GB1368379A - Electrostatic image production - Google Patents

Abstract

1368379 Discharge tubes; electrode materials XONICS Inc 8 Nov 1972 [12 Jan 1972 12 June 1972] 51572/72 Heading H1D [Also in Division G2] An electrostatic image corresponding to an X-ray image is produced on a dielectric sheet 32 by positioning the sheet at either the cathode 24 or-as shown-the anode 26 of a discharge tube having a filling of a gas of atomic number at least 36, i.e. krypton or xenon, at superatmospheric pressure, such that the incident X-ray image-e.g. of object 15-is wholly absorbed in ionizing the gas, the resulting charged particles being drawn to the electrodes, and forming the charge image, by a potential difference applied thereacross. The dielectric sheet 32 is of a flexible plastics material and, to maintain the charge image thereon upon removal of the sheet from the tube-e.g. for processing by a xerographic printer-a conductive layer is provided in or on the sheet, or a volatile conductive liquid such as alcohol is used to adhere the sheet to the electrode. As shown, the envelope includes an openable hinged cover portion 21 formed of, or, as shown, containing a window 41 of, beryllium, and the gas filling may include up to 10% methane as quenchant, at 10 atmospheres or higher pressure, and preferably in the pressure range 150 to 1500 p.s.i.g. The electrode gap is 0À25 to 5 mm., and the product of electrode gap and pressure lies in the range 10 to 200, and preferably 20 to 80, mm. atmospheres, the applied voltage being 1 to several kilovolts, and preferably chosen so that operation is on the plateau of the Townsend curve. That electrode through which the X-ray image is incident on the tube is of Al, Mg, Be, or carbon fibre sheet, and the other electrode of Al or steel, and the two electrodes may be curved (Figs. 5 and 6, not shown).