GB468623A - Improvements in and relating to electron multipliers - Google Patents

Abstract

468,623. Electron multipliers. KEYSTON, J. E. Nov. 8, 1935, No. 30989. [Class 39 (i)] An electron multiplier arrangement has means arranged outside the electron multiplier for producing a variation of the direction in which, or the position from which, input electrons enter the multiplier, by which variation the effective number of targets between the electron source and the output terminals of the multiplier is varied and hence the output thereof is varied. In one form the multiplier comprises two plates P1, P2, Fig. 1, between which an oscillatory voltage is applied. An electron beam from cathode C enters the multiplier through an aperture in plate P1, and travels in zigzag fashion between the plates with multiplication at each impact, until collected by the anode A. Deflecting plates D are provided which vary the angle at which the primary beam enters the multiplier and hence the number of impacts. The dotted lines show two positions of the deflected beam. In another form a number of targets E1, E2, E3, Fig. 3, are maintained at successively increasing positive potentials. An electron beam from cathode C strikes the first target E1 and, under the influence of accelerating electrodes F1, F2, and an external magnetic field, hops along the targets multiplying at each impact until collected by electrode A. The deflecting plates D enable the primary beam to be variably distributed between targets E1, E2, which are provided with inclined adjacent edges as shown in Fig. 4, and the effective number of targets is thereby varied. Upon extreme deflection the beam may be caught by anode F1, the output dropping to zero, and an apertured diaphragm in the tubular part of F1 may assist this action. In a modification, the multiplier comprises a continuous cylindrical electrode of resistive material along which a potential difference is maintained, and a central rod-like accelerating electrode. An electron beam is directed into one end at an angle which can be varied by deflecting plates and the variably multiplied beam is collected on a disc anode closing the other end. In a multiplier of zigzag type, two of the targets may comprise a photoelectric layer and a fluorescent layer on opposite sides of a glass plate. The primary electron beam can be deflected so as to fall on either of the fluorescent surfaces, producing a photoelectric beam which is multiplied. By this means the position at which the beam enters the multiplier may be varied. The fluorescent surfaces may be dispensed with and a deflectable beam of light substituted for the primary electron beam. The fluorescent and photoelectric surfaces may be continuous resistive coatings along which a potential difference may be maintained. The path of the primary electron beam may be varied by mechanical movement of part of the apparatus. Specification 465,144 is referred to.