A detailed reappraisal of the computer modelling of the rare-earth fluorides is presented. A new set of interionic potentials is obtained by empirical fitting to crystal structural data alone. These potentials are then tested by calculation of elastic and dielectric constants, whose values agree favourably with those measured experimentally. Calculations are then presented of the basic defect formation energies for each material, and predictions of the expected type of intrinsic disorder made.

A computational study of is presented. Interionic potentials are fitted to experimental data and the resulting potentials used to calculate the defect behaviour. Energies of formation of basic defects are obtained and used to predict intrinsic disorder and to calculate activation energies for ion migration. This information is used to suggest the possible mechanisms involved in the ionic conductivity of the material.

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The aim of the present work is to investigate the possibility of using the properties of the thermoluminescent emission (TL) of Brazilian natural topaz for dosimetric applications. Topaz is an aluminium fluorsilicate with general composition of Al2(SiO4)(F,OH)2 found with relative abundance in Brazil and in other parts of the world. Topaz from Santo Antonio do Jacinto, Minas Gerais. Brazil, was used in this work, in the form of pellets of topaz mixed with Teflon and composites made with topaz embedded in a glass matrix. The TL sensitivity was tested between 10(-4) and 10(4) Gy. The TL peak intensity increases with the dose before saturation, which occurs around 2 kGy. The peak intensity showed a strong dependence with radiation energy. The effect of visible light and the behaviour of the TL signals after successive irradiation-reading-annealing cycles are presented and discussed.

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In this work we investigate the effect of gamma and ultraviolet radiations on the thermoluminescence of Brazilian calcite. The irradiated samples presented three TL peaks at 150, 245 and 320 o C (at a linear heating rate of 1.8 o C/s), with a main emission band centered at 615nm due to the 4 G → 6 S transition of the Mn 2+ . The irradiated samples presented, besides the Mn 2+ signals, three lines related related to carbonate groups. The thermal treatment and the irradiation effects on the ESR signal lead to the conclusion that (CO3) 3− , stabilized in two different symmetries, and the (CO2) − ions are the electron trapping centers. It was found that the TL peaks follows a t −1 decay as a function of the UV illumination time. An alternative model for the TL emission of calcite is discussed, considering that the recombination of charges is processed via a thermally assisted tunnelling mechanism.

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Doping of BaLiF3 by rare-earth ions is considered using computer modelling techniques. Solution energies for a range of possible doping mechanisms are calculated, and predictions made of doping sites and charge-compensation schemes. It is shown that there are definite trends going along the rare-earth series. Comparisons with experimental measurements are made where these are available.