Straw detector for high rate, high resolution neutron imaging

Instrument requirements in soon to be commissioned and planned neutron scattering facilities call for large area detectors that can sustain rates up to 10⁸ cps and millimeter-level spatial resolution. Although ³He pressurized area detectors can provide good spatial resolution, sensitivity and gamma ray discrimination, this technology cannot achieve the required rates without further development. Moreover, achieving large detection areas with pressurized ³He technology is expensive because of the complexity of the pressure containing vessels required. We propose a detector technology, based on thin-walled straws, lined with a 1 mum thick sputter coating of enriched boron carbide (¹⁰B₄ C). Neutrons converted in ¹⁰B generate charged particles that subsequently ionize the gas contained within each straw. Because the ¹⁰B₄C coating is very thin, efficient escape of the reaction products can be achieved. A panel detector consisting of several thousand close-packed individual straws, which are read out independently, can easily support high event rates. We present performance testing of two 50-straw prototypes (non-enriched B₄ C), including detection efficiency, spatial resolution, and two-dimensional imaging. Each straw has a diameter of 4 mm and a length of 1 m. Additional tests of a single 50 cm long straw, 2 mm in diameter are also presented