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I. Leya H‐J. Lange M. LÜPke U. Neupert R. Daunke O. Fanenbruck R. Michel R. R
Sel B. Meltzow T. Schiekel F. Sudbrock U. Herpers D. Filges G. Bonani B. Dittrich‐Hannen M. Suter P. w. Kubik H‐a. Synal 《Meteoritics & planetary science》2000,35(2):287-318
Abstract— Thick spherical targets made of gabbro (R = 25 cm) and of steel (R = 10 cm) were irradiated isotropically with 1.6 GeV protons at the Saturne synchrotron at Laboratoire National Saturne (LNS)/CEN Saclay in order to simulate the interaction in space of galactic cosmic‐ray (GCR) protons with stony and iron meteoroids. Proton fluences of 1.32 × 1014 cm?2 and 2.45 × 1014 cm?2 were received by the gabbro and iron sphere, respectively, which corresponds to cosmic‐ray exposure ages of about 1.6 and 3.0 Ma. Both artificial meteoroids contained large numbers of high‐purity target foils of up to 28 elements at different depths. In these individual target foils, elementary production rates of radionuclides and rare gas isotopes were measured by x‐ and γ‐spectrometry, by low‐level counting, accelerator mass spectrometry (AMS), and by conventional rare gas mass spectrometry. Also samples of the gabbro itself were analyzed. Up to now, for each of the experiments, ～500 target‐product combinations were investigated of which the results for radionuclides are presented here. The experimental production rates show a wide range of depth profiles reflecting the differences between low‐, medium‐, and high‐energy products. The influence of the stony and iron matrices on the production of secondary particles and on particle transport, in general, and consequently on the production rates is clearly exhibited by the phenomenology of the production rates as well as by a detailed theoretical analysis. Theoretical production rates were calculated in an a priori way by folding depth‐dependent spectra of primary and secondary protons and secondary neutrons calculated by Monte Carlo techniques with the excitation functions of the underlying nuclear reactions. Discrepancies of up to a factor of 2 between the experimental and a priori calculated depth profiles are attributed to the poor quality of the mostly theoretical neutron excitation functions. Improved neutron excitation functions were obtained by least‐squares deconvolution techniques from experimental thick‐target production rates of up to five thick‐target experiments in which isotropic irradiations were performed. A posteriori calculations using the adjusted neutron cross sections describe the measured depth profiles of all these simulation experiments within 9%. The thus validated model calculations provide a basis for reliable physical model calculations of the production rates of cosmogenic nuclides in stony and iron meteorites as well as in lunar samples and terrestrial materials. 相似文献
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M. Atarashi-Andoh C. Schnabel G. Cook A.B. MacKenzie A. Dougans R.M. Ellam S. Freeman C. Maden V. Olive H.-A. Synal S. Xu 《Applied Geochemistry》2007
Accelerator Mass Spectrometry (AMS) was used to measure 129I/127I ratios in surface sea, lake, and river water samples collected in 2004 and 2005 from the English Lake District and from SW Scotland, areas which are in relatively close proximity to the Sellafield nuclear fuel reprocessing plant in NW England. The 129I/127I ratios in surface water collected from the shore of the Irish Sea were in the range 2.8 × 10−6 to 8.2 × 10−6. These ratios are one order of magnitude higher than that of seawater collected from the Irish Sea in 1992, correlating with the increase in 129I content of the Sellafield liquid effluent discharge over the last decade. The 129I/127I ratios in lakes in the Lake District were in the range 0.7 × 10−6 to 6.4 × 10−6 and decreased exponentially as a function of distance from Sellafield. Consideration of the relative variation of stable I concentrations and 129I/127I ratios suggests that Sellafield gaseous discharges may be the dominant source of 129I to the lakes. 相似文献
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Olivia Steinemann Susan Ivy-Ochs Sandra Grazioli Marc Luetscher Urs H. Fischer Christof Vockenhuber Hans-Arno Synal 《地球表面变化过程与地形》2020,45(6):1401-1417
Glacial erosion is the basic process that has shaped the landscapes of the Alps. Despite intense research over centuries, and the use of various techniques, determination of glacial erosion rates remains challenging. This is not only because the location where the process occurs is almost inaccessible, but also because it is dependent on many different factors, including ice thickness and velocity, glacier thermal regime and lithology. Reported glacial erosion rates range over several orders of magnitude (0.01 to >10 mm a−1). Most studies focus on crystalline bedrock, whereas few researchers have investigated glacial erosion on limestone. Here we analyse glacially polished bedrock surfaces at the recently deglaciated forefield of the Tsanfleuron glacier, Swiss Alps. The nearly horizontally bedded limestone hosts a well-developed karst system. Meltwater from the glacier drains into the subsurface within a few metres of the ice margin. By combining geomorphological mapping, measurement of cosmogenic 36Cl concentrations of glacially eroded bedrock surfaces and a numerical model (MECED), we quantify at each sample location the amount of rock removed during glacier occupation. The glacial erosion rates calculated from these values range from 0 to 0.08 mm a−1. These are orders of magnitude lower than values measured at comparable sites on crystalline bedrock. The high 36Cl concentrations we measured show that the Tsanfleuron glacier was unable to effectively erode the gently dipping, strongly karstified limestone. We suggest that this effect may play a key role in formation and preservation over many glacial cycles of high-elevation, low-relief limestone plateaus in the Alps. © 2020 John Wiley & Sons Ltd. 相似文献
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For groundwaters of tectonic active regions the problem of determining the residence time above the range of the tritium method arises. The usually applied isotope techniques are often not appropriate because of (i) the high amount of water-rock interaction, (ii) the underground production of nuclides in crystalline fissured rocks under geothermal conditions, (iii) the occurrence of highly saline waters at boiling temperature affected by waterrock interaction processes, as also the high fluxes of CO2 . However, the 36 Cl evolution will be affected by these processes, too. Nevertheless it gives an independent tool to investigate the groundwater evolution. Therefore the application of the 36 Cl method looks very promising. Within this publication the interpretation of 36 Cl measurements of three study areas along the North Anatolian Fault zone (from East to West) of Kuzuluk/Adapazari, Bursa and of Canakkale (Tuzla/Kestanbol) are discussed. By considering for each area the sources of 36 Cl and the water-rock interaction with respect to the chloride cycle, information on the ongoing processes of groundwater circulation and evolution have been derived. In addition, ranges of residence times of these waters were gained which are compatible with the results of geological, hydrogeological and hydrochemical investigations (Balderer et al ., 1991; Greber, 1992, 1994; lmbach, 1992, 1994; Imbach and Balderer, 1990; Mutzenberg, 1989) as well as with already developed conceptual groundwater flow models. 相似文献
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Christoph Schnabel Valérie Olive Mariko Atarashi-Andoh Andrew Dougans Robert M. Ellam Stewart Freeman Colin Maden Martin Stocker Hans-Arno Synal Lukas Wacker Sheng Xu 《Applied Geochemistry》2007
This work constitutes the first survey of I isotope ratios for Scottish sea water including the first data for the west of Scotland. These data are of importance because of the proximity to the world’s second largest emission source of 129I to the sea, the Sellafield nuclear reprocessing plant, because of the increasing importance of the sea to land transfer of 129I and also as input data for dose estimates based on this pathway of 129I. 129I/127I ratios in SW Scotland reached 3 × 10−6 in 2004. No strong variation of I isotope ratios was found from 2003 to 2005 in Scottish sea waters. Iodine isotope ratios increased by about a factor of 6 from 1992 to 2003 in NE Scotland, in agreement with the increase of liquid 129I emissions from Sellafield over that time period. It is demonstrated that 129I/127I ratios agree better than 129I concentrations for samples from similar locations taken in very close temporal proximity, indicating that this ratio is more appropriate to interpret than the radionuclide concentration. 相似文献
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The gravel aquifer within the Szigetköz Plain in northern Hungary is mainly fed by the infiltration of the Danube River. This infiltration process can be identified using the tritium/helium method to a distance of about 30 km away from the infiltration area of the Danube. In this study, chlorine-36 analyses are used as additional method. This natural radioisotope was also produced by nuclear bomb tests in the atmosphere. It is an ideal, stable constituent for this particular study due to its very long half-life (300,000 years), and consequently acts as an independent check of the established model of aquifer recharge. The chlorine-36 data of the analysed selected groundwater samples of this area clearly show the effect of the atmospheric nuclear bomb tests, with enhanced 36Cl/Cl ratios of up to a factor 10 higher than the unaffected groundwater of the pre-bomb period within the study area. Finally, the observed 36Cl values were introduced into a transport model with dispersion/advection-type flow of groundwater to deduce the transport parameters. 相似文献
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