[en] Full text: At the DREAMS (DREsden AMS) facility [1,2] we are implementing a so-called Super-SIMS (SIMS = Secondary Ion Mass Spectrometry) device [3] for specialized applications. The system combines the spatial resolution capability of a commercial SIMS (CAMECA IMS 7f-auto) with AMS capability, which should suppress molecular isobars in the ion beam allowing for the quantification of elemental abundances down to ~ E-9 - E-12. This would be more than an order of magnitude improvement over traditional dynamic SIMS (e.g. [4,5]). We aim to use this for the highly sensitive analysis of geological samples in the context of resource technology. In the present setup, high efficiency transmission in the low-energy ion optics segment remains a challenge, as the beam needs to traverse two existing magnet chambers without deflection, where no steering or lens elements are available over a flight distance of 4 m. We have now improved the low-energy injection just after the ion beam exits the 7f-auto, upgrading the steerers directly after the SIMS and by adding a beam intensity attenuator. This provides both more stable conditions for instrument tuning and simplifies transition between measurements of the beam intensity in Faraday cups and the gas ionization chamber. Regarding the measurement of C, N and O in silicon, we found that a simple Wien-filter using permanent magnets for the primary Cs-sputter beam significantly reduces the background at the detector, as the 7f-auto uses a Cs₂ CO₃ source – rather than metallic Cs – for the generation of the primary positive Cs beam. Once the remaining issues associated with ion beam-path are fully addressed, we will still need to tackle the issue of establishing suitable, well characterized reference materials needed for our first suite of resource and geoscience applications (e.g., halides in naturally occurring sulphide minerals). We present ongoing developments and results, as well as plans for extending to other matrices and isotope systems.

[en] Full text: One of the most important tasks in the design and construction of ultra-low background experiments is the radioassay of the materials used. This requires the selection of the materials and enables the calculation of expected detector background. The ASTREA project (Accelerator mass spectrometry Survey of Trace Radionuclides for Experiments in Astroparticle physics) addresses AMS radioassay challenges for a few rare event experiments. Some examples are nEXO, which is searching for neutrinoless double beta decay; and NEWS-G and DarkSide, which are attempting to directly detect dark matter. This project, led by the André E. Lalonde AMS Laboratory (AEL-AMS) at the University of Ottawa, is performed in collaboration with Carleton University, Queens University and University of Alberta. The main focus of the project is screening Pb-210 in various detector construction materials, with emphasis on low background copper and high-performance polymers. We have studied the possibility of using 2 different materials for the AMS measurements: lead fluoride (PbF₂) and lead oxide (PbO) targets, producing respectively (PbF₃)- and (PbO₂)- ions on the LE side. In both cases, the ²¹⁰Pb/²⁰⁶Pb blank ratio is in the 1e-14–1e-13 range. Measurements on 1-2 g Kapton films have established upper limits in the range 850-2500 mBq/kg at 90% C.L. Future ASTREA activities will focus on the Pb-210 assay in acrylic, which is considered for future low background dark matter detectors. Previous best results, obtained in 2014 by γ-counting 2 kg of acrylic, have established an upper limit for the Pb-210 concentration of 0.3 mBq/kg. Our proposed method, using AMS, should provide a limit of detection in the 0.01-0.1 mBq/kg range. Other important study looks at the Pb-210 contamination in the electroformation process of the copper for the NEWS-G and nEXO detectors. For the Pb-210 concentration in the copper, we estimate a limit of detection in the 0.3-1.0 mBq/kg range.

[en] Dealing with the ⁴¹K interference during ⁴¹Ca measurement with low energy AMS systems is challenging. The detection of ³⁹K to correct the measured ⁴¹Ca/⁴⁰Ca ratios is a powerful tool that improves precision and accuracy. However, the study of the sources of this interference can help to reduce it to its minimum. In this work, it is shown that iron is a factor enhancing the production of the ⁴¹K interference, since the (⁴¹K⁵⁷Fe)⁻ ion has the same mass as (⁴¹K¹⁹F₃)⁻. To validate this observation, we measured ⁵⁷Fe²⁺ together with ⁴¹M²⁺ (all ions with mass 41) and ³⁹K²⁺ in a blank sample and an aluminum target at the 600 kV AMS system at ETH Zurich. We also show the temporal evolution of ⁴¹M/⁴⁰Ca and ³⁹K/⁴⁰Ca ratios in two blank samples during a measurement on the 1 MV AMS system at CNA Seville. Even when unstable behavior for these ratios is observed for one of the blanks, the relationship between both, ⁴¹M/³⁹K, is relatively stable over time. This supports the accuracy of the K–correction method, providing that it is applied sequence by sequence. Two programs, one for each of these compact AMS systems, were written in FORTRAN code to deal with the complexity of the data analysis due to the K-correction.

[en] We present a detailed study of the performance parameters for ⁴¹Ca measurements at the 1 MV AMS system at the Centro Nacional de Aceleradores (CNA) in Seville. Mixing CaF₂ with Ag, we get stable (⁴⁰CaF₃)⁻ currents between 50 and 100 nA. Transmission of the 2+ state in the He stripper is 41%, while optical transmission in the HE sector is typically higher than 95%. At low energies we cannot separate ⁴¹Ca from the isobar ⁴¹K at the detector, but the interference is reduced by using (⁴¹CaF₃)⁻ ions. The remaining contribution is corrected by measurement of the other stable isotope of potassium, ³⁹K, to estimate this interference (K-correction). After this correction, we reach a ⁴¹Ca/⁴⁰Ca background level between 5 × 10⁻¹² and 8 × 10⁻¹², making possible measurements of ⁴¹Ca/⁴⁰Ca ratios higher than 4 × 10⁻¹¹. Intercomparisons with the 0.6 MV AMS system at ETH Zurich show a quite good correlation.

[en] Highlights: • Update of ¹²⁹I distribution in Central North Atlantic (NA) and the Nordic Seas. • Evolution of ¹²⁹I from 2002 to 2012 is associated to changes in releases from NFRPs. • Results suggest deep water formation in the eastern area of the Nordic Seas. • ¹²⁹I from NFRPs partly reaches Central NA and are not carried northwards by the NCC. Most of the anthropogenic radionuclide ¹²⁹I released to the marine environment from the nuclear fuel reprocessing plants (NFRP) at Sellafield (England) and La Hague (France) is transported to the Arctic Ocean via the North Atlantic Current and the Norwegian Coastal Current. ¹²⁹I concentrations in seawater provides a powerful and well-established radiotracer technique to provide information about the mechanisms which govern water mass transport in the Nordic Seas and the Arctic Ocean and is gaining importance when coupled with other tracers (e.g. CFC, ²³⁶U). In this work, ¹²⁹I concentrations in surface and depth profiles from the Nordic Seas and the North Atlantic (NA) Ocean collected from four different cruises between 2011 and 2012 are presented. This work allowed us to i) update information on ¹²⁹I concentrations in these areas, required for the accurate use of ¹²⁹I as a tracer of water masses; and ii) investigate the formation of deep water currents in the eastern part of the Nordic Seas, by the analysis of ¹²⁹I concentrations and temperature-salinity (T-S) diagrams from locations within the Greenland Sea Gyre. In the Nordic Seas, ¹²⁹I concentrations in seawater are of the order of 10⁹ at·kg^{− 1}, one or two orders of magnitude higher than those measured at the NA Ocean, not so importantly affected by the releases from the NFRP. ¹²⁹I concentrations of the order of 10⁸ atoms·kg^{− 1} at the Ellet Line and the PAP suggest a direct contribution from the NFRP in the NA Ocean. An increase in the concentrations in the Nordic Seas between 2002 and 2012 has been detected, which agrees with the temporal evolution of the ¹²⁹I liquid discharges from the NFRPs in years prior to this. Finally, ¹²⁹I profile concentrations, ¹²⁹I inventories and T-S diagrams suggest that deep water formation occurred in the easternmost area of the Nordic Seas during 2012.