Performance of the high-efficiency thermal neutron BAND-GEM detector

Newhigh-count-rate detectors are required for future spallation neutron sources where large-area and high-efficiency (>50%) detectors are envisaged. In this framework, Gas Electron Multiplier (GEM) is one of the detector technologies being explored, since it features good spatial resolution (<0.5 cm) and timing properties, has excellent rate capability (MHz/mm(2)) and can cover large areas (some m(2)) at low cost. In the BAND-GEM (boron array neutron detector GEM) approach a 3D geometry for the neutron converter cathode was developed that is expected to provide an efficiency >30% in thewavelength range of interest for small angle neutron scattering instruments. A system of aluminum grids with thin walls coated with a 0.59 mu m layer of (B4C)-B-10 has been built and positioned in the first detector gap, orthogonally to the cathode. By tilting the grid system with respect to the beam, there is a significant increase of effective thickness of the borated material crossed by the neutrons. As a consequence, both interaction probability and detection efficiency are increased. This paper presents the results of the performance of the BAND-GEM detector in terms of efficiency and spatial resolution.