The theory of compact and efficient circular-pore MCP neutron collimators

A novel type of thermal and cold neutron collimator based on microchannel plates (MCPs) doped with neutron-absorbing atoms is discussed. In contrast to widely used Soller slit collimators, the MCPs collimate a beam of neutrons in two dimensions simultaneously and they are very compact. A detailed model of the circular-pore MCP collimator performance, described in this paper, can be used for optimization of MCP parameters in order to achieve the most efficient collimation for a given application. Among these parameters are the MCP geometrical dimensions, the type of absorbing atoms and their concentration in the MCP glass mixture, all constrained by the manufacturing limitations. The model predicts that the MCP collimators can be very efficient (rocking curve <0.1° wide with high background suppression in the wings) and very compact (only a few mm thick). In addition to collimation, the same MCPs can also be used for neutron imaging with a high spatial (∼20 μm) and temporal (∼1 μs) resolution, opening up new possibilities for simultaneous beam collimation and monitoring.