Properties of neutron pixel detector based on Medipix-2 device

Neutron transmission radiography can serve as a complementary diagnostic method to X-ray radiography. It can produce contrast images of materials, which are indistinguishable in X-ray images (typically materials containing hydrogen). Good performance of a neutron detecting device is essential for the acquisition of high quality neutron images. The properties of the neutron pixel detector based on the single X-ray photon pixel detector device Medipix-1 (64 × 64 square pixels with pitch of 170 μm) were already demonstrated and published. Slow neutrons are captured and converted in a surface layer containing Li-6 to tritons and alpha particles which are subsequently detected by a silicon pixel detector. A Medipix-2 detector (256 × 256 square pixels with pitch of 55 μm) was adapted in a similar way. The detector performance was tested at the NEUTRA station of the Paul Scherrer Institute using a beam of slow neutrons from the spallation source SINQ with an intensity of 3·10⁶ neutrons/cm²s. The spatial resolution, detection efficiency and other detector properties have been determined and are compared with several types of contemporary neutron imaging systems (Medipix-1, CCD camera, imaging plates). The results demonstrate the superiority of the Medipix-2 based neutron imager in terms of spatial resolution, linearity and dynamic range. The system is very promising in applications for micro-neutron tomography, especially when large detector areas will become available.