Improvements in or relating to electron multipliers

992,938. Electron multipliers. ELECTRIC & MUSICAL INDUSTRIES Ltd. Oct. 27, 1961 [Oct. 20, 1960], No. 37040/60. Heading H1D. In an electron multiplier with at least two box dynodes 1 to 6, Fig. 1, arranged as shown, the electron exit aperture 11 of a preceding dynode is so formed as to be more open at the centre than at the ends defined by the end members of the box structure. This is in order to produce an increased field gradient at the centre of the exit aperture resulting in an improved focusing action. The exit edge may be set back by providing a lip in the adjoining secondary emissive quadrant surface or by cutting it in the form of a curve. Alternative dynodes only may have their edges set back.