Novel Neutron Detector Material: Microcolumnar Li<italic>x</italic>Na1–<italic>x</italic>I:Eu

Abstract

Current neutron detection relies on 3He detectors, which are prone to material shortages, and suffer from poor spatial resolution. Such inadequacies make 3He unsuitable for new applications in state-of-the-art spallation sources such as the Spallation Neutron Source at Oak Ridge National Laboratory. Here, we report on the synthesis and application of a novel scintillator material for neutron detection: a mixed halide compound, Eu-doped (0.05 mol. %) 6Li x Na1– x (6LNI:Eu). 6LNI:Eu is a bright and efficient scintillator that can be grown in large format, thin films that exhibit microcolumnar structure in their cross section. The ability to grow in a microcolumnar structure means that a resolution of approximately 1 lp/mm can be achieved with neutrons using an electron-multiplying charge coupled device camera, thereby conferring an advantage over other solid (not gaseous) neutron scintillators, such as Cs26LiYCl6:Ce (CLYC) and GS20. The large area format of 6LNI:Eu is a significant advantage for detecting specular reflections in neutron scattering experiments. Moreover, the microcolumnar nature of films permits high-resolution imaging when films are coupled to a-Si:H flat panels, CCD, or CMOS readouts. While not the primary focus, this also makes them suitable for digital neutron radiography. Enriched 6Li was used to increase the neutron absorption cross section of the thin films, while preserving the brightness of the scintillation response. Here, we describe the vapor deposition techniques used to fabricate the 6LNI:Eu scintillator screens and report on the test results. The films were tested at the High Flux Isotope Reactor (HFIR) at ORNL. An efficiency of approximately 43% for 4.1-A neutrons with a resolution of 650 $\mu \text{m}$ was measured for a 375- $\mu \text{m}$ thick film of 6LNI:Eu using a neutron sensitive Anger camera.