TlBr raw material purification, crystal growth, annealing, detector fabrication and characterisation for gamma-ray detector applications

The research reported in this thesis dealt with single crystals of thallium bromide grown for gamma-ray detector applications. The crystals were used to fabricate room temperature gamma-ray detectors. Routinely produced TlBr detectors often are poor quality. Therefore, this study concentrated on developing the manufacturing processes for TlBr detectors and methods of characterisation that can be used for optimisation of TlBr purity and crystal quality. The processes under concern were TlBr raw material purification, crystal growth, annealing and detector fabrication. The study focused on single crystals of TlBr grown from material purified by a hydrothermal recrystallisation method. In addition, hydrothermal conditions for synthesis, recrystallisation, crystal growth and annealing of TlBr crystals were examined. The final manufacturing process presented in this thesis deals with TlBr material purified by the Bridgman method. Then, material is hydrothermally recrystallised in pure water. A travelling molten zone (TMZ) method is used for additional purification of the recrystallised product and then for the final crystal growth. Subsequent processing is similar to that described in the literature. In this thesis, literature on improving quality of TlBr material/crystal and detector performance is reviewed. Aging aspects as well as the influence of different factors (temperature, time, electrode material and so on) on detector stability are considered and examined. The results of the process development are summarised and discussed. This thesis shows the considerable improvement in the charge carrier properties of a detector due to additional purification by hydrothermal recrystallisation. As an example, a thick (4 mm) TlBr detector produced by the process was fabricated and found to operate successfully in gamma-ray detection, confirming the validity of the proposed purification and technological steps. However, for the complete improvement of detector performance, further developments in crystal growth are required. The detector manufacturing process was optimized by characterisation of material and crystals using methods such as X-ray diffraction (XRD), polarisation microscopy, high-resolution inductively coupled plasma mass (HR-ICPM), Fourier transform infrared (FTIR), ultraviolet and visual (UV-Vis) spectroscopy, field emission scanning electron microscope (FESEM) and energy-dispersive X-ray spectroscopy (EDS), current-voltage (I-V) and capacity voltage (CV) characterisation, and photoconductivity, as well direct detector examination.

Purificação do brometo de tálio pelo refino zonal e análise da segregação das impurezas

Desde o conhecimento da radiação e seus efeitos a necessidade de mensurá-la intriga os cientistas. Os detectores de radiação mais difundidos atualmente fazem o uso de cristais semicondutores. Porém, esses detectores tem uma temperatura ótima de funcionamento que acaba sendo ultrapassada, já que o processo gera calor. Por isso, o resfriamento acaba sendo uma necessidade. O desenvolvimento de detectores de radiação com cristal semicondutor que opere a temperatura ambiente é tema de muitos estudos, já que evitaria o processo de resfriamento, trabalhoso e de alto custo. No Centro de Tecnologia das Radiações (CTR) do Instituto de Pesquisas Energéticas e Nucleares (IPEN) o sal de Brometo de Tálio (TlBr) é estudado para esta finalidade. Até ser um cristal semicondutor este sal deve passar por vários processos, entre eles o de purificação e o de cristalização. A técnica utilizada para purificar este cristal é a de Refino zonal. Após ser purificado por esta técnica o sal estará apto a ser cristalizado e consequentemente integrar um equipamento de detecção de radiação. Portanto, esta monografia teve como objetivo realizar a análise da segregação das impurezas do sal de TlBr através da técnica de espectroscopia de massa em fonte de plasma induzido (ICP-MS) e espectroscopia de emissão atômica (ICP-AES). Determinando assim se o mesmo está apto a ser cristalizado e vir a compor um detector de radiação

Thallium Bromide Deposited Using Spray Coating

Spray coating was used to produce thallium bromide samples on glass substrates. The influence of several fabrication parameters on the final structural properties of the samples was investigated. Substrate position, substrate temperature, solution concentration, carrying gas, and solution flow were varied systematically, the physical deposition mechanism involved in each case being discussed. Total deposition time of about 3.5 h can lead to 62-mu m-thick films, comprising completely packed micrometer-sized crystalline grains. X-ray diffraction and scanning electron microscopy were used to characterize the samples. On the basis of the experimental data, the optimum fabrication conditions were identified. The technique offers an alternative method for fast, cheap fabrication of large-area devices for the detection of high-energy radiation, i.e., X-rays and gamma-rays, in medical imaging.