Novel Microcomposite Scintillator Films for Thermal-Neutron Detection

Neutron scintillator films composed of a Eu
²
+-doped CaF2-AlF3
^-6
LiF (Eu:CALF) polycrystalline ceramic powder and a poly(vinylidene fluoride) (PVDF) polymer matrix have been fabricated for neutron position-sensitive detectors (n-PSDs). Scintillation light yield and neutron detection efficiency have been measured as a function of film thickness (L) in the range of L=0.08-1.0 mm. The light yields of the films are 17,000-19,000 photons per thermal neutron. Based on a photon diffusion model in disordered media, the mean-free path of scintillation photons is 1.25±0.35 mm. Light emission cone size, the Full-width-at-half-maximum (FWHM) of spatial distribution of emitted light, is expected to increase with the film thickness. There is a large difference in the longest lifetime component (~800 ns) between neutron and gamma events at L≤0.39 mm, but this difference diminishes for films thicker than 0.39 mm, making neutron-gamma-discrimination (NGD) harder for these thicker films. The NGD ratio, or neutron-gamma-efficiency ratio, has been estimated using primitive digital-signal processing and machine-learning algorithms for a 1.0-mm-thick film. It reaches (2-3) x 10
⁵
using Principle Component Analysis (PCA) and 2-feature based pulse-shape discrimination methods, but they give a low thermal-neutron detection efficiency (~10%). A conventional Nonnegative Matrix Factorization (NMF) and a Graph-regularized NMF (GNMF) algorithms generate NGD ratios of 1 x 10
⁷
and 8 x10
⁸
, and thermal-neutron detection efficiencies of 15 and 37%, respectively. Potential applications of our microcomposite scintillation films include neutron scattering for materials research, and neutron imaging and spectroscopy for nondestructive testing and security.