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New data about 129 I, 127 I concentrations and their isotopic ratios in aerosol samples from the trace survey station of the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig, Northern Germany, are presented and discussed in this paper. The investigated samples were collected on a weekly basis during the years 2011 to 2013. Iodine was extracted from aerosol filters using a strong basic solution and was separated from the matrix elements with chloroform and was analysed by accelerator mass spectrometry (AMS) for 129 I and by inductively coupled plasma mass spectrometry (ICP-MS) for 127 I. The concentrations of 127 I and 129 I in aerosol filters ranged from 0.31 to 3.71 ng m −3 and from 0.06 to 0.75 fg m −3 , respectively. The results of 129 I/ 127 I isotopic ratios were in the order 10 −8 to 10 −7 . The 129 I originated directly from gaseous emissions and indirectly from liquid emissions (via sea spray) from the reprocessing plants in Sellafield and La Hague. In comparison with the results of 131 I after the Fukushima accident, no contribution of 129 I from this accident was detectable in Central Europe due to the high background originating from the 129 I releases of the European reprocessing plants. 129 I atmospheric activity concentrations were compared with those of an anthropogenic radionuclide ( 85 Kr). We did not find any correlation between 129 I and 85 Kr, both having nuclear reprocessing plant as the main source. [ABSTRACT FROM AUTHOR]

In 2012, Miyake et al. reported a sudden and strong increase of the atmospheric radiocarbon ( 14 C) content in Japanese cedar trees of 1.2% between AD 774 and 775. While their findings were quickly confirmed by a German oak chronology for the Northern Hemisphere (NH), the question remained if the effect was seen in both hemispheres. Here we present the first annually resolved Southern Hemisphere (SH) 14 C record spanning the interval AD 760–787, using New Zealand kauri ( Agathis australis ) chronology wood. An almost identical distinct increase compared to Northern Hemisphere data was observed, suggesting a cosmic event with globally uniform impact as a potential cause for the increase. Deploying a carbon cycle box model a worldwide averaged net 14 C production of 2.2 × 10 8 C 14 atoms cm − 2 was estimated, which is 3.7 times higher than the average annual 14 C production. The immediate appearance of the event in tree rings on both hemispheres suggests a short duration event of significantly less than 1 yr. [ABSTRACT FROM AUTHOR]

Abstract: Recent improvements in isobaric suppression for medium-mass isotopes, e.g. 41Ca, offer new possibilities for tandem accelerators with terminal voltages of 3MV or lower; i.e. when dealing with particle energies ⩽1MeV/amu. In particular, detection of 41Ca requires sufficient discrimination of the stable isobar 41K. We explored the limits of 41Ca detection at our 3-MV AMS facility by means of different types of particle detectors: The ΔTOF method, which is based on the different flight-time of isobars after passing a thick absorber foil. The second method makes use of a new type of compact ionization chamber: 41K and 41Ca are separated in energy due to their different energy loss in the detector entrance foil and the detector gas, which is measured via a segmented anode. At VERA we measured 41Ca/Ca ratios below 10−13 for commercial CaF2 material serving as blank samples. CaH2 sputter targets, with the extraction of , yielded background ratios as low as 41Ca/Ca=1×10−15. The typical measurement precision at VERA for 41Ca measurements was between 2% and 5%. These results demonstrate that AMS facilities based on 3-MV tandems have reached the sensitivity level of larger AMS facilities for a wide range of applications, with the advantage of high overall efficiency and sample throughput. [Copyright &y& Elsevier]

Compared to heavy ion AMS at large tandem accelerators (TV⩾8 MV) and for cases where stable isobar interference is absent, a small facility like VERA (TV=3 MV) is shown to be able to offset the disadvantage of lower ion energy. After testing the system with 210Pb/208Pb isotope ratio measurements, we prove this by a measurement of 236U at natural levels in a material separated before 1918 and therefore free from anthropogenic contamination. An isotopic ratio of 236U/238U=(6.1±0.4)×10−11 was found for this material. [Copyright &y& Elsevier]

Abstract: The radioisotope 182Hf (t 1/2 =8.9Ma) is of great interest for astrophysical applications as a chronometer for the early solar system or as possible live supernova remnant on earth. However, AMS measurements of 182Hf are seriously influenced by the presence of the stable isobar 182W, which cannot be separated at typical AMS energies. Previous studies revealed a possible suppression of 182W against 182Hf by extracting the negatively charged pentafluoride from the ion source, leading to a detection limit for 182Hf/180Hf in the order of 10−11. However, this suppression behavior is in contrast to theoretical calculations of the electron affinity and recent measurements using SIMS instruments, where the achieved suppression cannot be reproduced. The aim of our study is to determine the effects of ion source background as well as further investigate the suppression of tungsten against hafnium by extracting negatively charged fluoride ions from different sample materials. The previously reported suppression factor of about 6000 could be increased to 36000 by careful tuning of the ion source using HfF4 as sample material. The trend of the theoretical electron affinities could be reproduced using atomic tungsten and hafnium instead of HfF4 as sample material. This supports the assumption that the major contribution of the tungsten background is not sputtered from the target matrix but comes from somewhere else in the ion source. Measurements from the second ion source show a higher background of tungsten and a lower suppression factor, i.e. careful design of the ion source is crucial. Moving the sputter beam over the target surface extending over the wheel holding the targets revealed the highest tungsten background was detected outside the sputter target position. Further investigations are necessary to locate the origin of the tungsten background in the ion source. Possible sources are the material used for the ion source construction or contaminations in the cesium used for sputtering. [Copyright &y& Elsevier]