GB1221823A - Thermoluminescent phosphor - Google Patents

Abstract

1,221,823. Luminescent materials and uses thereof. MATSUSHITA ELECTRIC INDUSTRIAL CO. Ltd. 27 Feb., 1968 [29 June, 1967; 28 Dec., 1967 (3)], No. 9492/68. Heading C4S. A thermoluminescent phosphor in a thermoluminescent radiation dosimeter for instance, comprises calcium sulphate as the principal constituent and at least one activator selected from Dy, Tm, Tb, and Pr and in amount 0À005 to 0À5 mol. per cent for instance. Triboluminescence is almost absent. The phosphor may be encapsulated as powder (e.g. 10 to 150 micron size) in polyethylene, fluorine resin or glass (Figs. 4 and 5, not shown) and in an Al container. Glasses should be non-fluorescent and of low melting point and boron, zinc oxide or lead oxide types only, the capsules being 0À2 to 0À5 mm. deep and the mix hot-pressed at 500‹ to 600‹ C. In the case of lead glass, the element should be as thin as 0À5 mm. to reduce radio-active radiation absorption. Resins should be heat-resistant at 300‹ C. or more and very transparent to U.V. and visible radiation; epoxy resins fluorescing at 100‹ C. or above and silicon resins being of low viscosity at high temperature are not suitable. Fluorine resins are preferred and include poly-tetra-fluoroethylene, the copolymer of tetra-fluoro-ethylene and hexa-fluoro-propylene poly-monochloro-trifluoro-ethylene, and poly-hexa-fluoro-ethylene and the mix may be cold-pressed at 280‹ to 420‹ C. The CaSO 4 crystallites are 0À01 to 0À3 mm. in grading and mixtures are equal parts by weight phosphor and encapsulating medium. In preparing the phosphor, calcium sulphate and the activators are added to hot concentrated sulphuric acid and the sulphuric acid is vaporized to recrystallize the sulphate. Doses specified are of visible and U.V. light, radio-active emanations and electrons. The main glow peaks and secondary peaks at specific temperatures are given for particular embodiments, e.g. for CaSO 4 : Dy heated at 30‹ C./min., the peak occurs at 210‹ C. and accumulated absorbed radiation may be removed by heating at 400‹ to 700‹ C. CaSO 4 : Tm peaks at 215‹ C. with a secondary peak at 100‹ C. Applications to health physics and measurements of small doses are mentioned. Reference is made to prior art CaF 2 [Mn]; CaSO 4 [Mn] and LiF phosphors.