Thermoluminescence of natural BeAl₂O₄:Cr³⁺ Brazilian mineral: Preliminary studies

Alexandrite (BeAl₂O₄:Cr³⁺) is a variety of the chrysoberyl mineral widely found in Brazil. This mineral is expected to have potential as a natural dosimeter since its composition contains 19.8 wt% BeO and 80.2 wt% Al₂O₃, both oxides being commercially used as dosimeters. We report the investigation of thermoluminescence (TL) properties from alexandrite in natural form. Samples 1.0 mm-thick and mass of 0.045 g were cut of a stone originated in Bahia, Brazil. Sample composition was determined through x-ray fluorescence and scanning electron microscopy/energy dispersive x-ray spectroscopy measurements. Irradiations were performed at room temperature using a ⁹⁰Sr/⁹⁰Y beta source of the Riso TL reader (dose rate = 10 mGy/s). TL measurements were made at 5 °C/s within the dose range from 1 to 50 Gy. The glow curve consists of a dominant peak at 350 °C and three additional peaks at 110, 160 and 280 °C. Results showed that the TL signal increases linearly with beta irradiation dose. Our results suggest that Fe and Cr ions together with the presence of secondary phases such as mica and apatite play important roles in the TL process. Based on the linearity of the TL response, we conclude that alexandrite shows potential for use in dosimetry.