GB756143A - Electron discharge device with photoconductive plate - Google Patents

Abstract

756,143. Pick-up tubes. BAZY, P. J. L., BRACHET, C. M. F., and LEAUTE, P. M. A. Jan. 9, 1952 [July 18, 1951], No. 720/52. Class 39 (1). [Also in Group XXXVI] The target electrode of an electron discharge device for analysing X-ray and γ-ray images comprises a photo-conductive layer 10 covered by a layer 14 of electrically insulating material of such thickness as to reduce the high velocity of the scanning beam to a value which does not mask the pattern of conductivity formed by the images. The insulating material may be zinc sulphide, sulphur, silica, calcium fluoride or calcium iodide. The thickness of a zinc sulphide layer is 3-4 tenths of a micron when the beam voltage is 700, and double that thickness for a voltage of 1000. There may be a further thin layer of insulating material between the photo-conductive layer and the signal plate (Fig. 3, not shown). Zinc sulphide may be applied to the photo-conductive plate 10 by vacuum deposition, the zinc sulphide being heated in troughs 15, 15<SP>1</SP>, 15<SP>11</SP> which are electrically heated in two stages to dark red heat and 1000‹ C. respectively. The plate is rotated or rocked during deposition. Thin silica layers produced by ionic discharges in a rarefied inert gas, e.g. nitrogen helium noon or argon, producing decomposition of a silicon'e or ethyl silicate. Potential of 2000-20,000 volts at frequencies of 20,000-200,000 cycles are quoted. (Fig. 5, not shown). Specifications 431,746, 450,393, 465,060, 470,552, 516,137, [all in Group XL], 652,241, 658,503, [both in Group XL (b)], 668,049, 706,173 and 731,118 are referred to.