MCNPX Modeling of Praseodymium-143 Production in the Tehran Research Reactor: A Comparative Study with Experimental Gamma Spectrometry Results

The production of therapeutic radionuclides with high radionuclidic purity is a critical requirement in targeted radionuclide therapy. In this study, the feasibility and optimization of praseodymium-143 production via neutron irradiation of natural cerium targets in a research reactor environment were investigated using a high-fidelity Monte Carlo framework. The production is mainly governed by (n,γ) neutron capture reactions on cerium isotopes followed by β⁻ decay of intermediate 143Ce to form 143Pr. Neutron transport and activation calculations were performed using MCNPX 2.6.0 with detailed reactor geometry and energy-dependent neutron spectra corresponding to the Tehran Research Reactor (5 MW, 20% enriched MTR-type fuel). Simulation results indicate that the peak thermal neutron flux reaches 1.3±0.04 × 10¹³ n·cm⁻²·s⁻¹ at the central irradiation position.Parametric analysis shows that 143Pr activity exhibits a nonlinear dependence on irradiation and cooling times due to coupled parent–daughter decay behavior. An optimal cooling period of approximately 4 days was identified, corresponding to peak 143Pr activity of approximately 2.9 MBq for a 1 mg target under reference conditions.Experimental validation using high-purity germanium (HPGe) gamma spectrometry was performed by comparing calculated and measured activities of the parent isotope 143Ce under identical irradiation conditions. The results show good agreement with a relative deviation of approximately 5.3%, confirming the predictive capability of the MCNPX-based model.