Benchmarking of the efficiency of the NaI(Tl) detector using FLUKA, MCNP, and experimental measurements at multiple source distances

Accurate calibration of NaI(Tl) scintillation detectors is essential for reliable gamma-ray spectrometry in nuclear safeguards and environmental radiation monitoring. This study investigates the full energy peak efficiency (FEPE) of a NaI(Tl) detector using experimental measurements and Monte Carlo simulation performed with FLUKA and MCNP. Standard point sources ( , , and ) were measured at four source-detector distances (4, 8, 12, and 16 cm) covering photon energies from 356 to 1333 keV. Both simulation tools demonstrated an average deviation of less then 6 % and a maximum deviation of 18 % from the experimental results in all configurations. Furthermore, source misalignment was numerically evaluated and found to have a measurable impact only at short source-detector distance. This work represents the first integrated benchmarking of FLUKA and MCNP against experimental FEPE data across multiple geometries, offering a validated framework for accurate detector modeling and calibration. • Monte Carlo-based FEPE benchmarking using FLUKA and MCNP. • Evaluation of geometric efficiency changes under misalignment. • Validation with experimental measurements for reliability.