131 research outputs found

    Luminescence dating of dune sand and sabkha sediments, Saudi Arabia

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    32 sediment samples recovered in April 2008 from active and relict dunes, and sabkhas/playas, in Saudi Arabia, were investigated using Optically Stimulated Luminescence (OSL) methods. This work follows an earlier investigation of similar sites over a larger area. The results of the current investigations are reported here. The sabkha and shoreline samples show ages ranging from very modern (with no measurable OSL signal) to 7.6ka, indicating that this study area appears to have some sabkhas significantly younger than those observed in the earlier work. One petrified dune sampled in this work produced an OSL date of 830±210 years, which is consistent with the age ranges of the petrified dunes sampled in the earlier work. Another showed very modern (with no measurable OSL signal) for the indurated sand at the top and an age of 200±150 years for the sand at the back of the dune; another sample taken nearby had an OSL age of 720±180 years. This dune appears to be much younger than the petrified dunes sampled in the previous study. Samples from low-rolling dunes in this study have ages between very modern and 580 years. A barchan dune sample had an age of 60±30 years, similar to ages for barchan dunes sampled in the earlier work. Samples from a low hill had ages of 2.5±0.3 and 5.7±0.5 ka. A buried dune was sampled, producing no measurable natural OSL signal

    Evaluation of forest decontamination using radiometric measurements

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    An experiment has been conducted to evaluate the additional dose reduction by clear felling contaminated forestry in Fukushima Prefecture, Japan, and using the timber to cover the areas with wood chips. A portable gamma spectrometry system, comprising a backpack containing a 3x3” NaI(Tl) detector with digital spectrometer and GPS receiver, has been used to map dose rate and radionuclide activity concentrations before, after and at stages during this experiment. The data show the effect of the different stages of the experiment on dose rate at different locations around the site. The spectrometric data have allowed the assessment of the contributions of natural and anthropogenic radionuclides to the dose rate at different parts of the site before and after the experiment. This has clearly demonstrated the value of radiometric methods in evaluating remediation, and the effect of other environmental processes. The value of spectrometric methods which directly measure radionuclide concentrations has also been shown, especially through the identification of the contribution of natural and anthropogenic activity to the measured dose rate. The experiment has shown that clearing trees and applying wood chips can reduce dose rates by 10-15% beyond that achieved by just clearing the forest litter and natural redistribution of radiocaesium

    Gravitational synchrotron radiation from cosmic strings

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    This work studies the gravitational synchrotron radiation emitted from arbitrary cusps of cosmic strings. The results are expressed in terms of four parameters describing the motion of such a cusp. The power spectrum is derived for cusps moving at unit velocity. By using a phenomenological approach the authors also derive the power emitted when the radiation reaction on the cusps is taken into account. In both cases, the synchrotron nature of the radiation produces a power spectrum emitted in a narrow forward cone. If cosmic strings do exist, the radiation emitted by their cusps would seem to be a potential candidate for gravitational-wave detectors

    The Use of Classification in Automated Mathematical Concept Formation

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    Concept formation programs aim to produce a high yield of concepts which are considered interesting. One intelligent way to do this is to base a new concept on one or more concepts which are already known to be interesting. This requires a concrete notion of the `interestingness' of a particular concept. Restricting the concepts formed to mathematical definitions in finite group theory, we derive three measures of the importance of a concept. These measures are based on how much the concept improves a classification of finite groups. Introduction One approach to automatic mathematical concept formation is to perform a heuristic search through a space of sentences which define mathematical concepts. In the space, there will be some sentences which are rubbish, some which are plausible but not very exciting, and some which are important. In order to be able to do an effective search, reducing the number of rubbish sentences, and increasing the yield of important concepts, it is..

    Integrating nuclide specific and dose rate based methods for airborne and ground based gamma spectrometry

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    Results of joint airborne survey work conducted by SUERC and JAEA are presented, for areas to the north and south of Fukushima Daiichi using four different airborne survey systems, cross calibrated at reference sites in Scotland and near Namie. Airborne measurements were made at a series of different survey heights using three high volume NaI based spectrometers, and for the first time using a high resolution system based on the Ortec IDM HPGe spectrometer. The JAEA data sets were analysed using the same methods applied to national scale mapping in Japan since the accident. The SUERC data sets were analysed using nuclide specific approaches validated in the European ECCOMAGS project. The data presented on a digital terrain model show marked correspondence with landscape features, which both suggest the initial deposition processes, and indicate trajectories for future re-deposition by natural processes. All data sets are traceable to each other, and to the ground based calibration sites. Nuclide specific inventories have been defined, which can serve as a future reference to evaluate environmental change

    Assessment of the calibration of gamma spectrometry systems in forest environments

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    A Monte Carlo simulation was used to develop a model of the response of a portable gamma spectrometry system in forest environments. This model was used to evaluate any corrections needed to measurements of 137Cs activity per unit area calibrated assuming an open field geometry. These were shown to be less than 20% for most forest environments. The model was also used to assess the impact of activity in the canopy on ground level measurements. For similar activity per unit area in the lower parts of the canopy as on the ground, 10-25% of the ground based measurement would be due to activity in the canopy, depending on the depth profile in the soil. The model verifies that an optional collimator cap can assess activity in the canopy by repeat survey

    Review of nuclear data for naturally occurring radionuclides applied to environmental applications

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    Accurate nuclear data, commonly using evaluated libraries, is essential in many applications, allowing confidence in derived parameters. An approach to assess the confidence with which these data can be used is proposed, not previously reported, comparing nuclear data presented by different evaluations. Variations between evaluations are used as an indication of potential inaccuracies in the nuclear data or evaluation procedure, and the relevant primary literature reviewed more fully. Applying this approach to naturally occurring radionuclides has identified eight radionuclides where the evaluations differ significantly. Where recommended data are supported by a single set of high precision measurements, independent verification of those measurements will increase confidence in the accuracy of the data (214Bi and 214Pb). Further measurements should be conducted where the decay schemes are incomplete ( 228Ac and 228Ra). For 40K, the mean beta energy in all the evaluations has been calculated using an incorrect shape factor, and log ft and branching ratios have been calculated using an inappropriate program. Precise measurements of beta spectra will allow the use of experimentally derived shape factors for the calculation of mean beta energies (40K and 210Bi). Parameters used for infinite matrix dose rate and geothermal heat production calculations have been derived for the data discussed here

    First luminescence geochronology of the beach-dune ridges of Nayarit strand-plain (west-central Mexico)

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    Strand-plains are composed by beach-dune ridges that constitute coastal sedimentological records of continental erosion and associated climatic and geological controls on their formation. The strand-plain of Nayarit is one the most prominent strand-plains around the world as it is composed by > 250 well-preserved beach-dune ridges that distributes along > 200 km between the states of Nayarit and Sinaloa (west-central Mexico) and extends for 14 km inland. Although the strand-plain of Nayarit is of broad interest for understanding the evolution of Quaternary landscapes, it has remained understudied. To contribute to a better understanding of the landscape evolution of the strand-plain of Nayarit we present here a complete geochronology based on sixteen OSL dating ages distributed across three different transects of beach-dune ridges located from the coast towards the inland. Our data indicate that in all cases the oldest ridges initiated 2 ka. The depositional rates range from 6.0 m a –1 toward the south of the strand-plain, where is the mouth of Santiago and San Pedro rivers, which are the largest of the study area, to 1.8 m a –1 toward the north. These depositional rates are among the highest denudation rates reported in strand-plains around the world. We estimate that the formation of the coastal plain of Nayarit initiated 6 to 7 ka, which correspond to last period of the global marine stabilization after sea level rise

    Chronostratigraphy of an eroding complex Atlantic Round House, Baile Sear, Scotland

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    The excavation team would like to thank Historic Scotland (now Historic Environment Scotland) and the University of St Andrews for providing funding.A high-resolution chronostratigraphy has been established for an eroding Atlantic round house at Sloc Sàbhaidh (North Uist, Scotland), combining detailed OSL profiling and dating of sediments encompassing the main bracketing events associated with the monument, radiocarbon AMS dates on bone recovered from excavated features and fills within it, and TL dates on pottery and burnt clay. Concordant OSL and radiocarbon evidence place construction of the wheelhouse in the first to second centuries AD, contemporary with dates from the primary occupation. Beneath the wheelhouse, clay deposits containing burnt material, attest to cultural activity in vicinity to the monument in the preceding second to first centuries BC. At a later date, the southern wall collapsed, was rebuilt, and the interior spaces to the monument re-structured. The chronology for the later horizons identified from the sediment luminescence dates extends to the second half of the first millennium AD, which goes beyond the range of the radiocarbon dates obtained. The data from ceramics encompass both periods. The juxtaposition of the dating evidence is discussed relative to short and longer chronologies for this Iron Age monument. Corollaries of this research are the implications that based on the long chronology, some of the ecofacts (bone) appear to be residual, and that the temporal duration of Hebridean Coarse Ware may extend into the second half of the first millennium AD.Publisher PDFPeer reviewe
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