Single Crystal LiF Thermoluminescence Dosemeters

Abstract

Abstract Commercial Thermoluminescence dosemeters (TLDs) currently used are finely powdered lithium fluoride (LiF), calcium sulphate or magnesium silicate etc. sealed in glass tubes or those melted with special resins. These are opaque or semi-transparent and therefore thermoluminescence light emitted inside does not come out efficiently due to the self-absorption. To avoid the self-absorption LiF single crystals have been examined. A cylindrical graphite crucible including LiF mixed with trace amounts of magnesium, copper and phosphorus was heated in a vacuum stainless tube with a slowly moving heater coil along the axis. The LiF single crystal grew gradually from the bottom tip of the crucible. Thermoluminescence emitted from a LiF single crystal after irradiation with ? rays increased as phosphorus in the LiF crystal increased. Thermoluminescence emitted from a single crystal with 0.25 mole percent phosphorus was one order higher than that emitted from powdered LiF with the same mole percent phosphorus and the same weight. A single crystal could not grow with phosphorus of more than 0.25 mole percent. However, lithium phosphate appears to be a better activator material than the ammonium phosphate used in our experiments to overcome this 0.25 mole percent barrier.