Monte Carlo Simulation of a Gamma-Induced Positron Annihilation Spectrometer Based on the ¹⁵⁷Gd(n,γ)¹⁵⁸Gd Reaction

The research first documented the initial neutron source parameter configuration input into MCNP6 in Figure 2, laying the foundation for subsequent simulations. Regarding material thickness optimization, based on the variation patterns of thermal neutron and γ-ray yields detected behind Gd targets of different thicknesses, combined with analysis results of neutron yields and γ-ray yields, the optimal combination thickness was determined to be 0.05mm Gd with 1mm Cd.

The angular distribution characteristics of γ-rays emitted from this composite target were detailed, revealing the spatial distribution properties of the γ-rays. For detector response analysis, the study systematically presented the counts of detected γ-rays and 0.511 MeV annihilation photons at various scattering angles, and calculated the maximum energy of Compton-scattered photons from 8MeV γ-rays at each scattering angle, determining the impact of Compton scattering on counting.