Red thermoluminescence of quartz and its application in dating archaeometallurgical slag

Slag is often the only relic of early pyrometallurgical processes. In archaeological research information about the age of slag deposits is needed and diflicult to obtain with traditional methods. Thermoluminescence has a great potential in this field, because the smelting process leads to a well defined resetting of the 'Luminescence Clock'. Metallurgical slag generally consists of many components, artificial secondary minerals, e.g. fayalite and glass phases usually being the dominant parts. Primary minerals, called relics, are also components or slag. Such a complex composition leads to large difficulties in palaeodose determation if the bulk slag is used. To overcome these problems defined phases of the slag have been separated. Palaeodose determination has been carried out on separated quartz fractions by 'Single Aliquot Regeneration' procedures using the 620 nm emission. The dose rate was determined by high-resolution gamma spectrometry. Alpha autoradiography was carried out to get information about the distribution of radionuclides. The study includes first dating results.     

Thermal shock of quartz lascas

As a pre-treatment to grinding, quartz lascas (crushed pieces) were thermally shocked into room-temperature water by quenching from temperatures between 50 and 800 °C. Comminuted particles exhibited two distinctive geometries, granular forT _q(quench) <T _c (573 °C) and needle-like whenT _q>T _c. The needle-like shapes become thinner and longer with increasing temperature aboveT _c. The differences in shape are believed to result from the differences in the crack generation patterns which are governed by the thermoelastic properties in the -phase and -phase of the quartz during the thermal shock process. Crack densities induced by the thermal shock were measured as a function ofT _q. For the temperature range of 200 °C<T _q<T _c andT _c<T _q<800 °C, the resulting crack densities were determined to be governed by the rate of crack nucleation, which is characterized by an Arrhenius-type equation. The activation energies associated with the crack nucleation rates for the two regions were determined to be 14 and 39 kJ mol^–1, respectively.     

Radiation effects in natural quartz crystals

Optically clear, as visually observed, natural quartz crystals of Brazilian and Arkansas origins, which exhibit Al–OH^?-centers in their as-received conditions, have been measured for their low temperature ESR spectra to see the presence of Al-hole centers. The ESR spectra revealed the presence of Al-hole centers in their as-received conditions. These centers showed an increase in their strength upon irradiation with a ⁶⁰C0 source. Such observations were exhibited by Al–OH^?-centers as noticed earlier. The crystals were thus noticed to exhibit the presence of Al–OH^?-centers and also Al-hole centers in their as-received conditions. The observations match with the results on cultured quartz where irradiation breaks away the Al-alkali centers into a mixture of Al–OH^?- and Al-hole centers. It is thus concluded that the natural crystals, which exhibit the presence of these centers in their as-received condition, have been irradiated in nature with a low dose.     

Thermal precipitation of silver nanoparticles and thermoluminescence in tellurite glasses

Silver metal and/or oxide precipitation of nanoparticles in thermally treated Ag-doped tellurite glasses was studied by optical absorption (OA) and transmission electron microscopy (TEM). The Lorentzian adjusted silver nanoparticles plasma resonance OA band was compared to the Drude model approach. The silver nanoparticles size distribution on the surface rather than in the bulk was determined by TEM. A model for the metallic silver precipitation is proposed. The characterization of the formation of silver nanoparticles was carried out with differential thermal analysis (DTA) to determine the glass transition temperature (Tg) and of crystallization (Tc). Previously γ-irradiated samples exhibited thermoluminescence (TL) peaks and the defect centers TeOHC, NBOHC and TeEC were identified by electron paramagnetic resonance (EPR), but no Ag⁰ signal was detected. The silver nanoparticles are known to introduce desired third-order optical nonlinearities in the composites, at wavelengths close to the characteristic surface-plasmon resonance of the metal precipitates. An increase of the glass density and refractive index with increasing AgNO₃ content was observed.     

Thermal stability of the thermoluminescence trap structure of bentonite

This work reports about the thermal stability of the blue thermoluminescence (TL) of a well-characterised natural bentonite from Almeria (Spain). The main interest of this clay, mainly composed of montmorillonite, is because of its application in the field of high-level radioactive waste (HLW) repository in deep-lying rocks. As observed in other aluminosilicates, bentonite exhibits a very complex structure of the emission spectra based on a wide broad maximum peaked at approximately 265 degrees C that can be associated to physico-chemical processes such as dehydroxylation processes, consecutive breaking linking of bonds, formation of hydrolysed ions and redox reactions. The thermal stability tests performed at different temperatures confirm a continuum in the distribution of traps. Hence, the glow curve analysis methods commonly used for synthetic materials based on single discrete traps cannot be applied for this material and the kinetic parameters were fitted assuming an exponential distribution of trapped electrons.     

石英纤维热损伤机制

通过TG/DSC和高温XRD对石英纤维的高温相转变行为进行了研究,通过高分辨SEM对经不同温度处理过的石英纤维的表面形貌进行了研究,并用抗拉强度实验机测量了这些石英纤维的抗拉强度。研究结果表明,低于1000℃ 处理的石英纤维热损伤可分为两个阶段: (1) 在低于600℃的热处理温度范围内,由于石英纤维表面处理剂的挥发 , 石英纤维直径逐渐减小,原来表面的裂纹、条状和圆形凸起等缺陷逐渐显露出来,导致石英纤维抗拉强度缓慢降低;(2) 在600～1000℃ 的热处理温度范围内 , 石英纤维表面处理剂挥发完毕,在热处理的升降温过程中,由于热应力的作用,表面的条状和圆形凸起开始剥落,造成一定数量的新的表面裂口和裂纹缺陷。温度越高,石英纤维表面的条状和圆形凸起剥落现象越明显,这是造成这一温度条件下石英纤维强度显著降低的主要因素之一。此外,结合TG/DSC和XRD的研究结果,石英纤维低于1000℃热处理后,虽然没有明显的相变化,但是晶体结构有序化程度提高,表面开始析出α-方石英并导致纤维表面形成一定数量的凸起缺陷,这也是导致高温处理后石英纤维热损伤的原因之一。      

Thermal behavior simulation of quartz resonators in an ovenenvironment

The fine performance of an ovenized oscillator is dependent on the thermal behavior of the quartz resonator, especially when there are thermal transients. In this paper, the thermal behavior of the quartz is simulated by a finite difference technique including nonlinearity as an effect of radiation. This method, based on the electrical analogs of the thermal parameters, provides an easy interaction with the electrical parameters of the oven control. A model fitting various resonator configurations, like a flat pack or a BVA resonator, is proposed. The temperature of the direct quartz environment is compared with a reference. It acts on the heating elements that are electronically driven into a closed loop. The simulation results obtained in practical situations are compared for various types of resonator assembly, in relation to heating and thermal loss parameters     

Characterisation of the thermally stimulated conductivity and thermoluminescence of natural topaz

Thermally stimulated conductivity (TSC) and thermoluminescence (TL) measurements were conducted to investigate the mechanisms of charge transfer and luminescence emission in natural samples of Brazilian topaz irradiated with beta particles from a 90Sr/90Y source or with a 1.75 MeV Van de Graaff electron beam. The luminescence and conductivity were simultaneously monitored during the heating of the samples, allowing direct comparison of the TL and TSC peaks. The results show that the three main TL peaks are accompanied by corresponding TSC peaks, usually shifted to higher temperatures. Comparison of the relative TL/TSC intensities of peaks 2 and 3 indicates that the process of thermal quenching of the luminescence is probably active, which is also supported by TL/TSC measurements at different heating rates. Results on the dose response of TL/TSC peaks also reveal an interesting feature: the TL intensity shows a monotonic increase with dose in the range of study (50 Gy-3 kGy) comprising a linear-supralinear-saturation characteristic, while the TSC peaks exhibit an increase from 50 Gy to 1 kGy, followed by a small decrease for doses greater than 1 kGy. This result is interpreted in terms of a model involving multiple traps and one recombination centre.     

Cleavage of natural and synthetic single crystal quartz

Fracture toughnesses of quartz single crystals of the natural Brazilian and both the hydroxide and carbonate synthetic varieties were measured for several low indice crystallographic planes. Although the synthetics appear to differ from the natural crystals, the results generally support the toughness isotropy of quartz, thus explaining the frequently observed conchoidal nature of macroscopic fractures. Differences are also noted relative to thermodynamic and fracture surface energy concepts.     

Thermal decomposition of natural dolomite

Thermal decomposition behaviour of dolomite sample has been studied by thermogravimetric (TG) measurements. Differential thermal analysis (DTA) curve of dolomite shows two peaks at 777·8°C and 834°C. The two endothermic peaks observed in dolomite are essentially due to decarbonation of dolomite and calcite, respectively. The TG data of the decomposition steps have also been analysed using various differential, difference-differential and integral methods, viz. Freeman-Carroll, Horowitz-Metzger, Coats-Redfern methods. Values of activation entropy, Arrhenius factor, and order of reaction have been approximated and compared. Measured activation energies vary between 97 and 147 kJ mol⁻¹. The large fluctuation in activation energy is attributed to the presence of impurities such as SiO₂, Al₂O₃, Fe₂O₃, Cl⁻ etc in the samples. FTIR and XRD analyses confirm the decomposition reaction. SEM observation of the heat-treated samples at 950°C shows cluster of grains, indicating the structural transformation.     

Thermal fatigue life of glass subjected to air blast quenching

Thermal fatigue life and thermal shock severity with soda-lime-silica glass rods subjected to air blast quenching were measured. On the basis of the data, the validity of prediction-formulae for thermal fatigue life under mechanical load which were previously derived was discussed. The data of thermal fatigue life proved the validity of the derived formulae for slow cooling conditions such by air blast quenching. Moreover, thermal stress induced on the glass rod subjected to air blast quenching was estimated as 22 MPa by using the formulae, and was in good agreement with the value which was calculated on the basis of heat diffusion theory (30 M Pa).     

Thermal decomposition of natural dolomite

We have studied thermal modification of natural dolomite chips, which has allowed us to optimize conditions for the preparation of supports for manganese oxide catalysts with appropriate physicochemical properties (elevated carbon dioxide partial pressure and calcination temperature no higher than 800°C).     

Models in thermoluminescence

The aim of this paper is to give a review of the main models of thermoluminescence, from the most simple postulated by Randal and Wilkins in 1945. After that, a computer simulation emphasizes some problems relative to the use of the models to describe the behaviour of the thermoluminescent glow curve. Some suggestions are also given for obtaining a correct interpretation from the experimental data.     

Sweeping and irradiation effects on hydroxyl defects in crystalline natural quartz

A study of electrodiffusion (sweeping) and irradiation effects on hydroxyl defects has been carried out on good quality optically clear natural quartz crystals. The crystals were of Arkansas and Brazilian origin which are used as starting material in hydrothermal synthesis of high purity cultured quartz crystals. In particular, various OH(- ) related point defects have been monitored using infrared absorption measurements in the 3100-3700 cm(-1) range. Our estimates from sweeping and irradiation results show that the Brazilian crystal had a much higher concentration of hydrogen than the Arkansas crystal. We have therefore designated the Brazilian crystal as "high-H" and Arkansas stone as "low-H" quartz. High- and low-H samples of natural quartz in three different conditions, unswept, Na-swept, and H-swept, were subjected to a sequence of low- and room-temperature irradiations that separate proton and alkali motion. Irradiation at 77 K reduces the strength of almost all the IR bands except the short-bond Al-OH(-) center. Warm up to room temperature results in significant recovery (85-95%). Al-OH(-) centers in natural quartz were found to exhibit irradiation characteristics similar to those of cultured quartz. For similar radiation doses (2 Mrad) the prominent bands, Li and H dependent at 3476 cm(-1) (designated as Li-n3a) and Na and H dependent at 3451 cm (-1) (designated as Na-n2a) showed a larger decay at 300 K-irradiation than at 77 K. The prominent H-dependent OH(-) band at 3468 cm(-1) (designated as H-n2a) did not show any depletion of peaks after 300 K-irradiation while the 77 K-irradiation reduced their strength to about 10% of the as-H-swept strength. The results have been discussed in terms of protons and alkali ions motion to shallow and deep traps and compared with cultured quartz.     

Usability of VTL from natural quartz grains for retrospective dosimetry

To develop retrospective dosimetry of unexpected radiation accident, basic studies on violet thermoluminescence (VTL) phenomena were conducted using natural quartz grains. All VTL glowcurves of as-received samples did not exhibit peaks <250 degrees C, although for artificially irradiated quartz samples there were VTL peaks in the temperature region <250 degrees C. Therefore, accident doses could be estimated without the interference of naturally accumulated doses by VTL measurements from natural quartz. The mean lives of VTL were evaluated by the various heating rates method and the range of values was found to be between some days and ten thousands of years depending on each peak. Especially, the mean life of VTL peak at 200 degrees C was years order. Furthermore, the lower detection limit was calculated to be tens of mGy from the response curve. This value was lower than that of other methods such as ESR dosimetry. From these results, we conclude that VTL dosimetry can be preferred for accidental evaluation.     

Thermal Tb emission quenching in YAlO3 matrix embedded in porous anodic alumina

Terbium doped YAlO₃ composites were fabricated by the co-precipitation method in a porous anodic alumina (PAA) films grown on silicon at three different Tb concentrations: 0.23, 0.87 and 2.11 at.%. To investigate the emission thermal quenching for all samples, we measured the emission spectra as a function of temperature in the range from 10 up to 500 K at 266 and 488 nm excitation wavelengths. Based on obtained results we proposed the physical model explaining the mechanism of Tb³⁺ emission quenching in YAlO₃ composites deposited into PAA film.