Performance of 1 Meter Straw Detector for High Rate Neutron Imaging

Instrument requirements at the newly commissioned Spallation Neutron Source call for large area detectors that can sustain rates up to ¹⁰7 neutrons/s and millimeter-level spatial resolution. Although ³He pressurized area detectors can provide good spatial resolution, sensitivity and gamma ray discrimination, this technology cannot support the required rates without further development. We propose a detector technology based on thin-walled straws, lined with enriched boron carbide (¹⁰B₄C. A panel detector consisting of several thousand close-packed individual straws, which are read out independently, can easily support high event rates. We present test results for a sub-scale 100times4 cm² prototype detector, consisting of three 50-straw array modules. Each straw in the array has a diameter of 4 mm and a length of 1 m. Tests conducted in a thermal neutron beam focused on the count rate capability of the detector and the effect of high neutron rates and a high gamma ray flux on spatial resolution. Results showed that the detector can maintain a 7times4 mm² resolution up to an integral rate of 40,000 cps, and a gamma ray flux of 1000 mrem/hr.