 m² Compton camera consisting of two planar arrays of photon detectors. Several scintillators were evaluated: LaBr₃, CaF₂, and NaI(Tl) (all inorganic scintillators), and C₉H₁₀ (plastic organic scintillator). The investigation was carried out with a ¹³⁷Cs source. A minimum detectable activity (MDA) was defined and used to assess the performance of cameras based on different detectors. The simulation results show that C₉H₁₀ is a reliable, low-cost, scatter-plane material, increasing the MDA by ∼0.2 mCi when compared to a CaF₂ scatter plane. On the other hand, the intrinsic background of LaBr₃ undermines its above-average energy resolution as the MDA increased by ∼0.5 mCi when compared to a NaI(Tl) absorption plane.