Showing papers in "Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms in 2010"

SRIM – The stopping and range of ions in matter (2010)

Abstract: SRIM is a software package concerning the S topping and R ange of I ons in M atter. Since its introduction in 1985, major upgrades are made about every six years. Currently, more than 700 scientific citations are made to SRIM every year. For SRIM-2010 , the following major improvements have been made: (1) About 2800 new experimental stopping powers were added to the database, increasing it to over 28,000 stopping values. (2) Improved corrections were made for the stopping of ions in compounds. (3) New heavy ion stopping calculations have led to significant improvements on SRIM stopping accuracy. (4) A self-contained SRIM module has been included to allow SRIM stopping and range values to be controlled and read by other software applications. (5) Individual interatomic potentials have been included for all ion/atom collisions, and these potentials are now included in the SRIM package. A full catalog of stopping power plots can be downloaded at www.SRIM.org . Over 500 plots show the accuracy of the stopping and ranges produced by SRIM along with 27,000 experimental data points. References to the citations which reported the experimental data are included.

Total pattern fitting for the combined size-strain-stress-texture determination in thin film diffraction

Abstract: A global approach has been developed to analyze complex thin film structures by X-ray diffraction The method is based on the fitting of multiple data, diffraction pattern and/or images, collected at different orientation of the sample to obtain all the information needed It requires the knowledge of the crystal structure for the phases present in the film, or if the amount/film thickness is sufficient, the crystal structure can be also determined or refined Reflectivity patterns can be added to the global refinement to improve the accuracy of the thickness determination and when coupled with total X-ray fluorescence can give the in depth chemical concentrations In addition, it constraints the solution for the quantitative phase analysis obtained from the diffraction patterns The principles of the analysis with the main methods will be presented from the theoretical point of view These cover the models from crystal structure to texture, residual strain/stresses, crystallite sizes and microstrains To make the method more effective, some specific models have been developed in the past few years Then some experimental/analysis examples will be given to enlighten how the method works and what kind of information can be obtained Not every model suits every analysis or kind of thin film and the examples will cover different cases from multiple phases to strong texture, epitaxial thin films or multilayers

A new value for the half-life of 10Be by Heavy-Ion Elastic Recoil Detection and liquid scintillation counting

Abstract: The importance of 10 Be in different applications of accelerator mass spectrometry (AMS) is well-known. In this context the half-life of 10 Be has a crucial impact, and an accurate and precise determination of the half-life is a prerequisite for many of the applications of 10 Be in cosmic-ray and earth science research. Recently, the value of the 10 Be half-life has been the centre of much debate. In order to overcome uncertainties inherent in previous determinations, we introduced a new method of high accuracy and precision. An aliquot of our highly enriched 10 Be master solution was serially diluted with increasing well-known masses of 9 Be. We then determined the initial 10 Be concentration by least square fit to the series of measurements of the resultant 10 Be/ 9 Be ratio. In order to minimize uncertainties because of mass bias which plague other low-energy mass spectrometric methods, we used for the first time Heavy-Ion Elastic Recoil Detection (HI-ERD) for the determination of the 10 Be/ 9 Be isotopic ratios, a technique which does not suffer from difficult to control mass fractionation. The specific activity of the master solution was measured by means of accurate liquid scintillation counting (LSC). The resultant combination of the 10 Be concentration and activity yields a 10 Be half-life of T 1/2 = 1.388 ± 0.018 (1 s, 1.30%) Ma. In a parallel but independent study (Chmeleff et al. [11] ), found a value of 1.386 ± 0.016 (1.15%) Ma. Our recommended weighted mean and mean standard error for the new value for 10 Be half-life based on these two independent measurements is 1.387 ± 0.012 (0.87%) Ma.

Determination of the 10Be half-life by multicollector ICP-MS and liquid scintillation counting

Abstract: A new method was designed and used for determining the half-life of the isotope 10 Be. The method is based on (1) accurate 10 Be/ 9 Be measurements of 9 Be-spiked solutions of a 10 Be-rich master solution using multicollector ICP mass spectrometry (MC-ICP-MS) and (2) liquid scintillation counting (LSC) using the CIEMAT/NIST method for determining the activity concentrations of the solutions whose 10 Be concentrations were determined by mass spectrometry. Important requirements for the success of this approach (a) was the previous coating of glass ampoules filled for counting experiments with 9 Be, thereby reducing the risk of the adsorptive loss of 10 Be; (b) the removal of Boron from solutions to be measured by MC-ICP-MS by cation chromatography without the introduction of mass fractionation and (c) the accurate determination of the mass bias of 10 Be/ 9 Be measurements by ICP-MS which are always affected by the space-charge effect. The mass bias factor was determined to be 1.1862 ± 0.071 for 10 Be/ 9 Be from careful fitting and error propagation of ratios of measured Li, B, Si, Cr, Fe, Cu, Sr, Nd, Hf, Tl and U standard solutions of known composition under the same measurement conditions. Employing this factor, an absolute 10 Be/ 9 Be ratio of 1.464 ± 0.014 was determined for a first dilution of the 10 Be-rich master solution. This solution is now available as an absolute Be ratio standard in AMS measurements. Finally, a half-life of (1.386 ± 0.016) My (standard uncertainty) was calculated. This value is much more precise than previous estimates and was derived from a fully independent set of experiments. In a parallel, fully independent study using the same master solution, Korschinek et al. [35] have determined a half-life of (1.388 ± 0.018) My. The combined half-life and uncertainty amounts to (1.387 ± 0.012) My. We suggest the use of this value in nuclear studies and in studies that make use of cosmogenic 10 Be in environmental and geologic samples.

A revolutionary graphitisation system: Fully automated, compact and simple

Abstract: A new graphitisation system, directly coupled to an elemental analyser, has been developed for convenient, fast and efficient sample preparations for radiocarbon measurement by means of accelerator mass spectrometry. We demonstrate an alternative to the cryogenic transport of CO2 into the graphitisation reactors with liquid nitrogen, which is used by others. Instead, the CO2 coming from an EA is absorbed on a single column filled with zeolite. The CO2 can then be easily released by heating the zeolite trap and transferred to the reactor by gas expansion. The system is simple and fully automated for sample combustion and graphitisation.

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

Abstract: 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

Bats: A new tool for AMS data reduction

Abstract: A data evaluation program was developed at ETH Zurich to meet the requirements of the new compact AMS systems MICADAS and TANDY in addition to the large EN-Tandem accelerator. The program, called “BATS”, is designed to automatically calculate standard and blank corrected results for measured samples. After almost one year of routine operation with the MICADAS C-14 system BATS has proven to be an easy to use data reduction tool that requires minimal user input. Here we present the fundamental principle and the algorithms used in BATS for standard-sized radiocarbon measurements.

Review of A2B2O7 pyrochlore response to irradiation and pressure

Abstract: This article reviews recent research on swift heavy-ion irradiations and high-pressure studies on pyrochlores of the Gd2Zr2−xTixO7 binary [1] , [2] , [3] , [4] . Applying three complementary analytical techniques (synchrotron X-ray diffraction, Raman spectroscopy and transmission electron microscopy) allowed for the investigation of the response of pyrochlore to irradiation and/or pressure. The chemical composition of pyrochlore has a strong effect on the character and energetics of the type of structural modifications that can be obtained under pressure or irradiation: For Ti-rich pyrochlores, the crystalline-to-amorphous transition is the dominant process. When Zr is substituted for Ti, an order–disorder transformation to the defect-fluorite structure becomes the increasingly dominant process. Except for Gd2Zr2O7, single ion tracks in pyrochlore consist of an amorphous core, surrounded by a crystalline, but disordered, defect-fluorite shell. This shell is surrounded by a defect-rich pyrochlore region. In contrast to similar effects observed when pressure or irradiation are applied separately, the response of the pyrochlore structure is significantly different when it is exposed simultaneously to pressure and irradiation. The combination of relativistic heavy ions with high pressure results in the formation of a new metastable pyrochlore phase. TEM and quantum–mechanical calculations suggest that these novel structural modifications are caused by the formation of nanocrystals and the modified energetics of nanomaterials.

10Be and 26Al measurements at the Zurich 6 MV Tandem AMS facility

Abstract: The setups for the 10 Be and 26 Al AMS measurements at the Zurich 6 MV EN Tandem AMS facility are presented and data analysis procedures for both radionuclides are discussed. Performance parameters of the system are shown. In-house AMS standards are compared to commercially available AMS standards.

The next chapter in radiocarbon dating at the Australian National University: Status report on the single stage AMS

Abstract: In February 2007, a single stage AMS from the National Electrostatics Corporation (NEC) was installed at the Research School of Earth Sciences at the Australian National University. This instrument is equipped with a gas/graphite hybrid ion source allowing direct analysis of CO 2 as well as traditional graphite targets. The instrument was funded by an Australian Research Council grant and by a consortium of eight universities plus the CSIRO Division of Land and Water. Its purpose is to support integrated environmental and archaeological research and access is open to the wider research community. In the first year ∼1500 samples have been analysed. A precision of ∼3‰ is routinely observed. The background for processed graphite (coal, calcite, Carrera marble) is better than 45,000 years. This paper summarizes the first year of measurements.

Basic properties of the F-type centers in halides, oxides and perovskites

Abstract: We present a short survey of the optical properties of primary radiation-induced point defects in alkali halides, simple oxides and some ABO3 perovskites. We discuss in details the optical properties of single electron F and F + centers in rock-salt (f.c.c.) alkali halides and oxides and show that the Mollwo–Ivey law well-known for the F-type centers in alkali halides may be extended for other rock-salt structure insulators. We also discuss the major differences in point defect production mechanisms in halides and oxides. We show that the Rabin–Klick diagram may be generalized for a whole family of alkali halides. The F-type center migration and aggregation into metal colloids in alkali halides and oxides is also discussed.

Optimization of GEANT4 settings for Proton Pencil Beam Scanning simulations using GATE

Abstract: This study reports the investigation of different GEANT4 settings for proton therapy applications in the context of Treatment Planning System comparisons. The GEANT4.9.2 release was used through the GATE platform. We focused on the Pencil Beam Scanning delivery technique, which allows for intensity modulated proton therapy applications. The most relevant options and parameters (range cut, step size, database binning) for the simulation that influence the dose deposition were investigated, in order to determine a robust, accurate and efficient simulation environment. In this perspective, simulations of depth-dose profiles and transverse profiles at different depths and energies between 100 and 230 MeV have been assessed against reference measurements in water and PMMA. These measurements were performed in Essen, Germany, with the IBA dedicated Pencil Beam Scanning system, using Bragg-peak chambers and radiochromic films. GEANT4 simulations were also compared to the PHITS.2.14 and MCNPX.2.5.0 Monte Carlo codes. Depth-dose simulations reached 0.3 mm range accuracy compared to NIST CSDA ranges, with a dose agreement of about 1% over a set of five different energies. The transverse profiles simulated using the different Monte Carlo codes showed discrepancies, with up to 15% difference in beam widening between GEANT4 and MCNPX in water. A 8% difference between the GEANT4 multiple scattering and single scattering algorithms was observed. The simulations showed the inability of reproducing the measured transverse dose spreading with depth in PMMA, corroborating the fact that GEANT4 underestimates the lateral dose spreading. GATE was found to be a very convenient simulation environment to perform this study. A reference physics-list and an optimized parameters-list have been proposed. Satisfactory agreement against depth-dose profiles measurements was obtained. The simulation of transverse profiles using different Monte Carlo codes showed significant deviations. This point is crucial for Pencil Beam Scanning delivery simulations and suggests that the GEANT4 multiple scattering algorithm should be revised. (C) 2010 Elsevier B.V. All rights reserved.

Gaseous radiocarbon measurements of small samples

Abstract: Radiocarbon dating by means of accelerator mass spectrometry (AMS) is a well-established method for samples containing carbon in the milligram range. However, the measurement of small samples containing less than 50 μg carbon often fails. It is difficult to graphitise these samples and the preparation is prone to contamination. To avoid graphitisation, a solution can be the direct measurement of carbon dioxide. The MICADAS, the smallest accelerator for radiocarbon dating in Zurich, is equipped with a hybrid Cs sputter ion source. It allows the measurement of both, graphite targets and gaseous CO2 samples, without any rebuilding. This work presents experiences dealing with small samples containing 1-40 μg carbon. 500 unknown samples of different environmental research fields have been measured yet. Most of the samples were measured with the gas ion source. These data are compared with earlier measurements of small graphite samples. The performance of the two different techniques is discussed and main contributions to the blank determined. An analysis of blank and standard data measured within years allowed a quantification of the contamination, which was found to be of the order of 55 ng and 750 ng carbon (50 pMC) for the gaseous and the graphite samples, respectively. For quality control, a number of certified standards were measured using the gas ion source to demonstrate reliability of the data.

Improved 10Be and 26Al-AMS with a 5 MV spectrometer

Abstract: Detector and ion source changes have increased Be and Al count rates and reduced measurement background at SUERC. Low energy 16 MeV 26Al3+ ions can be separated from interferences by adopting thin silicon nitride membrane detector windows. In contrast, a thick Havar detector window is used to preferentially slow boron ions for simplified 10Be vs. 10B separation without an additional gas cell.

Status of the AMS facility at the University of Georgia

Abstract: Since 2001, the Center for Applied Isotope Studies at the University of Georgia has analyzed more than 10,000 samples using a compact AMS system for carbon isotope measurement. The system, manufactured by National Electrostatics Corporation, utilizes a Model 1.5SDH-1 Pelletron accelerator with a maximum terminal voltage of 0.5 MV. The source has recently been modified, doubling the count rate and improving efficiency more than 50%. Background values have reached 0.12 pMC and the precision is below 0.4 pMC for modern samples. The control and data acquisition system has also been upgraded.

Bone preparation at the KCCAMS laboratory

Abstract: Collagen purification by ultrafiltration [1] is becoming widely accepted as a superior 14 C sample preparation method for removing environmental contamination from archaeological bone. We present an overview of bone sample preparation methods used at the KCCAMS laboratory, UC Irvine. Methods development data are also discussed, including results of tests of gelatinization temperature, evaluation of 10 kDa vs. 30 kDa molecular weight (MW) ultrafiltration, improvements to ultrafilter cleaning methods, tests of ultrafilter memory, and ultrafilter glycerin contamination. These tests were not intended to be exhaustive, but rather to show how standard procedures can be validated and improved with relatively little effort.

Assessment of atmospheric heavy metal deposition in the Tarkwa gold mining area of Ghana using epiphytic lichens

Abstract: In situ lichens (Parmelia sulcata) have been used to assess atmospheric heavy metal deposition in the Tarkwa gold mining area of Ghana. Total heavy metal concentrations obtained by instrumental neutron activation analysis (INAA) were processed by positive matrix factorization (PMF), principal component (PCA) and cluster (CA) analyses. The pollution index factor (PIF) and pollution load index (PLI) criteria revealed elevated levels of Sb, Mn, Cu, V, Al, Co, Hg, Cd and As in excess of the background values. The PCA and CA classified the examined elements into anthropogenic and natural sources, and PMF resolved three primary sources/factors: agricultural activities and other non-point anthropogenic origins, natural soil dust, and gold mining activities. Gold mining activities, which are characterized by dominant species of Sb, Th, As, Hg, Cd and Co, and significant contributions of Cu, Al, Mn and V, are the main contributors of heavy metals in the atmosphere of the study area.

Evaluated differential cross-sections for IBA

Abstract: The evaluation of the cross-sections for any particular reaction consists in the elaboration of the most accurate possible cross-sections through incorporation of the all relevant experimental data in the framework of nuclear physics theory. The evaluated differential cross-sections for ion beam analysis are presented, comparison with the available experimental information is made, and discrepancies and other problems are discussed. The evaluated cross-sections can be retrieved for any scattering angle from the web site SigmaCalc ( http://www.nds.iaea.org/sigmacalc/ ). They are also presented at the web site IBANDL ( http://www.nds.iaea.org/ibandl ) where a comparison of the available experimental data with results of the evaluation can be easily made.

XRD investigation of the strain/stress state of ion-irradiated crystals

Abstract: In this work, it is demonstrated that XRD is a powerful technique for the study of ion-irradiated materials. For this purpose, XRD experiments have been performed under different configurations on a 〈1 0 0〉-oriented yttria-stabilized zirconia single crystal implanted with 300 keV caesium-ions at 3 × 1014 cm−2. Initially, it is demonstrated that the depth strain profile can be determined from the refinement of a symmetric θ–2θ scan. Moreover, in order to explore the whole XRD data, a model that describes the strain/stress state of the damaged layer is proposed. This model takes into account the elastic response of the bulk material (substrate) underneath the irradiated layer. The measured elastic strain is then the sum of a free strain due to the formation of radiation-induced defects and of an additional strain arising from the substrate elastic reaction. Application of this model allowed the calculation of the different strain contributions and the stress experienced by the irradiated layer. It is shown that these parameters may reach large values (respectively 0.7% and −1.9 GPa) despite the low radiation damage level.

Validation of recent Geant4 physics models for application in carbon ion therapy

Abstract: Cancer treatment with energetic carbon ions has distinct advantages over proton or photon irradiation. In this paper we present a simulation model integrated into the Geant4 Monte Carlo toolkit (version 9.3) which enables the use of ICRU 73 stopping powers for ion transport calculations. For a few materials, revised ICRU 73 stopping power tables recently published by ICRU (P. Sigmund, A. Schinner, H. Paul, Errata and Addenda: ICRU Report 73 (Stopping of Ions Heavier than Helium), International Commission on Radiation Units and Measurements, 2009) were incorporated into Geant4, also covering media like water which are of importance in radiotherapeutical applications. We examine, with particular attention paid to the recent developments, the accuracy of current Geant4 models for simulating Bragg peak profiles of 12 C ions incident on water and polyethylene targets. Simulated dose distributions are validated against experimental data available in the literature, where the focus is on beam energies relevant to ion therapy applications (90–400 MeV/u). A quantitative analysis is performed which addresses the precision of the Bragg peak position and proportional features of the dose distribution. It is shown that experimental peak positions can be reproduced within 0.2% of the particle range in the case of water, and within 0.9% in the case of polyethylene. The comparisons also demonstrate that the simulations accurately render the full width at half maximum (FWHM) of the measured Bragg peaks in water. For polyethylene slight deviations from experimental peak widths are partly attributed to systematic effects due to a simplified geometry model adopted in the simulation setup.

Ion tracks in silica for engineering the embedded nanoparticles

Abstract: Swift heavy ions have unique feature of creating ion tracks in insulators of dimension from a few nm to about 10 nm This particular feature of the swift heavy ions is used to engineer the size and shape of the nanoparticles embedded in silica matrix On the basis of several experiments, it is evidenced that the embedded nanoparticles either grow in size or reduce in size, if they are smaller than or comparable to the ion track size The shape transformation from spherical to elongated along the beam direction occurs, when the nanoparticle size is larger than the ion track diameter in silica The reduction, growth and elongation of Au nanoparticles embedded in silica matrix under swift heavy ion irradiation have been discussed in the frame work of thermal spike model

XRD investigation of ion irradiated Ti3Si0.90Al0.10C2

Abstract: Ti3SiC2 is one of the most promising materials belonging to Mn+1AXn phases, which exhibit good damage tolerance, thermal stability and mechanical properties. Recently, in the frame of research on future gas cooled fast nuclear reactors, Ti3SiC2 has been considered as an innovative candidate material, which could be incorporated in some core components such as fuel cladding. At the present time, however, very few data are available concerning the behaviour of this material after irradiation. In this work, Ti3Si0.90Al0.10C2 samples were irradiated with high energy Kr and Xe ions and characterized by X-ray diffraction. Patterns were analysed in terms of change in peak intensity, peak position and width. Rietveld refinements were also performed. Increase in micro-strains and lattice parameter with irradiation dose was highlighted. The formation of β-Ti3SiC2, which has never been observed by experimental XRD on non irradiated material, was proposed for the highly irradiated samples. A partial recovery of the microstructure with temperature was found.

“Water window” compact, table-top laser plasma soft X-ray sources based on a gas puff target

Abstract: We have developed compact, high repetition, table-top soft-X-ray sources, based on a gas puff target, emitting in “water window” spectral range at λ = 2.88 nm from nitrogen gas target or, in 2–4 nm range of wavelengths, from argon gas target. Double stream gas puff target was pumped optically by commercial Nd:YAG laser, energy 0.74 J, pulse time duration 4 ns. Spatial distribution of laser-produced plasma was imaged using a pinhole camera. Using transmission grating spectrometer, argon and nitrogen emission spectra were obtained, showing strong emission in the “water window” spectral range. Using AXUV100 detector the flux measurements of the soft-X-ray pulses were carried out and are presented. These debris free sources are table-top alternative for free electron lasers and synchrotron installations. They can be successfully employed in microscopy, spectroscopy and metrology experiments among others.

A new mapping acquisition and processing system for simultaneous PIXE-RBS analysis with external beam

Abstract: The combination of ion beam analysis techniques is particularly fruitful for the study of cultural heritage objects. For several years, the AGLAE facility of the Louvre laboratory has been implementing these techniques with an external beam. The recent set-up permits to carry out PIXE, PIGE and RBS simultaneously on the same analyzed spot with a particle beam of approximately 20 μm diameter. A new mapping system has been developed in order to provide elemental concentration maps from the PIXE and RBS spectra. This system combines the Genie2000 spectroscopy software with a homemade software that creates maps by handling acquisition with the object position. Each pixel of each PIXE and RBS maps contains the spectrum normalised by the dose. After analysing each pixel of the PIXE maps (low and high energy X-ray spectra) with the Gupixwin peak-fitting software, quantitative elemental concentrations are obtained for the major and trace elements. This paper presents the quantitative elemental maps extracted from the PIXE spectra and the development of RBS data processing for light element distribution and thin layer characterization. Examples on rock painting and lustrous ceramics will be presented.

Challenges and opportunities in high-precision Be-10 measurements at CAMS

Abstract: We determined the overall efficiency for 10 Be of the high-intensity LLNL modified Middleton cesium sputter source in combination with the CAMS FN mass spectrometer. BeO − ionization efficiency is >3%. Charge exchange efficiency including transmission through the tandem for 7.5 MeV Be +3 is ∼34%, resulting in a total system efficiency of just over 1%. At this efficiency and with very low backgrounds, we estimate our detection limit to be ∼1000 10 Be atoms. Cathodes prepared with only ∼80 μg of 9 Be show only an ∼33% reduction in 9 Be beam current compared to a sample with ∼200 μg. These same samples, prepared from 07KNSTD1032 standard material, contained 1 × 10 7 and 5 × 10 6 10 Be atoms and exhibited similar ionization and total system efficiency. These results demonstrate the feasibility of pursuing applications that require precise measurement of samples with low 10 Be concentrations and/or small sample size.

Analysis and application of heavy isotopes in the environment

Abstract: A growing number of AMS laboratories are pursuing applications of actinides. We discuss the basic requirements of the AMS technique of heavy (i.e., above ∼150 amu) isotopes, present the setup at the Vienna Environmental Research Accelerator (VERA) which is especially well suited for the isotope 236 U, and give a comparison with other AMS facilities. Special emphasis will be put on elaborating the effective detection limits for environmental samples with respect to other mass spectrometric methods. At VERA, we have carried out measurements for radiation protection and environmental monitoring ( 236 U, 239,240,241,242,244 Pu), astrophysics ( 182 Hf, 236 U, 244 Pu, 247 Cm), nuclear physics, and a search for long-lived super-heavy elements ( Z > 100). We are pursuing the environmental distribution of 236 U, as a basis for geological applications of natural 236 U.

Plutonium as a tracer of soil and sediment movement in the Herbert River, Australia

Abstract: Plutonium fallout from atmospheric nuclear-weapons testing in the 1950s and 1960s constitutes an artificial tracer suitable for the study of recent soil erosion and sediment accumulation rates. Traditionally 137Cs has been the fallout isotope of choice for such studies, but the plutonium isotopes confer a number of advantages, which can be realised using the ultra-sensitive detection technique of Accelerator Mass Spectrometry (AMS). As a first application of plutonium to a whole-of-basin study, Pu has been measured in both soil and sediment across the catchment of the Herbert River, which is one of the major rivers draining into Australia’s Great Barrier Reef Lagoon. Its catchment includes undisturbed areas as well as regions of pasture and sugar cultivation. The Pu measurements allow the relative contributions of surface and gully erosion from the different land use areas to be determined, and permit the discharged material to be apportioned between the relevant sources.

Accelerator mass spectrometry with the 14UD accelerator at the Australian National University

Abstract: The present status of the AMS activities at the Australian National University is described. Particular attention is paid to methods and equipment that have evolved substantially since earlier reports.

Argon plasma irradiation of polypropylene

Abstract: Polypropylene samples were exposed to argon plasma discharge and the changes of the PP surface properties were studied by different methods. Surface wettability was derived from contact angle measured by standard goniometry and chemical structure of the plasma modified PP was studied using X-ray photoelectron spectroscopy (XPS) and by Rutherford backscattering spectroscopy (RBS), surface morphology and roughness of samples using AFM. Zeta potential of pristine and modified PP was determined with the SurPASS. The presence of incorporated oxygen in the PP surface layer, about 60 nm thick, was observed in RBS spectra. Oxygen concentration is a decreasing function of the depth. With progressing aging time the oxygen concentration on the PP surface decreases. Plasma treatment results in a rapid decrease of the contact angle, which increases again with increasing aging time. In XPS measurement the oxygen containing structures, created by the plasma treatment, were found on the very surface of the modified PP and the zeta potential being changed too. The significant difference in zeta potential between pristine and plasma treated PP clearly indicates that the plasma treatment leads to a more hydrophilic PP surface.

Competitive 10Be measurements below 1 MeV with the upgraded ETH–TANDY AMS facility

Abstract: Competitive 10Be measurements at energies as low as 0.75 MeV are now possible with the compact ETH AMS system TANDY. In this paper we describe and discuss the modifications that led to the significantly improved performance for 10Be at the 0.6 MV accelerator. Results from the first routine measurement show that 10Be on the upgraded TANDY is now fully competitive with larger AMS systems with respect to background and measurement precision. The total efficiency for 10Be is comparable to our large 6 MV Tandem system and thus sufficient for the full range of applications in the Earth and Environmental Sciences.