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We present measurements of energy loss and straggling of Si ions in gases. An energy range from 0.5 to 12 MeV/u was covered using the 6 MV EN tandem accelerator at ETH Zurich, Switzerland, and the K130 cyclotron accelerator facility at the University of Jyväskylä, Finland. Our energy-loss data compare well with calculation based on the SRIM and PASS code. The new straggling measurements support a pronounced peak in He gas at around 4 MeV/u predicted by recent theoretical calculations. The straggling curve structure in the other gases (N 2 , Ne, Ar, Kr) is relatively flat in the covered energy range. Although there is a general agreement between the straggling data and the theoretical calculations, the experimental uncertainties are too large to confirm or exclude the predicted weak multi-peak structure in the energy-loss straggling. [ABSTRACT FROM AUTHOR]

We present the performance of 41 Ca measurements using low-energy Accelerator Mass Spectrometry (AMS) at the 500 kV facility TANDY at ETH Zurich. We optimized the measurement procedure for biomedical applications where reliability and high sample throughput is required. The main challenge for AMS measurements of 41 Ca is the interfering stable isobar 41 K. We use a simplified sample preparation procedure to produce calcium fluoride (CaF 2 ) and extract calcium tri-fluoride ions ( CaF 3 - ) ions to suppress the stable isobar 41 K. Although 41 K is not completely suppressed we reach 41 Ca/ 40 Ca background level in the 10 - 12 range which is adequate for biomedical studies. With helium as a stripper gas we can use charge state 2+ at high transmission (∼50%). The new measurement procedure with the approximately 10 × improved efficiency and the higher accuracy due to 41 K correction allowed us to measure more than 600 samples for a large biomedical study within only a few weeks of measurement time. [ABSTRACT FROM AUTHOR]

Abstract: The use of helium as a stripper gas for Accelerator Mass Spectrometry (AMS) measurements of heavy ions is presented. At ion stripping energies of about 500keV and below we observe a significant increase of the mean charge state when using helium instead of other gases. Moreover, scattering losses are reduced with helium because of its lower mass compared to other commonly used stripper gases. Thus, highly efficient AMS measurements for 41Ca, 129I and 236U with transmissions through the accelerator in the range of 40–50% are now possible. [Copyright &y& Elsevier]

Abstract: The current performance of all three AMS systems in operation at ETH Zurich, the 6MV HVEC EN-Tandem facility “TANDEM”, the 0.5MV NEC Pelletron “TANDY”, and the 0.2MV system “MICADAS” is summarized. Radionuclides routinely measured with these AMS systems include 10Be, 14C, 26Al, 36Cl, 41Ca, 129I and the actinides. The reference materials used for the normalization of the AMS measurements at the ETH Zurich AMS facilities are presented. This paper therefore is a comprehensive status report of all three AMS systems currently operated by the Laboratory of Ion Beam Physics (LIP) at ETH Zurich and documents their performance and operation parameters. [Copyright &y& Elsevier]

Abstract: The DRAGON (Detector of Recoils And Gammas Of Nuclear reactions) is used to measure radiative proton and alpha capture reaction rates involving both stable and radioactive, heavy-ion reactants at the TRIUMF-ISAC high intensity radioactive beam facility. Completed in 2001 it has been used for several challenging studies for nuclear astrophysics, e.g. 12C(α, γ)16O, 21Na(p, γ)22Mg, 26gAl(p, γ)27Si and 40Ca(α, γ)44Ti. Since initial operation, a number of improvements have been incorporated which are described here. These include a beam centering monitor based on a CCD camera, a mechanical iris to skim of beam halo, a solid state stripper acting as a charge state booster for beams with A ≳30, beta and gamma detectors to monitor beam intensity and to determine beam contamination in experiments with radioactive beam and the ionization chamber for both recoil identification and isobar separation. [Copyright &y& Elsevier]

Abstract: Nuclear reactions play a key role in understanding nucleosynthesis in stars. Recoil mass spectrometers such as DRAGON are well suited to study reactions with respect to astrophysical production because of direct detection of reaction products. Here we present the first stage of an experiment running at the recoil mass spectrometer DRAGON at the ISAC/TRIUMF facility in Vancouver, Canada, to study the reaction 40Ca(α,γ)44Ti at astrophysically relevant energies. This reaction is one of the key reactions for production of 44Ti, which has been identified in young supernova remnants by space based γ-ray telescopes onboard COMPTEL and INTEGRAL. In this paper we focus on technical upgrade of DRAGON for 40Ca(α,γ)44Ti and preliminary results at resonances at E x ∼9.2MeV. [Copyright &y& Elsevier]

Abstract: The detection of 182Hf by Accelerator Mass Spectrometry (AMS) is greatly complicated because of the stable and common isobar 182W. Although significant W reduction can be achieved during negative ion formation using , additional separation is necessary to achieve detection sensitivities sufficient for astrophysical applications, i.e. detection of potential supernova-produced 182Hf on Earth. In this paper, we present a new development of isobar separation using the ΔTOF detection method at the Munich MP Tandem accelerator (TV=14MV), where ion energies for 182Hf of about 1MeV/amu can be achieved. Particular attention is drawn on specific energy loss and energy loss straggling measurements in various materials, the basis for our method of isobar separation. [Copyright &y& Elsevier]

In this study, the possibility of using a superhalogenide ion AlF 4 - extracted from Na 3 AlF 6 based target materials for 26Al/27Al measurements by Accelerator Mass Spectrometry (AMS) was investigated. Determination of 26Al by usual mass spectrometric methods is generally hampered by the presence of the isobar 26Mg. However, the AMS method enables significant suppression of this interference, particularly by negative ion formation. After initial current tests in a caesium sputtering ion source of the Tandetron system, performance of the fluoride materials was analysed on the MILEA AMS system at ETH Zürich. The AlF 4 - current was used to evaluate the performance of the respective samples. Additives as PbF 2 were tested to increase the extracted ion currents and samples containing MgF 2 were used to investigate the presence of isobaric ions. Subsequently, the ionization efficiency of AlF 4 - was determined by recording the 27Al2+ current on the high energy side and the signals of 26Al2+ were investigated with the gas ionization detector. [ABSTRACT FROM AUTHOR]

There is growing interest in geochronological applications of terrestrial in situ -produced cosmogenic nuclides, with the most commonly measured being 10Be and 26Al in quartz. To extract and then separate these radionuclides from quartz and prepare them in the oxide form suitable for accelerator mass spectrometry (AMS) requires extensive and careful laboratory processing. Here we discuss the suitability of a crushed, sieved and etched, sub-aerially exposed vein quartz specimen (CoQtz-N) to act as a reference material for chemical laboratory preparation and AMS measurements. Splits of CoQtz-N were distributed to eleven target preparation laboratories. The CoQtz-N 10Be targets were then measured at seven different AMS facilities and five of the preparation laboratories had their 26Al targets measured at four different AMS facilities. We show that CoQtz-N splits are sufficiently homogeneous with regard to nuclide concentrations, that it has been cleaned of any atmospheric derived (i.e. meteoric) 10Be and that it has low concentrations of the major elements that can interfere with Be and Al extraction chemistry and AMS measurements. We derive preliminary concentrations for 10Be and 26Al in CoQtz-N as 2.53 ± 0.09 × 106 at/g and 15.6 ± 1.6 × 106 at/g, respectively, at the 95% confidence limit. [ABSTRACT FROM AUTHOR]

This paper presents an evaluation of an alternate method for preparing environmental samples for 129 I analysis by accelerator mass spectrometry (AMS) at Idaho National Laboratory. The optimal sample preparation method is characterized by ease of preparation, capability of processing very small quantities of iodide, and ease of loading into a cathode. Electrodeposition of iodide on a silver wire was evaluated using these criteria. This study indicates that the electrochemically-formed silver iodide deposits produce ion currents similar to those from precipitated silver iodide for the same sample mass. Precipitated silver iodide samples are usually mixed with niobium or silver powder prior to loading in a cathode. Using electrodeposition, the silver is already mixed with the sample and can simply be picked up with tweezers, placed in the sample die, and pressed into a cathode. The major advantage of this method is that the silver wire/electrodeposited silver iodide is much easier to load into a cathode. [ABSTRACT FROM AUTHOR]

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

Abstract: The DRAGON facility at TRIUMF/ISAC detects reaction products following radiative capture of a hydrogen or helium target nucleus by an accelerated heavy ion. Capture reactions of interest in nuclear astrophysics may have reaction rates 10–14 orders of magnitude lower than the intensity of the incident beam: as well as efficiently transporting the heavy reaction product from the target to a suitable particle detector, the separator must provide most of the suppression of unreacted beam. We describe the features of beam background encountered in a range of proton- and alpha-capture experiments at the DRAGON facility. [Copyright &y& Elsevier]

Abstract: We present new measurements of the charge-state distribution (CSD) of a 1.068MeV/u C beam in He and of the 6+:5+ charge-state population ratio in the recoils of the 12C(α,γ)16O reaction, both measured at the DRAGON recoil mass spectrometer. A computer simulation to model the CSD of both beam and recoil particles in inverse-kinematics experiments is compared to data from this work and from previous work at ERNA. The simulation provides good agreement with both data sets. The results suggest that, for this fusion reaction on the J π =4+ resonance at E beam =1.064MeV/u, immediately after fusion, the recoil ions contain only the nucleons and not the electrons of the target He atom. [Copyright &y& Elsevier]

Compared to heavy ion AMS at large tandem accelerators (TV⩾8 MV) and for cases where stable isobar interference is absent, a small facility like VERA (TV=3 MV) is shown to be able to offset the disadvantage of lower ion energy. After testing the system with 210Pb/208Pb isotope ratio measurements, we prove this by a measurement of 236U at natural levels in a material separated before 1918 and therefore free from anthropogenic contamination. An isotopic ratio of 236U/238U=(6.1±0.4)×10−11 was found for this material. [Copyright &y& Elsevier]

Abstract: The radioisotope 182Hf (t 1/2 =8.9Ma) is of great interest for astrophysical applications as a chronometer for the early solar system or as possible live supernova remnant on earth. However, AMS measurements of 182Hf are seriously influenced by the presence of the stable isobar 182W, which cannot be separated at typical AMS energies. Previous studies revealed a possible suppression of 182W against 182Hf by extracting the negatively charged pentafluoride from the ion source, leading to a detection limit for 182Hf/180Hf in the order of 10−11. However, this suppression behavior is in contrast to theoretical calculations of the electron affinity and recent measurements using SIMS instruments, where the achieved suppression cannot be reproduced. The aim of our study is to determine the effects of ion source background as well as further investigate the suppression of tungsten against hafnium by extracting negatively charged fluoride ions from different sample materials. The previously reported suppression factor of about 6000 could be increased to 36000 by careful tuning of the ion source using HfF4 as sample material. The trend of the theoretical electron affinities could be reproduced using atomic tungsten and hafnium instead of HfF4 as sample material. This supports the assumption that the major contribution of the tungsten background is not sputtered from the target matrix but comes from somewhere else in the ion source. Measurements from the second ion source show a higher background of tungsten and a lower suppression factor, i.e. careful design of the ion source is crucial. Moving the sputter beam over the target surface extending over the wheel holding the targets revealed the highest tungsten background was detected outside the sputter target position. Further investigations are necessary to locate the origin of the tungsten background in the ion source. Possible sources are the material used for the ion source construction or contaminations in the cesium used for sputtering. [Copyright &y& Elsevier]