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With Accelerator Mass Spectrometry (AMS) ultra-low isotopic abundances (10–12to 10–16) of long-lived radionuclides, both natural and anthropogenic, are being measured by including an accelerator. Direct atom counting results in an enormous gain in detection sensitivity for long-lived radionuclides as compared to their rare decay. For the most-used radionuclide,14C (half-life = 5,700 yr), this means that instead of grams of carbon required for beta counting one can use milligrams or even micrograms to determine the14C content. In addition, an AMS measurement takes less than an hour rather than the several days required for beta counting. The gain becomes even larger for longer half-lives in the million-year range and beyond. [ABSTRACT FROM AUTHOR] more...

The formation of molecular hydrogen anions (H 2 − , D 2 − , HD − , H 3 − , HD 2 − , and D 3 − ) was investigated. These anion species were produced by sputtering of TiD 2 and HfH 2 targets with Cs + ions and were identified by secondary-ion mass spectrometry (SIMS), yielding the corresponding abundance distributions. The intensity ratios of both the diatomic (HD − /D 2 − ) and triatomic (HD 2 − /D 3 − ) molecular ions are (distinctly) lower than what would be expected from the respective statistical isotopic pattern. This observation indicates that the different lifetimes of these metastable anions are decisive for their formation probability in sputtering and their survival in the mass spectrometer. In addition to molecular ions, the isotopic fractionation of the atomic hydrogen ions, D − /H − , was determined. A strong depletion of the heavier D isotope in the sputtered ion flux by (47.0 ± 3.1)% was found. This pronounced isotope fractionation could be due to a velocity-dependence of the ionization probability, amplified by the large mass difference of the hydrogen isotopes. [ABSTRACT FROM AUTHOR] more...

236U, 237Np, and Pu isotopes and 243Am were determined in ground- and seawater samples at levels below ppq (fg/g) with a maximum sample size of 250 g. Such high sensitivity was possible by using accelerator mass spectrometry (AMS) at the Vienna Environmental Research Accelerator (VERA) with extreme selectivity and recently improved efficiency and a significantly simplified separation chemistry. The use of nonisotopic tracers was investigated in order to allow for the determination of 237Np and 243Am, for which isotopic tracers either are rarely available or suffer from various isobaric mass interferences. In the present study, actinides were concentrated from the sample matrix via iron hydroxide coprecipitation and measured sequentially without previous chemical separation from each other. The analytical method was validated by the analysis of the Reference Material IAEA 443 and was applied to groundwater samples from the Colloid Formation and Migration (CFM) project at the deep underground rock laboratory of the Grimsel Test Site (GTS) and to natural water samples affected solely by global fallout. While the precision of the presented analytical method is somewhat limited by the use of nonisotopic spikes, the sensitivity allows for the determination of ~105 atoms in a sample. This provides, e.g., the capability to study the long-term release and retention of actinide tracers in field experiments as well as the transport of actinides in a variety of environmental systems by tracing contamination from global fallout. [ABSTRACT FROM AUTHOR] more...

Abstract: “The techniques and equipment developed for AMS studies are well suited for identifying exotic negative ions”. With this sentence begins a pioneering paper by Roy Middleton and Jeff Klein (M&K) on small doubly-charged negative carbon clusters [Nucl. Instr. and Meth. B 123 (1997) 532]. M&K were the first to utilize Accelerator Mass Spectrometry to prove the existence of these clusters and a number of other exotic molecules. We review M&K’s efforts and show how their work is being continued at other laboratories. The latest developments are: (1) the discovery of long-lived molecular hydrogen anions and (2) the unambiguous identification of the smallest doubly-charged negative molecule (LiF3)2−. In particular we show new experimental data for , and for (LiF3)2−, and we try to answer the question why M&K’s search for this di-anion was unsuccessful. [Copyright &y& Elsevier] more...

Abstract: The detection of small doubly-charged molecular anions by means of highly sensitive mass spectrometry is discussed. The production of these gas-phase dianions is accomplished by sputtering the specimen with Cs+ ions with an energy of a few keV. It is demonstrated that dianions can be detected most easily when the molecular ion has an odd total mass; then, the dianions will show up at half-integral mass numbers in the mass spectrum. In addition, the agreement of the relative abundances of several isotopomers of a dianion with the nominal isotopic pattern corroborates the identification of a dianionic species in the mass spectrum. These features are exemplified by monitoring mixed silicon–oxygen dianions of the general form (with 2⩽ n ⩽8) in a low-energy mass spectrometer. They were formed by sputtering a silicon wafer at an elevated oxygen partial pressure in the vicinity of the sample’s surface. The flight time through the mass spectrometer of ∼15–30μs establishes a lower limit with respect to the intrinsic lifetimes of these dianions. Emission energy spectra of various singly- and doubly-charged ions illustrate the occurrence of fragmentation processes. The yields of the doubly- and singly-charged mixed silicon–oxygen anions increase with the ratio of the O2 arrival rate to the Cs+ flux density, but tend to saturate when this ratio approaches unity. The benefits of high-energy accelerator mass spectrometry in dianion detection are illustrated for and . [Copyright &y& Elsevier] more...

Abstract: The ΔTOF detector is a new approach for isobar separation at energies below 1MeV/amu. The specific energy loss after a degrader foil can be measured very precisely with time-of-flight (TOF). Small differences in the specific energy loss between isobars lead to clear separation even at low energies. The resolution is not deteriorated by angular scattering or charge state fluctuations. Highly homogeneous low stress silicon nitride foils are used as degrader foils which reduces energy-loss tails significantly. For 36Cl measurements at 0.5MeV/amu a reduction of 36S by 104 could be achieved. The proprieties of these foils for the ΔTOF detector are discussed and first AMS measurements of 36Cl at 0.5MeV/amu and 41Ca at 0.4MeV/amu with the 3MV tandem accelerator VERA are presented. [Copyright &y& Elsevier] more...

Abstract: The use of tandem accelerators for accelerator mass spectrometry (AMS) allows to literally “analyze” molecules. When a molecular ion with mass M and charge Q is injected at the low-energy side, it is efficiently broken up into its atomic constituents during the stripping process in the terminal. At the high-energy side the positively charged atomic ions are again analyzed by their mass-to-charge ratio and by their energy in the detector (and eventually by their nuclear charge, too). We show the usefulness of the AMS method by identifying unambiguously the doubly-charged negative molecule (43Ca19F4)2− for the first time. It considerably eases the task that the total mass M =119 is odd, so the di-anion is injected at the half-integer mass-to-charge ratio M/Q =59.5, where no singly charged ions can interfere. The full power of AMS is needed when we try to proof the existence of di-anions with an integer M/Q, e.g. (23Na35Cl3)2−, whose stability is of interest for atomic physics theory. [Copyright &y& Elsevier] more...

Abstract: With the Vienna Environmental Research Accelerator (VERA, based on a 3-MV tandem accelerator) we have systematically explored the limitations due to terminal voltage, both by modelling and by experiments. If no stable atomic isobars exist, e.g. for 236U or 244Pu, the same detection limits as for large machines have been achieved. In cases where isobar separation is required, the achievable energy is the limitation. To study isobar separation experimentally, we use a new method called ΔTOF: the different energy loss in a foil is measured with a time-of-flight (TOF) detector. Separation of 36Cl from 36S is possible. With diamond like carbon (DLC) stripper foils (0.6μg/cm2) and by pushing our Pelletron tandem to 3.6MV, we achieved a significant increase in energy compared to gas stripping at 3MV: e.g. 36Cl7+ at 28.8MeV instead of 36Cl5+ at 18MeV can be used. [Copyright &y& Elsevier] more...

182Hf is a so-called “extinct” radionuclide interesting for both geophysical and astrophysical studies. The discovery of live 182Hf in the early solar system through isotopic anomalies of stable 182W in meteorites opened up an important application as a chronometer for the formation of the Earth and Moon. In addition, 182Hf plays an important role for the understanding of nucleosynthesis of heavy elements in stellar environments, since both r- and s-processes can be responsible for the high abundance in the early solar system. In contrast to most other extinct radionuclides there is no significant natural or anthropogenic production of 182Hf on Earth. Thus finding live 182Hf on Earth today would be a strong indication for introduction of material from recent nucleosynthesis, e.g. from nearby supernovae. This paper gives a short overview of applications and summarizes recent and ongoing experimental nuclear physics measurements of 182Hf. [Copyright &y& Elsevier] more...

Free doubly-charged negative molecules are a challenge for both theory and experiment. Their stability depends on a very delicate balance between interatomic structure, electronic interaction and Coulomb repulsion. Detecting di-anions of mass M with conventional mass spectrometry always bears the risk of erroneously measuring contributions from singly charged negative ions near mass M/2, or from molecular fragments with different energy. Another possible source of errors are mass ambiguities, e.g. M(12C4)≈M(16O3).In this contribution we show how one can overcome the methodical limits of conventional mass spectrometry by using AMS techniques for the analysis of very rare doubly-charged negative molecules. As an example, a new class of di-anions will be presented, (OCn)2-, n⩾5, which were discovered recently by secondary ion mass spectrometry, and were analyzed in detail by AMS. [Copyright &y& Elsevier] more...

A detector with sufficient energy resolution at high count rates could alleviate a difficult problem in AMS measurements – the detection of rare particles in the vicinity of a large background. The exceptional properties of diamond lead one to expect that these detectors can outperform silicon detectors and ionization chambers for many applications. Only natural diamond detectors (NDDs) that are single crystals, allow energy spectrometry.We have explored a detector produced from a natural type-II diamond of highest purity mined from deposits in Yakutsk, Russian Federation. To late, we have characterized the energy resolution, linearity, stability and radiation degradation using beams of 13C, 180Hf and 238U in the energy range from 12 to 38 MeV. The influence of “priming” and “polarization” is discussed.Deterioration of the detector resolution was observed after irradiation with several 108 ions/mm2 of 238U at 18 MeV. The small detector size, unexpected high energy losses in the entrance window, and the low electrical strength of the assembly were identified as the main limitations in this first test. However, the results demonstrate its intriguing potential for AMS of heavy isotopes. [Copyright &y& Elsevier] more...

VERA, the Vienna Environmental Research Accelerator, was equipped from the start in 1996 with magnets strong enough to bend all known isotopic species. However, considerable improvements were needed to allow AMS analysis of nuclides above mass 150, leading to an almost complete rebuild of the high-energy analyzer. After the analyzer magnet, a new high-resolution electrostatic analyzer (ESA) was installed. First measurements of 182Hf, 236U and 244Pu were successfully performed. The higher background suppression has brought along a significant improvement for 26Al measurements, where a background of 26Al/27Al of ∼6 × 10−16 is reached. [Copyright &y& Elsevier] more...

The detection of small molecular dianions by secondary-ion mass spectrometry (SIMS) and by accelerator mass spectrometry (AMS) is compared. In SIMS, the existence of these dianions can be identified safely if the total mass number of the molecule is odd and the dianion is hence detected at a half-integral mass number. The occurrence of fragmentation processes which may interfere with this scheme, is illustrated by means of the energy spectra of singly and doubly charged negative cluster ions. As compared to SIMS, AMS can rely, in addition, on the break-up of molecular species in the stripping process: this allows to monitor the simultaneous arrival of several atomic constituents with a clear energetic pattern in coincidence at the detector. This feature is exemplified for the C102- dianion. [Copyright &y& Elsevier] more...

Spontaneous and photo-induced decay processes of HfF5− and WF5− molecular anions were investigated in the Double ElectroStatic Ion Ring ExpEriment (DESIREE). The observation of these reactions over long time scales (several tens of ms) was possible due to the cryogenic temperatures (13 K) and the extremely low residual gas pressure (∼10−14 mbar) of DESIREE. For photo-induced reactions, laser wavelengths in the range 240 to 450 nm were employed. Both anion species were found to undergo spontaneous decay via electron detachment or fragmentation. After some ms, radiative cooling processes were observed to lower the probability for further decay through these processes. Photo-induced reactions indicate the existence of an energy threshold for WF5− anions at about 3.5 eV, above which the neutralization yield increases strongly. By contrast, HfF5− ions exhibit essentially no enhanced production of neutrals upon photon interaction, even for the highest photon energy used in this experiment (∼5.2 eV). This suppression will be highly beneficial for the efficient detection, in accelerator mass spectrometry, of the extremely rare isotope 182Hf using the 182HfF5− anion while effectively reducing the interfering stable isobar 182W in the analyte ion 182WF5−. The radionuclide 182Hf is of great relevance in astrophysical environments as it constitutes a potential candidate to study the events of nucleosynthesis that may have taken place in the vicinity of the solar system several million years ago. [ABSTRACT FROM AUTHOR] more...

The detection of low abundances of 135Cs in environmental samples is of significant interest in different fields of environmental sciences, especially in combination with its shorter-lived sister isotope 137Cs. The method of Ion–Laser InterAction Mass Spectrometry (ILIAMS) for barium separation at the Vienna Environmental Research Accelerator (VERA) was investigated and further improved for low abundance cesium detection. The difluorides Ba F 2 − and Cs F 2 − differ in their electron detachment energies and make isobar suppression with ILIAMS by more than 7 orders of magnitude possible. By this method, samples with ratios down to the order of 135 , 137 Cs/133Cs ≈ 1 0 − 11 are measurable and the 135Cs/137Cs ratios of first environmental samples were determined by AMS. [ABSTRACT FROM AUTHOR] more...

Carbon cluster dianions (C 7)2− and (C 10)2− were produced by sputtering of a graphite sample and detected by accelerator mass spectrometry (AMS). The collisional activation of these dianions was studied via their interaction with He gas in an ion beam cooler device which is part of the AMS instrument. Contrary to the respective monoanion cluster, the stability of the dianions exhibits a very pronounced dependence on the gas pressure (i.e., the He gas density). Above a specific value, the transmitted intensity of both dianions decreases strongly pointing to the occurrence of collision-induced reactions. From the observed reaction products, it is concluded that both electron detachment and dissociation take place upon collisions with the gas atoms, following generic pathways such as (C n)2− → (C n)− + e− and (C n)2− → (C n - m)− + (C m)−. [Display omitted] • Accelerator mass spectrometry with ion beam cooler. • Collisional activation of carbon cluster dianions in He gas. • Competition between electron detachment and dissociation reactions. [ABSTRACT FROM AUTHOR] more...

Ion-Laser InterAction Mass Spectrometry (ILIAMS) has the potential to discriminate 99Tc against isobaric background caused by stable 99Ru to allow for the detection of environmental 99Tc concentrations (≈ 1 0 7 atoms/L) at low beam energies. As the electron detachment energies for Tc molecules are not available, Ru and Tc suppression for oxide and fluoride molecules using the available laser systems were determined experimentally for the first time. Tc F 5 − was identified as the most promising anion, as Ru F 5 − was suppressed by a factor 10 5 with the 2.33 eV laser while Tc F 5 − stayed unaffected. Additional Ru suppression in the ion source of another factor 100 was observed. We thus unambiguously identified the 99Tc signal from global fallout in an Austrian peat bog sample. However, no satisfactory suppression of stable 97Mo was achieved, thus hindering the use of the isotopic spike 97Tc for normalizing the detected 99Tc events. Therefore, alternative normalization methods need to be explored. [ABSTRACT FROM AUTHOR] more...

Possible ion output enhancement for C−, C 4 −, Al−, AlO−, CaF 3 − and SrF 3 − by pulsed operation of an NEC-MC-SNICS II ion source under AMS-conditions has been investigated. The cathode voltage was switched periodically between −5.0 kV for regular sputtering and an idle value of −0.8 kV. With normal Cs-supply, all investigated species showed a peak ion current in pulsed mode similar to their DC ion current. A study of ionization efficiency of Al− from Al 2 O 3 likewise revealed no enhancement. However, current enhancements of up to 400 % for C− and C 4 − were observed in pulsed mode when strongly reducing the cesium supply. This is not reflected in ionization efficiency. Under Cs-scarcity, the ionization efficiency of C− in pulsed mode was 12–13 % for samples graphitized with AGE-3. Irrespective of Cs-level, AGE-3 samples and powder mixed samples in DC operation yielded 15–16 % and 16–21 %, respectively. Summarizing, no immediate benefits for AMS could be identified. [ABSTRACT FROM AUTHOR] more...

Abstract: For 14C AMS measurements of samples at the microgram level, ion source related effects start to play a role, while generally the lower sample size limit is set by the carbon background introduced during chemical preparation procedures. Measurements of about 800 graphite targets in the mass range of 1–100μg were performed within 25AMS beam-times during the last three years at VERA, revealing a dependency of measured 14C3+/12C3+ ratios on 12C3+ currents. This dependency can be accounted for by assuming a background current, which was determined for each AMS measurement by least square fitting. 12C- ion currents extracted from microgram graphite samples were typically (1.0±0.5)μA / μg C. On average a 12C3+ background current of (0.14±0.14)μA with F14C=0.22±0.46 (skewness γ1 =3.0) was deduced with significant variations between single measurements. The determination of this background current for each AMS measurement of microgram graphite samples allowed to apply a quantitative correction and thereby to improve the AMS measurement precision. Furthermore, the yield of graphitization and ionization in a Cs sputter ion source of graphitized microgram CO2 samples was investigated. No dependency on the cathode target geometry was observed for 9 differently shaped cathode types. [Copyright &y& Elsevier] more...

Abstract: Accelerator mass spectrometry (AMS) of 36Cl (t 1/2 =0.30Ma) at natural isotopic concentrations requires high particle energies for the separation from the stable isobar 36S and was so far the exclusive domain of tandem accelerators with at least 5MV terminal voltage. Using terminal foil stripping and a detection setup consisting of a split-anode ionization chamber and an additional energy signal from a silicon strip detector, a 36S suppression of >104 at 3MV terminal voltage was achieved. To further increase the 36S suppression energy loss straggling in various counter gases (C4H10, Ar–CH4 and C4H10–Ar) and the effect of “energy focusing” below the maximum of the Bragg curve was investigated. The comparison of experimental data with simulations and published data yielded interesting insights into the physics underlying the detectors. Energy loss, energy straggling and angular scattering determine the 36S suppression. In addition, we improved ion source conditions, target backing materials and the cathode design with respect to sulfur output and cross contamination. These changes allow higher currents during measurement (35Cl− current≈5μA) and also increased the reproducibility. An injector to detector efficiency for 36Cl ions of 8% (16% stripping yield for the 7+ charge state in the accelerator, 50% 36Cl detection efficiency) was achieved, which can favorably be compared to other facilities. The memory effect in our ion source was also thoroughly investigated. Currently our measured blank value is 36Cl/Cl≈3×10−15 when samples with a ratio of 10−11 are used in the same sample wheel and 36Cl/Cl≈5×10−16 if measured together with samples with a ratio of 10−12 or below. This is in good agreement with the lowest so far published isotope ratios around 5×10−16 and demonstrates that 3MV tandems can achieve the same sensitivity for 36Cl as larger machines. [Copyright &y& Elsevier] more...

Abstract: The possibility of detecting 36Cl for geological exposure dating has been explored for several years at VERA (the Vienna Environmental Research Accelerator). First results on real samples were obtained with an ionization chamber (developed at the ETH/PSI, Zürich, Switzerland) with two anodes. To improve the suppression of 36S, we equipped the ionization chamber with an exit window and added a Time-of-Flight (TOF) system with a double-sided silicon strip detector (50×50mm2) as stop detector. We optimized the TOF setup by using silicon nitride foils to reduce scattering tails in the energy spectra. At 3MV terminal voltage, corresponding to a particle energy of 24MeV of 36Cl7+, we achieved a 36S7+-suppression of 21,500 (50% 36Cl-detector-efficiency). [Copyright &y& Elsevier] more...

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] more...

Abstract: This paper describes various modifications implemented at the 40-samples MC-SNICS Cs sputter source used at VERA. The pneumatic sample changer was replaced with a stepper motor drive, and also the adjustment collar for the vertical target wheel position was motorized. These two modifications allow now an automatic scanning of the target position with respect to the Cs-sputter beam. It also opens the way to use sample wheels holding more than 40 sample positions while keeping the original dimensions of the wheel. In order to hold the negative ion output constant, the control computer now regulates the Cs-capillary heater while the Cs-oven heater power supply stays fixed. Another modification was the replacement of the original conical ionizer with a spherical one, involving the enlargement of the diameter of the Cs-focus lens. This modification almost doubled the source output. To adapt the new ion optical geometry, we mounted a shield electrode in front of the target. [Copyright &y& Elsevier] more...

This paper describes the upgrade of the Vienna Environmental Research Accelerator (VERA) to a universal facility for accelerator mass spectrometry (AMS). As a result, it is now possible to measure many long-lived radionuclides at natural abundances across the nuclear chart, from the lightest (10Be) to the heaviest (244Pu). Particular emphasis is placed on measurements to understand the ion optics and the origin of background ions, which ultimately limit the sensitivity. VERA is now ready to venture into the realm of actinides (e.g., 236U, 244Pu), and other heavy radionuclides (e.g., 182Hf), which promise interesting applications in astrophysics and other fields. [Copyright &y& Elsevier] more...

Interest in the long-lived radioisotope 236U (T 1/2 = 23.4 million years) has significantly increased recently due to the emergence of environmental and earth science applications. Compared to the previous setup at VERA, which was based on oxygen stripping and a time-of-flight detector, we have improved the sensitivity of VERA by more than an order of magnitude by switching to helium stripping and by installing a second 90° magnet in our analyzer beamline. The new setup has been successfully employed for several research projects. Here, we present the characterization of the upgraded spectrometer. We discuss the design of the new beamline and present benchmark measurements, suggesting an instrumental sensitivity limit well below 236U/238U = 10−14. The yield for the 3+ charge state is 19%, of which 90% are recorded in the detector. In environmental samples, one in 4500 sputtered actinide atoms is detected. While this allows tackling natural 236U, also measurements of anthropogenic 236U or other actinides profit from the higher sensitivity. This allows analysis of smaller samples, but also has made the rare anthropogenic isotope 233U accessible. [ABSTRACT FROM AUTHOR] more...

The experimental setup at the Vienna Environmental Research Accelerator (VERA) was extended with an ion beam cooler and a 18 W laser to perform Ion-Laser InterAction Mass Spectrometry (ILIAMS). Gas collisions of the decelerated negative ion beam with He buffer gas inside a radio-frequency quadrupole slow down the ions, which facilitates element selective photodetachment to remove isobaric interferences. Here we present the first successful implementation of a suppression of the isobar of 36Cl via laser-photodetachment into an AMS measurement. Whereas conventional AMS measurements require separation of the isobar 36S at high beam energy, ILIAMS takes advantage of the higher electron affinities of Cl− (3.6 eV) compared to S− (2.1 eV). Using 532 nm photons (E ph = 2.3 eV) the isobar 36S is suppressed by 10 orders of magnitude. A high transmission of the Cl− beam through the ion cooler (up to 80%) and a quantitative suppression of the isobaric interference allows for competitive measurements at low accelerator voltages and with lower charge states. This results in high yields for 36Cl transport to the detector. The ILIAMS system is stable over several days of beamtime and blank levels below 36Cl/Cl = 10−15 are reached. The accomplishment of a 36Cl AMS measurement at a final beam energy as low as 5.4 MeV with full separation of isobars and m/q interferences shows the potential of the new isobar suppression method to widen the capabilities of smaller and middle-sized AMS facilities. [ABSTRACT FROM AUTHOR] more...

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. [ABSTRACT FROM AUTHOR] more...

The multiactinide analysis with accelerator mass spectrometry (AMS) was applied to samples collected from the run 13-05 of the Colloid Formation and Migration (CFM) experiment at the Grimsel Test Site (GTS). In this in situ radionuclide tracer test, the environmental behavior of 233U, 237Np, 242Pu, and 243Am was investigated in a water conductive shear zone under conditions relevant for a nuclear waste repository in crystalline rock. The concentration of the actinides in the GTS groundwater was determined with AMS over 6 orders of magnitude from ~15 pg/g down to ~25 ag/g. Levels above 10 fg/g were investigated with both sector field inductively coupled plasma mass spectrometry (SF-ICPMS) and AMS. Agreement within a relative uncertainty of 50% was found for 237Np, 242Pu, and 243Am concentrations determined with the two analytical methods. With the extreme sensitivity of AMS, the long-term release and retention of the actinides was investigated over 8 months in the tailing of the breakthrough curve of run 13-05 as well as in samples collected up to 22 months after. Furthermore, the evidence of masses 241 and 244 u in the CFM samples most probably representing 241Am and 244Pu employed in a previous tracer test demonstrated the analytical capability of AMS for in situ studies lasting more than a decade. [ABSTRACT FROM AUTHOR] more...

This work focuses on the occurrence of 236U in seawater along Danish coasts, which is the sole water-exchange region between the North Sea-Atlantic Ocean and the Baltic Sea. Seawater collected in 2013 and 2014 were analyzed for 236U (as well as 238U and 137Cs). Our results indicate that 236U concentrations in Danish seawater are distributed within a relatively narrow range of (3.6-8.2) x 107 atom/L and, to a certain extent, independent of salinity. 236U/238U atomic ratios in Danish seawater are more than 4 times higher than the estimated global fallout value of 1x 10-9. The levels of 236U/238U atomic ratios obtained are comparable to those reported for the open North Sea and much higher than several other open oceans worldwide. This indicates that besides the global fallout input, the discharges from the two major European nuclear reprocessing plants are dominating sources of 236U in Danish seawater. However, unexpectedly high 236U/238U ratios as well as high 236U concentrations were observed at low-salinity locations of the Baltic Sea. While this feature might be interpreted as a clue for another significant 236U input in the Baltic Sea, it may also be caused by the complexity of water currents or slow turnover rate. [ABSTRACT FROM AUTHOR] more...

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 μs 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 63 Cu − 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 26 Al 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. [ABSTRACT FROM AUTHOR] more...

The temporal distribution of 236 U in the Northwest Pacific Ocean was reconstructed through measurements of the annual changes in 236 U/ 238 U atom ratios in a coral core collected from Kume Island located within the Kuroshio Current region. In total, 74 years (1940–2014) of temporal trend of 236 U/ 238 U atom ratios were reconstructed using Accelerator Mass Spectrometry (AMS). The annually resolved 236 U/ 238 U ratios showed a strong increase from 1952, and two prominent peaks were found in the annual bands for 1954 (11.0 ± 1.2 × 10 − 9 ) and 1958 (8.55 ± 1.17 × 10 − 9 ); also an enhanced peak was observed for the band of 1963 (3.51 ± 0.20 × 10 − 9 ). These peaks coincided with the occurrence of large nuclear tests in the Pacific Proving Grounds and/or the highest global fallout rate, suggesting a clear influence of these nuclear events on 236 U/ 238 U atom ratios. Furthermore, the coral results showed some disagreement with the annual changes for 236 U in East Asian corals collected at the entrance to the Sea of Japan. Based on these results, the mixing ratios of the surface seawater currents in the Northwest Pacific Ocean have been estimated. [ABSTRACT FROM AUTHOR] more...

The concentration of plutonium (Pu) and the isotopic ratios of 240Pu to 239Pu and 241Pu to 239Pu were determined by accelerator mass spectrometry (AMS) in Pacific Ocean water samples (20 L each) collected in late 2012. The isotopic Pu ratios are important indicators of different contamination sources and were used to identify a possible release of Pu into the ocean by the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. In particular, 241Pu is a well-suited indicator for a recent entry of Pu because 241Pu from fallout of nuclear weapon testings has already significantly decayed. A total of 10 ocean water samples were prepared at the Radiochemie München of the TUM and analyzed at the Vienna Environmental Research Laboratory (VERA). Several samples showed a slightly elevated 240Pu/239Pu ratio of up to 0.22 ± 0.02 compared to global fallout (240Pu/239Pu = 0.180 ± 0.007), whereas all measured 241Pu-to-239Pu ratios were consistent with nuclear weapon fallout (241Pu/239Pu < 2.4 x 10-3), which means that no impact from the Fukushima accident was detected. From the average 241Pu-to-239Pu ratio of 8-2+3 x10-4 at a sampling station located at a distance of 39.6 km to FDNPP, the 1-s upper limit for the FDNPP contribution to the 239Pu inventory in the water column was estimated to be 0.2%. Pu, with the signature of weapon-grade Pu was found in a single sample collected around 770 km off the west coast of the United States. [ABSTRACT FROM AUTHOR] more...

93 Zr with a half-life of 1.6 Ma is produced with high yield in nuclear fission, and thus should be present as a natural or anthropogenic trace isotope in all compartments of the general environment. Sensitive measurements of this isotope would immediately find numerous applications, however, its detection at sufficiently low levels has not yet been achieved. AMS measurements of 93 Zr suffer from the interference of the stable isobar 93 Nb. At the Vienna Environmental Research Accelerator VERA a new multi-anode ionization chamber was built. It is optimized for isobar separation in the medium mass range and is based on the experience from AMS experiments of 36 Cl at our 3-MV tandem accelerator facility. The design provides high flexibility in anode configuration and detector geometry. After validating the excellent energy resolution of the detector with 36 S, it was recently used to study iron–nickel and zirconium–niobium–molybdenum isobar separation. To our surprise, the separation of 94 Zr ( Z = 40) from 94 Mo ( Z = 42) was found to be much better than that of 58 Fe ( Z = 26) from 58 Ni ( Z = 28), despite the significantly larger Δ Z / Z of the latter pair. This clearly contradicts results from SRIM-simulations and suggests that differences in the stopping behavior may unexpectedly favor identification of 93 Zr. At 24 MeV particle energy, a 93 Nb ( Z = 41) suppression factor of 1000 is expected based on a synthetic 93 Zr spectrum obtained by interpolation between experimental spectra from the two neighboring stable isotopes 92 Zr and 94 Zr. Assuming realistic numbers for chemical niobium reduction, a detection level of 93 Zr/Zr below 10 −9 seems feasible. [ABSTRACT FROM AUTHOR] more...

Neutron activation analysis using decay counting of the activated element is a well-established method in elemental analysis. However, for chlorine there is a better alternative to measuring decay of the short-lived activation product chlorine-38 ( t 1/2 = 37.24 min) – accelerator mass spectrometry (AMS) of 36 Cl: the relatively high neutron capture cross section of chlorine-35 for thermal neutrons (43.7 b) and combined the AMS technique for chlorine-36 ( t 1/2 = 301 ka) allow for determination of chlorine down to ppb-levels using practical sample sizes and common exposure durations. The combination of neutron activation and AMS can be employed for a few other elements (nitrogen, thorium, and uranium) as well. For bulk solid samples an advantage of the method is that lab contamination can be rendered irrelevant. The chlorine-35 in the sample is activated to chlorine-36, and surface chlorine can be removed after the irradiation. Subsequent laboratory contamination, however, will not carry a prominent chlorine-36 signature. After sample dissolution and addition of sufficient amounts of stable chlorine carrier the produced chlorine-36 and thus the original chlorine-35 of the sample can be determined using AMS. We have developed and applied the method for analysis of chlorine in steel samples. The chlorine content of steel is of interest to nuclear industry, precisely because of above mentioned high neutron capture cross section for chlorine-35, which leads to accumulation of chlorine-36 as long-term nuclear waste. The samples were irradiated at the TRIGA Mark II reactor of the Atominstitut in Vienna and the 36 Cl-AMS setup at the Vienna Environmental Research Accelerator (VERA) was used for 36 Cl/Cl analysis. [ABSTRACT FROM AUTHOR] more...

Laser photodetachment is the process when the extra electron of a negative ion is removed by means of laser radiation. This can happen only if the photon energy is larger than the electron affinity of the ion. The process can be used in mass spectrometry to selectively suppress unwanted isobars, provided that the electron affinity of the unwanted isobar is lower than that of the isobar under investigation. At the Ion Laser InterAction Setup (ILIAS) at the University of Vienna laser photodetachment of negative atomic and molecular ions is studied and its applicability for selective isobar suppression in accelerator mass spectrometry (AMS) is evaluated. The setup provides mass separated beams of negative ions with energies up to 30 keV. Negative ions are produced in a Middleton type cesium sputter ion source, mass selected and overlapped with a strong continuous wave laser beam. In order to extend the interaction time of ions and laser, the ion beam is decelerated to thermal energies in a gas-filled radio frequency quadrupole cooler. For an appropriate choice of the photon energy, unwanted isobars are neutralized while the isobar of interest is unaffected and remains negatively charged. A description of the ILIAS setup and results from the commissioning phase of the RFQ cooler are presented. Up to 8% ion beam transmission could be achieved after a recent redesign of the extraction system. Furthermore first results of photodetachment experiments of 63 Cu − within the RFQ cooler are presented. [ABSTRACT FROM AUTHOR] more...

Interest in the long-lived radioisotope 236 U ( t 1/2 = 23.4 million years) has significantly increased recently, due to the emergence of environmental and earth science applications. Presently, only a few (AMS) accelerator mass spectrometry instruments are suited for this measurement. One major limitation is the relatively low total detection efficiency (on the order of 10 −4 ), which is partly caused by a low stripping yield of the positive ion charge state selected after the tandem accelerator. It has been shown that high yield can be achieved using helium as stripper gas for uranium ion energies below 0.35 MeV. Here we investigate the potential of He stripping of U at the 3-MV tandem accelerator VERA. Phenomenological charge state distributions for U and Th are presented for terminal voltages from 1.0 to 1.7 MV. These terminal voltages provide better background rejection than possible below 1 MeV, and are suited to the widely used 1–3 MV workhorses of many accelerator mass spectrometry laboratories. The methods can be applied to other actinides also. [ABSTRACT FROM AUTHOR] more...

Radioisotopes produced in natural or anthropogenic fission are widely used for tracer studies of environmental processes, in nuclear forensics, and are important for nuclear waste disposal. Besides the well-known 137 Cs, the longer-lived sister isotope 135 Cs ( T 1/2 = 2.3 Myr) is also produced, and the combined measurement of the two isotopes would allow for assessment of contaminating sources. The insufficient suppression of the stable isobar 135 Ba presently prevents AMS measurements down to expected natural levels of 135 Cs/ 133 Cs ≈ 10 −11 . Via the difference in electron affinities between Cs and Ba further isobar suppression should be achievable after the installation of the Ion-Laser-Interaction System (ILIAS) at VERA. We present a preparatory study on the performance of the 3 MV VERA AMS facility for 135 Cs concerning ion formation, transmission and detection. Since the usual Cs sputtering would obscure the 135 Cs/ 133 Cs ratio of a sample, Rb sputtering was successfully applied and tested also for various other typical AMS elements. Partial suppression of 135 Ba is possible with the extraction of Cs − and negative Cs-fluorides. Cs − currents of several 10 nA were extracted over hours from mg amounts of Cs 2 SO 4 material. The transmission to various charge states was tested with gas (Ar, He) and foil stripping. Experiments showed that no suppression in the detection system is possible at high beam energies with the VERA facility. For this reason, gas stripping to low charge states (2 + , 3 + ) with transmissions up to 30% is favorable to guarantee optimal beam transport to the detector. In the present setup, utilizing a simple Bragg-type detector, the blank 135 Cs/ 133 Cs ratios from chemically pure samples are determined by the 135 Ba background to a value of (4.0 ± 1.3)·10 −9 . [ABSTRACT FROM AUTHOR] more...

Atmospheric radiocarbon has been monitored around the Nuclear Power Plant (NPP) Jaslovské Bohunice (Slovakia) using CO 2 absorption in NaOH solution since 1969. In 2012, tree ring samples were collected from Tilia cordata using an increment borer at Žlkovce monitoring station situated close to the Bohunice NPP. Each tree ring was identified and graphite targets were produced for 14 C analysis by accelerator mass spectrometry. The 14 C concentrations obtained from the tree-ring samples have been in a reasonable agreement with the averaged annual 14 C concentrations in atmospheric CO 2 . [ABSTRACT FROM AUTHOR] more...

Very sensitive methods, presently mainly accelerator mass spectrometry (AMS) are necessary for analysis of cosmogenic 10 Be in the environment. AMS is mainly limited by the stable isobar 10 B, while the requirements for mass separation are the least stringent of all standard isotopes analyzed by AMS. We tested a possibility to measure 10 Be using a small switching magnet as an analyzer of accelerated ions, and an ionization chamber with a silicon nitride foil stack used as a passive absorber. A detection limit of 10 −12 for the 10 Be/ 9 Be isotopic ratio was obtained using this technique, which was mainly determined by scattering of 9 Be +2 ions on residual gas inside the switching magnet. [ABSTRACT FROM AUTHOR] more...

An automated analytical method implemented in a flow injection (FI) system was developed for rapid determination of 236U in 10 L seawater samples. 238U was used as a chemical yield tracer for the whole procedure, in which extraction chromatography (UTEVA) was exploited to purify uranium, after an effective iron hydroxide coprecipitation. Accelerator mass spectrometry (AMS) was applied for quantifying the 236U/238U ratio, and inductively coupled plasma mass spectrometry (ICPMS) was used to determine the absolute concentration of 238U; thus, the concentration of 236U can be calculated. The key experimental parameters affecting the analytical effectiveness were investigated and optimized in order to achieve high chemical yields and simple and rapid analysis as well as low procedure background. Besides, the operational conditions for the target preparation prior to the AMS measurement were optimized, on the basis of studying the coprecipitation behavior of uranium with iron hydroxide. The analytical results indicate that the developed method is simple and robust, providing satisfactory chemical yields (80-100%) and high analysis speed (4 h/sample), which could be an appealing alternative to conventional manual methods for 236U determination in its tracer application. [ABSTRACT FROM AUTHOR] more...

A broad range of contaminants has been recorded in sediments of the Loire River over the last century. Among a variety of anthropogenic activities of this nuclearized watershed, extraction of uranium and associated activities during more than 50 years as well as operation of several nuclear power plants led to industrial discharges, which could persist for decades in sedimentary archives of the Loire River. Highlighting and identifying the origin of radionuclides that transited during the last decades and were recorded in the sediments is challenging due to i) the low concentrations which are often close or below the detection limits of routine environmental surveys and ii) the mixing of different sources. The determination of the sources of anthropogenic radioactivity was performed using multi-isotopic fingerprints (236U/238U, 206Pb/207Pb and 208Pb/207Pb) and the newly developed 233U/236U tracer. For the first time 233U/236U data in a well-dated river sediment core in the French river Loire are reported here. Results highlight potential sources of contamination among which a clear signature of anthropogenic inputs related to two accidents of a former NUGG NPP that occurred in 1969 and 1980. The 233U and 236U isotopes were measured by recent high performance analytical methods due to their ultra-trace levels in the samples and show a negligible radiological impact on health and on the environment. The determination of mining activities by the use of stable Pb isotopes is still challenging probably owing to the limited dissemination of the Pb-bearing material marked by the U-ore signature downstream to the former U mines. [Display omitted] • First results of 236U and 233U in a sediment core collected in the Loire River. • 236U source contribution was deciphered using 233U/236U atomic ratio. • Stable lead isotopes were used to discriminate past uranium mining activities. • Lead isotopes showed only the influence of gasoline lead. [ABSTRACT FROM AUTHOR] more...

Highlights: [•] Long-term memory effect in negative ion sources investigated for chlorine isotopes. [•] Interlaboratory comparison of four up-to date negative ion sources. [•] Ion source improvement at DREAMS for minimization of long-term memory effect. [•] Long-term memory effect is the limitation for precise AMS data of volatile elements. [•] Findings to be considered for samples with highly variable ratios of 36Cl/Cl &129I/I. [Copyright &y& Elsevier] more...

An automated analytical method implemented in a novel dual-column tandem sequential injection (SI) system was developed for simultaneous determination of 236U, 237Np, 239Pu, and 240Pu in seawater samples. A combination of TEVA and UTEVA extraction chromatography was exploited to separate and purify target analytes, whereupon plutonium and neptunium were simultaneously isolated and purified on TEVA, while uranium was collected on UTEVA. The separation behavior of U, Np, and Pu on TEVA-UTEVA columns was investigated in detail in order to achieve high chemical yields and complete purification for the radionuclides of interest. 242Pu was used as a chemical yield tracer for both plutonium and neptunium. 238U was quantified in the sample before the separation for deducing the 236U concentration from the measured 236U/238U atomic ratio in the separated uranium target using accelerator mass spectrometry. Plutonium isotopes and 237Np were measured using inductively coupled plasma mass spectrometry after separation. The analytical results indicate that the developed method is robust and efficient, providing satisfactory chemical yields (70-100%) of target analytes and relatively short analytical time (8 h/sample). [ABSTRACT FROM AUTHOR] more...

The Fukushima nuclear accident in March 2011 has released a large amount of radioactive pollutants to the environment. Of the pollutants, iodine-129 is a long-lived radionuclide and will remain in the environment for millions of years. This work first report levels and inorganic speciation of 129I in seawater depth profiles collected offshore Fukushima in June 2011. Significantly elevated 129I concentrations in surface water were observed with the highest 129I/127I atomic ratio of 2.2 × 10-9 in the surface seawater 40 km offshore Fukushima. Iodide was found as the dominant species of 129I, while stable 127I was mainly in iodate form, reflecting the fact that the major source of 129I is the direct liquid discharges from the Fukushima NPP. The amount of 129I directly discharged from the Fukushima Dai-ichi nuclear power plant to the sea was estimated to be 2.35 GBq, and about 1.09 GBq of 129I released to the atmosphere from the accident was deposited in the sea offshore Fukushima. A total release of 8.06 GBq (or 1.2 kg) of 129I from the Fukushima accident was estimated. These Fukushima-derived 129I data provide necessary information for the investigation of water circulation and geochemical cycle of iodine in the northwestern Pacific Ocean in the future. [ABSTRACT FROM AUTHOR] more...

Abstract: Recent progress with compact ionization chambers has opened new possibilities for isobar suppression in accelerator mass spectrometry (AMS). Separation of 36Cl (t 1/2 =0.30Ma) at natural isotopic levels from its stable isobar 36S became feasible at particle energies of 24MeV, which are also accessible for medium-sized tandem accelerators with 3MV terminal voltage like VERA (Vienna Environmental Research Accelerator). Investigations with an ionization chamber revealed how physics favors isobar separation even at energies below the maximum of the Bragg curve. The strong energy focusing effect at high energy losses reduces energy straggling significantly and isobar separation steadily increases up to almost full energy loss. With an optimized detection setup, sulfur suppression factors of 2×104 have been achieved. Refraining from the additional use of degrader foils has the benefit of high transmission to the detector (∼16%), but requires a low sulfur output from the ion source. Therefore several backing materials have been screened for sulfur content. The dependence of the sulfur output on the AgCl sample size has been investigated as well. Precision and accuracy have been thoroughly assessed over the last two years. Since drifts in the spectra are efficiently corrected by monitoring the position of the 36S peak, the reproducibility for high ratio samples (36Cl/Cl>10−12) is better than 2%. Our blank value of 36Cl/Cl≈(5±5)×10−16 is competitive to other labs. 36Cl has become a routine AMS-isotope at VERA. Recently we also explored novel techniques for additional sulfur suppression already in the ion source. While results with a small gas reaction cell in front of the sputter target were discouraging, a decrease in the sulfur/chlorine ratio by one order of magnitude was achieved by directing 300mW continuous wave laser beam at 445nm towards the cathode in the ion source. [Copyright &y& Elsevier] more...

Abstract: New techniques for suppression of atomic isobars in negative ion beams are of great interest for accelerator mass spectrometry (AMS). Especially small and medium-sized facilities can significantly extend their measurement capabilities to new interesting isotopes with a technique independent of terminal voltage. In a new approach, the effect of continuous wave laser light directed towards the cathode surface in a cesium sputter ion source of the Middleton type was studied. The laser light induced a significant change in oxygen, sulfur and chlorine negative ion production from a AgCl target. Approximately 100mW of laser light reduced the sulfur to chlorine ratio by one order of magnitude. The effect was found to depend on laser power and ion source parameters but not on the laser wavelength. The time constant of the effect varied from a few seconds up to several minutes. Experiments were first performed at the ion beam facility GUNILLA at University of Gothenburg with macroscopic amounts of sulfur. The results were then reproduced at the VERA AMS facility with chemically cleaned AgCl targets containing ∼1ppm sulfur. The physical explanation behind the effect is still unclear. Nevertheless, the technique has been successfully applied during a regular AMS measurement of 36Cl. [Copyright &y& Elsevier] more...

Abstract: A growing number of AMS laboratories are pursuing applications of actinides. We discuss the basic requirements of the AMS technique of heavy (i.e., above ∼150amu) isotopes, present the setup at the Vienna Environmental Research Accelerator (VERA) which is especially well suited for the isotope 236U, and give a comparison with other AMS facilities. Special emphasis will be put on elaborating the effective detection limits for environmental samples with respect to other mass spectrometric methods. At VERA, we have carried out measurements for radiation protection and environmental monitoring (236U, 239,240,241,242,244Pu), astrophysics (182Hf, 236U, 244Pu, 247Cm), nuclear physics, and a search for long-lived super-heavy elements (Z >100). We are pursuing the environmental distribution of 236U, as a basis for geological applications of natural 236U. [Copyright &y& Elsevier] more...

Abstract: Silverpoint drawings from the Renaissance are among the most precious and rarest treasures of graphical art. Our research group is particularly interested in the analysis of silverpoint drawings by Albrecht Dürer (1471–1528). A very sensitive and non-destructive analytical method, either spatially resolved synchrotron-radiation induced X-ray fluorescence (SY-XRF) or proton-induced X-ray emission (PIXE), is needed to determine the chemical composition of the very faint silver marks on such drawings. Dürer drawings from the collection of the Albertina, Vienna, were analyzed to amend existing data on Dürer drawings. For this purpose an external-beam PIXE setup was installed at the Vienna Environmental Research Accelerator (VERA). It allows to analyze a spot of ∼0.15mm on the object in air with 3MeV protons, and to detect the emitted X-rays that are characteristic for the chemical composition with very good sensitivity and without harming the precious objects. After successful measurements on artificial test samples, four original silverpoint drawings were investigated: two portraits from Albrecht Dürer’s very early period (self-portrait and portrait of his father) and two drawings from Dürer’s sketch book of his travel to the Netherlands 1520/21. [Copyright &y& Elsevier] more...

Abstract: The interaction of thermal neutrons with 235U results in fission with a probability of ∼85% and in the formation of 236U (t 1/2 =2.3×107 yr) with a probability of ∼15%. While anthropogenic 236U is, therefore, present in spent nuclear fuel at levels of 236U/U up to 10−2, the expected natural ratios in the pre-anthropogenic environment range from 10−14 to 10−10. At VERA, systematic investigations suggest a detection limit below 236U/U=5×10−12 for samples of 0.5mg U, while chemistry blanks of ∼2×107 atoms 236U per sample limit the sensitivity for smaller samples. We have found natural isotopic ratios in uranium reagents separated before the onset of human nuclear activities, in uranium ores from various origins and in water from a subsurface well in Bad Gastein, Austria. Anthropogenic contamination was clearly visible in soil and rivulet samples from Salzburg, Austria, whereas river sediments from Garigliano river (Southern Italy) were close to the detection limit. Finally, our natural in-house standard Vienna-KkU was calibrated against a certified reference material (IRMM REIMEP-18 A). [Copyright &y& Elsevier] more...