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The detection of low abundances of Cs-135 in environmental samples is of significant interest in different fields of environmental sciences, especially in combination with its shorter-lived sister isotope Cs-137. 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 cesiumdetection. The difluorides BaF2 and CsF2 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 Cs-135,137/Cs-133 ≈ 10^(−11) are measurable and the Cs-135/Cs-137 ratios of first environmental samples were determined by AMS.

The abstract is available here: https://uscholar.univie.ac.at/o:1646659

The validity of the 90Sr analysis by AMS was demonstrated by analyzing IAEA samples. This method achieves LOD of

The sensitive analysis of

Interest in the long-lived radioisotope 236U (T1/2 = 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.

The reactions $^{6,7}\mathrm{Li}+^{27}\mathrm{Al}$ were compared with the reactions $^{17,18}\mathrm{O}+^{16}\mathrm{O}$ which form the same compound nuclei $^{33,34}\mathrm{S}$. Cross-section data for the reactions $^{6,7}\mathrm{Li}+^{27}\mathrm{Al}$ were derived from experimentally determined \ensuremath{\gamma}-ray production cross sections for transitions in several residual nuclei. For the reactions $^{17,18}\mathrm{O}+^{16}\mathrm{O}$ experimental results from the literature were used. It could be shown that the weakly bound projectiles $^{6,7}\mathrm{Li}$ undergo not only fusion processes, but also breakup reactions quite in contrast to the tightly bound projectiles $^{18}\mathrm{O}$ and $^{17}\mathrm{O}$, respectively. Especially below the Coulomb barrier such direct reactions play an important role in competition to complete fusion. Calculations based on the statistical model agree well with the available data for $^{17,18}\mathrm{O}+^{16}\mathrm{O}$, but failed to represent the behavior of the experimentally determined production cross sections for the evaporation residues in the reactions $^{6,7}\mathrm{Li}+^{27}\mathrm{Al}$. But coupled-channel codes and calculations based on a nucleus-nucleus proximity potential are able to reproduce the energy dependence of the complete fusion cross sections.

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.

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 (Eph = 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.

Correction for ‘Novel 90Sr analysis of environmental samples by Ion-Laser InterAction Mass Spectrometry’ by Maki Honda et al., Anal. Methods, 2022, 14, 2732–2738, https://doi.org/10.1039/D2AY00604A.

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.

The passive absorber technique is one of the most common ways to suppress the 10B interference during 10Be measurements at facilities working with beam energies above 7 MeV. At lower energies, the range straggling complicates the application of absorbers, so that other suppression techniques are normally preferred. Several experiments were conducted at the SARA (hosted at Centro Nacional de Aceleradores, Seville, Spain) and VERA (Faculty of Physics, University of Vienna, Austria) AMS facilities to demonstrate the potential of the passive absorber technique also at and below 2.4 MeV. Two different absorber setups were installed and tested. For the detection of the rare isotopes both facilities used a gas ionization chamber optimized for light ions detection based on the same design. The absorber installed at the SARA facility was a combination of SiN foils and an isobutane gas volume, whereas VERA was equipped with an absorber constituted of a stack of SiN foils. In both cases, 10Be could be clearly separated from 10B and the use of a passive absorber at the entrance of the detector gave higher transmission compared to the degrader method. Depending on the absorber design, different background contributions could be identified: Rutherford scattering of 10B on the protons contained in the SiN foils and isobutane gas was responsible of a severe background at SARA, and fragments from 9Be1H molecules surviving the stripping process resulted in events partially overlapping the 10Be gate at VERA. The measured transmissions and background levels will be presented for the tested setups, as well as the advantages and disadvantages of each absorber design., Tests at SARA were funded by the project FIS2015-69673-P of the Spanish Ministry of Economy and Competitiveness.

The neutron capture cross section of Be9 for stellar energies was measured via the activation technique using the Karlsruhe Van de Graaff accelerator in combination with accelerator mass spectrometry at the Vienna Environmental Research Accelerator. To characterize the energy region of interest for astrophysical applications, activations were performed in a quasistellar neutron spectrum of kT=25 keV and for a spectrum at En=473±53 keV. Despite the very small cross section, the method used provided the required sensitivity for obtaining fairly accurate results of 10.4±0.6 and 8.4±1.0μb, respectively. With these data it was possible to constrain the cross section shape up to the first resonances at 622 and 812 keV, thus allowing for the determination of Maxwellian-averaged cross sections at thermal energies between kT=5 and 100 keV. In addition, we report a new experimental cross section value at thermal energy of σth=8.31±0.52 mb.

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.

93Zr 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 93Zr suffer from the interference of the stable isobar 93Nb. 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 36Cl 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 36S, it was recently used to study iron–nickel and zirconium–niobium–molybdenum isobar separation. To our surprise, the separation of 94Zr (Z = 40) from 94Mo (Z = 42) was found to be much better than that of 58Fe (Z = 26) from 58Ni (Z = 28), despite the significantly larger ΔZ/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 93Zr. At 24 MeV particle energy, a 93Nb (Z = 41) suppression factor of 1000 is expected based on a synthetic 93Zr spectrum obtained by interpolation between experimental spectra from the two neighboring stable isotopes 92Zr and 94Zr. Assuming realistic numbers for chemical niobium reduction, a detection level of 93Zr/Zr below 10−9 seems feasible.

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 .

Very sensitive methods, presently mainly accelerator mass spectrometry (AMS) are necessary for analysis of cosmogenic 10Be in the environment. AMS is mainly limited by the stable isobar 10B, while the requirements for mass separation are the least stringent of all standard isotopes analyzed by AMS. We tested a possibility to measure 10Be 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 10Be/9Be isotopic ratio was obtained using this technique, which was mainly determined by scattering of 9Be+2 ions on residual gas inside the switching magnet.

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 63Cu− within the RFQ cooler are presented.

A Centre for Nuclear and Accelerator Technologies (CENTA) has been established at the Comenius University in Bratislava comprising of a tandem laboratory designed for Ion Beam Analysis (IBA), Ion Beam Modification (IBM) of materials and Accelerator Mass Spectrometry (AMS). The main equipment of the laboratory, i.e. Alphatross and MC-SNICS ion sources, 3 MV Pelletron tandem accelerator, and analyzers of accelerated ions are described. Optimization of ion beam characteristics for different ion sources with gas and solid targets, for transmission of accelerated ions with different energy and charge state, for different parameters of the high-energy ion analyzers, as well as first AMS results are presented. The scientific program of the CENTA will be devoted mainly to nuclear, environmental, life and material sciences.

Accelerator mass spectrometry (AMS) represents a complementary approach for precise measurements of neutron capture cross sections, e.g., for nuclear astrophysics. This technique, completely independent of previous experimental methods, was applied for the measurement of the $^{54}\mathrm{Fe}(n,\ensuremath{\gamma})^{55}\mathrm{Fe}$ reaction. Following a series of irradiations with neutrons from cold and thermal to keV energies, the produced long-lived $^{55}\mathrm{Fe}$ nuclei (${t}_{1/2}=2.744+\ensuremath{-}0.009)$ yr) were analyzed at the Vienna Environmental Research Accelerator. A reproducibility of about 1% could be achieved for the detection of $^{55}\mathrm{Fe}$, yielding cross-section uncertainties of less than 3%. Thus, this method produces new and precise data that can serve as anchor points for time-of-flight experiments. We report significantly improved neutron capture cross sections at thermal energy (${\ensuremath{\sigma}}_{\mathrm{th}}=2.30\ifmmode\pm\else\textpm\fi{}0.07$ b) as well as for a quasi-Maxwellian spectrum of $kT=25$ keV ($\ensuremath{\sigma}=30.3\ifmmode\pm\else\textpm\fi{}1.2$ mb) and for ${E}_{n}=481\ifmmode\pm\else\textpm\fi{}53$ keV ($\ensuremath{\sigma}=6.01\ifmmode\pm\else\textpm\fi{}0.23$ mb). The new experimental cross sections have been used to deduce improved Maxwellian-averaged cross sections in the temperature regime of the common $s$-process scenarios. The astrophysical impact is discussed by using stellar models for low-mass asymptotic giant branch stars.

The present article reports on the results and interpretation of a total of 235 radiocarbon dates from Alpine sites in the Ötztal region. Out of these, 88 age determinations were performed on equipment and artifacts associated with the Neolithic Iceman (discovered in 1991), and on a variety of plant and animal specimens collected at his discovery site. Since the material was dispersed over a larger area,14C dates were important to establish the deposition time of the respective samples. About half of the samples fall into the time period where the Iceman lived, documenting synchronous deposition, whereas the others spread out over several thousand years before and after his lifetime. The other set of samples (147) were collected along the Ötztal Valley to the north, with a few samples collected also south of the Alpine watershed. The samples were mainly from soil profiles and peat bogs above the present-day timberline. Overall, the analysis of the data indicates human presence in these high regions of the Alps throughout the Holocene. While the older botanical and archaeological finds indicate activities of hunting and foraging, the younger ones (after ∼5000 BC) point to an intensification of pasturing. This suggests that early human activity was concentrated at altitudes where natural pastures were found, which were probably more favorable than locations at the bottom of the valleys where flooding and other hazards existed. Early users may have come from south of the water divide spreading into the northern regions, particularly during the summer season. It is possible that the Iceman perished at one of his crossings over the probably well-known high-altitude mountain pass due to reasons not yet fully resolved.

Natural 10Be (t1/2 = 1.387 ± 0.012 Ma) is produced by cosmic rays and is present on Earth's surface only at ultratrace concentrations (typically 104 to 1010 atoms/g). Its cosmogenic origin makes it an important tracer for many applications in Earth and environmental sciences. An improved accelerator mass spectrometry (AMS) method has been developed at the Vienna Environmental Research Accelerator (VERA) at the University of Vienna to detect the long-lived radionuclide 10Be and separate it from its isobar 10B. Recently installed and projected AMS facilities mainly apply a degrader foil followed by an electrostatic or magnetic separator to remove 10B from the ion beam. This provides the highest suppression of 10B, but suffers from significant transmission losses of 10Be ions. The new technique described here achieves comparable 10B suppression with a passive absorber, consisting of a stack of silicon nitride foils. Compared to a gas absorber, the smaller energy straggling in foils allows separation at lower energies. For a tandem accelerator operated at 3 MV, the charge state 2 + instead of 3 + can be used, with a stripping yield as high as 55%. This way, a high overall efficiency is gained. The setup is simple to operate, and provides good precision and accuracy. We compare this new approach with other methods used at VERA and at other AMS facilities. The foil stack setup was fully characterized with artificial samples from chemically and isotopically well-defined reagents, and is now routinely applied to real samples in various research projects at VERA. The new method is straightforward to be implemented, and was already adopted at another AMS facility with higher terminal voltage, the potential use at tandem accelerators with lower terminal voltage is under exploration.

VERA, the Vienna Environmental Research Accelerator, is especially equipped for the measurement of actinides, and performs a growing number of measurements on environmental samples. While AMS is not the optimum method for each particular plutonium isotope, the possibility to measure 239Pu, 240Pu, 241Pu, 242Pu and 244Pu on the same AMS sputter target is a great simplification. We have obtained a first result on the global fallout value of 244Pu/239Pu=(5.7±1.0)×10−5 based on soil samples from Salzburg prefecture, Austria. Furthermore, we suggest using the 242Pu/240Pu ratio as an estimate of the initial 241Pu/239Pu ratio, which allows dating of the time of irradiation based solely on Pu isotopes. We have checked the validity of this estimate using literature data, simulations, and environmental samples from soil from the Salzburg prefecture (Austria), from the shut down Garigliano Nuclear Power Plant (Sessa Aurunca, Italy) and from the Irish Sea near the Sellafield nuclear facility. The maximum deviation of the estimated dates from the expected ages is 6years, while relative dating of material from the same source seems to be possible with a precision of less than 2years. Additional information carried by the minor plutonium isotopes may allow further improvements of the precision of the method.

For 14 C 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 1–100 μg were performed within 25 AMS beam-times during the last three years at VERA, revealing a dependency of measured 14 C 3+ / 12 C 3+ ratios on 12 C 3+ currents. This dependency can be accounted for by assuming a background current, which was determined for each AMS measurement by least square fitting. 12 C - ion currents extracted from microgram graphite samples were typically (1.0 ± 0.5) μA / μg C. On average a 12 C 3+ background current of (0.14 ± 0.14) μA with F 14 C = 0.22 ± 0.46 (skewness γ 1 = 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 CO 2 samples was investigated. No dependency on the cathode target geometry was observed for 9 differently shaped cathode types.

Isobaric interference represents one of the major limitations in mass spectrometry. For a few cases in AMS with tandem accelerators, isobaric interference is completely excluded like the well-known major isotopes 14C, 26Al, 129I. Additional isotopes are 55Fe (t1/2 = 2.74 years), 68Ge (t1/2 = 270.9 days) and 202Pb (t1/2 = 52.5 kyr), with 68Ge and 202Pb never been used in AMS so far. Their respective stable isobars, 55Mn, 68Zn and 202Hg do not form stable negative ions. The exceptional sensitivity of AMS for 55Fe, 68Ge and 202gPb offers important insights into such different fields like nuclear astrophysics, fundamental nuclear physics and technological applications. VERA, a dedicated AMS facility is well suited for developing procedures for new and non-standard isotopes. AMS measurements at the VERA facility established low backgrounds for these radionuclides in natural samples. Limits for isotope ratios of

To unravel the mechanisms of ion formation in the Middleton type cesium sputter negative ion source, we have acquired and analyzed the spectrum of the light emitted from the source region during sputtering of three different cathode materials; carbon, aluminum and copper. All cathodes were analyzed under the same source settings but with different total current output. The cathode region was observed from a distance of 3 m and the emitted light was analyzed by a fiber coupled spectrometer with a wavelength range from 350 to 1100 nm. The spectra showed clear differences depending on the cathode material. The emitted light from the carbon cathode consisted almost entirely of lines from neutral cesium and no lines from ionized cesium. Both metallic cathodes additionally displayed several lines originating from positively ionized cesium. A weak, broad feature between 470 and 510 nm was also seen in the carbon spectrum. This feature was not present in spectra from the two metallic cathodes. These results may suggest different mechanisms of negative ion formation in the ion source depending on the cathode material. As a side effect of the measurement it proved relatively easy to determine the source temperature, in the range 1020–1215 K depending on source settings, to an accuracy of ±30 K from the black body radiation.

The requirements of extracting minute amounts of organic carbon in solution with high yield and minimum background are a prerequisite for radiocarbon dating of microgram amounts of carbon. Samples for biomedical or environmental research often arrive at the accelerator mass spectrometry (AMS) lab as concentrates dissolved in 1 mL of water or less. We have developed a new extraction method based on photo-oxidation by ultraviolet (UV) light. The solution is transferred into UV-transparent quartz vials with a head volume of pure oxygen and UV from low-pressure mercury discharge lamps is applied. To exclude the introduction of carbon background, we avoid any additional oxidizing agents. Under these conditions, only the 185 nm line is considered effective. To characterize the yield and the background, we have investigated artificial samples prepared from different materials. The setup developed allows parallel oxidation of 9 samples within typically 2 hr, connected directly to our graphitization setup for extremely small samples. The method was applied successfully for a study on dissolved organic carbon (DOC) in ice from 26 Austrian glaciers. A special advantage of the UV oxidation method in this case was that phosphoric acid could be used to remove carbonates, while its low vapor pressure prevented complete lyophilization. We see the most promising field of application in biomed research and compound-specific analysis. DOI: 10.2458/azu_js_rc.55.16368

Recent progress with compact ionization chambers has opened new possibilities for isobar suppression in accelerator mass spectrometry (AMS). Separation of 36 Cl ( t 1/2 = 0.30 Ma) at natural isotopic levels from its stable isobar 36 S became feasible at particle energies of 24 MeV, which are also accessible for medium-sized tandem accelerators with 3 MV 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 × 10 4 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 36 S peak, the reproducibility for high ratio samples ( 36 Cl/Cl > 10 −12 ) is better than 2%. Our blank value of 36 Cl/Cl ≈ (5 ± 5) × 10 −16 is competitive to other labs. 36 Cl 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 300 mW continuous wave laser beam at 445 nm towards the cathode in the ion source.

Concentrations of gases and particulate matter have been proven to be affected by meteorological and geographical variables from urban locations to high mountain clean air sites. Following our previous research in Vienna, we summarize here new findings about concentration levels of iodine isotopes in aerosols collected at two Alpine meteorological stations, Sonnblick (Austria) and Zugspitze (Germany) during 2001. The present study mainly focuses on the effect of altitude on the anthropogenic concentration of (129)I and on the isotopic ratio (129)I/(127)I. Iodine was separated from matrix elements by using either an anion exchange method or solvent extraction, and was analyzed by ICP-MS and AMS. Over the altitude change from Vienna to Zugspitze and Sonnblick (202 m to 2962 m and 3106 m above sea level), stable iodine level decreased from an average of 0.94 ng m(-3) to 0.52 ng m(-3) and 0.62 ng m(-3), respectively. Similarly, (129)I concentrations at both Alpine stations were about 1 order of magnitude lower (10(4) atoms m(-3)) than values obtained for Vienna (10(5) atoms m(-3)) and reveal a strong vertical concentration gradient of (129)I. A high degree of variability is observed, which is due to wide variation in the origin of air masses. Furthermore, air trajectory analysis demonstrates the importance of large scale air transport mostly from southeast Europe for influencing Sonnblick whereas influence from northwest Europe is strong at Zugspitze. In contrast to (129)I, a higher concentration of (7)Be was found at higher altitude stations compared to Vienna which probably results from its production in the upper atmosphere.

Accelerator mass spectrometry (AMS) of 36Cl (t1/2 = 0.30 Ma) 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 5 MV 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 3 MV 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 ≈ 5 μA) 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 3 MV tandems can achieve the same sensitivity for 36Cl as larger machines.

In the search for long-lived superheavy elements (SHEs) in nature the claim for the detection of a SHE species with A = 292 in a commercially available thorium solution at an abundance of (1–10) × 10 −12 relative to 232 Th using ICP-SFMS has been raised very recently by Marinov et al. The same group also claimed the finding of four long-lived isomeric states in neutron-deficient thorium isotopes at an abundance of (1–10) × 10 −11 relative to 232 Th using the same experimental method. The aim of our study was to examine, whether the ratios mentioned above could also be found in a natural thorium mineral, using AMS as a much more sensitive technique assuring the complete suppression of molecular background. Chemically untreated thorianite (ThO 2 ) was used for both measurements. In addition, commercial thorium(IV) oxide (thoria) powder was also analyzed in the SHE measurements. No events were observed in the A = 292 SHE search, resulting in an upper limit of 4 × 10 −15 for the abundance of such a species relative to 232 Th. For two neutron-deficient thorium isotopes, 211 Th and 218 Th, we find upper limits of 5 × 10 −15 . For 213 Th and 217 Th we observed a few events – albeit uncertain – which would put their abundance also into the 10 −15 range.

Recent improvements in isobaric suppression for medium-mass isotopes, e.g. 41 Ca, offer new possibilities for tandem accelerators with terminal voltages of 3 MV or lower; i.e. when dealing with particle energies 61 MeV/amu. In particular, detection of 41 Ca requires sufficient discrimination of the stable isobar 41 K. We explored the limits of 41 Ca detection at our 3-MV AMS facility by means of different types of particle detectors: The DTOF 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: 41 K and 41 Ca 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 41 Ca/Ca ratios below 10 13 for commercial CaF2 material serving as blank samples. CaH2 sputter targets, with the extraction of CaH 3 , yielded background ratios as low as 41 Ca/Ca = 1 10 15 . The typical measurement precision at VERA for 41 Ca 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.

The possibility of detecting 36 Cl 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, Zurich, Switzerland) with two anodes. To improve the suppression of 36 S, 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 × 50 mm 2 ) as stop detector. We optimized the TOF setup by using silicon nitride foils to reduce scattering tails in the energy spectra. At 3 MV terminal voltage, corresponding to a particle energy of 24 MeV of 36 Cl 7+ , we achieved a 36 S 7+ -suppression of 21,500 (50% 36 Cl-detector-efficiency).

Efforts to extract weak geomagnetic excursion signals from Chinese loess-paleosol 10Be have generally been unsuccessful due to the complexities of its accumulation, because the geomagnetic and climate (precipitation and dust) signals contained in loess-paleosol sequence are tightly overprinted. Here, we present a reconstruction of geomagnetic relative paleointensities for the past 130 kyr from 10Be records in 2 Chinese loess-paleosol sections using a correction based on the correlation of 10Be with magnetic susceptibility (SUS) to remove the climatic contamination. Both these records reveal the Laschamp and Blake events, which lie in the loess and paleosol (L1SS1 and S1SS3) horizons corresponding to mid-MIS 3 and 5e, respectively. The good agreement between our results and other geomagnetic intensities reconstructions from Atlantic and Pacific sediments indicates that our method is robust. Our study suggests the potential application of loess-paleosol 10Be for reconstructing geomagnetic intensity variations spanning the whole Quaternary.

Cosmogenic radionuclides in the one-million-year half-life range offer unique possibilities for age determinations in geophysics. In measurements where the radioactive decay is being utilized as a clock, uncertainties in age determinations may be reduced if the ratio of two radioisotopes with different half-lives can be used as a chronometer. In this work we investigate the atomic ratio of atmospheric 26Al (t1/2 = 0.717 Ma) to 10Be (t1/2 = 1.386 Ma) measured with accelerator mass spectrometry (AMS), and its potential as a chronometer for dating old ice. The 26Al/10Be ratio decreases with an effective half-life of t1/2(26Al/10Be) = 1.49 Ma. For its application as a chronometer, the atmospheric 26Al/10Be ratio has to be well characterized. However, the properties of atmospheric 26Al have been understood only poorly so far. At the VERA AMS facility of the University of Vienna, a first systematic study of the global variations of the 26Al/10Be ratio in the atmosphere and in surface firn has been carried out, and pilot measurements of the 26Al/10Be ratio in deep Antarctic ice have been performed. Our results indicate that this ratio is globally constant to within 5% in the atmosphere and in surface firn with a mean value of 1.89 × 10− 3. The data also suggest that non-atmospheric sources of 26Al, such as extraterrestrial, in situ produced or re-suspended 26Al, do not contribute significantly to the observed 26Al/10Be ratio. In addition, atmospheric mixing seems to exert only a minor influence. In a first application of the method, 26Al/10Be ratios were measured in chips collected in connection with the drilling of the lowest part of an ice core (2250 to 2760 m) in Dronning Maud Land, Antarctica. Surprisingly, variable 26Al/10Be ratios ranging between 0.5 and up to 2 times the atmospheric ratio were found at different locations in this deep ice core. While the cause for the ratios higher than atmospheric remains unexplained so far, the ratios lower than atmospheric may be caused by radioactive decay, allowing a first dating attempt using the 26Al/10Be ratio. Thus, at an ice depth of 2760 m an approximate date of (6.7 ± 2.6) × 105 years was established.

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 Goteborg 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.

The increasing demand for measuring long-lived radionuclides with small AMS machines at energies below 1 MeV per nucleon raises the need for compact detectors which still have a decent energy resolution and allow for a clear identification of the incident particles. Based on a design by the AMS group at the ETH Zurich a compact gas ionization chamber was built and installed at the 3 MV tandem AMS facility VERA (Vienna Environmental Research Accelerator). The main challenge in AMS is the detection of rare isotope species in the presence of strong isotopic and isobaric interferences. The task of the ionization chamber is the suppression of the unwanted isobar by separating the ions via their different stopping powers. Measurements of 36Cl at VERA showed an achieved suppression of the unwanted stable isobar 36S of 3 × 10−4 and measurements of 10Be showed an achieved suppression of 10B of at least 3 × 10−6. Additional suppression of the isobaric ions can be achieved by a degrader foil technique applied to 10Be measurements by G.M. Raisbeck. In combination with the new ionization chamber the achieved suppression of 10B is at least 10−10. Measurements of blank samples at VERA show that the background for AMS with 10Be is below 2 × 10−15.

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 Durer (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. Durer drawings from the collection of the Albertina, Vienna, were analyzed to amend existing data on Durer 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 ∼0.15 mm on the object in air with 3 MeV 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 Durer’s very early period (self-portrait and portrait of his father) and two drawings from Durer’s sketch book of his travel to the Netherlands 1520/21.

The potential for measuring the radionuclides 41 Ca and 55 Fe was investigated with the 3 MV tandem accelerator at VERA. Interestingly, up to now, no applications have been published for 55 Fe using the technique of AMS. This is in strong contrast to 41 Ca, which is routinely measured by medium and large tandem accelerators in various applications. Using CaF 2 samples the quantification of 41 Ca down to levels of a few 10 −13 for the isotope ratio 41 Ca/Ca has become possible with the use of the ΔTOF technique. Both nuclides, 41 Ca and 55 Fe were found to be of interest in nuclear astrophysics. A first application of 41 Ca detection at VERA is the measurement of the 40 Ca(n, γ) 41 Ca cross section at stellar temperatures. Similarly, of astrophysical interest is the production of 55 Fe via neutron capture on 54 Fe. To this end, different Ca and Fe blank and standard samples were investigated with the goal to establish an AMS method for 41 Ca and 55 Fe measurements. Indeed, low background levels for both radionuclides, 41 Ca and 55 Fe, were observed in these studies. The full separation power of VERA results in a very low detection limit, while still providing a high overall transmission.

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.

Equipment for automated phase–space measurements was developed at the VERA Lab. The measurement of the beam’s intensity distribution, as well as its relative position with respect to the reference orbit is performed at two locations along the beam line. The device basically consists of moveable slits and a beam profile monitor, which are both coordinated and controlled by an embedded controller. The operating system of the controller is based on Linux with real-time extension. It controls the movement of the slits and records the data synchronized to the movement of the beam profile monitor. The data is sent via TCP/IP to the data acquisition system of VERA where visualization takes place. The duration of one phase space measurement is less than 10 s, which allows for using the device during routine beam tuning.

The measurement of the paired cosmogenic radionuclides 26 Al and 10 Be in environmental samples has potential applications in atmospheric and climate research. For this study, we report the first measurements of the 26 Al/ 10 Be atomic ratio in tropospheric aerosol samples from sites in Europe and Antarctica performed at the Vienna Environmental Research Accelerator (VERA). These initial results show that the 26 Al/ 10 Be atomic ratio in tropospheric aerosols averages 1.78 × 10 −3 and does not vary significantly between the different locations. We also report results of systematic investigations of the ionization and detection efficiency which we performed to improve the measurement precision for 26 Al by AMS. Maximum detection efficiencies of up to 9 × 10 −4 (in units of 26 Al atoms detected/initial) were achieved for chemically pure Al 2 O 3 , while for atmospheric samples we reached efficiencies of up to 2.2 × 10 −4 .

“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 H 2 - , D 2 - and (2) the unambiguous identification of the smallest doubly-charged negative molecule (LiF3)2−. In particular we show new experimental data for D 3 - , and for (LiF3)2−, and we try to answer the question why M&K’s search for this di-anion was unsuccessful.

The cosmogenic radionuclide 10Be is produced by cosmic-ray spallation in Earth's atmosphere. Its production rate is regulated by the geomagnetic field intensity, so that its accumulation rate in aeolian sediments can, in principle, be used to derive high-resolution records of geomagnetic field changes. However, 10Be atmospheric fallout rate also varies locally depending on rainfall rate. The accumulation rate of 10Be in sediments is further complicated by overprinting of the geomagnetic and precipitation signals by 10Be attached to remobilized dust, which fell from the atmosphere at some time in the past. Here, we demonstrate that these signals can be deconvoluted to derive both geomagnetic field intensity and paleoprecipitation records of Asian Monsoon intensity in an 80,000-yr-long 10Be record from Chinese loess. The strong similarity between our derived paleomagnetic intensity record and the SINT 200 (Guyodo and Valet 1996) and NAPIS 75 (Laj et al. 2002) stacked-marine records suggests that this method might be used to produce multimillion-yr-long records of paleomagnetic intensity from loess. This technique also reveals a new method for extracting quantitative paleoprecipitation records from continental interior regions. Our derived precipitation record is broadly similar to the speleothem δ18O-based records of paleo-Asian Monsoon intensity from Dongge (Yuan et al. 2004) and Hulu (Wang et al. 2001) caves, and suggests that the paleo-Asian Monsoon intensity may be responding to a combination of both Northern and Southern Hemisphere insolation forcing.

Well-established data on production-rates of long-lived radionuclides are important for the understanding and calculation of various nucleosynthesis processes. However, lack of information exists for a list of nuclides as pointed out by nuclear-data requests. In addition, the search for supernova (SN)-produced radionuclides will give an improved insight into explosive scenarios. Accelerator mass spectrometry (AMS) represents a technique, which is capable to quantify such long-lived radionuclides using mass spectrometric methods. The potential of AMS is presented here as a powerful tool for probing nucleosynthesis. Applications of AMS are exemplified for a few specific cases: the detection of extraterrestrial radioactivity on Earth in terrestrial archives as a signature of nearby SN explosions, and the measurement of cross-sections, as an important ingredient for stellar as well as nuclear model calculations.

The ΔTOF detector is a new approach for isobar separation at energies below 1 MeV/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 0.5 MeV/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 0.5 MeV/amu and 41Ca at 0.4 MeV/amu with the 3 MV tandem accelerator VERA are presented.

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 (0.6 μg/cm2) and by pushing our Pelletron tandem to 3.6 MV, we achieved a significant increase in energy compared to gas stripping at 3 MV: e.g. 36Cl7+ at 28.8 MeV instead of 36Cl5+ at 18 MeV can be used.

A novel method to determine small cross-sections of nuclear reactions of astrophysical interest was implemented at the Vienna Environmental Research Accelerator laboratory (VERA). This method combines inverse-kinematics reactions taking place inside the stripper of a tandem accelerator with the identification of the recoil products using the accelerator mass spectrometry (AMS) technique. As a first test we studied the 1H(12C,γ)13N reaction, which is the starting reaction of the stellar CNO cycle of hydrogen burning. The 13N recoil products as well as the interfering isobar 13C were separated from the main 12C beam by common AMS techniques. Measurements with 13N recoil ions of different charge states were performed at center-of-mass energies of 229 and 206 keV, respectively. Notwithstanding the restrictions of VERA, the principle feasibility of the method could be demonstrated.

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.

182 Hf is a so-called “extinct” radionuclide interesting for both geophysical and astrophysical studies. The discovery of live 182 Hf in the early solar system through isotopic anomalies of stable 182 W in meteorites opened up an important application as a chronometer for the formation of the Earth and Moon. In addition, 182 Hf 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 182 Hf on Earth. Thus finding live 182 Hf 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 182 Hf.