Development of CaSO4:TR,Li (TR = Tm, Eu, Tb) composites for beta radiation dosimetry by means of luminescent techniques

Abstract

The study of new dosimetric materials for investigations in ionizing radiation dosimetry is extremely important to provide sensitive and low-cost detectors. Thus, this work proposed the development of CaSO4:Tm,Li, CaSO4:Tb,Li and CaSO4:Eu,Li composites for application in beta radiation dosimetry, using luminescent techniques such as thermoluminescence (TL) and optically stimulated luminescence (OSL). The CaSO4 crystals were produced by the adapted slow evaporation route and characterized using X-ray diffraction (XRD), radioluminescence, TL and OSL techniques. XRD analyses showed that the doped CaSO4 samples presented a single phase, with orthorhombic symmetry. The CaSO4:Eu,Li composites showed TL signals between 100°C and 200°C, with peaks around 145°C and 180°C. The CaSO4:Tb,Li and CaSO4:Tm,Li composites showed TL signals between 100 ºC and 350 ºC, with peaks around 165 ºC and 275 °C. All samples were irradiated with a 90Sr/90Y source from the TL/OSL Risø reader. For the CaSO4:Tb and CaSO4:Tm samples, the addition of lithium as co-dopant resulted into a significant increase (2x) in the total TL signal of the samples. The CaSO4:Tm,Li samples presented a very intense OSL signal, about 80x greater than the signal of the other samples produced. This allows the applicability of TL/OSL detectors even more sensitives. The OSL decay of the CaSO4:Eu,Li and CaSO4:Tb,Li samples is dominated by a fast decay while the OSL signal of CaSO4:Tm,Li composites decays slowly and remains stored for a long time. The TL emission spectra of the samples showed typical emissions of Eu2+ ions (280 nm), Eu3+ (614 nm), Tb3+ (544 nm) and Tm3+ (455 nm). As no emission corresponding to lithium was identified in the emission spectra, it can be assumed that lithium acts as a capture center and transfers its energy to the nearby TR3+, which increases the emission intensity. All the samples produced showed linearity in the dose range used, good reproducibility, with variations below 10%, and minimum detectable doses of the order of micrograys. The evaluated dosimetric characteristics denote that the developed composites have potential application as TL/OSL dosimeters.