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Wilcken K.M.,Scottish Enterprise | Freeman S.P.H.T.,Scottish Enterprise | Dougans A.,Scottish Enterprise | Xu S.,Scottish Enterprise | And 2 more authors.
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2010

Small changes to our ion source and gas ionization detector have significantly improved Cl measurement by reducing source memory and increasing interference rejection. Gas stripped low energy 30 MeV 36Cl5+ ions are still efficiently transported to the detector but 36S vs. 36Cl separation is improved by an order of magnitude. Accordingly 36Cl/Cl background is <10-15 before additional interference correction that is also newly automated. 35Cl- currents have increased to 30 μA and 36Cl/Cl inter-cathode repeatability is 3%. © 2009 Elsevier B.V. All rights reserved. Source

Ballantyne C.K.,University of St. Andrews | Rinterknecht V.,University of St. Andrews | Gheorghiu D.M.,NERC Cosmogenic Isotope Analysis Facility
Journal of Quaternary Science | Year: 2013

During the last glacial maximum, the Galloway Hills in southwest Scotland acted as a major centre of ice dispersion within the last British-Irish Ice Sheet (BIIS). Six new or recalibrated 10Be exposure ages for samples obtained from boulders near the former ice divide yielded uncertainty-weighted mean ages of 15.15±0.72 ka (Lm scaling), or 15.33±0.74 ka (Du scaling). These ages indicate that the former ice dome centred over the Galloway Hills had almost (or completely) disappeared by ca. 15 ka, imply prior deglaciation of all of southwest Scotland and refute suggestions that ice cover persisted in this area during the Lateglacial Interstade. They strongly support recent models advocating extensive deglaciation of all areas occupied by the last BIIS (apart from the Scottish Highlands) prior to warming at the onset of the Lateglacial Interstade (ca. 14.7 ka). Three samples obtained from boulders on a large latero-terminal moraine (Tauchers moraine) near the former ice divide yielded a weighted mean age of 11.91±0.77 ka (Lm scaling) or 12.01±0.78 ka (Du scaling), confirming that the moraine is of Loch Lomond (Younger Dryas) Stadial age, and suggesting that the moraine was deposited 200-500 years before the end of the stade. © 2013 John Wiley & Sons, Ltd. Source

Wilcken K.M.,Scottish Enterprise | Freeman S.P.H.T.,Scottish Enterprise | Schnabel C.,NERC Cosmogenic Isotope Analysis Facility | Binnie S.A.,University of Edinburgh | And 2 more authors.
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2013

Cosmogenic 36Cl analysis by accelerator mass spectrometry (AMS) is a valuable environmental and geological sciences research tool. Overcoming the stable nuclide 36S isobar interfering with measurement is challenging, however. Traditionally this has required large accelerators, but following recent technical advances it is now possible with ∼30 MeV ion energies. Consequently 5 MV or even smaller modern bespoke spectrometers are now 36Cl-capable, increasing accessibility and promoting wider and more varied 36Cl use. However, the technical ability to identify 36Cl ions is quite distinct from demonstrated high-performance AMS. Such is the theme of this paper. We present a systematic analysis of the accurate measurement of sample radioisotope relative to the stable chlorine, the normalisation of the measured ratio and correction for remaining 36S interference, all combined with the use of stable-isotope dilution to determine sample Cl concentration to begin with. We conclude by showing that repeated analyses support our claims for routine 3% 36Cl-AMS data. Accordingly, the modest SUERC spectrometer well competes with the performance of larger longer-established instruments, and the results may be quite generic for modern bespoke instruments. © 2012 Elsevier B.V. All rights reserved. Source

Ballantyne C.K.,University of St. Andrews | Wilson P.,University of Ulster | Gheorghiu D.,NERC Cosmogenic Isotope Analysis Facility | Rodes A.,NERC Cosmogenic Isotope Analysis Facility
Earth Surface Processes and Landforms | Year: 2014

The temporal pattern of rock-slope failures (RSFs) following Late Pleistocene deglaciation on tectonically stable terrains is controversial: previous studies variously suggest (1) a rapid response due to removal of supporting ice ('debuttressing'), (2) a progressive decline in RSF frequency, and (3) a millennial-scale delay before peak RSF activity. We test these competing models through beryllium-10 (10Be) exposure dating of five closely-spaced quartzite RSFs on the Isle of Jura, Scotland, to establish the relationship between timing of failure and those of deglaciation, episodes of rapid warming and periods of rapid glacio-isostatic uplift. All five dated RSFs occurred at least 720-2240 years after deglaciation, with the probability of failure peaking ~2 ka after deglaciation, consistent with millennial-scale delay model (3). This excludes debuttressing as an immediate cause of failure, though it is likely that time-dependent stress release due to deglacial unloading resulted in progressive development of failure planes within the rock. Thaw of permafrost ice in joints is unlikely to have been a prime trigger of failure as some RSFs occurred several centuries after the onset of interstadial warming. Conversely, the timespan of the RSFs coincides with the period of maximum glacio-isostatic crustal uplift, suggesting that failure was triggered by uplift-driven seismic events acting on fractured rock masses. Implications of this and related research are: (1) that retreat of the last Pleistocene ice sheets across tectonically-stable mountainous terrains was succeeded by a period of enhanced rock-slope failure due to deglacial unloading and probably uplift-driven seismicity; (2) that the great majority of RSFs in the British Isles outside the limits of Loch Lomond Stadial (= Younger Dryas) glaciation are of Lateglacial (pre-Holocene) age; and (3) numerous RSFs must also have occurred inside Loch Lomond Stadial (LLS) glacial limits, but that runout debris was removed by LLS glaciers. © 2013 John Wiley & Sons, Ltd. Source

Vermeesch P.,University of London | Fenton C.R.,NERC Cosmogenic Isotope Analysis Facility | Kober F.,ETH Zurich | Wiggs G.F.S.,University of Oxford | And 2 more authors.
Nature Geoscience | Year: 2010

The Namib Sand Sea is one of the world's oldest and largest sand deserts1, yet little is known about the source of the sand in this, or other large deserts2. In particular, it is unclear whether the sand is derived from local sediment or comes from remote sources. The relatively uniform appearance of dune sands and low compositional variability within dune fields3 make it difficult to address this question. Here we combine cosmogenic-nuclide measurements and geochronological techniques to assess the provenance and migration history of sand grains in the Namib Sand Sea. We use U-Pb geochronology of detrital zircons to show that the primary source of sand is the Orange River at the southern edge of the Namib desert. Our burial ages obtained from measurements of the cosmogenic nuclides 10Be, 26Al and 21Ne suggest that the residence time of sand within the sand sea is at least one million years. We therefore conclude that, despite large climatic changes in the Namib region associated with Quaternary -interglacial cycles4,5, the area currently occupied by the Namib Sand Sea has never been entirely devoid of sand during the past million years. © 2010 Macmillan Publishers Limited. All rights reserved. Source

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