A High Rate Pixelated Neutron Detector for Neutron Reflectometry at the Spallation Neutron Source

This work presents the development of a high-rate 6Li-based pixelated neutron detector for neutron reflectometry instruments at the Spallation Neutron Source (SNS), Oak Ridge National Laboratory. The current detector technology falls short on the instrument requirements, particularly on the counting rate capability. This detector was designed specifically to overcome the limitation in counting rate by having a fully pixelated design from neutron conversion layer to photodetector and readout system. For the neutron converting layer, a 6Li-based neutron scintillator was used. Each scintillator element was coupled to a photodetector, in this case, a silicon photomultiplier (SiPM). The output of each SiPM was read out independently. This design has been demonstrated to have a significantly higher rate capability compared to other charge-sharing designs due to the fact that each pixel is fully functional on its own, without relying on adjacent pixels. An experimental prototype was constructed and characterized using various standardized tests such as counting rate, neutron detection efficiency, spatial resolution, γ sensitivity, crosstalk, and uniformity. Lastly, neutron reflectivity experiments were conducted using the detector prototype to demonstrate the performance and capability of the detector in practice.