An investigation into the use of a microchannel plates as the photocathode for an SEE X-ray detector

Multi-wire proportional counters with delay line readout are the standard detectors in use on small angle X-ray diffraction beam lines at the Synchrotron Radiation Source (SRS). Their sensitivity and speed of readout would make them a desirable detector for large angle diffraction stations if it were not for the image distortion caused by ‘parallax smearing’. This aberration occurs because of the large range of path lengths prior to interaction in the gas for the photon energies of interest ∼10 keV (1.2 Å). A potential solution to this problem is the secondary electron emission (SEE) detector in which the secondary electrons from photoelectric interactions in a thin layer of suitable material are detected. Detectors based on this principle have been successfully built, and demonstrated at the ESRF. However, their detection efficiency is poor due to the low escape probability of the secondary electrons from the photoconverter. The SRS detector group in collaboration with the University of Leicester Physics and Astronomy department, have attempted to use a Csl coated microchannel plate as the photo-converter. It was initially thought that a carefully designed MCP might improve upon the efficiency of a single layer of material. When run at very low gain the MCP has been shown to be capable of operating in a low pressure MWPC with a standard readout system. An MCP designed for soft X-ray detection was used in this preliminary study and the detection efficiency was found to be poor. Alternative MCP designs are discussed.