GB1072276A - Improvements in and relating to electron multipliers - Google Patents

Abstract

1,072,276. Electron multipliers. WILLIAM H. JOHNSTON LABORATORIES Inc. June 22, 1965, No. 26356/65. Heading H1D. In an electron multiplier, each .dynode 10 has a plurality of passages 11 therethrough, each passage sloping outwardly in crater - like fashion from a hole 20 of radius r on the output side in such fashion that the surfaces of each set of four adjacent passages arranged at the corners of a square define a cusp at radius r+t from the centre of each passage, t being the thickness of the dynode. Each dynode, except possibly the first, has a thin focusing plate 13 in contact with its input face, apertures 15 in plate 13 being aligned with the cusps of the contacting dynode and with the passages through the dynode of the preceding stage. The passages through dynodes 10 may be formed by etching, all but holes 20 in the exposed surfaces of the dynodes being masked. The cusps may be rounded off to inhibit field emission. The dynodes and focussing plates may be circular and mounted on rods with insulating rings 16 between adjacent stages. Alternatively, the rings 16 may be of electrically resistive material, an accelerating voltage being applied between the first stage and anode plate (25), Fig. 3 (not shown). The dynodes may be of Be or an Ag-Mg alloy with oxidized surfaces and the rows of passages next adjacent perpendicular diameters of each dynode may be offset from these diameters by a quarter of the distance between adjacent holes so that all the dynodes may be identical, adjacent dynodes being rotated through 180 degrees relative to one another. The first stage of the multiplier may include a wire mesh grid instead of a focusing plate, or such as grid may be provided, spaced and insulated from the first stage. The multiplier may be used in a mass spectrometer.