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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: A new time-of-flight (TOF) system has been installed at the recoil mass separator DRAGON at the radioactive beam facility TRIUMF-ISAC in Vancouver, Canada. The addition of a velocity measurement to the existing energy measurement provides an effective separation of heavy ion reaction particles from remaining beam particles reaching the end detector, especially at low beam energies of interest to nuclear astrophysics research. The TOF detector system is based on two electrostatic mirrors equipped with thin carbon foils as a secondary electron emitter, and micro-channel plates for a fast timing signal. The system has been commissioned with stable , and beams in the energy range from 200 to . [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]

The presence of live 182Hf (t1/2∼9 Myr) in the early solar system is well established but the understanding of its abundance is still challenging. Live 182Hf is expected to be present in the interstellar medium (ISM) as a result of recent nucleosynthesis activity. We are attempting a search for live 182Hf possibly deposited on Earth. The search focuses on deep-ocean sediments and a method for chemical extraction of the Zr–Hf fraction from sediments has been developed. The detection of 182Hf is performed at the Vienna Environmental Research Accelerator (VERA). Measurements of Hf and W isotopic abundances for the Zr–Hf fraction extracted from deep-sea sediment samples were performed. Present limits for the 182Hf abundance derived from the measured isotopic abundances are discussed. [Copyright &y& Elsevier]

ISAC is an accelerator facility primarily dedicated to astrophysical studies. Off-line and online ion sources provide up to 65 keV of stable and radioactive beams to the ISAC accelerators. Initial acceleration is done via a constant velocity radio frequency quadrupole that requires 2 keV/u. Then the beam is further accelerated to 1.5 MeV/u at ISAC-I and 6.5 MeV/u at ISAC-II. To study radiative capture reactions relevant for astrophysics, the recoil mass spectrometer DRAGON was built in the experimental area. 40Ca(α,γ)44Ti is identified as one of the key reactions in supernovae to produce 44Ti and is given highest priority. For this experiment, an ultrapure Ca+2 beam was requested from the off-line ion source. Initial tests showed that, when using conventional ion sources, 40Ar and 40K are the impurities that are most difficult to eliminate. In order to overcome this problem, a new concept was needed and the hybrid surface arc discharge ion source was born. The hybrid surface ion source consists of a small surface ionizer and an arc discharge placed in a solenoid field. A very low ratio of 40Ar/40Ca=8×10-5 was achieved with this new source and the experiment was completed successfully. The source is described in detail and its performance is discussed in this article. [ABSTRACT FROM AUTHOR]

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]

Understanding past changes in the Antarctic ice sheets provides insight into how they might respond to future climate warming. During the Pliocene and Pleistocene, geological data show that the East Antarctic Ice Sheet responded to glacial and interglacial cycles by remaining relatively stable in its interior, but oscillating at its marine-based margin. It is currently not clear how outlet glaciers, which connect the ice sheet interior to its margin, responded to these orbitally-paced climate cycles. Here we report new ice surface constraints from Skelton Glacier, an outlet of the East Antarctic ice sheet, which drains into the Ross Ice Shelf. Our multiple-isotope ( 10 Be and 26 Al) cosmogenic nuclide data indicate that currently ice-free areas adjacent to the glacier underwent substantial periods of exposure and ice cover in the past. We use an exposure-burial model driven by orbitally-paced glacial–interglacial cycles to determine the probable ice surface history implied by our data. This analysis shows that: 1) the glacier surface has likely fluctuated since at least the Pliocene; 2) the ice surface was >200 m higher than today during glacial periods, and the glacier has been thicker than present for ∼75–90% of each glacial–interglacial cycle; and 3) ice cover at higher elevations possibly occurred for a relatively shorter time per Pliocene cycle than Pleistocene cycle. Our multiple-nuclide approach demonstrates the magnitude of ice surface fluctuations during the Pliocene and Pleistocene that are linked to marine-based ice margin variability. [ABSTRACT FROM AUTHOR]

The first basin-wide distribution of 236 U/ 238 U atom ratios and 129 I concentrations is presented for the Mediterranean Sea. During the GEOTRACES GA04S-MedSeA expedition in 2013 seawater was collected from 10 vertical profiles covering the principal sub–basins of the Mediterranean Sea. The main objective was to understand the distributions of 236 U and 129 I in relation to the water masses, and to constrain their sources in this region. The 236 U/ 238 U atom ratios and the 129 I concentrations ranged from (710 ± 40) × 10 − 12 to (2220 ± 60) × 10 − 12 and from (4.0 ± 0.1) × 10 7 to (13.8 ± 0.3) × 10 7 at·kg − 1 , respectively. The results show that radionuclide–poor Atlantic Water is entering at the surface through the Strait of Gibraltar whereas comparably radionuclide-enriched Levantine Intermediate Water is sinking in the Eastern Basin and flowing westward at intermediate depths. Low radionuclide levels were found in the oldest water masses at about 1000–2000 m depth in the Eastern Basin. At greater depths, waters were relatively enriched in 236 U and 129 I due to dense water formation occurring in both, the Eastern and Western Basins. The inventories of 236 U and 129 I cannot be explained only by global fallout from atmospheric nuclear bomb testings carried out in the 1950s and 1960s. We estimate that the liquid input of 236 U from the nuclear reprocessing facility of Marcoule (France), via the Rhône river, was of the same order of magnitude than the contribution from global fallout, whereas liquid and gaseous releases of 129 I from Marcoule were up to two orders of magnitude higher than global fallout. For both radionuclides, the contribution from the Chernobyl accident is found to be minor. [ABSTRACT FROM AUTHOR]

The Marocche di Dro deposits in the lower Sarca Valley are some of the most distinctive rock avalanche deposits of the Alps. We use geomorphology and cosmogenic 36 Cl exposure dating of boulders to divide the Marocche di Dro deposits into two rock avalanche bodies; the Marocca Principale to the north and the Kas to the south. The deposits were previously undated and had been mapped as up to five different events. The largest event Marocca Principale, which comprises an estimated 1000 10 6 m 3 of predominantly Rotzo Formation limestones, occurred 5300 ± 860 yr ago. The release area is located mainly in the alcove between Mt. Casale and Mt. Granzoline, but likely extends all the way to Mt. Brento. The Kas event took place 1080 ± 160 yr ago with detachment below Mt. Brento. The Kas debris, with an estimated volume of 300 10 6 m 3 , buried the southern third of the Marocca Principale deposit. Kas presents a barren, stark landscape dominated by house-sized Tovel Member Rotzo Formation boulders bearing distinctive chert lenses. Both the extreme relief of the rock wall (more than 1300 m) and the tectonic setting predispose the range front to massive failure. For the two events, initially translational movement likely quickly evolved into complex failure and massive collapse. Run-out across the valley of several kilometers and run-up on the opposite slope of hundreds of meters followed. A summary of all dated and large historical landslides in the Alps underlines the periods of enhanced slope activity discussed in the literature: 10-9 kyr, 5-3 kyr, and 2-1 kyr, the latter especially for the Southern Alps. No deposits of the first temporal cluster are found at Marocche di Dro. The age of Marocca Principale at 5300 ± 860 yr suggests occurrence during the second period. Failure may have been related to the shift to wetter, colder climate at the transition from the middle to the late Holocene. Nevertheless, a seismic trigger cannot be ruled out. For the Kas rock avalanche at 1080 ± 160 yr ago we implicate the “Middle Adige Valley” (1046 CE) earthquake as trigger. Its epicentral distance is much closer to the Sarca Valley in comparison to that of the Verona earthquake (1117 CE). [ABSTRACT FROM AUTHOR]

The denudation of landscapes is affected by temporal and spatial variations in tectonics, climate, and vegetation. However, deciphering the contributions of these different processes has proven challenging. In this study, cosmogenic nuclide-derived modern and paleo catchment-wide denudation rates in four European rivers are investigated. We present 12 new and 4 recalculated cosmogenic nuclide-derived denudation rates from modern river sediments and 14 paleo-denudation rates from terraces deposited over the last 2 Ma. The catchments studied are located in regions with minimal Quaternary tectonic activity and span different climates over 12 o latitude. Results indicate that modern denudation rates range between 16 ± 11 and 51 ± 7 mm/ka with no clear latitudinal variation. Modern denudation rates are compared with catchment geomorphic indices including slope, fluvial steepness index, and relief. The denudation rates correlate better to catchment topographic indices ( R 2 ≈ 0.4) rather than climate. Paleo-denudation rates range from 8 ± 7 to 56 ± 7 mm/ka and are associated with a possible increase in the average paleo-denudation rates over the past 2 Ma. Taken together, the results indicate that quantification of catchment-wide denudation rates over long (Quaternary) time scales because of climate change is difficult. Future work to study climate influence on denudation rates should focus on the successes of previous work that document transient denudation rates over shorter and more recent time scales, i.e., from the Last Glacial Maximum to present. [ABSTRACT FROM AUTHOR]

The first dataset of 236 U/ 238 U in the water column of the Arctic Ocean (AO) is presented and shows the widest range of ratios reported so far in the open ocean, from ( 5 ± 5 ) to ( 3840 ± 260 ) × 10 − 12 . Surface samples and depth profiles were collected during two GEOTRACES expeditions in 2011–2012 and analyzed for the concentrations of 236 U and 129 I, with the aim of investigating whether the combination of 236 U/ 238 U and 129 I/ 236 U can be used as a new oceanographic tool in the AO. Results show that the distributions of the 236 U/ 238 U and 129 I/ 236 U atomic ratios are consistent with the different water masses in the AO. High 236 U/ 238 U and 129 I/ 236 U ratios in the upper water column ( > 2000 × 10 − 12 and >200, respectively) illustrate the penetration of Atlantic waters (AW) into the AO. Lower values were found in Pacific waters (PW) and deep waters of the AO. Rivers seem to represent a temporally and spatially-constrained third anthropogenic source of 236 U but more data are needed to confirm this. In a simple mixing model, the combination of 236 U/ 238 U and 129 I/ 236 U reveals a high contribution (>99%) of natural background waters (pre-nuclear era) in the deep and bottom waters of the Amerasian basin, indicating an apparent water mass renewal time of >1000 years. Despite the relatively high apparent age of the Amerasian Basin deep waters, this work shows the potential of using the dual-tracer approach as a new oceanographic tool in the Arctic Ocean. [ABSTRACT FROM AUTHOR]

New data about 129 I, 127 I concentrations and their isotopic ratios in aerosol samples from the trace survey station of the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig, Northern Germany, are presented and discussed in this paper. The investigated samples were collected on a weekly basis during the years 2011 to 2013. Iodine was extracted from aerosol filters using a strong basic solution and was separated from the matrix elements with chloroform and was analysed by accelerator mass spectrometry (AMS) for 129 I and by inductively coupled plasma mass spectrometry (ICP-MS) for 127 I. The concentrations of 127 I and 129 I in aerosol filters ranged from 0.31 to 3.71 ng m −3 and from 0.06 to 0.75 fg m −3 , respectively. The results of 129 I/ 127 I isotopic ratios were in the order 10 −8 to 10 −7 . The 129 I originated directly from gaseous emissions and indirectly from liquid emissions (via sea spray) from the reprocessing plants in Sellafield and La Hague. In comparison with the results of 131 I after the Fukushima accident, no contribution of 129 I from this accident was detectable in Central Europe due to the high background originating from the 129 I releases of the European reprocessing plants. 129 I atmospheric activity concentrations were compared with those of an anthropogenic radionuclide ( 85 Kr). We did not find any correlation between 129 I and 85 Kr, both having nuclear reprocessing plant as the main source. [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]

In 2012, Miyake et al. reported a sudden and strong increase of the atmospheric radiocarbon ( 14 C) content in Japanese cedar trees of 1.2% between AD 774 and 775. While their findings were quickly confirmed by a German oak chronology for the Northern Hemisphere (NH), the question remained if the effect was seen in both hemispheres. Here we present the first annually resolved Southern Hemisphere (SH) 14 C record spanning the interval AD 760–787, using New Zealand kauri ( Agathis australis ) chronology wood. An almost identical distinct increase compared to Northern Hemisphere data was observed, suggesting a cosmic event with globally uniform impact as a potential cause for the increase. Deploying a carbon cycle box model a worldwide averaged net 14 C production of 2.2 × 10 8 C 14 atoms cm − 2 was estimated, which is 3.7 times higher than the average annual 14 C production. The immediate appearance of the event in tree rings on both hemispheres suggests a short duration event of significantly less than 1 yr. [ABSTRACT FROM AUTHOR]

In stellar helium burning, 16O represents the endpoint of the helium-burning sequence due to the low rate of 16O(α,γ)20Ne. We present a new direct measurement of the total capture reaction rate of 16O(α,γ)20Ne at Ec.m.=2.26 MeV employing the DRAGON recoil separator. For the first time, the total S factor and its contributing direct capture transitions could be determined in one experiment. [ABSTRACT FROM AUTHOR]

The 18F(p, α)150 reaction rate is crucial for understanding the final abundance of 18F predicted by nova models. The γ-ray emission in the first few hours after a nova outburst is expected to be dominated by 511 keV annihilation photons from the decay of 18F, and so understanding its production can provide important constraints on the conditions during the outburst when compared with observations. Results are presented from the lowest-energy direct measurement to date, performed at the Isotope Separator and Accelerator radioactive beam facility at the TRJUMF laboratory, Canada. Cross section measurements at center-of-mass energies of 250, 330, 453, and 673 keV are obtained and the results compared to previous data and R-matrix calculations. The implications for the overall reaction rate in the context of nova explosions have been discussed. [ABSTRACT FROM AUTHOR]

Gamma-ray telescopes in orbit around the earth are searching for evidence of the elusive radionuclide 22Na produced in novae. Previously published uncertainties in the dominant destructive reaction, 22Na(p,γ)23Mg, indicated new measurements in the proton energy range of 150 to 300 keV were needed to constrain predictions. We have measured the resonance strengths, energies, and branches directly and absolutely by using protons from the University of Washington accelerator with a specially designed beam line, which included beam rastering and cold vacuum protection of the 22Na implanted targets. The targets, fabricated at TRIUMF-ISAC, displayed minimal degradation over a ~20 C bombardment as a result of protective layers. We avoided the need to know the absolute stopping power, and hence the target composition, by extracting resonance strengths from excitation functions integrated over proton energy. Our measurements revealed that resonance strengths for Ep=213, 288, 454, and 610 keV are stronger by factors of 2.4-3.2 than previously reported. Upper limits have been placed on proposed resonances at 198, 209, and 232 keV. These substantially reduce the uncertainty in the reaction rate. We have re-evaluated the 22Na(p,γ) reaction rate, and our measurements indicate the resonance at 213 keV makes the most significant contribution to 22Na destruction in novae. Hydrodynamic simulations including our rate indicate that the expected abundance of 22Na ejecta from a classical nova is reduced by factors between 1.5 and 2, depending on the mass of the white-dwarf star hosting the nova explosion. [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]

The energy-sensitive detection of heavy ions with calorimetric low temperature detectors was investigated in the energy range of E=0.1–1 MeV/amu, commonly used for accelerator mass spectrometry (AMS). The detectors used consist of sapphire absorbers and superconducting aluminum transition edge thermometers operated at T∼1.5 K. They were irradiated with various ion beams (13C,197Au,238U) provided by the VERA tandem accelerator in Vienna, Austria. The relative energy resolution obtained was ΔE/E=(5–9)×10-3, even for the heaviest ions such as 238U. In addition, no evidence for a pulse height defect was observed. This performance allowed for the first time to apply a calorimetric low temperature detector in an AMS experiment. The aim was to precisely determine the isotope ratio of 236U/238U for several samples of natural uranium, 236U being known as a sensitive monitor for neutron fluxes. Replacing a conventionally used detection system at VERA by the calorimetric detector enabled to substantially reduce background from neighboring isotopes and to increase the detection efficiency. Due to the high sensitivity achieved, a value of 236U/238U=6.1×10-12 could be obtained, representing the smallest 236U/238U ratio measured at the time. In addition, we contributed to establishing an improved material standard of 236U/238U, which can be used as a reference for future AMS measurements. [ABSTRACT FROM AUTHOR]

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: The Nuclear Astrophysics program at TRIUMF, particular the one centered around the DRAGON and TUDA facilities, as well as some additional experiments will be discussed. In particular, measurements of the 12C(α,γ)16O, the 26Al(p,γ)27Si and the 40Ca(α,γ)44Ti reactions at DRAGON will be described. For the TUDA facility a measurement of 10B(α,p)13C as a test for the 18Ne(α,p)21Na measurement is presented. The development of the new cylindrical, large solid angle gas detector TACTIC will be described. In addition, new measurements refuting a temperature dependence of radioactive decay times in metals will be presented as well as GEANT4 simulations regarding the β-delayed α-spectrum of 16N will be given. [Copyright &y& Elsevier]

Abstract: The ground state structure of 9Li has been investigated through the one-neutron transfer reaction at . The 8Li sub-system in 9Li was observed in its lowest three energy levels. The spectroscopic factors derived from a DWBA analysis are fairly consistent in trend with model calculations. The understanding of the sub-shell closure from the spectroscopic information and neutron separation energies is discussed. [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]

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. [ABSTRACT FROM AUTHOR]

In previous experiments, diamond-like carbon (DLC) foils which are being produced at Kurchatov Institute, have proven well suited as long-lived stripper foils for high-energy heavy-ion tandem accelerators and ultra-thin secondary-electron (SE) emitting foils for TOF spectrometers. This paper presents the recent advances in DLC targetry with main emphasis given to development and applications of ultra thin foils (maximum diameter up to 70 mm) with high uniformity and minimal possible effective thickness, the latter has been evaluated by measurements of both energy loss and angular scattering of heavy ions transmitting through the foils. Comparative lifetimes of DLC stripper foils irradiated with high intensity (150 μA) He+ beams at 2 MeV are reported, which demonstrate the favorable use of DLC foils as supplemental strippers at RFQ linacs. In conclusion, the attractive results of application of ultra-thin DLC foils to TOF detectors for heavy ion AMS as well as to compact tandem accelerators are presented. [Copyright &y& Elsevier]

Diamond is an attractive alternative to silicon as a heavy ion detector owing to its exceptional radiation hardness and very fast timing. These remarkable properties of diamond allow one to expect that diamond detectors can outperform silicon detectors and ionization chambers for many applications, in particularly, for heavy ion accelerator mass spectrometry (AMS) measurements. However, most reported diamond particle detectors have been based on polycrystalline chemical-vapor-deposited diamond films and exhibited poor energy resolution (due to loss of charge carriers in the grain boundaries) resulting in limited applications, primarily for counting ions at hundreds of MeV/u. In this paper the evaluation of a thin single-crystal natural diamond detector as an energy spectrometer for 13C, 180Hf, and 238U ions in the energy range from 12 to 38 MeV is presented. The influence of “priming” and “polarization” effects is discussed. Initial measurements of energy resolution, stability and radiation hardness of the natural diamond detector have demonstrated its suitability for heavy ion AMS, in spite of some technical problems to be solved. [Copyright &y& Elsevier]

For the first time, calorimetric low-temperature detectors were applied in accelerator mass spectrometry, a well-known method for determination of very small isotope ratios with high sensitivity. The aim of the experiment was to determine with high accuracy the isotope ratio of 236U/238U for several samples of natural uranium, 236U being known as a sensitive monitor for neutron flux. Measurements were performed at the VERA tandem accelerator at Vienna, Austria. The detectors consist of sapphire absorbers and superconducting transition edge thermometers operated at T≈ 1.5 K. The relative energy resolution obtained for 17.39 MeV 238U is ΔE/E=4–9×10−3, depending on the experimental conditions. This performance enabled to substantially reduce background from neighbouring isotopes and to increase the detection efficiency. Due to the high sensitivity achieved, a value of 236U/238U=6.5×10−12 could be obtained, representing the smallest 236U/238U ratio measured until now. [Copyright &y& Elsevier]

The presence of 244Pu (t1/2=81 Ma) in the early solar system is long established [Nature 187 (1960) 36; Science 172 (1971) 837]. 244Pu is also one of a number of isotopes which may be detectable as live radioactivity on earth, originating from the Interstellar Medium (ISM). There has been a recent attempt to measure a ISM isotope signature of 244Pu [ApJ 558 (2001) L133]. This rises the question of the presence of an anthropogenic contribution in the environment. In order to better assess the 244Pu fall-out on earth, we have started a program at VERA to measure 244Pu in surface sediments of Lake Michigan, routinely sampled for 239,240Pu measurements. Considerable amount of information on other isotopes exist for Lake Michigan. We have reproduced the expected 241Pu/239Pu and 240Pu/239Pu ratios for the global fallout. The measured 244Pu/239Pu was considerably higher than expected and was therefore most likely the result of contamination. Measurement of samples specifically prepared for the measurement of 244Pu will be tried in the future. [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]