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

Abstract

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 × 10 × 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.