Diamond material demonstrates excellent temperature and radiation resistance properties, and detectors made from diamond exhibit good potential for use under harsh environments.

This study aims to analyze the structure and working principle of diamond thermal neutron detectors, and establish a physical model of such a detector applied to 2 MW thorium molten salt experimental reactor-liquid fueled (TMSR-LF1) radiation field by using MCNP program.

First of all, ⁶Li and ¹⁰B were selected as neutron conversion materials considering the neutrons of TMSR-LF1 mainly concentrated in the 10^-8~10^-6 MeV energy range, and the Stopping and the Range of the Ions in Matter (SRIM) program was employed to calculate the range of secondary charged particles generated by the reaction in the neutron conversion layer and diamond layer. Then, the MCNP program was used to establish a physical model of diamond neutron detector applied to 2 MW TMSR-LF1 radiation field. Finally, the effects of the neutron conversion layer thickness (⁶LiF, ¹⁰B), diamond thickness, and γ screening threshold on the neutron detection efficiency, γ detection efficiency, and n/γ suppression ratio of the detector were determined through simulation results.

The results reveals that ⁶LiF is more suitable than ¹⁰B for use in the neutron conversion layer in neutron and γ mixed fields. With the increase of the ⁶LiF thickness, the neutron detection efficiency first increases and then decreases, and the optimal thickness of ⁶LiF is 25 μm. The n/γ discrimination performance of the detector deteriorates with the increase of diamond thickness, but the diamond thickness must be greater than 20 μm to ensure insensitivity of the detector to γ, hence a γ screening threshold is needed to prevent excessive γ interference for thick diamond layers.

The influence of detector structural parameters on detector performance obtained by this study has guiding significance for the subsequent fabrication of and research on such detectors.