GB792071A - Improvements in or relating to scintillation material and methods of making same - Google Patents

Abstract

792,071. Luminescent materials. ARMOUR RESEARCH FOUNDATION OF ILLINOIS INSTITUTE OF TECHNOLOGY. Feb. 7, 1956 [Feb. 24, 1955], No. 3843/56. Class 39(1). Scintillation phosphor material comprises an autogenously bonded polycrystalline compact of a host compound and an activator. A mixed crystal may be crystallized from a solution of an activator in a molten mass of the host crystals, e.g., thallium chloride or iodide crystals are added to fused sodium iodide or lithium iodide. The mixture is cooled and the mixed crystals are further sub-divided by grinding and then compacted in a device as in Fig. 2 comprising a base plate 18, top plate 19 and body 17, seal rings 21, 22 of resilient material, split cones 24, 25 and a reciprocating plunger 28. A further sealing ring 30 and a helical returns spring 31 are provided round the neck of the plunger. Pressures of 120,000 lbs./sq. in. can be applied. A bore 36 connects the moulding cavity to a source of reduced pressure so as to eliminate vacuum spaces between the crystals and prevent hydrolysis. The mixed crystals may also be formed by dissolving in a solvent and evaporating ; or a solution of host and activator compounds in a mixture of acetone and dry ice is rapidly cooled, subjected to freeze drying and dried over dessicating material. Cadmium sulphide crystals containing excess cadmium, naphthalene or anthracene may be similarly compacted. In a further method, microcrystalline particles of the host and the activator are compacted and heat treated to cause solid state diffusion. Zinc sulphide with a salt of silver, copper or manganese and a flux, e.g., sodium chloride, may be treated in this manner at a temperature below the melting point of the phosphor. The content of thallium in NaI/Tl may be 0À005-1 per cent, preferably 0À1 per cent.