Abstract
Fluorapatite [Ca10(PO4)6F2] is a mineral of the apatite group of the highest occurrence in the world among phosphates. The material is known for its diverse luminescent properties, as fluorescent lamps and lasers. The thermoluminescence (TL) signal of apatite from various origins has been investigated in the past years, mainly of the Mexican origin. In this work, the objective was to investigate the TL of samples of the Brazilian natural fluorapatites submitted to beta-ionizing radiation. The chemical composition of the samples was obtained by the technique of X-ray fluorescence and the electronic transitions were verified by optical absorption in the visible region. The mineral presented a wide optical absorption band between 500 nm and 750 nm, typical of fluorapatite, and SEM/EDS showed a high percentage of purity. The registered Raman spectrum exhibits the characteristics modes from the PO43− tetrahedra, observed in fluorapatite, and a band at 1103 cm−1 characteristic of the (CaO3)2- carbonate group. The TL measurements were carried out using a commercial Risø TL/OSL reader, model DA-20, equipped with a built in 90Sr/90Y beta source, with different radiation doses (1–5 Gy). The TL glow curve showed three peaks located at about 350 K, 470 K and 570 K (heating rate of 1 K/s). The activation energy and the frequency factor associated with each peak were determined by different methods. In addition, the TL response (area under the peaks) has shown linear behavior in relation to the doses.
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