36Cl exposure dating with a 3-MV tandem

³⁶Cl AMS measurements at natural isotopic concentrations have yet been performed only at tandem accelerators with 5 MV terminal voltage or beyond. We have developed a method to detect ³⁶Cl at natural terrestrial isotopic concentrations with a 3-MV system, operated above specifications at 3.5 MV.An effective separation was obtained with an optimized split-anode ionization chamber design (adopted from the ETH/PSI Zurich AMS group), providing a suppression factor of up to 30,000 for the interfering isobar ³⁶S. Despite the good separation, a relatively high sulfur output from the ion source (³⁶S^?/³⁵Cl^? ≈ 4 × 10^?10 for samples prepared from chemically pure reagents), and a possibly cross contamination resulted in a background corresponding to ³⁶Cl/Cl ≈ 3 × 10^?14. The method was applied to samples containing between 10⁵ and 10⁶ atoms ³⁶Cl/g rock from sites in Italy and Iran, which were already investigated by other laboratories for surface exposure dating. The ³⁶Cl/Cl ratios in the range from 2 × 10^?13 to 5 × 10^?12 show a generally good agreement with the previous results.These first measurements demonstrate that also 3-MV tandems, constituting the majority of dedicated AMS facilities, are capable of ³⁶Cl exposure dating, which is presently the domain of larger facilities.     

Status and research programs of the multinuclide accelerator mass spectrometry system at the University of Tsukuba

We present the current status and research programs of a multinuclide accelerator mass spectrometry (AMS) system on the 12UD Pelletron tandem accelerator at the University of Tsukuba (Tsukuba AMS system), Japan. A maximum terminal voltage of 12 MV is available for the AMS system. The Tsukuba AMS system can measure environmental levels of long-lived radioisotopes of ¹⁴C, ²⁶Al, ³⁶Cl and ¹²⁹I by employing a molecular pilot beam. Recently, enhancements in AMS techniques and equipment, including sample preparation, the ion source and the data acquisition system, have improved the performance of ³⁶Cl-AMS. The standard deviation of fluctuations is typically ±2%, and the machine background level for the ³⁶Cl/Cl ratio is lower than 1 × 10^?15 with a halite sample. We have measured over 500 samples in 1 year, including samples for earth and environmental sciences and nuclear safety research.     

Comparison of detector systems for the separation of 36Cl and 36S with a 3-MV tandem

The possibility of detecting ³⁶Cl 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, Zürich, Switzerland) with two anodes. To improve the suppression of ³⁶S, 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 mm²) 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 ³⁶Cl⁷⁺, we achieved a ³⁶S⁷⁺-suppression of 21,500 (50% ³⁶Cl-detector-efficiency).     

Highly sensitive AMS measurements of 53Mn

Our AMS system, with the gas-filled detector system GAMS, has been optimized for measurements with ⁵³Mn. A high sensitivity has been achieved. A newly installed cesium sputter ion source yields an improved emittance, and thus a higher mass resolution. By the extraction of the manganese molecule MnF^? instead of MnO^? we can suppress the isobaric chromium background in the ion source by more than a factor of three. The GAMS system achieves an isobaric suppression factor of about 3 × 10⁸. Measurements on blank samples yielded upper limits for the ⁵³Mn/⁵⁵Mn ratios of 7 × 10^?15.     

Selective isobar suppression for accelerator mass spectrometry and radioactive ion-beam science

A new method of selective isobar suppression by photodetachment in a radio-frequency quadrupole ion cooler is being developed at HRIBF with a twofold purpose: (1) increasing the AMS sensitivity for certain isotopes of interest and (2) purifying radioactive ion beams for nuclear science. The potential of suppressing the ³⁶S contaminants in a ³⁶Cl beam using this method has been explored with stable S^? and Cl^? ions and a Nd:YLF laser. In the study, the laser beam was directed along the experiment’s beam line and through a RF quadrupole ion cooler. Negative ³²S and ³⁵Cl ions produced by a Cs sputter ion source were focused into the ion cooler where they were slowed by collisions with He buffer gas; this increased the interaction time between the negative-ion beam and the laser beam. As a result, suppression of S^? by a factor of 3000 was obtained with about 2.5 W average laser power in the cooler while no reduction in Cl^? current was observed.     

The French accelerator mass spectrometry facility ASTER: Improved performance and developments

Following the installation and acceptance test of the French 5 MV AMS facility ASTER, the focus has been on improving the capability for routine measurements of ¹⁰Be and ²⁶Al. Quality assurance has been established by the introduction of traceable AMS standards for each nuclide, by self-monitoring through participation in round-robin exercises and proficiency testing, and by surveillance of long- and short-time variability of blank and reference materials. A background level of 3 × 10^?14 makes ASTER well-suited for measuring ⁴¹Ca/⁴⁰Ca in the10^?12 region, which is sufficient for a wide range of applications. Routine AMS measurements of volatile elements like ³⁶Cl and ¹²⁹I will most likely become feasible in the very near future as the result of significant improvements in the ion source design.     

Comparison of 41Ca analysis on 0.5 MV and 5 MV-AMS systems

A comparative study was made between the compact AMS system at the PSI/ETH Laboratory of Ion Beam Physics in Zurich with 0.5 MV terminal voltage and the 5 MV-AMS system at the Scottish Universities Environmental Research Centre (SUERC), Glasgow. Overall 34 urinary samples with ⁴¹Ca/⁴⁰Ca ratios in the range from 4 × 10^?11 to 3 × 10^?10 were processed to CaF₂ and aliquots of the same material were measured on both instruments.Measurements on the compact AMS system were performed in charge state 3+ achieving a transmission of 4% at 1.7 MeV beam energy. Under these conditions a suppression of the interference ⁴¹K is virtually impossible. However, samples with an excess of potassium can be identified by a shift of the ⁴¹Ca/⁴¹K peak in the ΔE ? E histogram of the gas ionization detector employed and a criterion for data rejection can be defined. An overall precision of ～4% and a ⁴¹Ca/⁴⁰Ca background level of 5 × 10^?12 have been reached.For studies with higher demands on the detection limit AMS systems like the one at SUERC are attractive: in charge state 5+ and using a gas stripper beam energy of 27 MeV, a transmission of 5%, a ⁴¹K suppression factor of ～500 and a ⁴¹Ca/⁴⁰Ca background level of 3 × 10^?14 are achieved.We demonstrate that both systems are well suited for large-scale ⁴¹Ca biomedical applications.     

SUERC AMS ion detection

In a short time Be, C, Al, Cl, Ca and I accelerator mass spectrometry (AMS) have been established on the National Electrostatics Corporation (NEC) 5 MV pelletron system at the Scottish Universities Environmental Research Centre (SUERC). While summarising the present performance of the system, this report will focus on the details of ion detection, which sample materials are used and the analytical procedures employed for each individual species during routine analysis.All rare isotope detection is with a single flexible detector and ion event analysis system, but switching of analysed species typically requires a detector reconfiguration. Configurations for routine ¹⁰Be, ¹⁴C, ²⁶Al, ³⁶Cl, ⁴¹Ca and ¹²⁹I detection have been established and will be presented here. Notably, there has proven to be sufficient suppression of the isobaric interferences of ³⁶Cl and ⁴¹Ca in the 5+ charge state using an argon gas stripper at a terminal voltage of 5.0 MV to allow for routine analysis of these isotopes.     

Development of an integrated sampler based on direct 222Rn/220Rn progeny sensors in flow-mode for estimating unattached/attached progeny concentration

A flow-mode integrated sampler consisting of a wire-mesh and filter-paper array along with passive solid state nuclear track detectors has been developed for estimating unattached and attached fraction of ²²²Rn/²²⁰Rn progeny concentration. The essential element of this sampler is the direct ²²²Rn/²²⁰Rn progeny sensor (DRPS/DTPS), which is an absorber-mounted-LR115 type nuclear track detector that selectively registers the alpha particles emitted from the progeny deposited on its surface. During sampling at a specified flow-rate, the unattached progeny is captured on the wire-mesh; while the attached progeny gets transmitted and is captured on the filter-paper. The alpha particles emitted by the deposited progeny atoms are registered on the sensors placed at a specified distance facing the wire-mesh and the filter-paper, respectively. The various steps involved in the development of this flow-mode direct progeny sampler such as the optimization of the sampling rate and the distance between the sensor and the deposition substrate are discussed. The sensitivity factor of the DTPS-loaded sampler for ²²⁰Rn progeny deposited on the wire-mesh and filter-paper is found to be 23.77 ± 0.64 (track cm^?2 h^?1) (Bq m^?3)^?1 and 22.30 ± 0.18 (track cm^?2 h^?1) (Bq m^?3)^?1, respectively; while that of DRPS-loaded sampler for ²²²Rn progeny deposition, is 3.03 ± 0.14 (track cm^?2 h^?1) (Bq m^?3)^?1 and 2.08 ± 0.07 (track cm^?2 h^?1) (Bq m^?3)^?1, respectively. The highlight of this flow-mode sampler is its high sensitivity and that it utilizes the passive technique for estimating the unattached and attached progeny concentration, thus doing away with the alpha counting procedures.     

129I AMS at 0.5 MV tandem accelerator

The ¹²⁹I measurement program has been established at the 0.5 MV ‘Tandy’ accelerator of the PSI/ETH Zürich AMS facility. This development was made possible by using a SiN window instead of Mylar one in a gas ionization detector. The setting up of the ¹²⁹I measurement at Tandy is simple, the acquired performance is stable and reliable, and the quality of results is equal to or better than at our larger EN-tandem. With this setup, high sample throughput, which is required in many ¹²⁹I studies, can be easily achieved. The measurements are performed in the +3 charge state. At this charge state the major difficulty in the ¹²⁹I⁺³ identification is caused by a highly abundant 43⁺¹ (m = 43, q = +1) molecule interference. This is a positive molecular ion, because its intensity reduces exponentially with an increase in gas stripper pressure. We conclude that this molecule is ²⁷Al¹⁶O⁺ (m/q = 43/1 = 129/3) and comes from the break-up of (Al₂O₃ + Al)^? (m = 129) precursor at the terminal: (Al₂O₃ + Al)^? → ²⁷Al¹⁶O⁺. The expected isobaric interferences ⁴³Ca⁺¹ and ⁸⁶Sr⁺², which also originate from the break-up of molecules in the stripper, were found to be low and do not disturb the ¹²⁹I⁺³ measurements. The best repeatable performance with our standard sample material was achieved at 0.14 μg/cm² Ar gas stripper pressure with machine blanks showing ～6 × 10^?14 normalized ¹²⁹I/I ratio and 9% transmission through the accelerator. However, high ²⁷Al¹⁶O⁺ molecular rates were observed from the user samples, and in order to destroy these molecules we had to increase the stripper pressure to ～0.22 μg/cm². This increase in the stripper pressure degraded the machine blank values to ～9 × 10^?14 and reduced transmission to 8%. Nevertheless, the achieved measurement conditions are sufficient for measurement of nearly all ¹²⁹I samples that have been submitted to PSI/ETH over the last few years.     

Negative ion beam extraction in ROBIN

The RF based single driver ?ve ion source experiment test bed ROBIN (Replica Of BATMAN like source in INDIA) has been set up at Institute for Plasma Research (IPR), India in a technical collaboration with IPP, Garching, Germany. A hydrogen plasma of density 5 × 10¹² cm^?3 is expected in driver region of ROBIN by launching 100 kW RF power into the driver by 1 MHz RF generator. The cesiated source is expected to deliver a hydrogen negative ion beam of 10 A at 35 kV with a current density of 35 mA/cm² as observed in BATMAN.In first phase operation of the ROBIN ion source, a hydrogen plasma has been successfully generated (without extraction system) by coupling 80 kW RF input power through a matching network with high power factor (cos θ > 0.8) and different plasma parameters have been measured using Langmuir probes and emission spectroscopy. The plasma density of 2.5 × 10¹¹ cm^?3 has been measured in the extraction region of ROBIN. For negative hydrogen ion beam extraction in second phase operation, extraction system has been assembled and installed with ion source on the vacuum vessel. The source shall be first operated in volume mode for negative ion beam extraction. The commissioning of the source with high voltage power supply has been initiated.     

Improvement of initial vacuum condition along 2008–2010 KSTAR campaign by vessel baking

Korea Superconducting Tokamak Advanced Research (KSTAR) is upgraded for its KSTAR 3rd campaign for new target mission to produce the D-shaped plasma with a target plasma current of 500 kA and/or pulse length of 5 s. New Plasma Facing Components (PFCs) are installed which leads to the increase of the surface area of the vessel by a factor of about 5. The vacuum conditioning such as the vessel baking has been performed in order to remove various kinds of impurities including H₂O, carbon and oxygen for the plasma. The total outgassing rate in the KSTAR 1st campaign was measured as 1.5 × 10^?4 mbar ? s^?1 which is increased by a factor of 3 (6.49 × 10^?4 mbar ? s^?1) in the KSTAR 3rd campaign. Nevertheless, the outgassing rates per unit area have been decreased from 9.31 × 10^?5 mbar ? m^?2 s^?1 to 1.22 × 10^?5 mbar ? m^?2 s^?1 due to the upgrade of baking system and series of baking operation.     

Ohmic contacts on n-type layers formed in GaN/AlGaN/GaN by dual-energy Si ion implantation

Electrical properties of Si-implanted n-type GaN/AlGaN/GaN layers and contact resistances of ohmic electrodes (TiAl) formed on these layers have been examined. Experimental results have clearly shown that ohmic electrodes with a low specific-contact resistance of 1.4 × 10^?7 Ω cm² can be fabricated on the n-type layer having a low sheet resistance of 145 Ω/sq, which has been formed by the dual-energy Si ion implantation (80 keV:1.01 × 10¹⁵/cm² + 30 keV:1.6 × 10¹⁴/cm²) and subsequent annealing at 1200 °C for 2 min using a Si₃N₄ layer as an encapsulant.     

Fatigue lifetime of repaired high heat flux components for ITER divertor

Thermal fatigue behaviour of repaired monoblocks was assessed from High Heat Flux (HHF) tests up to 20 MW m^?2 on 11 components. Among these components, 8 monoblocks were repaired (2 CFC and 6 tungsten). These components were manufactured by two EU industries: ANSALDO Ricerche and PLANSEE. Non destructive examination was performed on SATIR thermography test bed before and after HHF tests. SATIR results show that repaired monoblocks have a good thermal exhaust capability before HHF tests. For all monoblocks, no degradation of thermal properties was noticed during cycles at 10 MW m^?2. After hundreds of cycles at 20 MW m^?2, two W repaired monoblock melted. Post-HHF SATIR examination revealed a degradation of thermal properties which is systematic for W melted monoblocks and non-systematic for W repaired ones. For CFC repaired monoblocks, no damage was observed up to 20 MW m^?2. For the first ITER divertor set, specifications for the pre-qualification are that CFC (Resp. W) components have to sustain in steady state 1000 cycles at 10 MW m^?2 (Resp. 3 MW m^?2) followed by 1000 cycles at 20 MW m^?2 (Resp. 5 MW m^?2). For the first ITER divertor set, the repair process is validated for CFC and W monoblocks.     

Negative ion test facility ELISE—Status and first results

The new test facility ELISE (Extraction from a Large Ion Source Experiment) has been designed and installed since November 2009 at IPP Garching to support the development of the radio frequency driven negative ion source for the Neutral Beam System on ITER. The test facility is now completely assembled; all auxiliary systems have been commissioned and are operational. First plasma and beam operation is starting in October 2012.The source is designed to deliver an ion beam of 20 A of D^? ions, operating at 0.3 Pa source pressure at an electron to ion current ratio below 1. Beam extraction is limited to 60 kV for 10 s every 3 minutes, while plasma operation of the source can be performed continuously for 1 hour. The ion source and extraction system have the same width as the ITER source, but only half the height, i.e. 1 × 1 m² source area with an extraction area of 0.1 m². The aperture pattern of the extraction system and the multi driver source concept stay as close as possible to the ITER design. Easy access to the source for diagnostic tools or modifications allows to analyze and optimize the source performance. Among other possibilities many different magnetic filter field configurations inside the source can be realized to enhance the negative ion extraction and to reduce the co-extraction of electrons. Beam power and profiles are measured by calorimetry and thermography on an inertially cooled target as well as by beam emission spectroscopy. Cs evaporation into the source is done via two dispenser ovens.     

Design of a large irradiation channel at MNSR facility in Ghana

In the design of new slant tube for large sample irradiation in the Ghana Research Reactor-1 facility, Monte Carlo N-Particle Code version 5 (MCNP-5) was employed to simulate the neutron flux profile of the new design. The results show that the neutron flux peaks at different points, at an average thermal neutron flux of (1.1406 ± 0.0046) × 10¹¹, (1.1849 ± 0.0047) × 10¹¹ and (1.0580 ± 0.0044) × 10¹¹ n cm^?2 s^?1 around the reactor vessel. The first two peaks happened to coincide with pneumatic transfer pipes in the pool, but the third peak happened to be in line with the slant tube position. It was observed that as the diameter of the tube varies from 3.90 cm to 23.40 cm, the average thermal neutron flux decreased exponentially from (1.1849 ± 0.0047)10¹¹ n cm^?2 s^?1 to (3.3241 ± 0.0100) × 10¹⁰ n cm^?2 s^?1. The average thermal neutron flux decreases exponentially along the diameter of the designed slant tube from (1.0366 ± 0.0042) × 10¹¹ n cm^?2 s^?1 to (9.7396 ± 0.0136) × 10⁹ n cm^?2 s^?1. From the results, it is evident that a slant tube of diameter 15.00 cm can be installed at the original slant tube position for large sample irradiation.     

Optimization of aluminum thickness for absorption of undesired Ti K X-rays in the measurement of low energy brachytherapy source strength

The contribution of Ti K X-rays to total air kerma strength for low energy brachytherapy sources (¹²⁵I and ¹⁰³Pd) are calculated for different source-to-aperture distances of an indigenously designed free air ionization chamber. For 30 cm source-to-aperture distance, calculated contribution of Ti K X-rays is 4%. The Ti K X-rays can be eliminated by a relatively thin aluminum filter, but the primary photons emitted by the source will also be attenuated. This effect should be compensated by applying a suitable correction factor. The uncertainty in the attenuation correction factor has been also calculated for different thicknesses of aluminum by a Monte Carlo uncertainty analysis algorithm programmed in FORTRAN. The results show that the optimum thickness of the aluminum absorber is 100 μm, for which the contribution of Ti K X-rays in air kerma strength is reduced to less than one hundredth of the uncertainty in the correction factor, ensuring that the uncertainty in the air kerma strength will be mainly due to the uncertainty in the correction factor. The calculated uncertainties are 1.7 × 10^?3, and 3.4 × 10^?3 for ¹²⁵I and ¹⁰³Pd sources, respectively.     

The ITER full size plasma source device design

In the framework of the strategy for the development and the procurement of the NB systems for ITER, it has been decided to build in Padova a test facility, including two experimental devices: a full size plasma source with low voltage extraction and a full size NB injector at full beam power (1 MV). These two different devices will separately address the main scientific and technological issues of the 17 MW NB injector for ITER. In particular the full size plasma source of negative ions will address the ITER performance requirements in terms of current density and uniformity, limitation of the electron/ion ratio and stationary operation at full current with high reliability and constant performances for the whole operating time up to 1 h. The required negative ion current density to be extracted from the plasma source ranges from 290 A/m² in D₂ (D^?) and 350 A/m² in H₂ (H^?) and these values should be obtained at the lowest admissible neutral pressure in the plasma source volume, nominally at 0.3 Pa. The electron to ion ratio should be limited to less than 1 and the admissible ion inhomogeneity extracted from the grids should be better than 10% on the whole plasma cross-section having a surface exposed to the extraction grid of the order of 1 m².The main design choices will be presented in the paper as well as an overview of the design of the main components and systems.     

Ion beam synthesis of SiC by C implantation into SIMOX(1 1 1)

We report the conversion of a 65 nm Si(1 1 1) overlayer of a SIMOX(1 1 1) into 30–45 nm SiC by 40 keV carbon implantation into it. High temperature implantation (600 °C) through a SiO₂ cap, 1250 °C post-implantation annealing under Ar ambient (with 1% of O₂), and etching are the base for the present synthesis. Sequential C implantations (fluence steps of about 5 × 10¹⁶ cm^?2), followed by 1250 °C annealing, has allowed to estimate the minimum C fluence to reach the stoichiometric composition as ～2.3 ×  10¹⁷ cm^?2. Rutherford Backscattering Spectrometry was employed to measure layer composition evolution. A two-sublayers structure is observed in the synthesized SiC, being the superficial one richer in Si. Transmission electron microscopy has shown that a single-step implantation up to the same minimum fluence results in better structural quality. For a much higher C fluence (4 × 10¹⁷ cm^?2), a whole stoichiometric layer is obtained, with reduction of structural quality.     

Nickel,Zn and Cd localisation in seeds of metal hyperaccumulators using μ-PIXE spectroscopy

Metal hyperaccumulators are a rare group of plant species that accumulate exceptionally high concentrations of metals in above ground tissues without showing symptoms of phytotoxicity. Quantitative localisation of the accumulated metals in seed tissues is of considerable interest to help understand the eco-physiology of these unique plant species. We investigated the spatial localisation of metals within seeds of Ni hyperaccumulating Hybanthus floribundus subsp. adpressus, H. floribundus subsp. floribundus and Pimelea leptospermoides and dual-metal (Cd and Zn) hyperaccumulating Thlaspi caerulescens using quantitative micro-proton induced X-ray emission (μ-PIXE) spectroscopy. Intact seeds were hand-sectioned, sandwiched between Formvar films and irradiated using the 3 MeV high energy heavy ion microprobe at ANSTO. Elemental maps of whole H. floribundus subsp. adpressus seeds showed an average Ni concentration of 5.1 × 10³ mg kg^?1 dry weight (DW) with highest Ni concentration in cotyledonary tissues (7.6 × 10³ mg kg^?1 DW), followed by the embryonic axis (4.4 × 10³ mg kg^?1 DW). Nickel concentration in whole H. floribundus subsp. floribundus seeds was 3.5 × 10² mg kg^?1 DW without a clear pattern of Ni localisation. The average Ni concentration in whole P. leptospermoides seeds was 2.6 × 10² mg kg^?1 DW, and Ni was preferentially localised in the embryonic axis (4.3 × 10² mg kg^?1 DW). In T. caerulescens, Cd concentrations were similar in cotyledon (4.5 × 10³ mg kg^?1 DW) and embryonic axis (3.3 × 10³ mg kg^?1 DW) tissues, whereas Zn was highest in cotyledonary tissues (1.5 × 10³ mg kg^?1 DW). In all species, the presence of the accumulated metal within the cotyledonary and embryonic axis tissues indicates that the accumulated metal was able to move apoplastically within the seed.