Although the neutron image conversion screen is a key component of thermal neutron radiograph, its parameters can severely affect both the spatial resolution and thermal neutron-photon conversion efficiency.

This study aims to design a neutron image conversion screen for a thermal neutron transmission imaging system based on a compact D-D neutron source.

Firstly, the Geant4 (Geometry and Tracking) program was used to simulate the physical process of thermal neutron transmission imaging and two-dimensional images of transmitted photons, and establish a thermal neutron radiography model based on LiF(ZnS) and LiF(GOS) image conversion screens, and the Siemens star image indicator model. Then, the line spread function (LSF) was employed to calculate spatial position resolution of neutron transmission imaging, and the relationships between the thickness of thermal neutron image conversion screens and the spatial resolution, as well as that between the thickness of thermal neutron image conversion screens and neutron-photon conversion efficiency were evaluated and calculated. Finally, based on parameters of thermal neutron radiography imaging system based on compact D-D neutron source at Lanzhou University, recommended thicknesses for LiF(ZnS) and LiF(GOS) conversion screens were applied to the spatial resolution test experiments.

The recommended thicknesses for LiF(GOS) and LiF(ZnS) image conversion screens are 40 μm and 80 μm, respectively, the spatial resolution of the thermal neutron radiography reach 45 and 63 μm, respectively, and the neutron-photon conversion efficiencies are 136.34 and 126.81, respectively.

This study lays the technical basis for the development of a thermal neutron radiography based on compact D-D neutron sources. It may be also applicable to other thermal neutron imaging systems.