CASCADE: A new efficient and position sensitive detector for thermal neutrons on large areas

We present the CASCADE-detector, a new concept for efficient and position sensitive detection of thermal neutrons on large areas. The detector concept is based on solid neutron converter layers in a common gas detector system, which guarantees insensitivity to gamma-rays. High detection efficiency is reached by cascading several solid neutron converter layers each coated onto a charge transparent carrier substrate. The GEM-foils are employed as such a transparent substrate. In this design position information, the locus of neutron conversion, can undistortedly be imaged through a cascade of several converter layers onto a readout structure underneath. The detector works with ordinary counting gases under normal pressure. Lightweight, easy to handle and in particular large area detectors can be constructed at low costs. A constant flow of fresh, purging counting gas avoids aging effects, which guarantees long term stability as well as long lifetime. The use of GEM-foils provides a high dynamic range from single neutron counting up to high count rates of 10(7) n/cm(2) s and sub-ps absolute time resolution. This feature is required for modem spallation source instrumentation and opens the door towards new ambitious TOF applications. The concept of the detector, together with first results from a prototype device are presented.