Corrections for contamination background in AMS {sup 14}C measurements

Measurements of {sup 14}C/{sup 13}C ratios were made on samples of Oxalic Acid and {sup 14}C dead materials spanning the mass range from 10 {micro}g to {approximately} 1 mg. These measurements have allowed the determination of both the amount, and the {sup 14}C content, of the contaminant carbon introduced during sample processing in the laboratory. These data were used to correct measured {sup 14}C/{sup 13}C ratios obtained from ANU Sucrose and {approximately} one-half-life old test samples for the influence of the contaminant. The test samples spanned the 10 {micro}g to {approximately} 1 mg mass range and the corrections were made using three different formulae. The results obtained from these calculations allow the accuracy of these background correction formulae to be evaluated

Ultra small-mass AMS 14C sample preparation and analyses at KCCAMS/UCI Facility

We have developed techniques for accurately and precisely measuring samples containing less than a few hundred micrograms of carbon, using a compact AMS system (NEC 0.5 MV 1.5SDH-1). Detailed discussions of the sample preparation, measurement setup, data analysis and background corrections for a variety of standard samples ranging from 0.002 to 1 mgC are reported. Multiple aliquots of small amounts of CO2 were reduced to graphite with H2 over pre-baked iron powder catalyst. A reduction reaction temperature of 450 °C was adopted for graphite samples below 0.05 mgC, rather than the usual 550 °C used on samples of 0.1–1 mgC. In our regular reactors (∼3.1 cm3), this reduction in temperature improved the graphite yield from ∼60 to 90–100% for samples ranging from 0.006–0.02 mgC. The combination of lower reaction temperature with a reduced reactor volume (∼1.6 cm3) gave yields as high as 100% on graphite samples <0.006 mgC. High performance measurements on ultra-small samples are possible also due to a modified NEC MC-SNIC ion-source that generates C− currents of 1 μA per μg of carbon for samples in the 0.002 to 0.010 mgC range, combined with on-line measurement of 12C and 13C (AMS δ 13C) to correct machine-induced isotopic fractionation. Source efficiencies are in excess of 10%, which enables 4–5% of the radiocarbon atoms in 0.005–0.010 mgC samples to be measured. Examination of the background samples revealed two components: (a) 0.2–1 μg of modern carbon and (b) 0.1–0.5 μg of dead carbon. The latter component can be ignored when measuring unknown samples paired to small standards of precisely identical size (matching size normalizing standard method). Otherwise, one must make corrections for both background components. Ultra-small samples from 0.002 to 0.01 mgC can be measured with accuracy and precision of a few percent, based on scatter in results for multiple aliquots of a primary standard and deviations of secondary standards from their known values

Ultra small-mass AMS 14C sample preparation and analyses at KCCAMS/UCI Facility

We have developed techniques for accurately and precisely measuring samples containing less than a few hundred micrograms of carbon, using a compact AMS system (NEC 0.5 MV 1.5SDH-1). Detailed discussions of the sample preparation, measurement setup, data analysis and background corrections for a variety of standard samples ranging from 0.002 to 1 mgC are reported. Multiple aliquots of small amounts of CO2 were reduced to graphite with H2 over pre-baked iron powder catalyst. A reduction reaction temperature of 450 °C was adopted for graphite samples below 0.05 mgC, rather than the usual 550 °C used on samples of 0.1–1 mgC. In our regular reactors (∼3.1 cm3), this reduction in temperature improved the graphite yield from ∼60 to 90–100% for samples ranging from 0.006–0.02 mgC. The combination of lower reaction temperature with a reduced reactor volume (∼1.6 cm3) gave yields as high as 100% on graphite samples <0.006 mgC. High performance measurements on ultra-small samples are possible also due to a modified NEC MC-SNIC ion-source that generates C− currents of 1 μA per μg of carbon for samples in the 0.002 to 0.010 mgC range, combined with on-line measurement of 12C and 13C (AMS δ 13C) to correct machine-induced isotopic fractionation. Source efficiencies are in excess of 10%, which enables 4–5% of the radiocarbon atoms in 0.005–0.010 mgC samples to be measured. Examination of the background samples revealed two components: (a) 0.2–1 μg of modern carbon and (b) 0.1–0.5 μg of dead carbon. The latter component can be ignored when measuring unknown samples paired to small standards of precisely identical size (matching size normalizing standard method). Otherwise, one must make corrections for both background components. Ultra-small samples from 0.002 to 0.01 mgC can be measured with accuracy and precision of a few percent, based on scatter in results for multiple aliquots of a primary standard and deviations of secondary standards from their known values

10Be in a deep-sea core: implications regarding10Be production changes over the past 420 ka

International audienc

Late Glacial to Holocene radiocarbon constraints on North Pacific Intermediate Water ventilation and deglacial atmospheric CO2 sources

Radiocarbon reconstructions of past ocean ventilation rates constrain oceanic sources and sinks of CO2 and mechanisms of subsurface hypoxia. Here, 14C in coexisting benthic and planktonic foraminifera from a sediment core 682 m deep off Southeast Alaska documents paleoventilation over the past ?17,000 years?17,000 years. A chronology based on calibrated planktonic foraminiferal dates, consistent with independent terrestrial dates for regional glacial retreat, yields deglacial projection ages moderately greater than those of the Holocene, suggesting comparatively limited ventilation. The observed Holocene increase of apparent ventilation at intermediate depths tracks inundation of the Bering Strait between ?11,800?11,800 and 13,200 years13,200 years ago, suggesting that flooding of continental shelves and export of low-salinity surface waters to the Arctic enhanced intermediate water formation in the North Pacific. An abrupt increase in the benthic–planktonic radiocarbon age gradient, implying homogenization of abyssal radiocarbon in deep and intermediate waters, aligns with the younger of two episodes of rapid rise of atmospheric CO2 and depletion of atmospheric View the MathML source?C14 during deglaciation (?11,500–13,000 years?11,500–13,000 years ago), suggesting the North Pacific as a possible pathway for venting of oceanic CO2 to the atmosphere during the second half of the deglacial transition

Toxikologische Beurteilung von Daemmstoffen aus kuenstlichen Mineralfasern

Available from TIB Hannover: RN 7632(112) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman