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Description
A comprehensive spectral and dosimetric assessment of a thermoluminescent neutron personal dosimetry system was performed using Monte Carlo simulations to reproduce reference irradiation conditions at the Neutron Standards Laboratory (LPN-CIEMAT, Spain). The system, composed of paired TLD-600 and TLD-700 detectors, was positioned on the surface of an ISO water phantom and exposed to a ²⁴¹Am/⁹Be neutron field. The computational model was developed in MCNP6, incorporating detailed material compositions, detector geometry, and phantom specifications.
Special emphasis was placed on the characterization of the neutron energy spectrum at the detector location. Energy-dependent neutron fluence distributions were obtained through track-length (F4) tallies with fine energy binning, allowing separation of thermal, epithermal, and fast components. The resulting spectra were folded with fluence-to-personal dose equivalent conversion coefficients to determine Hp(10) as a function of source-to-detector distance (50, 75, 100, and 125 cm). This approach enabled a direct correlation between spectral modifications and dosimetric response.
Two environmental configurations were considered: an idealized free-field geometry and a realistic laboratory model including structural elements responsible for neutron scattering and moderation. The comparison revealed significant spectral softening due to room-return neutrons, particularly affecting the thermal and epithermal regions. The incorporation of cadmium filters in selected detector configurations facilitated experimental discrimination of thermal contributions, validating the simulated spectral decomposition.
The results demonstrate that accurate prediction of personal dose equivalent in Am–Be reference fields requires explicit modeling of energy-dependent fluence and environmental scattering. The study highlights the sensitivity of LiF-based TLD pairs to spectral variations and underscores the importance of detailed Monte Carlo spectral analysis for calibration, optimization, and traceable neutron dosimetry under ISO 8529 reference conditions.