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Routine measurements of the last years at the 6 MV AMS system showed a good isobar suppression for all light isotopes, measured with the Degrader-Foil-Method, especially Cl-36 and Be-10. However, the efficiency is reduced due to the charge state distribution generated by the degrader-foil. For measurements injecting atomic Al-26, the ionization efficiency becomes the bottleneck, which leads to a relatively low ion source output. In the case of AlO-, the output is expected about one order of magnitude higher. However, to use AlO- the isobar interference of Mg-26 will become an issue. It has to be suppressed in several steps, e.g. by different dE/dx methods like TOF, degrader-foil or gas-filled magnet. In order to minimize the efficiency losses generated by the degrader-foil method, the 120 degrees-magnet at the 6 MV AMS system was modified to enable a gas-filled operation, and therefore focus the beam to a mean charge state. A constraint for all modification of the detection beam line was that the operation of the degrader-foil method is not affected. In this paper, we report on the performed construction work, as well as test measurements for Al-27 at 40 MeV ion energy. Isobar separation for Cl-36 and S-36 was measured as a function of the gas pressure. We compare measured data with Monte Carlo simulations performed with a computer code developed by our group. In addition, we will present a new dedicated gas ionization chamber designed for particle detection directly after the gas-filled magnet.

A new multi-isotope plutonium standard for isotopic ratio measurements with Accelerator Mass Spectrometry (AMS) was created by gravimetric mixing of different single-isotope standards provided by IRMM (Pu-239, Pu-240, Pu-242, Pu-244). This standard material has been measured at the AMS facilities at Canberra (Australia), Cologne (Germany), Caserta (Italy), Sevilla (Spain) and Zurich (Switzerland). Additionally, the material was characterized using a Neptune MC-ICPMS (multi-collector inductively coupled plasma mass spectrometry) at the joint Cologne-Bonn isotope facility. The results of this laboratory intercomparison are presented and consensus values for the isotope compositions of the standard material are proposed.

A new accelerator mass spectrometer was successfully designed for the Cologne FN accelerator to enlarge the measurement capability of CologneAMS to medium mass radionuclides. With this AMS-system (Mn-53/Mn-55) isotopic ratios are measurable at a 10 MV tandem accelerator in the range of 10(-9) to 10(-10) for the first time, with a detection limit of C-L = 5.0 x 10(-12). A high Cr-53 suppression in the (Mn-53/Mn-55) isotopic ratio measurement was achieved by using the optimal silicon nitride degrader foil thickness in combination with an electrostatic analyzer (ESA). The new system opens the field of research for CologneAMS users to the medium mass region of cosmogenic nuclides, like Mn-53 for geological applications of long term erosion, exposure and burial dating and Fe-60 for nuclear astrophysical models. The presented definition of an error normalized sensitivity S-x allows an inter laboratory comparison of isotopic ratio measurements.

The motivation of this work is to establish a new multi-isotope plutonium standard for isotopic ratio measurements with accelerator mass spectrometry CAMS), since stocks of existing solutions are declining. To this end, certified reference materials (CRMs) of each of the individual isotopes (PU)-P-239, (240)pu, (242)pu and Pu-244 were obtained from JRC IRMM (Joint Research Center Institute for Reference Materials and Measurements). These certified reference materials (IRMM-081a, IRMM-083, IRMM-043 and IRMM-042a) were diluted with nitric acid and mixed to obtain a stock standard solution with an isotopic ratio of approximately 1.0:1.0:1.0:0.1 ((239)pu:(240)pu:(242)pu:(244)pu). From this stock solution, samples were prepared for measurement of the plutonium isotopic composition by AMS. These samples have been measured in a round-robin exercise between the AMS facilities at CologneAMS, at the ANU Canberra and ETH Zurich to verify the isotopic ratio and to demonstrate the reproducibility of the measurements. The results show good agreement both between the different AMS measurements and with the gravimetrically determined nominal ratios. (C) 2015 Elsevier B.V. All rights reserved.

Following demands for AMS measurements of medium mass isotopes, especially for Mn-53 and Fe-60, we started to build a dedicated AMS setup at the Cologne FN tandem accelerator. This accelerator with a maximum terminal voltage of 10 MV can be reliably operated at a terminal voltage of 9.5 MV which corresponds to energies of 93-102 MeV for Fe-60 or Mn-53 beams using the 9(+) or 10(+) charge state. These charge states can be obtained by foil stripping with efficiencies of 30% and 20%, respectively. Energies around 100 MeV are sufficient to effectively suppress the stable isobars Ni-60 and Cr-53 by (dE/dx) techniques using combinations of energy degrader foils and dispersive elements like electrostatic analyzers and time of flight (TOF) systems as well as (dE/dx)E ion detectors. In this contribution we report on the actual status of the AMS setup and discuss details and expected features. (C) 2015 Elsevier B.V. All rights reserved.

The motivation of this work is to establish a new multi-isotope plutonium standard for isotopic ratio measurements with accelerator mass spectrometry (AMS), since stocks of existing solutions are declining. To this end, certified reference materials (CRMs) of each of the individual isotopes 239Pu, 240Pu, 242Pu and 244Pu were obtained from JRC IRMM (Joint Research Center Institute for Reference Materials and Measurements). These certified reference materials (IRMM-081a, IRMM-083, IRMM-043 and IRMM-042a) were diluted with nitric acid and mixed to obtain a stock standard solution with an isotopic ratio of approximately 1.0:1.0:1.0:0.1 (239Pu:240Pu:242Pu:244Pu).From this stock solution, samples were prepared for measurement of the plutonium isotopic composition by AMS. These samples have been measured in a round-robin exercise between the AMS facilities at CologneAMS, at the ANU Canberra and ETH Zurich to verify the isotopic ratio and to demonstrate the reproducibility of the measurements. The results show good agreement both between the different AMS measurements and with the gravimetrically determined nominal ratios.