A two-dimensional radiation detector in which the electron image produced by a photo-emitting surface, usually a photocathode, is focused in the plane of a defining aperture. Magnetic or electric fields scan this image across the defining aperture.
Source:
PAC, 1995, 67, 1745. 'Nomenclature, symbols, units and their usage in spectrochemical analysis-XI. Detection of radiation (IUPAC Recommendations 1995)' on page 1756 (https://doi.org/10.1351/pac199567101745)