Applicability of OSL pre-dose phenomenon of quartz in the estimation of equivalent dose

The feasibility of utilizing the pre-dosed OSL signal in the estimation of the equivalent dose has been investigated. The results based on (i) the behavior of growth curve, (ii) dose recovery tests and (iii) non-bleachability of reservoir centres, R-centres, suggests that (i) the pre-dosed OSL does not seem to work satisfactorily in dose estimation unlike the pre-dosed 110 °C TL emission and (ii) it may not be applicable in case of bleached specimen.     

Variations in luminescence properties of single quartz grains and their consequences for equivalent dose estimation

In this paper examples of variability of luminescence properties between single grains of quartz extracted from natural samples or from crushed single crystals are shown. It is demonstrated how measurements of glow curves, PSL (photon stimulated luminescence) decay curves, thermal activation characteristics using multi-grain aliquots can lead to a misinterpretation of the obtained data. The possible consequences for different D_E estimation techniques applied to multi-grain aliquots or to single grains and normalisation techniques applied to multi-grain aliquots are discussed. In particular pre-dose, multi-aliquot additive, and single grain PSL SAR D_E estimation methods are considered.     

Non-monotonic dose dependence of the Ge- and Ti-centres in quartz

The dose response of the Ge- and Ti-centres in quartz is studied over a large dose range. After an initial signal increase in the low dose range, both defects show a pronounced decrease in signal intensities for high doses. The model by Euler and Kahan [1987. Radiation effects and anelastic loss in germanium-doped quartz. Phys. Rev. B 35 (9), 4351–4359], in which the signal drop is explained by an enhanced trapping of holes at the electron trapping site, is critically discussed. A generalization of the model is then developed, following similar considerations by Lawless et al. [2005. A model for non-monotonic dose dependence of thermoluminescence (TL). J. Phys. Condens. Matter 17, 737–753], who explained a signal drop in TL by an enhanced recombination rate with electrons at the recombination centre. Finally, an alternative model for the signal decay is given, based on the competition between single and double electron capture at the electron trapping site. From the critical discussion of the different models it is concluded that the double electron capture mechanism is the most probable effect for the dose response.     

Distinguishing dose populations in sediment mixtures: a test of single-grain optical dating procedures using mixtures of laboratory-dosed quartz

Many natural deposits contain grains that have different burial histories, but reliable procedures to extract the component doses from mixed-dose samples have not been developed in optical dating. Here we present results for synthetic two- and three-component mixtures of data derived from laboratory-dosed sedimentary quartz using a single-aliquot regenerative-dose protocol and statistical models for finite mixtures. Composite sets of data were created from the doses measured for individual grains that had been bleached by sunlight and then given a beta dose of 5, 10 or 20 Gy. We found that the correct number of dose components, corresponding doses, and relative proportions of each component may be estimated if the within-component dispersion is small or is known. We also found, however, that recuperation of the OSL signal in sun-bleached quartz may produce artificially high dose estimates for some grains, an effect that should be taken into account when modelling natural mixtures.     

The estimation of basic experimental parameters in the fine-grained quartz multiple-aliquot regenerative-dose OSL dating of Chinese loess

The sensitivity-corrected multiple-aliquot regenerative-dose (MAR) protocol provides a reliable approach for fine-grained quartz optically stimulated luminescence (OSL) dating. For reliable estimation of the equivalent dose (D_e), we investigated certain basic experimental parameters in the fine-grained quartz MAR OSL dating of Chinese loess. (1) For suitable bleaching of the natural OSL signal of the regenerative-dose aliquots, the effect of bleaching duration using sunlight, SOL2 and blue LEDs on D_e was studied, and it is found that the appropriate method is a short-duration SOL2 (e.g. 5 min) or blue LEDs (e.g. 60 s) bleaching. (2) To select the appropriate test dose, the relationship between the test dose and D_e was investigated based on three samples having D_e values of approximately 11, 31 and 137 Gy respectively. It is suggested that the test dose for sensitivity correction may be limited to less than approximately 10–20 Gy. (3) Three commonly used fitting modes for quartz OSL growth curve were compared at three regenerative-dose scales. The results indicate that the mode of two saturating exponential functions plus a constant is appropriate and universal. (4) The comparison of D_e values derived using OSL approach with those obtained using the recuperated OSL (ReOSL) protocol shows that the reliable D_e estimation in the fine-grained quartz MAR OSL dating of Chinese loess may be limited to less than approximately 300 Gy. (5) The comparison of growth curves for 18 samples from the Weinan, Xifeng and Jingyuan sites shows that it is feasible to construct a standardized growth curve (SGC) for fine-grained quartz OSL signal in the Chinese Loess Plateau (CLP).     

Pseudogap and its temperature dependence in YBCO from the data of resistance measurements

The temperature dependence of the excess conductivity Δσ for Δσ = A(1 ? T/T^*)exp(Δ^*/T) (YBCO) epitaxial films is analyzed. The excess conductivity is determined from the difference between the normal resistance extrapolated to the low-temperature range and the measured resistance. It is demonstrated that the temperature dependence of the excess conductivity is adequately described by the relationship Δσ = A(1 ? T/T^*)exp(Δ^*/T). The pseudogap width and its temperature dependence are calculated under the assumption that the temperature behavior of the excess conductivity is associated with the formation of the pseudogap at temperatures well above the critical temperature T _c of superconductivity. The results obtained are compared with the available experimental and theoretical data. The crossover to fluctuation conductivity near the critical temperature T _c is discussed.     

Cross-calibration between beta and gamma sources using quartz OSL: Consequences of the use of the SAR protocol in optical dating

The radiation dose delivered by the ⁹⁰Sr beta source of a TL-OSL reader and the one delivered by a ¹³⁷Cs gamma source were compared using OSL dating techniques and tools. Three sets of quartz of different origins (rock, sediment and loess) were studied and measured by the SAR protocol (Single aliquot regenerative dose protocol) after irradiations carried out either by the ⁹⁰Sr source or by a ¹³⁷Cs source. Measurements show that the values obtained by the SAR protocol must be corrected in order to provide an acceptable cross-calibration of the beta and gamma source. Once applied, measurement sets become self-consistent and compatible with expected values. The consequences of the above mentioned observations on the methodology of OSL dating are discussed and suggest that a mixed protocol be used including both the SAR protocol and an added dose techniques close to the SARA protocol (Single aliquot regenerative and added dose protocol).     

Real time dose rate measurements with fiber optic probes based on the RL and OSL of beryllium oxide

This work covers the examination of fiber optical probes based on the radioluminescence and real time optically stimulated luminescence of beryllium oxide. Experiments are carried out to determine the fundamental dosimetric and temporal properties of the system and evaluate its suitability for dose rate measurements in brachytherapy and other applications using non-pulsed radiation fields. For this purpose the responses of the radioluminescence and optically stimulated luminescence signal have been investigated in the dose rate range of 20 mGy/h to 3.6 Gy/h and for doses of 1 mGy up to 6 Gy. Furthermore, a new, efficient analysis procedure, the double phase reference summing, is introduced, leading to a real time optically stimulated luminescence signal. This method allows a complete compensation of the stem effect during the measurement. In contrast to previous works, the stimulation of the 1 mm cylindrical beryllium oxide detectors is performed with a symmetric function during irradiation. The investigated dose rates range from 0.3 to 3.6 Gy/h. The real time optically stimulated luminescence signal of beryllium oxide shows a dependency on both the dose rate and the applied dose. To overcome the problem of dose dependency, further experiments using higher stimulation intensities have to follow.     

Improving the accuracy and precision of equivalent doses determined using the optically stimulated luminescence signal from single grains of quartz

Optically stimulated luminescence (OSL) measurements of quartz are widely used to measure equivalent dose (D_e). At radiation doses above ～100 Gy, saturation of traps results in a decrease in the rate of growth of the OSL signal, and this makes calculation of D_e increasingly difficult. A series of dose recovery experiments was undertaken using single grains of quartz from Kalambo Falls, Zambia to explore saturation of single grains. When the OSL signal from many grains is averaged, the characteristic dose (D₀) is 47 Gy, typical of published values for quartz. However, D₀ for individual grains varies from ～10 to 100 Gy. Doses up to two times the average D₀ could be accurately recovered, but above this dose the D_e became increasingly underestimated. Overdispersion for this type of experiment should be zero, but was observed in all data sets; furthermore the value of overdispersion increased with D_e. An additional acceptance criterion, the Fast Ratio, is suggested for single grain OSL analysis. This criterion assesses the relative contribution of the fast component of the OSL signal. Including this as an additional acceptance criterion leads to an improved precision, with overdispersion reduced to zero, and improved accuracy in dose recovery at high doses.     

Assessing the impact of pulsed-irradiation procedures on the thermally transferred OSL signal in quartz

Thermally transferred optically stimulated luminescence (TT-OSL) dating protocols have been suggested as a means of extending the age range of luminescence dating. Several studies demonstrate that TT-OSL signals increase with large radiation doses (>2000 Gy) and yet, few studies report older TT-OSL ages (>400 Gy) in agreement with independent absolute age control. In one such study, agreement with independent chronology was only achieved for the old samples by implementing a pulsed-irradiation procedure. Pulsed-irradiation is suggested to compensate for dose rate dependent competition effects by dividing the laboratory irradiation into discrete irradiation steps interspersed with heat treatments. However, every inter-step heat treatment has the potential to anneal part of the TT-OSL dating signal. This study compares constant- and pulsed-irradiation TT-OSL protocols and investigates the degree of partial thermal annealing. The results suggest that almost all of the difference in outcome between constant- and pulsed-irradiation protocols can be explained by partial annealing of the TT-OSL signal rather than by competition effects. Partial annealing distorts the laboratory dose response curve but has no impact on the natural signal, resulting in unreliable equivalent dose estimates. This means that pulsed-irradiation procedures may not be viable for TT-OSL dating measurements. Future studies implementing pulsed-irradiation procedures should carefully consider the extent to which inter-step thermal treatments partially anneal the signal.     

Protocol for TL dating with zircon: Computer simulation of temperature and dose rate effects

Natural zircon is irradiated internally by U and Th impurities. After exposure to ionizing irradiation zircon exhibits thermoluminescence (TL), which can be used to calculate the irradiation dose and the sample age. A kinetic model for TL of zircon developed earlier is used to model the processes relevant for dating. The response of zircon to irradiation at different dose rates is simulated for different temperatures. Several scenarios for the dating procedure are considered, including laboratory added irradiation, fading and preheat. It is shown that by irradiating the sample at elevated temperatures one can imitate natural irradiation, i.e. it is possible to reproduce the structural state of the trap system (distribution functions of filled electron and hole traps), which is responsible for the TL behavior. This implies that the dose dependence of the TL signal from samples, which had been irradiated under natural conditions, can be produced by irradiation at an elevated temperature.     

Cavitation dose in an ultrasonic cleaner and its dependence on experimental parameters

The aluminum foil erosion method is widely used in cavitation activity studies of ultrasonic cleaners. However, owing to its limited sensitivity, it is difficult to observe the effects of various experimental parameters on the cavitation activity using this method. In the present work, a higher-sensitivity method for quantifying cavitation activity as a cavitation dose based on passive cavitation detection was presented. The influences of various factors (e.g., insonation duration, driving power, gas content, temperature and cleaning agents) were studied for this system. The results showed that the cavitation dose became unstable over long insonation times, and that the instability was more significant at high power. Generally, the cavitation activity could be enhanced by increasing the power, gas content, and the concentration of a cleaning agent. However, due to the exhaustion of the cavitation gas nuclei, the cavitation activity might tune to saturate of even decrease slightly when some impact parameters (e.g., acoustic driving power, gas content and the concentration of the cleaning agent) are above a certain level of each of these parameters.     

Investigations into the reliability of SAR-OSL equivalent doses obtained for quartz samples displaying dose response curves with more than one component

Fast component dominated quartz single aliquot regenerative dose optically stimulated luminescence (SAR-OSL) dose response curves that display continuing growth at high doses are increasingly reported in literature. This behaviour would result in higher equivalent doses being obtained. Here we document the characteristics of OSL signals from fine (4–11 μm) and coarse (63–90 μm) quartz extracted from Romanian loess that display such behaviour. For very high doses (>1 kGy up to 5–15 kGy) the data could be closely fitted to a double saturating exponential regression model. Nonetheless, the saturation charcteristics of these fine and coarse quartz grains are very different, with average saturation chracteristic doses of D₀₁ ≈ 175 Gy and D₀₂ ≈ 1800 Gy in the case of the fine material, while in the case of the coarse material values of D₀₁ ≈ 55 Gy and D₀₂ ≈ 600 Gy have been obtained. Our results imply a hitherto unexplained mechanism in OSL production at high doses and question the reliability of obtaining SAR-OSL equivalent doses in the high dose region when a second function is needed to describe the dose response.     

On the Néel temperature of βFeOOH: Structural dependence and its implications

Using ⁵⁷Fe Mössbauer thermoscanning, the magnetic transition temperature T_N of a number of synthetic βFeOOH samples (akaganeite) is studied. Mössbauer spectra in external fields up to 6 T reveal the sextet-doublet transition to be a true magnetic order-disorder transition and that no superparamagnetic relaxation occurs. It is shown that the value of T_N in particular and the strength of the magnetic interactions in general are highly variable and depend upon the chemical circumstances during synthesis; this is due to spin reduction, induced by a variable amount of interstitial water molecules in the compound.     

On the temperature dependence of the level density parameter and its effect upon neutron evaporation spectra

Effects associated with the temperature dependence of the level density parameter,a(T), are investigated in connection with neutron evaporation processes. Different approximations, for this temperature dependence, are compared for the case of neutron emission from the compound nucleus²⁰⁹Pb.     

On the dependence of the critical temperature on pressure in the bisoliton model of high temperature superconductors

Abstract

In the framework of the bisoliton model we have studied the critical temperature T _c, as a function of the pressure P and of the hole concentration δ for the high temperature superconductors YBa₂Cu₃O_x and (La_1-xM_x)₂CuO₄. Our results for δ ln T_c/δ ln V as a function of T _c describe quite satisfactorily the general trend of the experimental data. Furthermore we show that in the bisoliton model the energy gap δ (in units of Jg³/3, where J is the nearest-neighbour exchange integral and g is the nonlinearity parameter) is an universal function of δ/g. An analogous property is valid for T _c By fitting the maximum value of T _c we are able also to reproduce the experimental data for T _c(δ).     

The electric field gradient and its temperature dependence for indium in beryllium

The electric field gradient (EFG) for¹¹⁷InBe has been determined by a TDPAC measurement to be eq_tot=1.83(1) 10¹⁷V/cm² at room temperature. The sources were prepared by ion — implantation of¹¹⁷Cd in a Be single crystal. The EFG was found to decrease considerably with increasing temperature. The results are compared to those of other impurities in Be.     

On the temperature dependence of coercivity in bubble garnets films

Accurate measurements of magnetic aftereffect and coercivity in a magnetic bubble garnet are presented in the temperature range (-35°C, +60°C). The bubble material is an epitaxial Y_2.6Sm_0.4Ga_1.1Fe_3.9O₁₂ composition supporting 4 μm bubbles. The duration of the drive field pulse is varied between 100 ns and 2 ms. The curves taken at different temperatures of the minimum drive field duration versus its amplitude show similar hyperbolic shape. They are shifted towards small magnetic fields when the temperature increases. The experimental data are compared with a phenomenological model based on thermal activation. A good fit is obtained by taking the values at 20°C as a reference and comparing the experimental data with the calculated values for the different temperatures.