Wavelength-shifting-fiber scintillation detectors for thermal neutron imaging at SNS

We have developed a wavelength-Shifting-fiber Scintillator Detector (SSD) with a 0.3 m² area per module. Each module has 154 × 7 pixels and a 5 mm × 50 mm pixel size. Our goal is to design a large area neutron detector offering higher detection efficiency and higher count-rate capability for Time-Of-Flight (TOF) neutron diffraction in the Spallation Neutron Source (SNS). A ZnS/⁶LiF scintillator combined with a novel fiber encoding scheme (v.3) was used to record the neutron events. A Cross-fiber Read-Out-Card (CROC) based digital-signal processing electronics and position-determination algorithm was applied for neutron imaging. Neutron-gamma discrimination was carried out using Pulse-Shape Discrimination (PSD). A sandwiched flat scintillator detector can have a detection efficiency close to He-3 tubes (about 10 atm). A single layer and sandwiched flat scintillator detectors have count rate capabilities of about 6,000 and 35,000 cps/cm², respectively, which can satisfy the count rate requirement of powder diffractometers at SNS. Detectors with v.3 fiber encoding have better image quality and higher spatial resolution than those with previous v.2 fiber encoding.