Development of the very low angle detector (VLAD) for detection of epithermal neutrons at low momentum transfers

New perspectives for epithermal neutron spectroscopy are opened up by the recent development of new instrumentation for inverse geometry time of flight spectrometers at pulsed neutron sources. One example is the Very Low Angle Detector (VLAD) bank which will be installed as an upgrade of the VESUVIO neutron spectrometer, at the ISIS pulsed neutron source. VLAD is developed for detecting epithermal neutrons in the 1- 100 eV energy range at very low scattering angles (1°-5°). VLAD will extend the kinematical region covered by today’s neutron scattering experiments to the region of low wave vector transfers (<10 Å-1) and high energy transfers (>1 eV). Accessing such kinematical region will allow new experimental studies in condensed matter systems. The neutron detection is based on Resonance Detectors (RD), which consist of the combination of a resonance foil used as neutron-to-gamma converter and a photon detector. The results obtained with a prototype VLAD detector confirm the potential of this kind of experiments at scattering angles as low as 2°-5°. GEANT4 simulations are used to address issues, such as detector cross talk, which arise with the construction of compact RD arrays.