This paper describes the manufacturing process of quartz-pellets and shows their potential use as thermoluminescence dosimeters (TLD) for those applications where low-levels of ionising radiation are present. Two batches of cold-pressed pellets were produced and their resistance were evaluated by vibration tests and weight-loss measurements. The batch manufactured with 75 × 150 µm particles showed enough resistance to be employed as TLD. The dosimetric properties of the 310 °C peak appearing in the glow curves of these pellets were characterized together with commercial TLD-100 units using γ- and X-ray beams with different energies. The uncertainties related to reproducibility and stability of the TL signal were better than 10%. The sensitivity and the linearity of the TL response of quartz-pellets were better than that measured for TLD-100 for doses ranging from 0.5 to 200 mGy. The energy dependence of the quartz-pellets was higher than that of TLD-100 but it cannot be considered a restriction to their use in clinical procedures and industrial applications.

This work investigates the effect of particle size in the thermoluminescence (TL) response of a quartz crystal that was initially crushed and classified into ten size fractions between 38 μm and 5 mm. Aliquots of each size fraction were sensitized with a dose of 25 kGy of γ rays and heat-treatments at 400 °C. TL glow curves of sensitized and non-sensitized samples were recorded as a function of different test-doses of γ rays. For the non-sensitized samples, the TL peak near 325 °C increases with the decrease in particle size. In the case of sensitized samples, a strong TL peak near 300 °C increases with the increase in particle size up to mean grain size equal to 304 μm. Above 304 μm, an abrupt reduction in the TL intensity is noticed for the sensitized peak. These effects are discussed in relation to the specific surface area of quartz particles and the intensity of the electron paramagnetic resonance signal of the E'1 center induced by the sensitization process.

O objetivo desse trabalho foi caracterizar os defeitos pontuais relacionados aos grupos OH e H2O em quartzos e ametistas, crescidos em cavidades do tipo geodo em basalto da Formação Serra Geral (RS), usando a espectroscopia infravermelha (IV) a -175°C. Em um dos cristais, os espectros foram realizados separadamente nos setores de crescimento r{10<IMG SRC="/img/revistas/rem/v62n3/a050i01.gif" ALIGN="absmiddle">1} e z{01<IMG SRC="/img/revistas/rem/v62n3/a050i01.gif" ALIGN="absmiddle">1}. Na faixa entre 3800 e 3000 cm-1, os espectros apresentaram várias bandas de absorção superpostas a uma intensa banda larga. As bandas atribuídas ao defeito [H4O4]0 foram observadas independentemente da coloração dos cristais, enquanto que as bandas atribuídas ao centro [AlO4/H]0 ocorreram nos quartzos translúcido e levemente amarelado (citrino). Além da intensidade da banda larga, os espectros desses cristais se caracterizaram pela existência da banda a 3595 cm-1. Ao contrário do reportado por outros autores, verificou-se que a concentração de OH e H2O e a coloração violeta da ametista são maiores nos setores z do que nos setores r. Essa inversão foi discutida em função da não uniformidade das condições de crescimento, confirmada pelo tamanho das faces romboédricas do cristal. Concluiu-se que a intensidade da coloração da ametista não é afetada pelas altas concentrações de defeitos OH e H2O.

The aim of this study is to characterize OH-related defects in natural quartz and amethyst grown in geodic cavities formed during basaltic flow. For this, infrared (IR) spectroscopy at low temperature (-175°C) was carried out in amethyst and quartz crystals taken from two deposits located in the State of Rio Grande do Sul in Brazil. For one specimen, IR spectra were recorded directly upon the growth sectors r{10<IMG SRC="/img/revistas/rem/v62n3/a050i01.gif" ALIGN="absmiddle">1} and z{01<IMG SRC="/img/revistas/rem/v62n3/a050i01.gif" ALIGN="absmiddle">1} appearing in (0001) plates. IR spectra recorded from 3800 to 3000 cm-1 showed an intense broad band superposed upon sharp bands assigned to [H4O4]0 point defects. These bands were observed in all samples and growth sectors independently from the intensity of its violet color. On the other hand, sharp bands assigned to [AlO4/H]0 defects were observed only in translucent and pale citrine quartz and also in the colorless regions of r and z growth sectors in amethyst. Contrarily to previously reported data, it was observed that z growth sectors have the highest content of OH-related defects and the darkest violet color when compared to r sectors. This reversal relation was discussed taking into account the malformed habitus of the amethyst specimen probably caused by the anisotropic solution flow inside the geode. It was concluded that the amethyst color is independent of the concentration of OH-related defects. Besides the intense broad OH-band, the IR spectra of such crystals were characterized by the presence of a sharp band near 3595 cm-1.

Esse trabalho apresenta uma proposta para efetuar, em escala de laboratório, a separação do epídoto presente em estéreis da lavra de scheelita da Província da Borborema. Para tanto, um fragmento de rocha foi britado e classificado em três faixas granulométricas, entre 150 µm e 600 µm. A concentração do epídoto foi realizada em mesa vibratória, seguida de separação magnética usando o separador isodinâmico Franz. As frações magnética e não-magnética foram analisadas por difratometria e espectrometria por fluorescência de raios X. Para a faixa de 150 a 300 µm, foi possível efetuar a concentração do epídoto com um teor de 75% após quatro passagens pelo separador magnético usando correntes de 0,5 e 0,6 A, correspondendo a 0,5 e 0,6 T, respectivamente. Constatou-se que a fração de maior susceptibilidade magnética é constituída de andradita e que os principais contaminantes do concentrado de epídoto são a calcita, a andradita e o quartzo.

This paper presents a laboratory procedure to concentrate epidote from fragments associated with country rocks of the scheelite mineralization in the Borborema Province (Rio Grande do Norte, Brazil). A block weighting 17.5 kg was crushed and classified in grain sizes ranging from 150 to 600 µm. The concentration was carried out in a shaking table followed by four cycles of magnetic separation using a Frantz isodynamic separator with currents ranging from 0.5 and 0.6 A (0.5 to 0.6 T). The mineralogical characterization of the pre-concentrate and the fractions resultant from magnetic separation were carried out by X-ray powder diffractometry and X-ray fluorescence spectrometry. The separation of the epidote allowed close to 75% epidote for the 150x300 µm size class. The fraction with the highest magnetic susceptibility in the mineral assemblage was mainly composed of andradite. Calcite, andradite and quartz were found to be the contaminants within the concentrate.

In the present study, the morphology and the impurity distribution were investigated in growth sectors formed around the [0001] axis of synthetic quartz crystals. Plates containing cylindrical holes and cylindrical bars parallel to [0001] were prepared by ultrasonic machining and further used as seed-crystals. The hydrothermal growth of synthetic quartz was carried out in a commercial autoclave under NaOH solution during 50 days. The morphologies of crystals grown from cylindrical seeds were characterized by X-ray diffraction topography. For both types of crystals, +X- and X- growth sectors were distinctly observed. Infrared spectroscopy and ionizing radiation were adopted to reveal the distribution of point defects related to Si-Al substitution and OH-species. It was found a different distribution of Al-related centers in relation to the crystals grown from conventional Y-bar and Z-plate seeds.