GB1159609A - Amplification of Gas-Detector Images - Google Patents

Abstract

1,159,609. Detecting radiation. COMMISSARIAT A L'ENERGIE ATOMIQUE. 16 Nov., 1966 [27 Nov., 1965], No. 51368/66. Heading H5R. A gas-filled radiation detector is operated so that instead of an incident particle or photon of radiation producing a spark, the voltage between the electrodes is reduced to a level such that the incident photon produces an avalanche of electrons without the spark, and the slight luminosity of these phenomena are intensified via a standard photo - electric image intensifier, and the resulting image recorded, e.g. with a photographic camera. In a preferred embodiment (Fig. 2) a radioactive source 16 shielded by a plate 18 is placed in front of a detector A which consists of a sealed chamber containing a thin metallic cathode 6, e.g. a strip of Al foil, an auxiliary electrode 12, in the form of a metallic grid, and a transparent anode 14 having a conductive surface, e.g. a mesh or a conductive glass, all these electrodes being parallel to each other, the chamber being gas-filled, e.g. with a mixture of xenon and methylol having partial pressures of 730 and 30 torr respectively. The cathode 6 is supported by a metal plate 10, having perforations which effectively collimate the beam from source 16, and the chamber has a transparent top closure so the interior is visible. The cathode and plate 10 are at ground potential, whilst auxiliary electrode 12 and anode 14 are respectively coupled to a low voltage source and a high voltage source B.T. and H.T. through resistors 20 and 22. A photon from source 16 incident on cathode 6 gives rise to electrons which pass through grid 12 to initiate avalanche phenomena in the gap, given a suitable potential. The slight luminosity of these phenomena is amplified in an image intensifier being focused on the photo-cathode thereof by lens 30. The resulting intense image on screen 32 may be photographed with camera 24.