Radiation Detectors on Base of TlBr Crystal
Development of Single Crystal TlBr Radiation Detectors (Thallium Bromide)
Tech Area / Field
- INS-DET/Detection Devices/Instrumentation
- PHY-SSP/Solid State Physics/Physics
8 Project completed
Senior Project Manager
Lapidus O V
Institute of Physical-Technical Problems, Russia, Moscow reg., Dubna
- State Research and Design Institute of Rare-Metal Industry, Russia, Moscow
- Brookhaven National Laboratory, USA, NY, Upton\nBubble Technology Industries Inc., Canada, ON, Chalk River
Project summaryThe goal of this project is to develop, investigate, and determine the areas of application of the non-cooled single crystal TlBr x-ray and g-radiation detectors.
Development and manufacturing of detectors are very important for technological advancement and wide spread application of the nuclear-physical diagnostics and monitoring methods in the areas like nuclear power, geology, medical and industrial tomography, therapeutic radiology, astrophysics, crime detection, etc.
In the last few years, considerable interest was attracted to TlBr crystals. This compound is highly effective for detecting x-ray and g radiation (the atomic numbers of the component elements are 81 and 35), possesses considerable density (7,5 g/cm3) and wide energy gap (2,68 eV), which ensures a very small inherent noise at room temperature.
TlBr crystals were mostly used in nonlinear optics and, thus, their manufacturing technique was determined by optic and not radiation parameters. It was not until recently that the progress in growth technology permitted to obtain chemically pure, structurally homogeneous crystals with electric-physical parameters (specific resistance and the product of lifetime of the carriers and their mobility) meeting the requirements to detector materials. In the laboratories of some countries pilot detecting structures were built with those crystals and the evaluation of their electric-physical and spectrometric parameters were performed. The best samples possessed the resistance 5×1010÷2×1011 Om×cm and the product of the lifetime of electrons and holes lied within the range of 10-6÷10-4 cm2/V. It has been shown that these detectors can perform the spectrometry of x-ray and g radiation within the wide energy range.
However, the techniques known from the foreign publications (multiple zone melting, film sputtering from the gas phase, etc.) do not permit to obtain single crystals with the active face more than few mm2, and in addition, these crystals are very inhomogeneous. This makes the manufacturing of discrete detectors technologically difficult and expensive and makes practically unfeasible the manufacturing of matrix detectors.
The team of the Project are the technologists, successfully developing a technology of growth of high quality TlBr single crystals up to 30 mm in diameter with high probability of homogeneity of electrophysical and optical properties, the physicists-technologists experienced in development and investigation of wide-zone semiconductor detectors (C, GaAs, HgI2) and application of these detectors in various fields.
The tasks of the project will be solved in four stages.
The first stage comprises perfection of purity and growth technology of TlBr single crystals by the Bridgeman-Stockbarger method, creation of back-feed between the crystal growth regimes and electrophysical properties determining detector operation. At the same time, pilot detecting structures are to be built and their spectrometric and radiometric properties evaluated.
The second stage involves development of technology of mounting stable ohm contacts, fabrication and study of a pilot lot of discrete and matrix structures, and preparation of technical documentation for updated installation of TlBr crystal growth using the Bridgeman-Stockbarger method.
The third stage includes preparation, mounting, and setting into operation of the upgraded growth installation, study of the influence of crystal electrophysical properties on the detector parameters, and study of the nature and characteristics of the polarization effect.
And, finally, the fourth stage plans the development of methods of detector depolarization, preparation of pilot detecting units (DU) with TlBr detectors, and their testing at the biological and geological facilities.
It is assumed that the fulfillment of the project will yield the perfect technology of growth of pure, structurally-perfect TlBr single crystals up to 40 mm in diameter, 100÷120 mm high, with r = 5×1010 ÷ 1011 Om×cm, (mt)e ≥ 5×10-5 cm2/V, and (mt)h ≥ 10-6 cm2/V. Using those crystals the detecting units will be built, operating at room or close-to-room temperatures, with energy resolution <600 eV on the line 5,9 keV; <3,0 keV on the line 59,6 keV; and ≤30 keV on the line 662 keV. In conclusion, it is planned to test TlBr detectors at the biological facilities as counters of human radiation (CHR) for local determination of radionuclides, incorporated into the organism, and for prompt analysis of polymetallic ores.
The feasibility of the Project is based on the fact that the performers of the Project possess certain novel developments in growth technology of perfect TlBr crystals as well as some experience in development of non-cooled semiconductor detectors on wide-zone materials. Different groups of scientists and experts are involved in the Project, among them those, dealing with military research (determination of parameters of nuclear explosion, radiation monitoring, development of IR guidance system, etc.).
During the work within the Project, consultations and contacts with collaborator organizations are planned (Los Alamos National Laboratory and others).