Position sensitive detectors in (e,2e) coincidence measurements

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Abstract
The two outgoing electrons from (e,2e) scattering processes are selected by two 180° electrostatic analyzers whose energy dispersed output spectra are detected by microchannel plates followed by resistive anodes. These detectors permit the identification of all multiple coincident events occurring within the dispersal width of the analyzers. It was found that the time difference between the two detectors for correlated events is strongly dependent on the energy of the incident electrons, which consequently causes the time coincidence window to move systematically. This behavior has been accounted for by a model that determines the time taken by an electron to go around a hemispherical analyzer. A description is given of a data collection system that can compensate for the shift in the coincidence spectra and that records all multiple coincidence events with an increase in the overall coincidence count rate of about two orders of magnitude relative to conventional non position sensitive detectors without position sensing. The performance of the system is shown for an (e,2e) spectrum of argon.