José Fernandes de Lima

Influence of thermal treatment on the Raman, infrared and TL responses of natural topaz

Abstract Analyses of thermoluminescence (TL) and thermally stimulated exoelectron emission have proved that the natural Brazilian topaz is a promising material for dosimetry of ionizing radiation. Topaz is an aluminum fluorosilicate with a general composition of Al 2 (SiO 4 )(F,OH) 2 whose main defect is the presence of OH − groups substituting for the F − ions. Analyses of topaz samples from Santo Antonio do Jacinto, MG, Brazil, showed that their TL responses are strongly affected by the temperature of pre-irradiation thermal treatment. This behavior was correlated to the changes observed in the infrared and Raman spectra and a model could be proposed for the charge trapping and recombination process in colourless topaz.

Thermoluminescence of brazilian topaz

Abstract Thermoluminiscence measurements were performed on samples of yellowish Brazilian Topaz from Acari, MG. Virgin samples revealed peaks 2 and 4 at about 150 and 300°C. respectively, while in samples with extra dose of y-rays, we observed another peak at 80°C. When topaz samples were thermally treated, peak 4 vanished and peak 3 at about 180°C, became visible. Isothermal decay of peak 2 performed on virgin samples showed that peak 3 is present on this samples too. The spectra of the first 3 peaks are very similar in the range of 350 to 500 nm indicating that the recombination processes related to these 3 peaks could be the same. The dose dependency of the TL intensity of the first 3 peaks was mesured from 0.5 to 400 Gy and it sems to start saturating above 400 Gy.

Evaluation of doses in radiotherapy using solid-state composites based on natural colourless topaz

The thermoluminescent properties of composites containing powdered topaz embedded in Teflon or glass were studied and compared with the corresponding properties of the well known TLD-100 commercial dosimeters. Relative sensitivity, TL fading, reproducibility of the sample preparation process, and possibility of re-utilisation of the dosimeters were investigated. Measurements of absorbed doses in simulated radiotherapy treatments were also taken. The irradiations were performed using gamma rays from a 60Co source in the dose range from 1cGy to 2Gy. The dosimeters were installed in badges and attached inside acrylic plates of various thicknesses in the radiation fields. The dose profiles obtained with this procedure are very similar to the ones obtained with equivalent tissues. It is concluded that these composites of natural colourless topaz crystals can be efficiently used as TL dosimeters.

The use of pellets of brazilian natural topaz as radiation dosimeters

Abstract The properties of the thermoluminescent emission (TL) and thermally stimulated exoelectron emission (TSEE) of pellets of colourless natural topaz samples from Santo Antonio do Jacinto, Minas Gerais, Brazil, were studied with the aim of use as solid state dosimeters. Standardized fields of 60Co, 137Cs, 241Am, 90Sr/90Y and X-rays were used for the tests. The TSEE and TL responses were studied as a function of the radiation energy (photons and particles) and as a function of the absorbed dose. The results indicate that colourless topaz from Minas Gerais, Brazil, is a promising material for dosimetric purposes.

Effects of ion implantation on the thermoluminescent properties of natural colourless topaz

Abstract Natural colourless topaz samples were implanted with different fluences of Cr + , Al + and Fe + ions. The thermoluminescence (TL) sensitivity to beta and gamma rays were tested and it was found that for Cr + implantations in the range of 10 14 –10 16 ions/cm 2 and for Al + in the range 10 14 –10 15 ions/cm 2 , the overall TL emissions of the samples were enhanced. The TL of the Fe + implanted samples, on the other hand, was reduced after implantation.

Computer modelling of intrinsic defects and migration processes in KY3F10

Abstract The computer modelling technique was used in the present work to study the intrinsic defects and the migration processes in KY3F10. The main intrinsic disorder was found to be F Frenkel pairs but at higher temperatures it is possible that KF pseudo-Schottky defects could also be present in the material. The ionic conduction process is mainly due to the fluorine ions migrating via both vacancy and interstitialcy mechanisms.

On the error in the activation energy obtained by the initial rise method for thermally stimulated processes in dielectrics

Abstract TL glow curves were computer simulated for Randall-Wilkins, Garlick-Gibson, May-Patridge and Adirovitch models in a range of activation energies (0.1 to 2.0 eV) which were afterwards recovered by the initial rise method. The systematic error of the recovered energies is always the same independent of the energy used in the simulated curves. It was found that there is no dependence of the error onto the heating rate and there is a dependence of error curves on the models used in computer simulated TL emission. A correction factor can be plotted against the percentage of the peak maxima used in the initial rise for each model and we could apply it even if more than 50% of the ascending part of the glow peak has to be considered.

Ionic transport in barium lithium fluoride

Abstract In this contribution we will report a study of the a.c. electrical conductivity of a variety of barium lithium fluoride crystals containing aliovalent dopants. The analysis of the results allows the evaluation of the defect energies. These will be compared with the results of the computer simulations.