Development of a neutron imaging detector based on the μPIC micro-pixel gaseous chamber

A new detector employing the micro-pixel gaseous chamber (μPIC) is currently being developed as a thermal neutron imaging detector for applications in small angle neutron scattering (SANS), neutron radiography, and radioactive material detection. Neutron detection is achieved through the ³He(n, p)³H absorption reaction by adding ³He to the usual Argon-Ethane gas mixture. The μPIC, with a pixel pitch of 400 microns, is coupled with an FPGA-based data acquisition system with a 100 MHz internal clock. This combined system has excellent spatial (< 1mm) and time (10 ns) resolutions and is capable of handling counting rates greater than 5 MHz. These qualities make it well suited to SANS measurements at pulsed neutron sources. Here, we report the performance of a new dedicated μPIC-based neutron imaging detector system along with the results of a test experiment at a small Tandem accelerator-based neutron source currently under development at Kyoto University. This new detector features a 10 x 10 x 5 cm³ active volume and operates at gas pressures up to 2 atm. With this design, we expect a neutron detection efficiency of ∼30% for a gas mixture containing 30% ³He at a total pressure of 2 atm. Additionally, an improved FPGA encoder program allows the simultaneous measurement of the track length and energy deposition, allowing a finer position resolution and strong rejection of the gamma-ray and fast neutron backgrounds.