查看更多>>摘要：Techniques for spatially resolved measurements of infrared-stimulated luminescence (IRSL) and novel Infraredphotoluminescence (IRPL) emissions have recently been developed for applications of rock surface dating. Such spatially resolved measurements overcome the need for separating out mineral fractions, speed-up sample preparation and measurement times, and data can be quickly processed provide high-resolution luminescencedepth profiles. Here, we investigate the potential of using spatially resolved IRPL and IRSL measurements for rock surface burial dating using two large (cm-scale) rock samples with controlled exposure and surface dose histories. We use a SAR style measurement protocol, with a test-dose normalisation step to monitor sensitivity changes, a preheat to remove unstable charges and a bleaching step to reset the IRPL signal. Through establishing the response of IRPL and IRSL to dose, we are able to construct 2D maps of equivalent doses (Des) for each sample. The results here indicate that spatially resolving IRSL and IRPL from large rock samples has the potential to be used for rock surface burial dating and offers a means to investigate the spatial distribution of dose and mineral-dependent sensitivity changes through cm-scale rock samples.
查看更多>>摘要：Monte Carlo (MC) simulations of medical linear accelerators applying the phase space approach provide excellent results and substantially reduce execution time. This approach becomes impractical because a new complete MC simulation is needed for any new generation of linac heads. To overcome this disadvantage, the investigation exhibits an innovative hybrid Virtual Source Model (VSM) based on a theoretical reconstruction model utilizing the unchangeable parameters of linacs, taking as input the distribution of dose profiles and energy spectra weight. This VSM involves a couple of principal components, virtual source of photons and scattered particle sources from the Virtual Flattening Filter (VFF) and the asymmetric jaws. Extensive calculations and comparisons between the experimental dose distributions and the hybrid VSM are performed to evaluate VSM accuracy. The TOpas and Gate MC codes are utilized to achieve dose computational speedup and memory management optimization. For validation, several regular squared fields of varying sizes ranging from 3 x 3 to 20 x 20 cm(2) are considered, as well as two complex IMRT plans based on head & neck and pelvic treatments. Examining the VSM accuracy in the penumbra and the high dose gradient regions, applying gamma index (2%/2 mm) criterion confirmed satisfactory results. A two and three dimensional gamma index examination demonstrated an excellent agreement concerning the (3%/3 mm) criteria for IMRT treatments. Furthermore, the speedup factor reached is 290 when applying this hybrid VSM compared to the entire simulation. Consequently, and according to the results achieved in this task, the hybrid VSM proposed is considered suitable for treatment planning systems (TPS) calculation purposes.
查看更多>>摘要：Testing the upper limit of infrared radiofluorescence (IR-RF) dating in nature is a critical step in developing our understanding of the signal and its potential. The Luochuan loess-palaeosol sequence on the Chinese Loess Plateau is a well-documented sequence spanning over 2.5 Ma, that has served as a proving ground for many trapped charge dating techniques, for example: feldspar post-infrared infrared stimulated luminescence (pIRIR), quartz electron spin resonance (ESR), and quartz violet stimulated luminescence (VSL). This study evaluates the IR-RF signal from coarse-grained feldspar on 10 samples from the loess-palaeosol sequence with depositional ages ranging from 25 ka to 900 ka. Initial work tested 6 samples using the RF70 protocol with a bleaching duration of 1500 s using UV-LEDs between the natural and regenerated IR-RF measurements which resulted in consistent and significant underestimation across all but the youngest sample. The bleaching duration was increased to 20 000 s and tested on 10 samples. The IR-RF ages of 5 samples younger than 300 ka (1100 Gy) were consistent with the reference ages while the IR-RF ages for samples older than 300 ka were still significantly underestimated. Natural and laboratory dose response curves were constructed, and they revealed significantly different curves in the case of the shorter bleaching duration, but consistent curves in the case of the longer bleaching duration, confirming the importance of the selected bleaching duration. Furthermore, our study suggests that while the IR-RF signal of feldspar can be used successfully to date samples up to 1100 Gy (-300 ka at our site), it may not be possible to reach the theoretical laboratory-generated dating limit of 3500 Gy.
查看更多>>摘要：The applicability of optically stimulated luminescence (OSL) dating on quartz from South Island, New Zealand is hampered by the poor behaviour of the targeted signals. However, most OSL dating studies have been focused on using coarse quartz fractions. Since a previous study conducted from a nearby site demonstrated that coarse quartz (63-90, 90-125, 125-180 and 180-250 mu m) is not suitable for OSL dating, we attempt using fine quartz here. Therefore, the standard SAR protocol was applied on 4-11 mu m quartz extracted from a loess/paleosol section. Unlike the coarser fractions, the OSL signal of fine quartz displayed satisfactory characteristics which allowed estimating ages ranging from 0.3 & PLUSMN; 0.04 ka to 16 & PLUSMN; 1 ka. In order to understand the differences between the two quartz fractions, we characterise fine (4-11 mu m) as well as the usually used coarser grain sizes (> 63 mu m) of quartz by electron spin resonance (ESR). No significant differences are reported in qualitative terms between the grain sizes investigated and calibration quartz. We report a higher abundance of intrinsic defects in the fine grain fraction; however, this is typical for quartz from other regions as well, that was amenable for OSL dating. As such, the differences between the fine quartz fraction and the coarse fraction is not yet understood. In addition, two elevated temperature post-infrared infrared protocols (pIRIR(225) and pIRIR(290)) were applied and polymineral grains extracted from the same samples. Despite residual dose corrections being performed using a modern analogue, pIRIR ages overestimate quartz ages by 19-122% in the case of the application of the pIRIR(225) protocol and by 25-217% in the case of the application of the pIRIR(290) protocol. The effect could not be circumvented by the application of a test dose with a magnitude of 50% of the equivalent dose in the pIRIR(290) protocol. In the case of the application of pIRIR(290) protocol, dose recovery tests ratios vary from 1.07 & PLUSMN; 0.06 to 1.23 & PLUSMN; 0.05. While not ideal, these results cannot fully explain the differences reported between the ages obtained by fine quartz OSL and the polymineral fine grains pIRIR methods.
Odlum, Margaret L.Rittenour, TammyAult, Alexis K.Nelson, Michelle...
8页
查看更多>>摘要：Quantitative constraints on the timing and temperatures associated with Quaternary fault slip inform earthquake mechanics and seismic hazard analyses. Optically stimulated luminesce (OSL) and thermoluminescence (TL) are tools that can provide these constraints from fault gouge and localized slip surfaces. This study investigates the quartz luminescence properties of five 2-mm-thick slices of rock as a function of distance perpendicularly from a discrete, m-scale mirrored fault surface that cuts quartz-rich conglomerate along the Hurricane fault, UT, USA. We use pulsed annealing linearly modulated OSL experiments to determine the response of OSL signals to annealing temperatures. Results were used to estimate trap depths and trap lifetimes. We also calculated changes in OSL and TL sensitivity across the fault-perpendicular transect. All five subsamples show a strong initial fast component peak following annealing steps of 200-300 ?, which is absent following higher pre-heat steps of 320-420 ?. The fast component trap lifetimes and depths indicate they are stable over the Quaternary and suitable for OSL dating. Data exhibit increasing trap depth, trap lifetime, and sensitivity with distance from the fault surface. We suggest mechanical processes, fluids, and/or elevated temperatures during seismicity work constructively to transform fault materials and affect the quartz luminescence properties at a mm-scale from this fault surface. Results highlight the importance of assessing the scale of fault-related impacts on host rock and luminescence properties when applying trapped-charge techniques to recover fault-slip chronologies and/or paleotemperature information.
查看更多>>摘要：We present the results of the first detailed comparative and quantitative study of various cryogenic systems that can be used for ESR measurements of quartz grains. Three experimental setups were tested: (i) a standard liquid nitrogen Variable Temperature Unit (VTU), operating at 90-100 K and used in most ESR dating studies; (ii) a helium-based VTU that can reach measurement temperatures as low as 15-20 K; and a (iii) finger dewar filled with liquid nitrogen operating at 77 K. As expected, our results show significant gains in signal intensity and resolution when working at temperatures below 90 K, which is extremely useful when dealing with samples with weak intensities or poorly-resolved spectra. The improved signal resolution at 40 K allows the differentiation of the Ti-Li and Ti-H absorption lines around g = 1.913 that are typically merged at 90 K or above. It is therefore possible to extract the ESR intensity of a resolved Ti-Li signal for dating. The results obtained with each experimental configuration are highly consistent for both the Al and Ti centres. In particular, equivalent dose values obtained from eleven of the twelve samples analysed agree at a 1 sigma confidence level. The various cryogenic systems do no induce any significant systematic bias for ESR dose evaluation.
查看更多>>摘要：The aim of this work is to experimentally investigate the role of Internal Bremsstrahlung (IB) in the decay of 32P, a pure beta-emitter with end-point energy of 1.71 MeV and half-life of 14.28 days. IB is a continuous electromagnetic radiation occurring in beta-decay, that had been widely studied in the past years. Its contribution, even if appreciable, is neglected in Monte Carlo (MC) simulation as well as in dosimetric and radiation protection calculations.Ionization current measurements were carried out using a well ionization chamber and compared with MC simulations, performed in the GAMOS (GEANT4-based Architecture for Medicine-Oriented Simulations) framework. Two experimental data sets of 32P IB spectra, taken from the literature, were used to model the IB photon spectral distribution and to include IB emission as an additional source term in MC calculation.Without IB, MC simulations underestimate up to about -18% the measured exposure, whereas the inclusion of IB according to either of the two spectra lead to differences of +2% or +8%. Consequently, the IB process is relevant for high-energy pure beta-emitters such as 32P, and its contribution should be considered in all the dosimetric and radioprotection calculations.
查看更多>>摘要：Durridge Company offers RAD7 and H2O accessory to measure the radon concentration in water based on bubbling method. There are two types of small sample bottles: 40 mL and 250 mL. The company also provided a big bottle with the volume of 2500 mL to measure the radon concentration in water. For the 40 mL and 250 mL sample bottles, the conversion coefficients are 25 and 4, respectively. The small drying tube of water accessory contains only 30 g desiccant, which makes it inconvenient to measure for a long time and needs to be replaced frequently. Besides, the 2500 mL sample bottle with big drying tube needs longer response time. In this paper, a big drying tube with long lifetime is utilized to measure the radon concentration in water. Generally, the response time and the sensitivity depend on the volume of the sample bottles and the gas circuit, so it is important to obtain the conversion coefficients under different conditions to meet different measurement demands. A novel model is proposed for describing the radon concentration in the gas circuit to obtain the con -version coefficients for any volume of sample bottle and drying tube. By choosing the appropriate time of bubbling and measuring, this model can be utilized to obtain the radon concentration in water.
Herrera, JorgeCogollo, RafaelGutierrez, Omar D.Chithambo, M. L....
5页
查看更多>>摘要：Thermoluminescence of aquamarine, the cyan variety of beryl (Be3Al2(SiO3)6), is reported. Samples were irradiated at room temperature using a 90Sr/90Y beta source at a rate of 0.10 Gys-1. Measurements made at 1 degrees C/s after irradiation to 10 Gy show a prominent glow peak at 75 degrees C and three secondary peaks at 113, 188 and 306 degrees C. Kinetic analysis of the main peak performed using the initial rise, whole glow peak and curve fitting methods show that the peak follows first order kinetics, that its activation energy is of the order of 1 eV and that it has a frequency factor of ~1012 s-1. Reproducibility analysis shows that the material reproduces its response under identical experimental conditions with a maximum uncertainty of 2.0%.
查看更多>>摘要：A new radon monitor with a 50 mL hemispherical internal cell (Hynu EIRM) is designed to develop a radon monitor with less influence of humidity based on electrostatic collection and CR-39. The collection efficiency of Po-218 ions in the Hynu EIRM while the cell-wall voltage is 2000 V is estimated by a model established previously. The collection efficiency of Po-218 ions under the relative humidity of 1% is 4.81% higher than that under the relative humidity of more than 10%. Several verification experiments are performed. The Hynu EIRMs are used to measure the Rn-222 concentration under three relative humidity ranges: 5%-10%, 60%-70% and 98%-100%. Results show that the largest difference of the calibration factors of the three experiments is 9.24%, which is a little larger than the difference (4.81%) estimated by the model. The reasons for this outcome may be that the simplified model underestimates the differences of the collection efficiency under different relative humidities and the statistical uncertainty in the experiments. The difference of the calibration factors of the Hynu EIRM at any relative humidity is less than 10%. This study is the first time that the influence of humidity on the detection efficiency of radon monitors based on electrostatic collection and CR-39 is reduced by decreasing the volume of the internal cell and increasing the cell-wall voltage.
NSTL
Elsevier