Abstract:
The current response of a TlBr detector to $^{137}$Cs $\gamma$-ray radiation has been studied in the dose-rate range 0.033–3.84 Gy/min and within the voltage range 1–300 V; the detectors are based on pure and doped TlBr crystals grown from the melt by the Bridgman-Stockbarger method. The mass fraction of Pb or Ca introduced into the TlBr crystals was 1–10 ppm for Pb and 150 ppm for Ca. The current response of nominally undoped TlBr samples was nearly linear over two decades of studied dose rates. Deep hole levels associated with cationic vacancies $V^-_c$ determine the dependence of the current response on the voltage in the high electric fields. The parameters of the carriers’ transport $\mu\tau$ are determined. The TlBr crystals grown in vacuum and in the bromine vapor exhibit a large mobility-lifetime product of 4.3 $\times$ 10$^{-4}$ and 6.4 $\times$ 10$^{-5}$ cm$^2$V$^{-1}$, respectively. The value of $\mu\tau$ is in the range (4–9) $\times$ 10$^{-5}$ cm$^2$V$^{-1}$ for crystals doped with a divalent cation.
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