| 1. |
- Martschini, M., et al.
(författare)
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AMS of Cl-36 with the VERA 3 MV tandem accelerator
- 2013
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Ingår i: Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms. - : Elsevier BV. - 0168-583X. ; 294, s. 115-120
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Tidskriftsartikel (refereegranskat)abstract
- Recent progress with compact ionization chambers has opened new possibilities for isobar Refraining from the additional use of degrader foils has the benefit of high transmission to the detector Precision and accuracy have been thoroughly assessed over the last two years. Since drifts in the Recently we also explored novel techniques for additional sulfur suppression already in the ion source.
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| 2. |
- Martschini, M., et al.
(författare)
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Selective laser photodetachment of intense atomic and molecular negative ion beams with the ILIAS RFQ ion beam cooler
- 2017
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Ingår i: International Journal of Mass Spectrometry. - : Elsevier BV. - 1387-3806. ; 415, s. 9-17
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Tidskriftsartikel (refereegranskat)abstract
- The Ion Laser InterAction Setup (ILIAS) project at the University of Vienna aims at the exploration of negative ion beam filtering by selective laser photodetachment for applications in accelerator mass spectrometry (AMS). A gas-filled radio frequency quadrupole (RFQ) is used to decelerate and cool negative atomic and molecular ion beams with intensities of up to several-hundred nA, and overlap them collinearly with a continuous wave (cw) laser beam. Ion-laser interaction times ranging from 500 mu s to several ms allow for highly efficient, selective photodetachment depletion of disturbing ion species within these beams. The elemental selectivity of this technique is based on the differences in electron affinities, and therefore does not depend on relative differences in atomic numbers. It may therefore provide sufficient isobar suppression for new trace isotopes, which are not accessible with existing AMS techniques. The ILIAS RFQ cooler was characterized at a purpose-built test bench with respect to ion beam transmission, ion cooling capabilities and ion residence times as a function of injected ion current to assess its suitability for future AMS use. A Cu-63(-) test beam of 600 nA was photodetached with more than 99.999% efficiency with a 532 nm laser at 10.8 W power. At the same time, ions of interest having electron affinities higher than the photon energy passed the cooler unaffected. Total ion losses were thus found to be below 50% of the sputter source output. Finally, first photodetachment experiments in connection with Al-26 detection demonstrated selective isobar suppression of MgO- vs. AlO- by more than 4 orders of magnitude. Currently, the RFQ cooler is moved to a new injector beamline at the Vienna Environmental Research Accelerator (VERA) for first applications of this novel technique at a state-of-the-art AMS facility. (C) 2016 Elsevier B.V. All rights reserved.
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| 3. |
- Martschini, M., et al.
(författare)
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The ILIAMS project - An RFQ ion beam cooler for selective laser photodetachment at VERA
- 2019
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Ingår i: Nuclear Instruments & Methods in Physics Research Section B-Beam Interactions with Materials and Atoms. - : Elsevier BV. - 0168-583X. ; 456, s. 213-217
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Tidskriftsartikel (refereegranskat)abstract
- Selective laser photodetachment of anions is a novel technique for isobar suppression in Accelerator Mass Spectrometry (AMS). Ion-laser interaction times on the order of ms required for near-complete isobar suppression are achieved by retarding the ions in a gas-filled radio frequency quadrupole cooler. Inside this RFQ, the cooled anion beam is overlapped collinearly with an intense cw-laser beam. Within the Ion Laser InterAction Mass Spectrometry (ILIAMS) project at the University of Vienna, a dedicated injector beamline has been coupled to the VERA-AMS facility to explore and develop this method. In this work, experimental investigations on ion beam transmission, stability and elemental selectivity of the new setup are presented. A 532 nm laser at 10 W transmitted power provides suppression factors larger than ten orders of magnitude for S- and MgO- under AMS conditions with simultaneous beam transmission for the ions of interest of up to 80%. The excellent ion identification capabilities of the subsequent AMS system also facilitate the study of destruction and formation of molecular anions inside the ion cooler. These kinetic and chemical reactions with the buffer gas provide additional elemental selectivity in certain cases, whereas others constitute a source of background.
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| 4. |
- Bergmann, O., et al.
(författare)
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The Age of Olfactory Bulb Neurons in Humans
- 2012
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Ingår i: Neuron. - : Elsevier BV. - 0896-6273 .- 1097-4199. ; 74:4, s. 634-639
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Tidskriftsartikel (refereegranskat)abstract
- Continuous turnover of neurons in the olfactory bulb is implicated in several key aspects of olfaction. There is a dramatic decline postnatally in the number of migratory neuroblasts en route to the olfactory bulb in humans, and it has been unclear to what extent the small number of neuroblasts at later stages contributes new neurons to the olfactory bulb. We have assessed the age of olfactory bulb neurons in humans by measuring the levels of nuclear bomb test-derived C-14 in genomic DNA. We report that C-14 concentrations correspond to the atmospheric levels at the time of birth of the individuals, establishing that there is very limited, if any, postnatal neurogenesis in the human olfactory bulb. This identifies a fundamental difference in the plasticity of the human brain compared to other mammals.
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| 5. |
- Forstner, O., et al.
(författare)
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Isobar suppression in AMS using laser photodetachment
- 2008
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms. ; 266:19-20, s. 4565-4568
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Tidskriftsartikel (refereegranskat)abstract
- We are investigating the possibility of using laser photodetachment of negative atomic and molecular ions as an additional isobaric selection filter in accelerator mass spectrometry. The aim of this study is to find a possibility to further improve the detection limit for long-lived heavy radionuclides at AMS facilities. We will focus on the astrophysical relevant radionuclide 182Hf, which is one of the isotopes measured with the 3 MV tandem AMS facility VERA (Vienna Environmental Research Accelerator) at the University of Vienna. Laser-induced isobar suppression is also of importance for radioactive-beam facilities. The present detection limit for measuring the isotope ratio 182Hf/Hf at VERA is 1×10-11. The limiting factor is the strong background of the stable isobar 182W. Currently this background is suppressed using suitable molecular ions in the injection stage. Selective laser photodetachment of the negative ions at the injector can lead to an additional suppression of the interfering isobar. Test experiments have been carried out at the negative ion laser spectroscopy setup at Göteborg University. In a small ion beam apparatus pulsed tunable laser radiation is used to measure the photodetachment cross-section of different atomic and molecular negative ions. We will present studies of the photodetachment process for various tungsten and hafnium molecules with the aim to find a selective isobaric suppression scheme using laser photodetachment spectroscopy in combination with AMS.
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| 6. |
- Forstner, Oliver, et al.
(författare)
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Reassessment of 182Hf AMS measurements at VERA
- 2011
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms. - : Elsevier BV. - 0168-583X. ; 269:24, s. 3180-3182
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Tidskriftsartikel (refereegranskat)abstract
- The radioisotope 182Hf (t1/2 = 8.9 Ma) 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.
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| 7. |
- Losiak, A., et al.
(författare)
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Dating a small impact crater : An age of Kaali crater (Estonia) based on charcoal emplaced within proximal ejecta
- 2016
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Ingår i: Meteoritics and Planetary Science. - : Wiley. - 1086-9379 .- 1945-5100. ; 51:4, s. 681-695
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Tidskriftsartikel (refereegranskat)abstract
- The estimates of the age of the Kaali impact structure (Saaremaa Island, Estonia) provided by different authors vary by as much as 6000years, ranging from similar to 6400 to similar to 400 before current era (BCE). In this study, a new age is obtained based on C-14 dating charred plant material within the proximal ejecta blanket, which makes it directly related to the impact structure, and not susceptible to potential reservoir effects. Our results show that the Kaali crater was most probably formed shortly after 1530-1450 BCE (3237 +/- 10 C-14 yr BP). Saaremaa was already inhabited when the bolide hit the Earth, thus, the crater-forming event was probably witnessed by humans. There is, however, no evidence that this event caused significant change in the material culture (e.g., known archeological artifacts) or patterns of human habitation on Saaremaa.
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| 8. |
- Riisager, K., et al.
(författare)
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Be-11(beta p), a quasi-free neutron decay?
- 2014
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 732, s. 305-308
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Tidskriftsartikel (refereegranskat)abstract
- We have observed beta(-)-delayed proton emission from the neutron-rich nucleus Be-11 by analyzing a sample collected at the ISOLDE facility at CERN with accelerator mass spectrometry (AMS). With a branching ratio of (8.3 +/- 0.9). 10(-6) the strength of this decay mode, as measured by the B-GT-value, is unexpectedly high. The result is discussed within a simple single-particle model and could be interpreted as a quasi-free decay of the Be-11 halo neutron into a single-proton state.
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| 9. |
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| 10. |
- Wild, E. M., et al.
(författare)
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C-14 DATING OF HUMIC ACIDS FROM BRONZE AND IRON AGE PLANT REMAINS FROM THE EASTERN MEDITERRANEAN
- 2013
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Ingår i: Radiocarbon. - : Cambridge University Press (CUP). - 0033-8222. ; 55:2-3, s. 599-607
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Tidskriftsartikel (refereegranskat)abstract
- Radiocarbon dating of plant remains is often difficult due to the complete dissolution of the samples in the alkaline step of the ABA pretreatment. At the VERA laboratory, this problem was encountered frequently when numerous Bronze and Early Iron Age samples from the eastern Mediterranean were dated in the course of the special research program SCIEM2000 and in other collaborations with archaeologists focused on that area and time period. For these samples, only a C-14 age determination of the humic acid fraction was possible. Humic acids from archaeological samples are always assessed as a second-choice material for C-14 dating. It is assumed that the C-14 ages may be affected by the presence of humic acids originating from other (younger) organic material, e. g. from soil horizons located above a sample. Therefore, when humic acids are dated a verification of the dates is crucial. To address this basic requirement, we started some time ago to date both fractions of charred seeds, wood, and charcoal samples whenever available, i. e. the residue after the ABA treatment and the humic acids extracted from the samples in the alkaline step. The results of this comparison showed that for the investigated eastern Mediterranean archaeological sites, 50 (out of 52) humic acid dates were in agreement with the C-14 dates of the respective ABA-treated samples. Statistical analysis of the age differences leads to the conclusion that the extracted humic acids originated from the samples themselves or from contemporaneous material and were not appreciably contaminated by extraneous material of different age.
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