The sensitivity of pure and doped TlBr crystals

The sensivity of TlBr detectors to ¹³⁷Cs gamma-ray in dose rate range from 0,033 Gy/min to 3,84 Gy/min has studied in current mode. The pure and doped crystals have grown by the Bridgman-Stockbarger technique in various atmospheres: vacuum, in the vapor of bromine, in an atmosphere of hydrogen and air. Mass fraction of Pb or Ca introduced in the doped TlBr crystals was 1-10 ppm and 150 ppm respectively. The parameters of the carriers transport μτ have calculated. Photocurrent measurements performed on crystal TlBr have demonstrated high sensitivity to ¹³⁷Cs γ-radiation. The sensitivity of samples for all investigated crystals was in the range from 0,15×10^-6 C / Gy to 10×10^-6 C / Gy. Most specific sensitivity 9,0×10^-7 C / Gy mm² at a voltage of 10 V has been obtained on the samples made of pure crystals grown in vacuum, the value of μτ for these was found to be 4,3×10^-4 cm² V^-1. The growing atmosphere and the degree of doping have a significant impact on the sensitivity TlBr samples and the dependence of the photocurrent on dose rate. The results are explained by the formation of donor-acceptor pairs associated with cationic vacancies V_c^- and anionic V_a⁺ vacancies, as well as complexes {Pb²⁺ V_c^-}, controlling recombination in TlBr.