Showing papers in "Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms in 2003"

Plasma treatment of polymers for surface and adhesion improvement

Abstract: Different plasma treatments in a rf discharge of Ar, He, or N 2 are used to etch, cross-link, and activate polymers like PC, PP, EPDM, PE, PS, PET and PMMA. Due to the numerous ways a plasma interacts with the polymer surface, the gas type and the plasma conditions must be adjusted on the polymer type to minimize degradation and aging effects. Wetting and friction properties of polymers can be improved by a simple plasma treatment, demonstrated on PC and EPDM, respectively. However, the deposition of ultra-thin layers by plasma enables the adjustment of wetting properties, using siloxane-based or fluorocarbon films, and further reduction of the friction coefficient, applying siloxane or a-C:H coatings. Nevertheless, the adhesion of plasma-deposited coatings should be regarded, which can be enhanced by depositing a graded layer.

X-ray micro-tomography an attractive characterisation technique in materials science

Abstract: X-ray tomography is a non-destructive technique which provides 3D information of materials. It is consequently very attractive in Materials Science since the relation between macroscopic properties and the micro-structure of a material is very frequently required. The aim of this paper is to present selected results obtained in various investigations of metallic materials such as superplastic deformation, materials in the semi-solid state and metallic foams. Depending on the studied features, several tomography analysis modes were used: conventional absorption mode, phase contrast and holotomography, a new technique, which provides the 3D distribution of the electron density in the bulk of the material. Furthermore micro-tomography enables one to perform in situ experiments either by using a mechanical test machine or a furnace.

The electronic structure and spectral properties of ZnO and its defects

Abstract: The electronic structure of ZnO and its defects, which include intrinsic point defects and their complexes, have been calculated using full-potential linear Muffin-tin orbital method. According to our calculation data, the positions of the defect state levels have been determined in the energy band of ZnO. Based on the results above, we analysis the mechanism of the absorption and emission spectra of ZnO and discuss the effects of the electronic structure of complete ZnO and its defects on the spectral properties.

Commissioning the A1900 projectile fragment separator

Abstract: An important part of the recent upgrade of the NSCL facility is the replacement of the A1200 fragment separator with a new high acceptance device called the A1900. The design of the A1900 device represents a third generation projectile fragment separator (relative to the early work at LBL) as it is situated immediately after the primary accelerator, has a very large acceptance, a bending power significantly larger than that of the cyclotron and is constructed from large superconducting magnets (quadrupoles with 20 and 40 cm diameter warm bores). The A1900 can accept over 90% of a large range of projectile fragmentation products produced at the NSCL, leading to large gains in the intensity of the secondary beams. The results of initial tests of the system with a restricted momentum acceptance (±0.5%) indicate that the A1900 is performing up to specifications. Further large gains in the intensities of primary beams, typically two or three orders of magnitude, will be possible as the many facets of high current extraction from the ion sources, acceleration of intense, low charge-state ions in the K500 cyclotron, transfer and stripping injection in K1200 cyclotron are optimized. A liquid-lithium cooled beryllium target system is being constructed to use with the high power beams (up to ≈5 kW) that will be available from the coupled-cyclotron facility. An overview of the design, construction and commissioning studies of the A1900 device will be presented along with some of the results from the initial exotic isotope production studies.

Space environment effects on polymers in low earth orbit

Abstract: Polymers are widely used in space vehicles and systems as structural materials, thermal blankets, thermal control coatings, conformal coatings, adhesives, lubricants, etc. The low earth orbit (LEO) space environment includes hazards such as atomic oxygen, UV radiation, ionizing radiation (electrons, protons), high vacuum, plasma, micrometeoroids and debris, as well as severe temperature cycles. Exposure of polymers and composites to the space environment may result in different detrimental effects via modification of their chemical, electrical, thermal, optical and mechanical properties as well as surface erosion. The high vacuum induces material outgassing (e.g. low-molecular weight residues, plasticizers and additives) and consequent contamination of nearby surfaces. The present work reviews the LEO space environment constituents and their interactions with polymers. Examples of degradation of materials exposed in ground simulation facilities are presented. The issues discussed include the erosion mechanisms of polymers, formation of contaminants and their interaction with the space environment, and protection of materials from the harsh space environment.

Experimental benchmarks of the Monte Carlo code penelope

Abstract: The physical algorithms implemented in the latest release of the general-purpose Monte Carlo code penelope for the simulation of coupled electron–photon transport are briefly described. We discuss the mixed (class II) scheme used to transport intermediate- and high-energy electrons and positrons and, in particular, the approximations adopted to account for the energy dependence of the interaction cross-sections. The reliability of the simulation code, i.e. of the adopted interaction models and tracking algorithms, is analyzed by means of a comprehensive comparison of simulation results with experimental data available from the literature. The present analysis demonstrates that penelope yields a consistent description of electron transport processes in the energy range from a few keV up to about 1 GeV.

In-flight RI beam separator BigRIPS at RIKEN and elsewhere in Japan

Abstract: Presented are features of the in-flight radioactive isotope (RI) beam separators in Japan as well as of a next-generation separator BigRIPS being built at RIKEN for the RI-beam factory project. Characteristic features and present status of the existing separators are reviewed for the RIPS at RIKEN, the Secondary Beam Line at RCNP, the Secondary Beam Course at NIRS, the CRIB at CNS and the RMS at JAERI. Design features are outlined for the BigRIPS, which is characterized by two major features: large acceptances and a tandem (or two-stage) separator scheme. The large acceptances allow one to produce RI beams efficiently by using in-flight fission of uranium ions, being achieved by using superconducting quadrupoles with a large aperture. The tandem separator scheme allows one to deliver tagged RI beam. The integrated capability of the BigRIPS and the accelerators of the project can significantly enlarge the scope of future RI-beam experiments. A low-energy course following the BigRIPS can provide energy-degraded and -bunched RI beams to be applied for a gas catcher system with an RF ion guide, aiming at realizing a projectile fragmentation based ISOL system.

Thermal stability of helium-vacancy clusters in iron

Abstract: Molecular dynamics calculations were performed to evaluate the thermal stability of helium–vacancy clusters (HenVm) in Fe using the Ackland Finnis–Sinclair potential, the Wilson–Johnson potential and the Ziegler–Biersack–Littmark–Beck potential for describing the interactions of Fe–Fe, Fe–He and He–He, respectively. Both the calculated numbers of helium atoms, n, and vacancies, m, in clusters ranged from 0 to 20. The binding energies of an interstitial helium atom, an isolated vacancy and a self-interstitial iron atom to a helium–vacancy cluster were obtained from the calculated formation energies of clusters. All the binding energies do not depend much on cluster size, but they primarily depend on the helium-to-vacancy ratio (n/m) of clusters. The binding energy of a vacancy to a helium–vacancy cluster increases with the ratio, showing that helium increases cluster lifetime by dramatically reducing thermal vacancy emission. On the other hand, both the binding energies of a helium atom and an iron atom to a helium–vacancy cluster decrease with increasing the ratio, indicating that thermal emission of self-interstitial atoms (SIAs) (i.e. Frenkel-pair production), as well as thermal helium emission, may take place from the cluster of higher helium-to-vacancy ratios. The thermal stability of clusters is decided by the competitive processes among thermal emission of vacancies, SIAs and helium, depending on the helium-to-vacancy ratio of clusters. The calculated thermal stability of clusters is consistent with the experimental observations of thermal helium desorption from α-Fe during post-He-implantation annealing.

The Super-FRS project at GSI

Abstract: The GSI projectile fragment separator FRS has demonstrated with many pioneering experiments the research potential of in-flight separators at relativistic energies. Although the present facility has contributed much to the progress in the field of nuclear structure physics, major improvements are desirable in the future. The characteristics of the proposed next-generation facility at GSI, the Super-FRS, will be presented and compared to other projects. The Super-FRS is a large-acceptance superconducting fragment separator followed by different experimental branches including a combination with a new storage-cooler ring system. This system consists of a collector ring (CR) and a new experimental storage ring (NESR) which allow precision mass and lifetime measurements as well as in-ring reaction studies. The NESR can be operated in combination with an electron ring to measure electron scattering with exotic nuclei. This electron heavy-ion collider will open up new fields for nuclear structure research.

A new 3D micro X-ray fluorescence analysis set-up - First archaeometric applications

Abstract: A new 3D micro X-ray fluorescence (micro-XRF) analysis method based on a confocal X-ray set-up is presented. The capabilities of this new method are evaluated and illustrated with depth sensitive investigations of paint layers in ancient Indian Mughal miniatures. Successive paint layers could be distinguished non-destructively with a depth resolution of about 10 μm. Major and minor elements are detectable and can be discriminated in different layers. New light could be shed on ancient painting techniques and materials with this new 3D micro-XRF set-up.

Plasma surface modification of polymers for biomedical use

Abstract: Polymeric materials can be used in many application areas due to their mechanical (e.g. elastic) characteristics, chemical stability, and their light weight, as well as for their many design possibilities. Even in the fields of medicine and biotechnology many products are completely or partly made of polymers. In contact with biological systems, compatibility of these materials is not always given. To fulfill the requirements for medical applications, the surfaces have to be modified. Plasma techniques are demonstrated as an appropriate tool for the generation of the demanded surface properties. Experimental data are given for surface modification by plasma polymerization, with retention of the functional groups of the monomers used. Qualitative and quantitative characterization of the thin films with respect to the type and density of available groups at the surfaces is presented. Some possible applications of plasma-modified polymers are also discussed.

The S800 spectrograph

Abstract: The high resolution S800 spectrograph built at the National Superconducting Cyclotron Laboratory (NSCL) is specially designed for reactions studies with radioactive beams. Its large acceptances both in solid angle and momentum are well adapted to the large emittances of secondary beams produced by projectile fragmentation. The high resolution is achieved via an analytical reconstruction method in which the aberrations of the spectrograph are calculated a priori from the magnetic field maps and used directly to correct the raw data. Following the coupled cyclotron upgrade now completed at the NSCL, the S800 has undergone a number of improvements. An overview of past and future experiments is also presented.

Ion transport through asymmetric nanopores prepared by ion track etching

Abstract: Transport properties of single asymmetric nanopores in polyethylene terephthalate (PET) and polyimide (Kapton) membranes are investigated. The pores are produced by the track-etching technique based on irradiation of the polymer with heavy ions and subsequent chemical etching. Electrolytic conductivity measurements show that asymmetric pores in both polymeric materials rectify the ionic current. The PET and Kapton pores differ however significantly in their transient transport properties. The ion current through the PET nanopore fluctuates with the amplitudes reaching even 100% of the mean current, whereas nanopores in Kapton exhibit a stable current signal. We show that the transient properties of the pores depend on the chemical structure of the polymer as well as on the irradiation and etching procedures used in this work.

The National University of Singapore high energy ion nano-probe facility: Performance tests☆

Abstract: The Research Centre for Nuclear Microscopy, National University of Singapore incorporates three state-of-the-art beam lines, connected to a high brightness High Voltage Engineering Europa 3.5 MV Singletron accelerator. One of these lines is a NEC (National Electrostatics Corporation, USA) ion channeling facility, utilising broad beam ion beam analysis techniques for advanced materials research. The other two lines are microbeam facilities; one is designed for nuclear microscopy of biomedical samples and advanced materials, where relatively high currents (>50 pA) are required, and the other for proton beam micromachining (PBM) and materials modification, where lower currents can be utilised. The resolution performances of the two microbeam lines have been measured, and the results are as follows: (1) The nuclear microscope line incorporates the Oxford Microbeams OM2000 endstation with the OM50 quadrupole lenses configured in the high excitation triplet mode. This line has achieved the world’s best performances for analytical applications of 290 × 400 nm for a 50 pA current of 2 MeV protons. (2) The PBM line, which is the first of its kind worldwide, utilizes the new generation of compact (OM52) quadrupole lenses (Oxford Microbeams Ltd.) also configured in a high excitation, triplet configuration. This facility, which has superior demagnification properties, has achieved the world’s best performances for low current applications. Spot sizes of 35 × 75 nm have been measured using direct scanning transmission ion microscopy for beam currents of 10,000 protons per second.

Applications for radiation processing of materials

Abstract: The physical and chemical properties of polymeric materials can be modified by treatment with ionizing radiation in the form of gamma rays, X-rays and energetic electrons. High-energy electron beams are especially useful in this regard. Polymerizing (curing), grafting, crosslinking and chain scissioning reactions can be initiated by irradiation. The results of such reactions can enhance the utility and value of commercial products. Brief reviews of a variety of successful applications are given in this paper. Additional information is provided about reaction yields (G-values), temperature rises during treatment and the radiation stability of common polymers.

The GREAT spectrometer

Abstract: The GREAT spectrometer is designed to measure the decay properties of reaction products transported to the focal plane of a recoil separator. GREAT comprises a system of silicon, germanium and gas detectors optimised for detecting the arrival of the reaction products and correlating with any subsequent radioactive decay involving the emission of protons, α particles, β particles, γ rays, X-rays or conversion electrons. GREAT can either be employed as a sensitive stand-alone device for decay measurements at the focal plane, or used to provide a selective tag for prompt conversion electrons or γ rays measured with arrays of detectors deployed at the target position. A new concept of triggerless data acquisition (total data readout) has also been developed as part of the GREAT project, which circumvents the problems and limitations of common dead time in conventional data acquisition systems.

Slow RI-beams from projectile fragment separators

Abstract: The projectile fragment separator provides a wide variety of short-lived RI-ions with less restrictions on their chemical property or lifetime limit. The beam energy and quality is, however, not adequate for low-energy beam experiments, in particular for trapping experiments. Recently, one has proposed to obtain a low-energy beam from an energetic RI-beam leaving a projectile fragment separator by using a large gas-catcher and an rf ion-guide system. In off-line and in on-line test experiments, the principle of the rf ion-guide was proven. An overall efficiency of 0.2% for 70 MeV/u 8 Li from the RIKEN projectile fragment separator (RIPS) was obtained so far.

ZnO–PbO–B2O3 glasses as gamma-ray shielding materials

Abstract: Values of the gamma-ray mass-attenuation coefficient, the photon mean free path (MFP), the effective atomic number and the effective electron density have been determined experimentally for x ZnO · 2 x PbO · (1−3 x )B 2 O 3 ( x =0.1–0.26) glasses at photon energies 511, 662, 1173 and 1332 keV and compared with theoretical data. The specific volume of the glasses has been derived from density measurements and studied as a function of composition. It is pointed out that these glasses have potential applications in radiation shielding.

Fluorine-doping in titanium dioxide by ion implantation technique

Abstract: We implanted 200 keV F+ in single crystalline titanium dioxide (TiO2) rutile at a nominal fluence of 1 × 1016 to 1 × 1017 ions cm−2 and then thermally annealed the implanted sample in air. The radiation damage and its recovery process during the annealing were analyzed by Rutherford backscattering spectrometry in channeling geometry and variable-energy positron annihilation spectroscopy. The lattice disorder was completely recovered at 1200 °C by the migration of point defects to the surface. According to secondary ion mass spectrometry analysis, the F depth profile was shifted to a shallower region along with the damage recovery and this resulted in the formation of an F-doped layer where the impurity concentration steadily increased toward the surface. The F doping proved to provide a modification to the conduction-band edge of TiO2, as assessed by theoretical band calculations.

Track-etch templates designed for micro- and nanofabrication

Abstract: This paper reports on the advances made in the laboratory in the development of porous media by track-etching process, and on their use by research partners as templates for the micro- or nanofabrication of polymeric and metallic wires or tubules with interesting properties. It mainly relates to the development of nanoporous polycarbonate-based templates, and more precisely to pore-shape control in polycarbonate films, to the development of supported track-etch templates and to the feasibility of template patterning; recent results on the development of templates from polyimide support are also reported. Finally, some nanontaterial synthesis processes and properties are listed, with references to published papers. (C) 2003 Elsevier B.V. All rights reserved.

Hydrogels of polysaccharide derivatives crosslinked with irradiation at paste-like condition

Abstract: Polysaccharides such as cellulose, starch, chitin/chitosan and their water-soluble derivatives have been known as degradable type polymers under action of ionizing radiation. Recently, we found that water-soluble polysaccharides derivatives such as carboxymethylcellulose (CMC), carboxymethylstarch (CMS) and carboxymethylchitin (CMCT), carboxymethylchitosan (CMCTS) lead to radiation crosslinking at high concentrated aqueous solution (more than 10%, paste-like state). It was proved that the crosslinking was remarkably affected by their concentration. It was assumed that radiation formation of hydrogels of these polysaccharides derivatives were mainly due to the mobility of side chains. Side-chains radicals were formed mostly via indirect effects, by the abstraction of H atoms by the intermediate products of water radiolysis. Some important characteristics of these novel hydrogels were also investigated. These hydrogels exhibited good swelling in water and possess satisfying biodegradability. In addition, the antibacterial activity against E.coli was also found in CMCTS hydrogel.

Development and operation of gas catchers to thermalize fusion–evaporation and fragmentation products

Abstract: A new approach to the production of low energy radioactive beams involves the stopping of fast beams produced by fragmentation, in-flight fission or fusion–evaporation reaction into a large gas catcher where the reaction products are thermalized in high-purity helium and extracted as singly charged ions for post-acceleration. This removes the limitation present in standard ISOL technique for species that are difficult to extract from the target/ion source assembly. This approach has been implemented at Argonne since 1998 to inject fusion–evaporation products in an ion trap system. Via a series of improvements since then, we now reach efficiencies for these devices of close to 50% with delay times below 10 ms. In preparation for the RIA project, a larger device for stopping fragmentation products is in preparation. The basic principles behind these devices together with results obtained and experience gained operating these devices will be presented. Preparation for a test of the large gas cell at the full RIA energy at GSI will also be presented.

Sputtering of water ice

Abstract: We present results of a range of experiments of sputtering of water ice together with a guide to the literature. We studied how sputtering depends on the projectile energy and fluence, ice growth temperature, irradiation temperature and external electric fields. We observed luminescence from the decay of H(2p) atoms sputtered by heavy ion impact, but not bulk ice luminescence. Radiolyzed ice does not sputter under 3.7 eV laser irradiation.

Wide variety of flower-color and -shape mutants regenerated from leaf cultures irradiated with ion beams

Abstract: The efficiency of ion-beam irradiation combined with tissue culture in obtaining floral mutants was investigated and compared with those of gamma rays and X-rays in carnation. Leaf segments of carnation plants in vitro were irradiated with the 220 MeV carbon ions, and cultured till the shoot regenerated. The carbon ion had the highest effect in reducing the regeneration frequency, and the RBE value with respect to gamma-rays was four. The higher mutation frequency and the wider mutation spectrum were obtained in plants irradiated with the carbon ions than low LET radiations. Three new carnation varieties developed by ion-beam irradiation were applied for the registration of the Japanese Ministry of Agriculture, Forestry and Fisheries. The results indicate that ion beam irradiation could induce wide variety of flower-color and -shape mutants, and that the combined method of ion-beam irradiation with tissue culture is useful to obtain the commercial varieties in a short time.

Swift ion effects in polymers: industrial applications

Abstract: This paper is a review about methods of polymeric material modification based on the irradiation with accelerated heavy ions in the 1–10 MeV/u energy range Chemical etching of ion tracks in polymers is a method which is widely used in the fabrication of micro- and nanostructures with pre-determined characteristics Micro- and ultrafiltration membranes produced in this way and known as “track-etch membranes” have found several niches in the market since the seventies This is an example of mature technology based on irradiation with swift ions Apart from the membrane technology, the ion track pores find diverse applications as templates for the synthesis of micro- and nanowires and tubes, textured surfaces and bodies with special optical properties Some recent achievements and promising ideas utilizing swift ion beams are presented

Development of the program LISE: application to fusion-evaporation

Abstract: A new fusion–evaporation model LisFus for fast calculation of fusion residue cross-sections has been developed in the framework of the code LISE . This model can calculate very small cross-sections quickly due to its compared to programs using the Monte-Carlo method. Such type of fast calculations is necessary to estimate fusion residue yields. Using this model the program LISE has now the possibility to calculate the transmission of fusion residues through a fragment separator. It is also possible to use fusion residues cross-sections calculated by the program PACE , which has been incorporated in the LISE package. The code PACE is a modified version of JULIAN - the Hillman–Eyal evaporation code using a Monte-Carlo code coupling angular momentum. A comparison between PACE and the LisFus model is presented.

Applications of digital pulse processing in nuclear spectroscopy

Abstract: Data acquisition systems for nuclear spectroscopy have traditionally been based on hybrid systems with analog shaping amplifiers followed by analog-to-digital converters. Recently, however, new systems based on digital signal processing concepts have been developed. For example, one specific design, the Digital Gamma Finder (DGF-4C), has been used extensively for particle- and gamma-spectroscopy of nuclei far from stability. Using the DGF-4C, a variety of data acquisition systems have been implemented and used for measurements with semiconductor and scintillator detectors at recoil separators like the RMS at ORNL, the FRS at GSI and LISE at GANIL. Some novel features and unique advantages, such as trigger-less operation and pulse shape recording, are discussed in the context of selected studies.

Radiation depolymerization of chitosan to prepare oligomers

Abstract: Radiation depolymerization of chitosan was carried out by gamma irradiation in the solid state The radiation-chemical depolymerization yield of chitosan in the solid state, Gd, determined by gel permeation chromatography, is 09 for chitosan 10B and 18 for chitosan 8B Low molecular weight chitosan/or oligochitosans were separated from a chitosan depolymerized by gamma radiation, using mixtures of methanol–water and acetone as the solvents Due to the differences in solubility revealed upon radiolysis, extracts became subdivided into precipitates and soluble fractions The biological effect of oligochitosan in each fraction was evaluated; the preliminary results indicated that the oligochitosan with M w =2×10 4 inhibited the growth of fungi at 100 ppm and that with M w =800 only enhanced the growth of the same typical fungi

The proposed TITAN facility at ISAC for very precise mass measurements on highly charged short-lived isotopes

Abstract: One of the necessary experimental quantities required for the test of unitarity of the fundamental Cabbibo–Kobayashi–Maskawa (CKM) quark mixing matrix can be gained from nuclear beta decay. However, the short-lived beta-decaying nuclei have to be produced on-line in order to provide a large enough sample to carry out the experiments. At the new ISAC (Isotope Separator and Accelerator) facility at the TRIUMF national laboratory in Vancouver, Canada, ideal conditions are provided for the production of some of the most interesting nuclides in that respect. The experimental information that is needed are branching ratio, half-life and Q-value of the specific beta decay. For the first two components experiments have already been carried out or are in preparation at ISAC (Ball et al., Phys. Rev. Lett. 86 (2001) 1454, and experiments E823 and E909 approved at TRIUMF), for the third one, we are proposing to set up a unique facility capable of high accuracy mass measurements δm/m⩽1×10−8 on very short-lived isotopes (T 1/2 ⩽50 ms ) employing a Penning trap spectrometer coupled to an electron beam ion trap (EBIT) for charge breeding. The main goal of TITAN is mass measurements, however, the unique combination of the systems will allow to carry out high precision measurements in other fields of nuclear and also atomic physics.

Accelerated radioactive beams from REX-ISOLDE

Abstract: In 2001 the linear accelerator of the Radioactive beam EXperiment (REX-ISOLDE) delivered for the first time accelerated radioactive ion beams, at a beam energy of 2 MeV/u. REX-ISOLDE uses the method of charge-state breeding, in order to enhance the charge state of the ions before injection into the LINAC. Radioactive singly-charged ions from the on-line mass separator ISOLDE are first accumulated in a Penning trap, then charge bred to an A/q < 4.5 in an electron beam ion source (EBIS) and finally accelerated in a LINAC from 5 keV/u to energies between 0.8 and 2.2 MeV/u. Dedicated measurements with REXTRAP, the transfer line and the EBIS have been carried out in conjunction with the first commissioning of the accelerator. Thus the properties of the different elements could be determined for further optimization of the system. In two test beam times in 2001 stable and radioactive Na isotopes (Na-23-Na-26) have been accelerated and transmitted to a preliminary target station. There Ni-58- and Be-9- and H-2-targets have been used to study exited states via Coulomb excitation and neutron transfer reactions. One MINIBALL triple cluster detector was used together with a double sided silicon strip detector to detect scattered particles in coincidence with gamma-rays. The aim was to study the operation of the detector under realistic conditions with gamma-background from the beta-decay of the radioactive ions and from the cavities. Recently for efficient detection eight tripple Ge-detectors of MINIBALL and a double sided silicon strip detector have been installed. We will present the first results obtained in the commissioning experiments and will give an overview of realistic beam parameters for future experiments to be started in the spring 2002.