Wedge-and-strip anodes for centroid-finding position-sensitive photon and particle detectors

Abstract

We discuss new anode geometries, employing position-dependent charge partitioning, which can be used with microchannel plates, planar proportional counters, and mesh dynode electron multipliers to obtain a two-dimensional position signal from each detected photon or particle. Only three or four anode electrodes and signal paths are required, yet images comprised of a number of detected events have little geometric distortion and the resolution is not limited by thermal noise inherent in resistive sheet anodes. We present an analysis of the geometrical image nonlinearity in the relationship between event centroid location and the charge partition ratios. Fabrication and testing of two wedge-and-strip anode systems are discussed. Images obtained with EUV radiation and microchannel plates that verify the predicted performance of this readout system are shown. We emphasize that the spatial resolution of the wedge-and-strip anode is in no way limited by the coarseness of the anode conductor pattern. The resolution is of the order of 0.4% of the image field size, and could be further improved by adopting low noise signal circuitry. Tradeoffs encountered in the design of practical x-ray, EUV, and charge particle image systems are discussed.