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The Twannberg iron meteorite is one out of only six members of the group IIG. The combined noble gas and radionuclide data obtained in this new systematic study indicate that Twannberg with its ~570 recently recovered specimens was a large object with a preatmospheric radius in the range of ~2 m, which corresponds to ~250 × 103 kg. The cosmic-ray exposure age for Twannberg is 182 ± 45 Ma. The most surprising result is the long terrestrial age of Tterr = [ABSTRACT FROM AUTHOR]

A first international 26Al interlaboratory comparison was initiated and evaluation of the results of the eight participating accelerator mass spectrometry (AMS) laboratories on four synthetic samples shows no difference in the sense of simple statistical significance. However, certain interlaboratory bias is observed with more detailed statistical analyses. Some laboratories seem to underestimate the uncertainties of their measurements, and others may overestimate measurement reproducibility. [Copyright &y& Elsevier]

A primary obstacle in understanding the fate and transport of the toxic radionuclide 129 I (a thyroid seeker) is an accurate method to distinguish it from the stable isotope, 127 I, and to quantify the various species at environmentally relevant concentrations (~ 10 − 8 M). A pH-dependent solvent extraction and combustion method was paired with accelerator mass spectrometry (AMS) to measure ambient levels of 129 I/ 127 I isotope ratios and iodine speciation (iodide (I − ), iodate (IO 3 − ), and organo-I (OI)) in aquatic systems. The method exhibited an overall uncertainty of 10% or less for I − and IO 3 − , and less than 30% for OI species concentrations and enabled 129 I measurements as low as 0.001 Bq/L (1 Bq/L = 10 − 13 M). The method was used to analyze groundwater from the Savannah River Site (SRS), South Carolina, USA, along a pH, redox potential (Eh), and organic carbon gradient (8–60 μM DOC). The data confirmed that the 129 I/ 127 I ratios and species distribution were strongly pH dependent and varied in a systematic manner from the strongly acidic source. While 129 I speciation in plume samples containing total I concentrations > 1.7 Bq/L was similar whether measured by AMS or GC–MS ([I − ] ≫ [IO 3 − ] = [OI]), AMS enabled 129 I speciation measurements at much lower concentrations than what was possible with GC–MS. AMS analyses demonstrated that groundwater samples minimally impacted by the plume were still orders of magnitude higher than ambient 129 I concentrations typically found elsewhere in the USA groundwaters and rivers. This is likely due to past atmospheric releases of volatile 129 I species by SRS nuclear reprocessing facilities near the study site. Furthermore, the results confirmed the existence of 129 I not only as I − , but also as OI and IO 3 − species. [ABSTRACT FROM AUTHOR]

The Pamir mountains at the western end of the Himalaya–Karakorum–Tibet mountain belt are characterized by landscape extremes: The western Pamir has an extreme local relief of >2000 m. The eastern Pamir is a low-relief orogenic plateau at ~4100 m. In most of the Pamir, modern glaciers are small and often are rock glaciers restricted to the north sides of the crests but significant ice caps occur in the eastern Pamir (Muztagh Ata, Kongur Shan) and in the northwestern Pamir, where the Fedchenko glacier is the longest glacier outside the polar regions. Glaciation of the Pamir contrasts with the strong glaciation of the Karakorum ranges farther south reflecting differences in annual precipitation beween the Monsoon-influenced Karakorum and the arid, Westerlies-controlled Pamir.Glacial and glaciogenic sediments that have been mapped throughout the Pamir suggest much more widespread glaciation during the Pleistocene. Cosmogenic radionuclide (CRN) dates indicate that one or several glacial maxima occurred ≥100 ka, but the extent of the mid-Pleistocene ice cover is currently not known. While CRN exposure ages of glacially polished bedrock in the west-Pamir valleys suggest that these may have been formed by mid-late Pleistocene Alpine glaciers there is little record of the glacial advances on the east-Pamir plateau. We present new CRN exposure ages that elucidate the glacial and post-glacial history of the Pamir. We also present a geomorphological analysis focusing on the strong east-west difference in topography and on morphological evidence of glaciation in the eastern Pamir. Our analysis sheds light on the landscape evolution and on the competing effects of fluvial and glacial erosion and mass-wasting processes in an arid mountain environment. [ABSTRACT FROM AUTHOR]

DREAMS, the DREsden AMS-facility, is performing routine accelerator mass spectrometry of 10 Be, 26 Al, 36 Cl, 41 Ca, and 129 I for a wide range of applications. All DREAMS-data is normalised directly to primary standards or traceable to those via cross-calibration of secondary standards. Recent technical developments such as a low-memory ion source for 36 Cl and 129 I and sophisticated tuning strategies for 129 I led to improved-accuracy data. Tests of ion source output have been performed with different metal binders, sample-to-binder mixing ratios, and compaction pressures in order to find optimal parameters. The highest and most stable outputs have been obtained for 10 Be, 26 Al, and 41 Ca for the following binders and mixing ratios (by weight): BeO:Nb, 1:4; Al 2 O 3 :Ag, 1:1; CaF 2 :Ag, 1:4. Higher beam currents generally result in reduced statistical uncertainty. Cross-contamination and long-term memory seem to be underestimated problems asking for further tests and improvements such as the development of low-level in-house-standards. [ABSTRACT FROM AUTHOR]

Abstract: Since the acceptance tests of the French 5MV accelerator mass spectrometry facility ASTER in 2007, routine measurement conditions for the long-lived radionuclides 10Be and 26Al have been established. Yearly sample throughput as high as over 3300 unknowns has been reached for 10Be in 2010. Cross-contamination for volatile elements has been largely solved by an ion source upgrade allowing 36Cl measurements at ASTER. However, recent long-term tests using 35Cl/37Cl samples with strongly varying ratios have shown that identical targets lead to different 35Cl/37Cl results at the 2–4% level when being measured after a time gap of 24h while the source is running other samples. Besides time dependent mass fractionation, another likely reason for this effect might be source memory, thus, asking for sophisticated measurement strategies and improved data evaluation and eventually further ion source improvement. Finally, after establishing quality assurance by cross-calibration of secondary in-house 26Al and 41Ca standards and taking part in round-robin exercises of 10Be and 36Cl, a two-step cross-calibration of secondary in-house 129I standards has been performed. The NIST 3231 standard containing 129I/127I at (0.981±0.012)×10−6 has been used for step-wise dilution with NaI to produce gram-quantities of lower-level standards for every-day use. The resulting material SM-I-9 (129I/127I: ∼1×10−9) has been measured vs. AgI produced using minimum chemistry from the two NIST ampoules containing a solution with a nominal ratio 129I/127I of (0.982±0.012)×10−8. In a second stage, SM-I-10 and SM-I-11 with ratios of ∼1×10−10 and ∼1×10−11, respectively, have been cross-calibrated against SM-I-9. Individual uncertainties of the traceable secondary standards are 1.3–1.4% (2σ), mainly originating from the given uncertainty of the primary NIST 3231 at the 10−8 level. The cross-contamination for iodine is in the range of 0.4–0.6% within the first 20h of running the source. [Copyright &y& Elsevier]

Abstract: A new 6MV electrostatic tandem accelerator has been put into operation at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The system is equipped for accelerator mass spectrometry and opens a new research field at HZDR and the Helmholtz Association. It will be also used for ion beam analysis as well as for material modification via high-energy ion implantation. The research activity at the DREsden Accelerator Mass Spectrometry facility (DREAMS) based on a 6MV Tandetron is primarily dedicated to the long-lived radioisotopes of 10Be, 26Al, 36Cl, 41Ca, and 129I. DREAMS background levels have been found to be at 4.5×10−16 for 10Be/9Be, 8×10−16 for 26Al/27Al, 3×10−15 for 36Cl/35Cl and 8×10−15 for 41Ca/40Ca, respectively. The observed background of 2×10−13 for 129I/127I originates from intrinsic 129I from AgI produced from commercial KI. The introduction of quality assurance approaches for AMS, such as the use of traceable calibration materials and taking part in interlaboratory comparisons, guarantees high accuracy data for future DREAMS users. During first experiments an energy calibration of the accelerator has been carried out using the nuclear reaction 1H(15N,γα)12C yielding an energy correction factor of 1.019. [Copyright &y& Elsevier]

Abstract: 36Cl AMS measurements at natural isotopic concentrations have yet been performed only at tandem accelerators with 5MV terminal voltage or beyond. We have developed a method to detect 36Cl at natural terrestrial isotopic concentrations with a 3-MV system, operated above specifications at 3.5MV. An effective separation was obtained with an optimized split-anode ionization chamber design (adopted from the ETH/PSI Zurich AMS group), providing a suppression factor of up to 30,000 for the interfering isobar 36S. Despite the good separation, a relatively high sulfur output from the ion source (36S−/35Cl− ≈4×10−10 for samples prepared from chemically pure reagents), and a possibly cross contamination resulted in a background corresponding to 36Cl/Cl≈3×10−14. The method was applied to samples containing between 105 and 106 atoms 36Cl/g rock from sites in Italy and Iran, which were already investigated by other laboratories for surface exposure dating. The 36Cl/Cl ratios in the range from 2×10−13 to 5×10−12 show a generally good agreement with the previous results. These first measurements demonstrate that also 3-MV tandems, constituting the majority of dedicated AMS facilities, are capable of 36Cl exposure dating, which is presently the domain of larger facilities. [Copyright &y& Elsevier]

Earth is constantly bombarded with extraterrestrial dust containing invaluable information about extraterrestrial processes, such as structure formation by stellar explosions or nucleosynthesis, which could be traced back by long-lived radionuclides. Here, we report the very first detection of a recent 60Fe influx onto Earth by analyzing 500 kg of snow from Antarctica by accelerator mass spectrometry. By the measurement of the cosmogenically produced radionuclide 53Mn, an atomic ratio of 60Fe/53Mn=0.017 was found, significantly above cosmogenic production. After elimination of possible terrestrial sources, such as global fallout, the excess of 60Fe could only be attributed to interstellar 60Fe which might originate from the solar neighborhood. [ABSTRACT FROM AUTHOR]