Development of a Neutron Imaging Detector Based on the μPIC Micro-Pixel Gaseous Chamber

A new detector employing the micro-pixel chamber (mu PIC) is currently being developed as a neutron imaging detector for applications in small angle scattering (SANS), neutron radiography, and radioactive detection. Neutron detection is achieved through the He-3(n, p)(3) absorption reaction by adding 3He to the usual gas mixture. The mu PIC, with a pixel pitch of 400 microns, coupled with an FPGA-based data acquisition system with 100 MHz internal clock. This combined system has spatial (< 1mm) and time (10 ns) resolutions and is of handling counting rates greater than 5 MHz. These make it well suited to SANS measurements at pulsed sources. Here, we report the performance of a new mu PIC-based neutron imaging detector system along with 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 cm(3) active volume and operates at gas pressures up to 2 atm. With this design, we expect a neutron detection efficiency of similar to 30% for a gas mixture containing 30% He-3 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.