Two-dimensional position sensitive detection for medium-energy ion scattering

We have designed and built a two-dimensional position sensitive ion detector for use in combination with a toroidal electrostatic analyser. The detector is part of a medium-energy ion scattering set-up, which we exploit to determine the atomic structure and composition of surfaces and interfaces. The ion position is resolved in the angular and energy dispersive directions of the analyser by means of microchannel plates and a charge-dividing collector. The analyser/detector combination has an acceptance in the angular direction of 20³ and in the backscatter energy direction of 2.0% of the central pass energy. The detection system has an angular resolution of 0.10³ and a relative energy resolution of 1.0x10^-3 (FWHM). All detection events are processed individually by a transputer system controlling a VME-bus interface and capable of handling a periodic count rate of 65 kHz. A Silicon Graphics workstation serves as a user-interface.