A comprehensive simulation study of a Liquid-Xe detector for contraband detection

Recently, a new detector concept, for combined imaging and spectroscopy of fastneutrons and gamma rays was presented. It encompasses a liquid-xenon (LXe) converter-scintillator coupled to a UV-sensitive gaseous Thick Gas Electron Multiplier (THGEM)-based imaging photomultiplier (GPM). In this work we present and discuss the results of a systematic computer-simulation study aiming at optimizing the type and performance of LXe converters. We have evaluated the detector spectral response, detection efficiency and spatial resolution for gamma-rays and neutrons in the energy range of 2-15 MeV for 50 mm thick converters consisting of plain LXe volume and LXefilled capillaries, of Teflon, Polyethylene or hydrogen-containing Teflon (Tefzel). Neutron detection efficiencies for plain LXe, Teflon-capillaries and Tefzel-capillaries converters were about 20% over the entire energy range. In polyethylene capillaries converters the neutron detection efficiency was about 10% at 2 MeV and increased up to about 20% at 14 MeV. Detection efficiencies of gammas in Teflon, Tefzel and polyethylene converters were ∼ 35%. The plain-LXe converter provided the highest gamma-ray detection efficiency, of ∼ 40-50% in the 2-15 MeV energy range. Optimization of LXe-filled Tefzel capillary dimensions resulted in spatial resolution of ∼ 1.5mm (FWHM) for neutrons and up to 3.5mm (FWHM) for gamma-rays. Simulations of radiographic images of various materials using two discrete energy gammarays (4.4 MeV and 15.1 MeV) and neutrons in a broad energy range (2-10 MeV) were performed in order to evaluate the potential of elemental discrimination.