LiF/CsI:Tl Scintillator for High-Resolution Neutron Imaging

Abstract

We have developed a novel scintillator for neutron imaging by combining enriched <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> LiF with the well-known CsI:Tl scintillator screens. The CsI:Tl scintillator is attractive for imaging applications due to its high light yield (60 000 photons/MeV) and its columnar form that provides a high spatial resolution by collimating the scintillation light to the detector. To make the scintillator sensitive to neutrons, the powdered <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> LiF (95% enriched) was applied to the surface of the columnar CsI:Tl screen. Further studies to optimize performance are underway, varying the thickness of both layers. These screens can be produced with excellent uniformity over large areas. The samples were tested by coupling to charge-coupled device (CCD) cameras at the high-flux isotope reactor (HFIR) CG-1D neutron imaging beamline at the Oak Ridge National Laboratory (ORNL). Excellent quality images were acquired with an observed spatial resolution of 7 lp/mm. When coupled to a photomultiplier tube (PMT), a gamma equivalent energy (GEE) of 2.1 MeV was obtained, indicating a light signal of ~100 000 photons/neutron. In addition, the neutron and gamma signals were well-separated by pulse shape discrimination (PSD). The details of the radiographic results, including tomographic imaging, are presented here.