Cryst. Res. Technol. 39, No. 10, 849 – 854 (2004) / DOI 10.1002/crat.200310264 © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Purification and crystal growth of TlBr for application as a radiation detector I. B. Oliveira* 1 , J. F. D. Chubaci 2 , M. J. A. Armelin 3 , and M. M. Hamada 1 1 CTR, IPEN-CNEN/SP, São Paulo, Brazil 2 LACIFID, Physics Institute, São Paulo, Brazil 3 CRPq, IPEN-CNEN/SP, São Paulo, Brazil Received 4 December 2003, revised 13 January 2004, accepted 25 February 2004 Published online 1 September 2004 Key words thallium bromide crystals, zone refining, Bridgman’s method, radiation detector. PACS 29.40.-Wk Thallium bromide is a semiconductor compound with high atomic number and density. It has a CsCl-type simple cubic crystal structure and it is non-hygroscopics. The TlBr crystals are relatively soft with a knoop hardness number of 12. In this work, the TlBr commercial powder was purified by zone refining and the purest material section was used for crystal growth by Bridgman method. Efforts have been concentrated on the purification of the TlBr. The purification efficiency has been evaluated (NAA and ICP-MS) by impurities reduction results after zone refining passes. The crystalline quality was evaluated by X-ray diffraction. The characterized TlBr crystal as a detector has shown good response to gamma radiation. © 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 Introduction Thallium bromide has been the subject of many investigations due to its specific technological features, for instance, its large applicability, at room temperature, as an X- and gamma-ray semiconductor detector and photodetector coupled to scintillator crystals. The development of these devices requires good quality substrates [1]. The common denominator for the room temperature semiconductors, is the difficulty of growing highly crystallographic perfect crystals having high chemical purity and exact stoichiometry [2]. Thallium bromide is a high atomic number semiconductor compound (Z Tl =81, Z Br =35) with a high density (7.5g/cm 3 ) and excellent gamma ray stopping power [3], which makes it very attractive for applications as a radiation detector. TlBr has a CsCl-type simple cubic crystal structure [4] and it is non-hygroscopics [3]. The low melting point (480ºC) and unique solid phase of TlBr are advantageous for melt purification and crystal growth[5]. TlBr crystals are relatively soft with a knoop hardness number of 12 [1,6]. This is important from the viewpoint of device processing, because a soft semiconductor requires more carefull handling techniques. Since all thallium compounds are toxic and as thallium is rapidly absorbed through all exposed epithelia, it is essential that the correct precautions should be observed during handling and use. Several studies [7,8] have been carried out about the preparation of the TlBr semiconductor and progresses have been made by the improvement of the purification and crystal growth techniques. Hitomi et al. [5,8] have demonstrated that TlBr crystals properly purified by zone refining and subsequently grown from the melt present spectrometry with excellent energetic resolution for X and gamma-rays. It is known that the radiation detector quality is extremely dependent on the crystal purity [9]. The purification efficiency of the material can be evaluated by the reduction of the traces impurities, in function zone refining passes. The impurity migration efficiency is characterized by a parameter k named as ____________________ * Corresponding author: e-mail: ibolivei@ipen.br