Patent GB-1025322-A (GB)
Title: Radiation sources
IPC: G21G4/02
Filed: 1962-10-04
Abstract: 1,025,322. Radio-active materials. MINNESOTA MINING & MANUFACTURING CO. Oct. 4, 1962 [Oct. 4, 1961], No. 37656/62. Heading G6R. A radiation source comprises a solid isotope dispersed in or integral with a ceramic carrier and an external ceramic shield therefor which is permeable to the isotope radiation, there being a barrier layer between the carrier and the ceramic shield which is bonded to the shield. Sources of alpha, beta, gamma and bremsstrahlung radiation are described, and in all the embodiments the radiation source is fixedly mounted on a stainless steel, aluminium, polyethylene or polystyrene base prior to the ceramic shield being applied. Two basic methods of encasing the isotope are described; in both methods the isotope material comprises microspheres of under 600 microns diameter of leached zirconium phosphate glass which absorb the isotope from an aqueous solution, and are then fired to fix the absorbed isotopes in the microspheres. In the first method the microspheres are encapsulated in a tube, forming the barrier, and in the second method they are individually coated with barrier material. The sources are suitable for use in industrial furnaces and are readily sterilizable for medical use. Tube encapsulated sources.-Depending on the type of radiation required from the source, the tube material may be copper, brass, iron, beryllium, steel, aluminium, stainless steel, lead, gold, platinum, magnesium, graphite, ceramics or uranium. The materials of high atomic weight are used in bremsstrahlung sources. The method of manufacturing entubed sources is succinctly described in Fig. 1, and the following notes merely give further details of some of the operations. The particulate ceramic, tube and loading apparatus are heated prior to loading to drive off moisture and the tube loading end closed by crimping. The loading apparatus is placed on a vibrator to assist packing of the particles. The completed tube may be bent to any required shape and is then placed in a correspondingly shaped groove in the base. If a 180-degree field of radiation is required, then the tube is mounted on the base surface. The silver soldering of the tube to the base also provides additional sealing of the tube ends. The enamel applied to the source base and exposed parts of the tube after roughening of these surfaces may be a sprayed porcelain enamel. The ceramic chosen has a composition 95% and preferably 79% of which comprises elements having an atomic number less than 23; an example given is 50-70% SiO2, 10-40% TiO2, 0-10% Na2O, 0-10% K2O, 0-10% CaO and 0-5% CoO. The ceramic should have an expansion coefficient similar to the base material chosen. Fig. 11 shows a cross-section of the completed source. In the manufacture of low bremsstrahlung sources, the tube is staked to the base; the bremsstrahlung generator may be gold powder intimately mixed with the microspheres in the tube, or the tube itself may be made just thick enough to absorb the highest energy beta particle produced. Planar sources may be made by mounting a series of parallel tubes on a common base. Sources formed from individually coated microspheres.-The individual microspheres already described may be nickel coated by electrolytic or non electrolytic processes. This method is particularly suitable for forming alpha radiation point and line sources. The source material is bonded in the required pattern, with or without insetting, to the base and an outer coating of ceramic or organic polymer applied.