Optimization of LaBr₃(Ce) Scintillator Parameters for PGNAA Applications

Prompt Gamma Neutron Activation Analysis (PGNAA) is a non-destructive method for elemental analysis of bulk and heterogeneous materials and is widely used in industrial applications such as metal sorting and quality control. This work determines practical design parameters of a LaBr₃(Ce) scintillation detector—its thickness and angular placement—by explicitly addressing the trade-off between full-energy peak (FEP) efficiency and energy resolution. A hybrid Monte Carlo framework was developed, in which MCNP6 generates prompt gamma-ray source terms from neutron–sample reactions and GEANT4 simulates detector response including optical photon transport. The GEANT4 detector model was validated using a measured ¹³⁷Cs spectrum, and a Gaussian energy broadening (GEB) model calibrated for a 2” × 2” detector was incorporated to produce realistic spectra. For thicknesses of 1–4 inches and angles of 45º–180º, increasing thickness improved absolute efficiency but reduced light collection efficiency, resulting in degraded energy resolution; the 4-inch detector showed ~58% degradation in energy resolution than the 1-inch detector. In addition, the 180º configuration was excluded due to the elevated risk of neutron-induced activation when aligned with the beam axis. Considering both performance and engineering constraints, a 2-inch-thick detector positioned at 90º was selected as the best feasible configuration, providing a balanced efficiency–resolution performance and sufficient clearance for shielding and system integration. The proposed methodology offers practical guidelines for designing advanced PGNAA systems with geometry-dependent spectral performance.