Silver doped lithium tetraborate (Li2B4O7) single crystals as efficient dosimeter material with sub-micro-Gy sensitivity

Single crystals of Li2B4O7 (LTB) with varying Ag content were grown using the Czochralski technique and studied for their optical absorption, photo-luminescence (PL) and thermally stimulated luminescence (TSL) properties. The optimum Ag concentration in the LTB was found to be about 500 ppm for the best TSL properties. A TSL readout set-up has been described that uses a solar blind photo-multiplier tube (PMT) to match the emission from Ag which is in the UV region (peak at 270 nm). This has significantly improved the performance of the TSL set-up by lowering dark counts and enhancing the signal due to a better matching between the emission from Ag ions and PMT response. In addition, the use of the solar blind PMT also minimized the thermal noise generated from heating of sample in the TSL set-up. Radiation doses lower than 5 μGy could be measured using this set-up with small LTB:Ag crystal samples (100 mg). The lower detection limit has been estimated to be 500 nGy.