<title>Neutron field imaging with microchannel plates</title>

Abstract

Rapid and spatially resolved imaging of neutron fields is not a well-developed technology relative to photon- and electron- based imaging techniques, However, glass-based microchannel plate (MCP) technology is relatively mature, enabling its application to neutron imaging to be straightforward. NOVA's approach to improved neutron detection efficiency and spatial resolution is derived from the suggestion of Fraser and Pearson, where <SUP>10</SUP>B is directly incorporated into the glass matrix of the MCP structure. The <SUP>10</SUP>B(n,(alpha) )<SUP>7</SUP>Li capture conversion stimulates the emission of secondary electrons into the adjacent microchannel structure. An electron cascade ensues, amplifying the detection event into a subnanosecond electron pulse emitted from the microchannel. The pulse can be electronically registered by a radiation-hard readout device and processed as a digital image. The image corresponds to spatial variations in the neutron flux striking the MCP input face. NOVA has constructed and tested a number of prototype neutron imaging detectors using cold and thermal neutron beams at the NIST Center for Neutron Research (NCNR) in Gaithersburg, MD. Features having a spatial separation of 30 micrometer are clearly resolvable in the raw images. Software processing further improves the image resolution. Conversion efficiency for thermal neutrons of an initial iteration of the specially modified MCPs is approximately 20%, with negligible gamma ray-induced background. In-progress modifications to the MCP base material and structure should produce imaging detectors with neutron detection efficiencies that exceed 50%.