Showing papers in "Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms in 2013"

On the use of SRIM for computing radiation damage exposure

Abstract: The SRIM (formerly TRIM) Monte Carlo simulation code is widely used to compute a number of parameters relevant to ion beam implantation and ion beam processing of materials. It also has the capability to compute a common radiation damage exposure unit known as atomic displacements per atom (dpa). Since dpa is a standard measure of primary radiation damage production, most researchers who employ ion beams as a tool for inducing radiation damage in materials use SRIM to determine the dpa associated with their irradiations. The use of SRIM for this purpose has been evaluated and comparisons have been made with an internationally-recognized standard definition of dpa, as well as more detailed atomistic simulations of atomic displacement cascades. Differences between the standard and SRIM-based dpa are discussed and recommendations for future usage of SRIM in radiation damage studies are made. In particular, it is recommended that when direct comparisons between ion and neutron data are intended, the Kinchin–Pease option of SRIM should be selected.

High Intensity heavy ion Accelerator Facility (HIAF) in China

Abstract: HIAF (High Intensity heavy ion Accelerator Facility), a new facility planned in China for heavy ion related researches, consists of two ion sources, a high intensity Heavy Ion Superconducting Linac (HISCL), a 45 Tm Accumulation and Booster Ring (ABR-45) and a multifunction storage ring system. The key features of HIAF are unprecedented high pulse beam intensity and versatile operation mode. The HIAF project aims to expand nuclear and related researches into presently unreachable region and give scientists possibilities to conduct cutting-edge researches in these fields. The general description of the facility is given in this article with a focus on the accelerator design.

The ETH Zurich AMS facilities: Performance parameters and reference materials

Abstract: The current performance of all three AMS systems in operation at ETH Zurich, the 6 MV HVEC EN-Tandem facility “TANDEM”, the 05 MV NEC Pelletron “TANDY”, and the 02 MV 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

A versatile gas interface for routine radiocarbon analysis with a gas ion source

Abstract: In 2010 more than 600 radiocarbon samples were measured with the gas ion source at the MIni CArbon DAting System (MICADAS) at ETH Zurich and the number of measurements is rising quickly. While most samples contain less than 50 μg C at present, the gas ion source is attractive as well for larger samples because the time-consuming graphitization is omitted. Additionally, modern samples are now measured down to 5 per-mill counting statistics in less than 30 min with the recently improved gas ion source. In the versatile gas handling system, a stepping-motor-driven syringe presses a mixture of helium and sample CO2 into the gas ion source, allowing continuous and stable measurements of different kinds of samples. CO2 can be provided in four different ways to the versatile gas interface. As a primary method, CO2 is delivered in glass or quartz ampoules. In this case, the CO2 is released in an automated ampoule cracker with 8 positions for individual samples. Secondly, OX-1 and blank gas in helium can be provided to the syringe by directly connecting gas bottles to the gas interface at the stage of the cracker. Thirdly, solid samples can be combusted in an elemental analyzer or in a thermo-optical OC/EC aerosol analyzer where the produced CO2 is transferred to the syringe via a zeolite trap for gas concentration. As a fourth method, CO2 is released from carbonates with phosphoric acid in septum-sealed vials and loaded onto the same trap used for the elemental analyzer. All four methods allow complete automation of the measurement, even though minor user input is presently still required. Details on the setup, versatility and applications of the gas handling system are given.

Identification and separation of radioactive isotope beams by the BigRIPS separator at the RIKEN RI Beam Factory

Abstract: We have developed a method for achieving excellent resolving power in in-flight particle identification of radioactive isotope (RI) beams at the BigRIPS fragment separator at the RIKEN Nishina Center RI Beam Factory (RIBF). In the BigRIPS separator, RI beams are identified by their atomic number Z and mass-to-charge ratio A/Q which are deduced from the measurements of time of flight (TOF), magnetic rigidity (Bρ) and energy loss (ΔE), and delivered as tagged RI beams to a variety of experiments including secondary reaction measurements. High A/Q resolution is an essential requirement for this scheme, because the charge state Q of RI beams has to be identified at RIBF energies such as 200–300 MeV/nucleon. By precisely determining the Bρ and TOF values, we have achieved relative A/Q resolution as good as 0.034% (root-mean-square value). The achieved A/Q resolution is high enough to clearly identify the charge state Q in the Z versus A/Q particle identification plot, where fully-stripped and hydrogen-like peaks are very closely located. The precise Bρ determination is achieved by refined particle trajectory reconstruction, while a slew correction is performed to precisely determine the TOF value. Furthermore background events are thoroughly removed to improve reliability of the particle identification. In the present paper we present the details of the particle identification scheme in the BigRIPS separator. The isotope separation in the BigRIPS separator is also briefly introduced.

SPARC_LAB present and future

Abstract: A new facility named SPARC_LAB has been recently launched at the INFN National Laboratories in Frascati, merging the potentialities of the former projects SPARC and PLASMONX. We describe in this paper the status and the future perspectives at the SPARC_LAB facility.

SAMURAI spectrometer for RI beam experiments

Abstract: A large-acceptance multiparticle spectrometer SAMURAI has been constructed at the RIKEN RI Beam Factory (RIBF) for RI beam experiments. It was designed primarily for kinematically complete experiments such as the invariant-mass spectroscopy of particle-unbound states in exotic nuclei, by detecting heavy fragments and projectile-rapidity nucleons in coincidence. The system consists of a superconducting dipole magnet, beam line detectors, heavy fragment detectors, neutron detectors, and proton detectors. The SAMURAI spectrometer was commissioned in March 2012, and a rigidity resolution of about 1/1500 was obtained for RI beams up to 2.4 GeV/c.

MAMS – A new AMS facility at the Curt-Engelhorn-Centre for Achaeometry, Mannheim, Germany

Abstract: A new AMS lab has been established at the Curt-Engelhorn-Centre for Achaeometry, Mannheim, Germany, based on the compact MICADAS (Mini Carbon Dating System). After 1 year of operation we can demonstrate the high stability and ease of operation of the MICADAS concept. We are confident that we can obtain a precision of modern samples, e.g. for carbon cycle studies, at the 2 permille level. The 200 kV design results in a comparatively low initial budget and economic operational costs.

CologneAMS, a dedicated center for accelerator mass spectrometry in Germany

Abstract: CologneAMS is a new centre for accelerator mass spectrometry (AMS) at the University of Cologne It has been funded by the German Research Foundation (DFG) to improve the experimental conditions especially for those German scientists that apply the AMS technique for their geologic, environmental, nuclear chemical, and nuclear astrophysical research The new AMS-device has been built by High Voltage Engineering Europe (HVEE) and has been installed in the existing accelerator area of the Institute of Nuclear Physics The AMS-facility is designed for the spectrometry of 10Be, 14C, 26Al, 36Cl, 41Ca, 129I in and heavy ions up to 236U and 244Pu The central part of the AMS-facility is a 6 MV Tandetron™ accelerator Downstream of the high energy mass spectrometer an additional switching magnet is used as a further filter element which supplies also additional ports for future extensions of the detector systems The current status of CologneAMS and the results of the first test measurements will be presented

Improving a gas ion source for 14C AMS

Abstract: For more than 4 years, gaseous samples of 1–50 μg carbon have been routinely measured with the gas ion source of the small AMS (Accelerator Mass Spectrometer) facility MICADAS (MIni CArbon DAting System) at ETH Zurich. The applied measurement technique offers a simple and fast way of 14C measurements without the need of sample graphitization. A major drawback of gaseous 14C measurements, however, is the relatively low negative ion current, which results in longer measurement times and lower precision compared to graphitized samples. In December 2009, a new, improved Cs sputter ion source was installed at MICADAS and we began to optimize conditions for the measurement of gaseous samples. 12C− currents from the new ion source were improved from initially 3 to 12–15 μA for routine measurements and the negative ion yield was increased by a factor of 2, reaching 8% on average during routine operation. Moreover, the new measurement settings enable a doubled CO2 flow, thus substantially reducing measurement times. The achieved performance allows closing the sample size gap between gaseous and solid samples and makes the gas ion source a promising tool for dating with a measurement precision of 5‰ on samples as small as 50 μg carbon.

Towards commissioning the new IGISOL-4 facility

Abstract: The Ion Guide Isotope Separator On-Line facility at the Accelerator Laboratory of the University of Jyvaskyla is currently being re-commissioned as IGISOL-4 in a new experimental hall. Access to intense beams of protons and deuterons from a new MCC30/15 cyclotron, with continued possibility to deliver heavy-ion beams from the K = 130 MeV cyclotron, offers extensive opportunities for long periods of fundamental experimental research, developments and applications. A new layout of beam lines with a considerable increase in floor space offers new modes of operation at the facility, as well as a possibility to incorporate more complex detector setups. We present a general overview of IGISOL-4 and the current status of several projects, including the collinear laser spectroscopy station and the future of neutron-induced fission. Recent milestones from the first commissioning experiments are presented.

The state of nuclear forensics

Abstract: Nuclear terrorism has been identified as one of the most serious security threats facing the world today. Many countries, including the United States, have incorporated nuclear forensic analysis as a component of their strategy to prevent nuclear terrorism. Nuclear forensics involves the laboratory analysis of seized illicit nuclear materials or debris from a nuclear detonation to identify the origins of the material or weapon. Over the years, a number of forensic signatures have been developed to improve the confidence with which forensic analysts can draw conclusions. These signatures are validated and new signatures are discovered through research and development programs and in round-robin exercises among nuclear forensic laboratories. The recent Nuclear Smuggling International Technical Working Group Third Round Robin Exercise and an on-going program focused on attribution of uranium ore concentrate provide prime examples of the current state of nuclear forensics. These case studies will be examined and the opportunities for accelerator mass spectrometry to play a role in nuclear forensics will be discussed.

The FRS Ion Catcher: A facility for high-precision experiments with stopped projectile and fission fragments

Abstract: At the FRS Ion Catcher at GSI, projectile and fission fragments are produced at relativistic energies, separated in-flight, range-focused, slowed down and thermalized in a cryogenic stopping cell. A multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) is used to perform direct mass measurements and to provide an isobarically clean beam for further experiments, such as mass-selected decay spectroscopy. A versatile RF quadrupole transport and diagnostics unit guides the ions from the stopping cell to the MR-TOF-MS, provides differential pumping, ion identification and includes reference ion sources. The FRS Ion Catcher serves as a test facility for the Low-Energy Branch of the Super-FRS at the Facility for Antiproton and Ion Research (FAIR), where the cryogenic stopping cell and the MR-TOF-MS will be key devices for the research with stopped projectile and fission fragments that will be performed with the experiments MATS and LaSpec. Off-line tests of the stopping cell yield a combined ion survival and extraction efficiency for 219Rn ions of about 30% and an extraction time of about 25 ms. The stopping cell and the MR-TOF-MS were commissioned on-line as part of the FRS Ion Catcher. For the first time, a stopping cell for exotic nuclei was operated on-line at cryogenic temperatures. Using a gas density almost two times higher than ever reached before for a stopping cell with RF ion repelling structures, various 238U projectile fragments were thermalized and extracted with very high efficiency. Direct mass measurements of projectile fragments were performed with the MR-TOF-MS, among them the nuclide 213Rn with a half-life of 19.5 ms only.

Installation and commissioning of EURICA - Euroball-RIKEN Cluster Array

Abstract: EURICA is a project at RIKEN Nishina Center aimed at studying a wide range of exotic nuclei through β -decay measurements and high-resolution γ -ray spectroscopy. The setup is located behind the BigRIPS fragment separator and the ZeroDegree spectrometer at the RIBF. EURICA consists of the HPGe cluster detectors from the previous Euroball and RISING projects, together with double-sided silicon-strip detectors for β -decay counting and lifetime measurements. In total, this setup provides us with the possibility to study several aspects of the exotic nuclei produced at the RIBF.

Determination of muon attenuation lengths in depth profiles from in situ produced cosmogenic nuclides

Abstract: Cosmogenic nuclides are important tools to understand and quantify the processes that control the development and evolution of landscapes during the quaternary. Among all published studies, few are related to the accurate and precise determination of the physical parameters governing their production in the Earth’s crust surface (in situ produced cosmogenic nuclides) and its evolution as a function of depth below the Earth’s surface. Currently, it is nearly impossible to advocate global parameters that could be used worldwide. Indeed, at each sampling site, not only the geometry and the mineralogy will differ but also their evolution as a function of depth. In this paper, a new approach based on the measurement of the evolution of cosmogenic nuclide concentrations along depth profiles to determine the muon attenuation lengths is proposed. Contrarily to previous studies that used to describe both slow and fast muons, only one type of muons will be considered in this paper and nuclide accumulation at depth will be described by a single exponential. The determined attenuation length integrates the potential effect of the chemical composition of the overlying matrix and takes into account the entire energy range of the incident particles. Additionally, when denudational steady state is reached, muon contributions can be determined. When scaled to sea level, these contributions appear to be comparable for a given nuclide whatever the site where they have been determined. The average weighted muon contributions are 0.028 ± 0.004 atoms g−1 a−1 for 10Be, 0.233 ± 0.045 atoms g−1 a−1 for 26Al and 1.063 ± 0.329 atoms g−1 a−1 for 36Cl and are valid within the depth range 0–6500 g cm−2.

Status report on sample preparation facilities for 14C analysis at the new CologneAMS center

Abstract: The new AMS facility at the University of Cologne (CologneAMS), Germany, was established in 2010 with the delivery of the HVE 6 MV Tandetron AMS, which will be used for 14C, 26Al, 36Cl, 41Ca, 129I, 239U and 244Pu analyses. Parallel to the AMS installation the radiocarbon group has started to set up and test sample preparation methods and instruments for different materials. We present first results of reference and standard materials that have been processed and graphitized in our lab and measured at the ETH and CologneAMS facilities. The graphitization blank and its influence on small samples sizes processed with an automated graphitization system have been determined. Work on isolation of individual organic compounds with a preparative gas chromatography system has been started. The focus of our future work will be on reducing process blank levels and sample sizes as well as on the application of compound-specific radiocarbon analyses in (paleo-) environmental research.

The in-gas-jet laser ion source: resonance ionization spectroscopy of radioactive atoms in supersonic gas jets

Abstract: New approaches to perform efficient and selective step-wise resonance ionization spectroscopy (RIS) of radioactive atoms in different types of supersonic gas jets are proposed. This novel application results in a major expansion of the in-gas laser ionization and spectroscopy (IGLIS) method developed at KU Leuven. Implementation of resonance ionization in the supersonic gas jet allows to increase the spectral resolution by one order of magnitude in comparison with the currently performed in-gas-cell ionization spectroscopy. Properties of supersonic beams, obtained from the de Laval-, the spike-, and the free jet nozzles that are important for the reduction of the spectral line broadening mechanisms in cold and low density environments are discussed. Requirements for the laser radiation and for the vacuum pumping system are also examined. Finally, first results of high-resolution spectroscopy in the supersonic free jet are presented for the 327.4 nm 3d104s 2S1/2→ 3d104p 2P1/2 transition in the stable 63Cu isotope using an amplified single mode laser radiation.

Optimization of Sealed Tube Graphitization Method for Environmental C-14 Studies Using MICADAS

Abstract: The original sealed tube zinc reduction graphitization process was first developed for rapid low-precision measurements of biomedical tracer samples and later also applied for high precision measurements of not too old samples. In this study we tested the MICADAS (mini radiocarbon dating system [1] ) radiocarbon measurements of targets prepared by sealed tube graphitization process. We found the optimal iron catalyst and reagents (TiH 2 and Zn) amount whereby we can reach a relatively low background level, and minimized the overall δ 13 C fractionation during the graphitization. Repeated measurements of normalization standards and real samples with known 14 C activities were very well reproduced. Finally, we demonstrated the applicability of the sealed tube graphitization on real environmental samples covering a wide range of 14 C concentrations.

The new 6 MV AMS-facility DREAMS at Dresden

Abstract: A new 6 MV electrostatic tandem accelerator has been put into operation at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The system is equipped for accelerator mass spectrometry and opens a new research field at HZDR and the Helmholtz Association. It will be also used for ion beam analysis as well as for material modification via high-energy ion implantation. The research activity at the DREsden Accelerator Mass Spectrometry facility (DREAMS) based on a 6 MV Tandetron is primarily dedicated to the long-lived radioisotopes of 10Be, 26Al, 36Cl, 41Ca, and 129I. DREAMS background levels have been found to be at 4.5 × 10−16 for 10Be/9Be, 8 × 10−16 for 26Al/27Al, 3 × 10−15 for 36Cl/35Cl and 8 × 10−15 for 41Ca/40Ca, respectively. The observed background of 2 × 10−13 for 129I/127I originates from intrinsic 129I from AgI produced from commercial KI. The introduction of quality assurance approaches for AMS, such as the use of traceable calibration materials and taking part in interlaboratory comparisons, guarantees high accuracy data for future DREAMS users. During first experiments an energy calibration of the accelerator has been carried out using the nuclear reaction 1H(15N,γα)12C yielding an energy correction factor of 1.019.

A novel approach to process carbonate samples for radiocarbon measurements with helium carrier gas

Abstract: Most laboratories prepare carbonates samples for radiocarbon analysis by acid decomposition in evacuated glass tubes and subsequent reduction of the evolved CO2 to graphite in self-made reduction manifolds. This process is time consuming and labor intensive. In this work, we have tested a new approach for the preparation of carbonate samples, where any high-vacuum system is avoided and helium is used as a carrier gas. The liberation of CO2 from carbonates with phosphoric acid is performed in a similar way as it is often done in stable isotope ratio mass spectrometry where CO2 is released with acid in septum sealed tube under helium atmosphere. The formed CO2 is later flushed in a helium flow by means of a double-walled needle mounted from the tubes to the zeolite trap of the automated graphitization equipment (AGE). It essentially replaces the elemental analyzer normally used for the combustion of organic samples. The process can be fully automated from sampling the released CO2 in the septum-sealed tubes with a commercially available auto-sampler to the graphitization with the automated graphitization. The new method yields in low sample blanks of about 50000 years. Results of processed reference materials (IAEA-C2, FIRI-C) are in agreement with their consensus values.

Nuclear physics experiments with ion storage rings

Abstract: In the last two decades a number of nuclear structure and astrophysics experiments were performed at heavy-ion storage rings employing unique experimental conditions offered by such machines. Furthermore, building on the experience gained at the two facilities presently in operation, several new storage ring projects were launched worldwide. This contribution is intended to provide a brief review of the fast growing field of nuclear structure and astrophysics research at storage rings. © 2013 Elsevier B.V. All rights reserved.

Effect of γ-rays irradiation on Mn–Ni ferrites: Structure, magnetic properties and positron annihilation studies

Abstract: Manganese–nickel ferrites powder with general formula MnxNi1−xFe2O4 (x = 0.0, 0.2, 0.4) were synthesized through oxalate precursor route and sintered at 1000 °C. The X-ray diffraction (XRD) patterns were measured for the prepared samples to confirm the existence of single-phase structure. The crystallite size was estimated and found to be within the range 125–170 nm. To study the radiation effect on the structure and magnetic properties, a representative group of the investigated samples were irradiated by γ-rays of 60Co source with a dose of 310 kGy. The XRD spectra were performed for the irradiated samples and compared with that of the pristine samples to estimate changes in the structure. The obtained results showed that the crystallite size increased by a factor of 10–16% after gamma irradiation. The lattice parameter also was increased due to the conversion of Fe3+ (0.64 A) to Fe2+ (0.76 A). The formula of the cation distribution of the ferrites samples was suggested at x = 0, 0.2, 0.4 before and after irradiation. The theoretical lattice parameter, sample density and porosity were calculated and compared with that obtained from the experimental data. Good agreement was found between theoretical and experimental structural data which confirms the proposed formula of cations distribution. The hysteresis curves were measured using vibrating sample magnetometer (VSM) for the unirradiated and irradiated samples and the saturation magnetization was estimated. The obtained results showed increase in saturation magnetizations (Ms) for all the samples by irradiation due to redistribution of the cations between A and B sites and changing the net magnetic moments. Theoretical calculation of magnetic moments and saturation magnetization using the proposed cations distribution of A and B sites confirmed the experimental results. The positron annihilation lifetime spectroscopy (PALS) was used to investigate the defects and changes in electron density after irradiation. The PAL parameters (τ1, I1, τ2, I2 and mean lifetime) show that the irradiation affects the size and concentration of the vacant type defects. The results reveal that there are some large voids (with radius ranged from 0.28 to 0.38 nm and mean value of 0.34 ± 0.04 nm in the studied samples). The obtained results indicate the high sensitivity of PALS technique to the enhanced structure changes due to gamma rays irradiation.

MD simulations of onset of tungsten fuzz formation under helium irradiation

Abstract: When helium (He) escapes a fusion reactor plasma, a tungsten (W)-based divertor may, under some conditions, form a fuzz-like nano-morphology. This is a highly undesired phenomenon for the divertor, and is not well understood. We performed molecular dynamics simulations of high fluence He and also C-seeded He (He+C) irradiation on W, focusing on the effect of the high fluence, the temperature and the impurities on the onset of the structure formation. We concluded that MD reproduces the experimentally found square root of time dependence of the surface growth. The He atomic density decreases when increasing the number of He atoms in the cell. A higher temperature causes a larger bubble growth and desorption activity, specially for the pure He irradiation cases. It also it leads to W recrystallization for the He+C irradiation cases. Carbon acts as a local He trap for small clusters or single atoms and causes a larger loss of crystallinity of the W surface.

Status report of AMS sample preparation laboratory at GADAM Centre, Gliwice, Poland

Abstract: The laboratory for 14 C AMS sample preparation in the Gliwice Radiocarbon Laboratory has gradually evolved since its start in 1999 to cater for an increase in volume and variety of radiocarbon dating samples. To date, nearly 2000 graphite targets have been produced from materials such as plant macrofossils, charcoal, peat, bones, shells and wood. The equipment comprises a station for chemical preparation and high vacuum lines for production, purification and graphitization of sample carbon dioxide. The present capacity allows preparation of up to 400 targets annually for the needs of scientific projects and external orders for radiocarbon dating continuously received by the GADAM Centre of Excellence. The laboratory’s sample preparation protocols and recent improvements are described and its performance during the 10 years of activity is discussed in terms of parameters obtained from reference materials prepared in this laboratory and demonstrated with a few science applications.

Comparing deuterium retention in tungsten films measured by temperature programmed desorption and nuclear reaction analysis

Abstract: Tungsten (W) films with thicknesses ranging between 1 and 12 μm deposited by magnetron sputtering on silicon substrates were used as a model system for comparing the deuterium (D) retention measured by both temperature programmed desorption (TPD) and nuclear reaction analysis (NRA). Samples were loaded with deuterium ex-situ with an ECR plasma at 370 and 600 K with an energy of 38 eV per deuteron. To avoid diffusion of D into the silicon substrate and to increase adhesion a copper interlayer was applied. The results show that all implanted D atoms were retained exclusively in the W films. The distribution of D is homogenous throughout the W layer with an atomic fraction of 3 ± 0.4 × 10 −3 . With increasing W thickness the D profile extends to correspondingly larger depths with practically identical D concentration. For W films with a thickness lower than the NRA information depth of about 8 μm the total retained D amount measured by TPD and NRA is in excellent agreement. As expected, for films thicker than the NRA information depth, TPD deviates from NRA.

Towards radiocarbon dating of single foraminifera with a gas ion source

Abstract: Carbonate shells from foraminifera are often analysed for radiocarbon to determine the age of deep-sea sediments or to assess radiocarbon reservoir ages. However, a single foraminiferal test typically contains only a few micrograms of carbon, while most laboratories require more than 100 μg for radiocarbon dating with an accelerator mass spectrometry (AMS) system. The collection of the required amount of foraminifera for a single analyses is therefore time consuming and not always possible. Here, we present a convenient method to measure the radiocarbon content of foraminifera using an AMS system fitted with a gas ion source. CO 2 is liberated from 150 to 1150 μg of carbonate in septum sealed vials by acid decomposition of the carbonate. The CO 2 is collected on a zeolite trap and subsequently transferred to a syringe from where it is delivered to the ion source. A sample of 400 μg (50 μg C) typically gives a 12 C − ion source current of 10–15 μA over 20 min, yielding a measurement precision of less than 7 per mil for a modern sample. Using this method, we were able to date a single 560 μg Cibicides pseudoungerianus test at 14,030 ± 160 radiocarbon years. Only a minor modification to our existing gas handling system was required and the system is fully automatable to further reduce the effort involved for sample preparation.

The potential of He stripping in heavy ion AMS

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 500 keV 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.

The effects of high energy electron beam irradiation in air on accelerated aging and on the structure property relationships of low density polyethylene

Abstract: The response of low density polyethylene (LDPE) to high energy electron beam irradiation in air (10 MeV) between 25 and 400 kGy was examined and compared to non-irradiated polyethylene in terms of the mechanical and structural properties. To quantify the degree of crosslinking, swelling studies were performed and from this it was observed that the crosslink density increased as the irradiation dose increased. Furthermore, a reduction was observed in the numerical data for molar mass between adjacent crosslinks and the number of monomeric units between adjacent crosslinks as the irradiation dose was conducted incrementally. Accelerated aging provided evidence that radicals became trapped in the polymer matrix of LDPE and this in turn initiated further reactions to transpire as time elapsed, leading to additional alteration in the structural properties. Fourier transform infrared spectroscopy (FTIR) was implemented to provide insight into this. This technique established that the aging process had increased the oxidative degradation products due to oxygen permeation into the polymer and double bonds within the material. Mechanical testing revealed an increase in the tensile strength and a decrease in the elongation at break. Accelerated aging caused additional modifications to occur in the mechanical properties which are further elucidated throughout this study. Dynamic frequency sweeps investigated the effects of irradiation on the structural properties of LDPE. The effect of varying the irradiation dose concentration was apparent as this controlled the level of crosslinking within the material. Maxwell and Kelvin or Voigt models were employed in this analytical technique to define the reaction procedure of the frequency sweep test with regards to non-crosslinked and crosslinked LDPE.

Design of the Advanced Rare Isotope Separator ARIS at FRIB

Abstract: The Facility for Rare Isotopes Beams (FRIB) at Michigan State University will use projectile fragmentation and induced in-flight fission of heavy-ion primary beams at energies of 200 MeV/u and higher and at a beam power of 400 kW to generate rare isotope beams for experiments in nuclear physics, nuclear astrophysics, and fundamental symmetries, as well as for societal needs. The Advanced Rare Isotope Separator (ARIS) has been designed as a three-stage fragment separator for the efficient collection and purification of the rare isotope beams of interest. A vertically bending preseparator (first stage) with production target and beam dump is fully integrated into a production target facility hot cell with remote handling. The new separator compresses the accepted momentum width of up to ±5% of the beam by a factor of three in the standard operational mode. Provisions for alternate operational modes for specific cases are included in the design. This preseparator is followed by two, horizontally-bending separator stages (second and third stages) utilizing the magnets from the existing A1900 fragment separator at the National Superconducting Cyclotron Laboratory (NSCL). These stages can alternatively be coupled to a single high-resolution separator stage, resulting in the flexibility to optimize the operation for different experiments, including momentum tagging and in-flight particle identification of rare isotope beams. The design of ARIS will be presented with an emphasis on beam physics characteristics, and anticipated operational modes will be described.

Comparison of molecular dynamics and binary collision approximation simulations for atom displacement analysis

Abstract: Molecular dynamics (MD) and binary collision approximation (BCA) computer simulations are employed to study surface damage by single ion impacts. The predictions of BCA and MD simulations of displacement cascades in amorphous and crystalline silicon and BCC tungsten by 1 keV Ar + ion bombardment are compared. Single ion impacts are studied at angles of 50 , 60 and 80 from normal incidence. Four parameters for BCA simulations have been optimized to obtain the best agreement of the results with MD. For the conditions reported here, BCA agrees with MD simulation results at displacements larger than 5 A for amorphous Si, whereas at small displacements a dierence between BCA and MD arises due to a material ow