Efficient Monte Carlo framework for evaluating thermal and epithermal neutron self-shielding in electron-beam-driven neutron activation analysis

摘要: Neutron self-shielding factors play a crucial role in accurately interpreting neutron activation analysis by accounting for neutron flux attenuation within specimens, however calculating these factors in complex systems is computationally intensive and time-consuming. This study introduces a two-stage “sequence-calculation” framework that significantly enhances the efficiency of Monte Carlo simulations for neutron self-shielding analysis, particularly when one needs to consider multiple specimens and irradiation positions. The proposed method is validated through a cross-code validation using the Particle and Heavy Ion Transport Code System (PHITS) and Monte Carlo N-Particle Transport Code version 6 (MCNP6), both of which express a reasonable agreement with the conventional Monte Carlo method. The method was applied to evaluate thermal and epithermal neutron self-shielding factors for Au, Cu, W, and Zr activation specimens, which are irradiated using the Intense Resonance Neutron Source (IREN) at the Joint Institute for Nuclear Research (JINR), Dubna. These values are fundamental for upcoming researches with IREN. Thanks to the significant reduction in computational time enabled by the proposed approach, the study is able to explore the sensitivity of self-shielding effect to specimen thickness and neutron flux variation, emphasizing the need for geometry-specific corrections. Beyond the neutron self-shielding problem, the proposed framework offers a robust and versatile solution for a wide range of radiation transport problems involving complex geometries and source terms.