Development of a radiation detector from a Brazilian mineral

Full text: Alexandrite (BeAl₂O₄:Cr³⁺) is a mineral of the chrysoberyl species found in abundance in Brazil. It is expected to have potential as a natural dosimeter for ionizing radiation since its composition contains 19.8 wt % BeO and 80.2 wt % Al₂O₃, both oxides being commercially used as dosimeters. A new composite material, based on alexandrite powder dispersed in a fluorinated polymer, was developed in the form of pellets with 3 different proportions of alexandrite, being 50%, 40% and 20% of the mineral incorporated in the polymer matrix. Pellets had their effects evaluated as a function of exposure to ionizing radiation using the OSL technique, which is the process by which a previously irradiated material emits light when illuminated. The OSL measurements were performed using a Risø equipment (⁹⁰Sr/⁹⁰Y beta source). OSL emission was stimulated using blue light emitting diodes (470nm, FWHM = 20nm) delivering 80mW/cm² at the sample position in constant mode. The characteristics studied were dose-response (0.1 up to 5 Gy), reproducibility and fading. Results obtained with these pellets showed sensitivity in a large range of doses. In addition, the results showed that the OSL intensity signal varied linearly with the dose and that the OSL signal from the pellets remained stable at room temperature for 5 hours after irradiation. It was also noted that the shape of the OSL decay curve was independent of the radiation dose, an important characteristic for an OSL dosimetric material. Radioluminescence (RL) measurements were also performed, which revealed luminescent centers that can be attributed to Cr³⁺, and Fe³⁺ impurities. Finally, composites based on alexandrite powder were successfully fabricated and our results showed that alexandrite mineral is a promising natural material for OSL dosimetry. (author)