APPARATUS FOR PRODUCING AND RECORDING DIFFRACTION PATTERNS

1,209,788. X-ray diffraction apparatus. COMMISSARIAT A L'ENERGIE ATOMIQUE. 14 Dec., 1967 [14 Dec., 1966], No. 56762/67. Heading H5R. In a diffraction apparatus a collimator 32 directs a beam of X or gamma radiation from source 30 towards a crystal 34 in holder 36; the undeviated beam is stopped by trap 40 from reaching the gas-type detector 20, but the diffracted beam, for example 42, impinges on a cathode member 24 of detector 20. The Xray or #-ray photon enters the space between cathode 24 and an auxiliary grid electrode 26, here electrons produced by the ionisation of the gas in the detector migrate towards and through the auxiliary electrode 26 and enter the space between the auxiliary electrode 26 and the anode 28. Between these electrodes, the potential is sufficient to produce avalanche phenomena, which phenomena produce in the gap an image of the diffraction pattern of the crystal which image is recorded photographically e.g. on camera 46 or electronically via an image intensifier and TV system (Fig. 3, not shown). For photographic recording, the potential between 26 and 28 is such as to produce sparks between the two electrodes, and the anode 28 may be transparent and/or coated a layer of a luminous substance having a persistence of one second, the spark pattern being photographed for example through transparent wall 25. Alternatively the voltage between 26 and 28 is selected to avoid the formation of sparks and the image due to the avalanche phenomena is projected on to the photocathode of an image intensifier and thence to a TV tube. The cathode of the detector e.g. 24 is preferably a beryllium window.