Showing papers in "Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms in 1992"

The GSI projectile fragment separator (FRS): A Versatile magnetic system for relativistic heavy ions

Abstract: The projectile fragment separator FRS designed for research and applied studies with relativistic heavy ions was installed at GSI as a part of the new high-energy SIS/ESR accelerator facility. This high-resolution forward spectrometer has been successfully used in first atomic and nuclear physics experiments using neon, argon, krypton, xenon, and gold beams in the energy range from 500 to 2000 MeV/u. For the first time relativistic xenon and gold fragments have been isotopically separated. In this contribution we describe first experiments characterizing the performance of this spectrometer.

Structural modification of polymer films by ion irradiation

Abstract: The atomic and electronic structure of polymer films undergoes deep modifications during high energy (keV-MeV) ion irradiation, from molecular solid to amorphous material. At low energy density (10 22 –10 24 eV cm 3 ) typical effects include chain scissions, crosslinks, molecular emission and double bonds formation. In hydrocarbon polymer (polystyrene, polyethylene) the main effect of irradiation is the formation of new bonds as detected by molecular weight distribution, solubility and optical measurements. Moreover the concentration of trigonal carbon (sp 2 ) in the polymer changes with ion fluence (10 11 –10 14 ions cm 2 ) and stabilizes to a value of 20% independently on the initial chemical structure of the irradiated sample. Photoemission spectroscopy shows an evolution of valence band states from localized to extended states. At high energy density (10 24 –10 26 eV cm 3 ) the irradiated polymer continues to evolve showing spectroscopic characteristics close to those of hydrogenated amorphous carbon. Trigonal carbon concentration changes with ion fluence (10 14 –10 16 ions cm 2 ) reaching the steady state value of 60% and the hydrogen concentration decreases to 20%. Moreover the values of the optical gap (2.5–0.5 eV) suggest the presence of medium range order in the obtained hydrogenated amorphous carbon. These values are consistent with the formation of graphitic clusters, whose size goes from 5 A to 20 A by changing the ion fluence (or energy density).

The RIKEN radioactive beam facility

Abstract: A radioactive beam facility based on projectile fragmentation, RIPS, has been constructed at RIKEN to enable radioactive-beam experiments. The facility is characterized by the production of high-intensity beams and spin-polarized beams. Since the beginning of 1990, experiments on exotic nuclei have been extensively performed exploiting these useful features. The characteristics and the present status of the RIPS are described.

Interactive personal-computer data analysis of ion backscattering spectra

Abstract: A new personal computer program package for ion backscattering data analysis with an interactive graphical interface has been developed. The assumed target composition is modified directly by pointing at the corresponding signals on the screen. Special attention has been paid to the physics details included. All projectile ions may be treated. A data base of non-Rutherford 1H and 4He scattering cross sections of several light elements, readily extendable by the user, is included. The most recent stopping power formulations are used. Contributions from electronic screening, corrected Bohr straggling and nonlinear detector response are taken into account. A procedure for subtracting the low energy tail background is provided. Smooth variations of elemental composition as a function of sample depth, as needed in diffusion or implantation profile analysis, as well as spectra taken in channeled sample orientations may be assumed. A short review of published computer methods for ion backscattering is included. Examples and applications of the present procedure to the analysis of 4He ion non-Rutherford and 12C ion RBS spectra are presented.

A solenoid retarding spectrometer with high resolution and transmission for keV electrons

Abstract: We have built an electrostatic electron spectrometer combining both high resolution and large luminosity. The instrument consists essentially of two superconducting solenoids separated by a system of ring electrodes of 4 m in length. Source and detector are placed in the high-field regions of the superconducting solenoids, whereas the repellent analyzing electrostatic potential of the ring electrodes peaks at the minimum of the magnetic field in between these solenoids. The magnetic guiding field provides (i) the acceptance of the full foreward solid angle of 2π, (ii) the transformation of the transverse cyclotron motion into longitudinal motion parallel to the magnetic field. The energy resolution of the electrostatic filter is determined by the ratio of the magnetic fields at the source and in the analyzing plane. It is typically 5 × 10 3 in our case. The spectrometer will serve first of all to investigate the limits of the rest mass of the electron antineutrino from 3 H 2 s-decay. It has been tested by measuring conversion lines from a 83m Kr source which yielded an energy of Eγ = 32151.5(11) eV for the corresponding nuclear transition.

Self-absorption corrections for well-type germanium detectors

Abstract: Corrections for self-absorption are of vital importance to accurate determination by gamma spectroscopy of radionuclides such as 210Pb, 241Am and 234Th which emit low energy gamma radiation. A simple theoretical model for determining the necessary corrections for well-type germanium detectors is presented. In this model, self-absorption factors are expressed in terms of the mass attenuation coefficient of the sample and a parameter characterising the well geometry. Experimental measurements of self-absorption are used to evaluate the model and to determine a semi-empirical algorithm for improved estimates of the geometrical parameter.

The new CERN-ISOLDE on-line mass-separator facility at the PS-Booster

Abstract: The ISOLDE on-line isotope separators have been operated since 1967 at the CERN-SC. This 600 MeV proton synchro-cyclotron had to be shut down in December 1990 after 33 years of service and it was decided to move ISOLDE to a new experimental area. The new on-line mass-separator facility is now under construction at the CERN PS-Booster. This accelerator provides an average current of about 2-mu-A of 1 GeV protons in very short high intensity pulses at low repetition rate. The beam can hit either one of the two target stations, the general purpose separator (GPS), a reconstructed ISOLDE-2 type machine (which can deliver beams simultaneously into three beam lines), and the high resolution separator (HRS), which is essentially the slightly modified ISOLDE-3 separator. The central GPS beam line and the HRS feed a common beam transport system to which most of the experiments will be connected. The new facility will be taken into operation in spring 1992.

Startup of the Fragment Mass Analyzer at ATLAS

Abstract: The Fragment Mass Analyzer (FMA) is currently being brought into operation at the Argonne Tandem Linear Accelerator System (ATLAS) The FMA is a recoil mass spectrometer, 8 m in length, which will be used to separate nuclear reaction products from the primary beam ad disperse them by mass/charge (m/q) at the focal plane It has a solid angle of 8 msr, an energy acceptance of {plus minus}20% around the central energy, and an m/q acceptance of {plus minus}7% around the central mass The FMA will allow the study of gamma rays originating from weak fusion-reaction channels by gating the gamma spectra by the desired ion identified at the FMA focal plane Production and decay of nuclei far from stability will be studied at the FMA focal plane by implanting exotic recoils directly into detectors or by using a fast tape system to transport the recoils to shielded detector systems With its capability of rotating from {minus}5 to +45 degrees around the target, the FMA will also be used for reaction mechanism studies Beta-NMR and nuclear moment measurements will be made behind the focal plane A facility description and a progress report on the commissioning of the FMA are presented 13more » refs, 9 figs, 1 tab« less

Analysis for hydrogen by nuclear reaction and energy recoil detection

Abstract: The use of MeV ion beams to measure hydrogen concentration profiles is reviewed. Both nuclear reaction analysis (NRA) and energy recoil detection (ERD) methods are discussed. Details of experimental approaches used and the effects of these different approaches on the analytic characteristics obtained are considered. The use of Doppler spectroscopy in both NRA and ERD to study the bonding of hydrogen in solids is briefly reviewed. The different methods are compared in terms of their advantages and disadvantages for certain analytic characteristics including accuracy, beam damage effects, sensitivity, and depth resolution.

On the release and ionization efficiency of catcher-ion-source systems in isotope separation on-line

Abstract: It is shown that the critical steps in isotope separation on-line - diffusion, effusion, and ionization - can be studied in a very efficient way by stimulating the separation process using beam particles of the UNILAC accelerator as tracer instead of reaction products. The analysis of the measured release profiles readily yields the ionization efficiency and the half-life dependence of the separation efficiency on an absolute scale. For the cases in which surface desorption is a fast process compared to solid state diffusion, additionally the decisive delay parameters μ 0 for diffusion and ν for effusion can be extracted. These are closely related to material constants such as diffusion coefficients and enthalpies for surface adsorption and in favourable cases permit extraction of the Arrhenius coefficients. Thus the assumed release model can be tested by comparison with literature values or, in turn, enables the conversion of known material constants into estimates for the half-life dependence of the separation efficiency. Since ion sources have reached a high degree of sophistication, the ionization efficiency is hardly ever the limiting factor of on-line mass separation. This is in general also true for the diffusion step, if the distribution of the reaction products in the catcher is either homogeneous or very close to the surface. As a consequence it turns out that effusion decisively causes the limitations in mass separation on-line, i.e. surface adsorption for refractory elements and the intrinsic delay for very short half-lives.

An improved multiple scattering model for charged particle transport

Abstract: An extended model for charged particle transport through the multiple scattering formalism based on the Moliere theory has been developed (by A.F. and P.S.). The new model has been implemented independently through two different algorithms in the Monte Carlo codes FLUKA (used predominantly in high energy applications for transport of hadrons and leptons) and MCNPE-BO (based on MCNP3a and employed in the field of radiation protection and dosimetry). The codes are currently being benchmarked on a variety of referee problems in their respective fields of applications.

Induced damage by high energy heavy ion irradiation at the GANIL accelerator in semiconductor materials

Abstract: The advantages of using a high energy (several GeV) heavy ion accelerator for irradiation are first recalled: the ranges of ions in materials are significant; an a priori relative evaluation of the damage creation rates from elastic collisions is possible; last, the ratio of the electronic stopping power to the nuclear stopping power is very large. The experimental methods used are in situ resistance and Hall mobility measurements. The irradiated samples are also analyzed in the laboratory by means of different methods (DLTS, photoluminescence, electron microscopy). The resistance has the same behaviour in silicon and gallium arsenide. It increases continuously during the irradiation. On the other hand, in n-type germanium, the resistance first increases, passes through a maximum, and decreases afterwards. A type-conversion takes place in the material. Moreover, the comparison of damage creation rates from one irradiation to another, in germanium and gallium arsenide, seems to show that the electron excitation produces a relative decrease of the damage creation rate. This effect is not visible in silicon.

Ion source with combined cathode and transfer line heating

Abstract: The plasma-discharge ion-source concept used in connection with the high temperature thick targets at the CERN-ISOLDE facility is described Derived from the construction of the tubular surface ionizer, the same current which heats the transfer line between the target and the ion source is also used to heat the disc-shaped cathode This construction has the advantage that the less volatile nuclear reaction products are transferred to the center of the source by diffusion along a rising temperature gradient, so that adsorption losses on the walls are minimized The design, which exists in several versions dependent on the element to be ionized and the coupling between the target and ion source, is discussed and examples of the measured efficiencies are given

Absolute cross section for hydrogen forward scattering

Abstract: The differential cross section for hydrogen recoil scattering from helium ions has been determined for energies in the range 1–3 MeV and forward scattering angles of 20, 25, 30 and 35°. Polystyrene (C 8 H 8 ) n thin films were used as a reference standard, enabling the recoil cross section to be determined with reference to the backscattering cross section for carbon, which was itself newly determined in terms of the simple Rutherford cross section.

Energy loss of 70 MeV protons in elements

Abstract: Measurements of the average stopping power relative to Al of 70 MeV protons losing energies of about 30 MeV in many elements and in water have been made with a simple apparatus, using Bragg ionization curves. Based on an l -value of 166 eV for aluminum, the value l = 79.7 eV was obtained for water. The standard deviation of the ratio of average stopping powers is ±0.08% for aluminum and water, and is estimated to be ±0.25% for other substances. Fluctuations of up to 1.2% in the mean range of the proton beam from the cyclotron were measured.

Primary and secondary mechanisms in laser-pulse sputtering

Abstract: Primary sputtering mechanisms are conventionally grouped in terms of the categories collisional, thermal , and electronic . With pulsed photons one must. in addition, consider the emission of droplets and fragments in thermomechanical processes. Pulsed photons also lead to the situation that the density of emitted particles is sufficiently high for gas-dynamic effects to enter and for the system therefore to lose memory of the primary mechanism. One then distinguishes secondary mechanisms which include outflow, as when a finite reservoir expands, effusion , effusive release from the outer surface without recondensation, and recondensation . effusive release with recondensation. If the photon pulse interacts with the emitted particles then still further secondary mechanisms are relevant due to energy deposition in the plume of emitted particles as well as due to ionization. Finally. the laser-pulse sputtering of the polymer PMMA (polymethylmethacrylate) and the superconductor YBCO ( YBa 2 Cu 3 O 7− x ) is discussed on the basis of explicit photographs of the sputtered particles. In the case of PMMA there are two groups of particles. the first group having primary and secondary mechanisms which are presently unestablishable but the second group being reasonably attributed to thermal primary release and to secondary behavior of the effusion (or recondensation) type. In the case of YBCO there is only one group of particles having a primary mechanism which is almost certainly electronic and a secondary mechanism which is tentatively identified with outflow .

Ion beam enhancement of metal-insulator adhesion

Abstract: Ion beam mixing and substrate surface tailoring may be used to enhance the adhesion at metal-glass, metal-ceramic and metal-polymer interfaces. Some recent publications on the chemical and structural nature of such bonding are reviewed, with special reference to the roles of interface chemistry and morphology.

Plastic deformation in SiO2 induced by heavy-ion irradiation

Abstract: Samples of vitreous silica and quartz were irradiated by different high-energy heavy ions at various temperatures The dimensions of the samples were measured at room temperature before and after irradiation with different fluences In the low-fluence range vitreous silica exhibits a long-known compaction which saturates at a density increase of about 3% In the high-fluence range vitreous silica is, like other amorphous materials, subject to radiation-induced plastic deformation: the dimensions perpendicular to the ion beam grow without tendency to saturation whereas the dimension parallel to it shrinks The deformation yield per incident ion is the higher, the lower the temperature and the larger the electronic energy loss The samples of quartz are amorphized in the low-fluence range and subsequently undergo plastic deformation in the same way as vitreous silica A model describing this plastic deformation is proposed and compared to the experimental results

Irradiation damage in magnetic insulators

Abstract: Using high energy heavy ion irradiation, the damage induced in magnetic insulators (Y3Fe5O12, BaFe12O19, SrFe12O19, NiFeO4, MgFe2O4, ZnFe2O4, Fe3O4) in the electronic stopping power (dE/dx) regime is studied. The amorphization cross section Ap is extracted from the paramagnetic fraction observed on Mossbauer spectra. Electronic stopping power threshold for damage creation appears. The damage efficiency ϵ = A/(dE/dx) is calculated and can be fitted by a general amorphization law ϵ = ϵmax(1− exp(− k(dE/dx)4)). The damage morphology has been correlated to the damage efficiency. Spherical extended defects appear for low values of ϵ at low values of dE/dx. When increasing dE/dx and consequently ϵ, the spherical defects overlap to give discontinuous cylindrical defects. Then for the higher values of dE/dx, the defects are continuous cylinders of amorphous phase. The change of the physical properties induced by the irradiation has been studied. Depending on the shape of the defects, the evolution of the electrical conductivity and the change in the orientation of the hyperfine magnetic field are different. Specific crystallographic sites in BaFe12O19 are more sensitive to the irradiation than others. Local order in the new amorphous phase is determined using X-ray absorption at Fe K-edge and Mossbauer spectroscopies. The creation of magnetization is observed in irradiated ZnFe2O4 which initially shows only a paramagnetic behavior at room temperature.

LISE 3: a magnetic spectrometer—Wien filter combination for secondary radioactive beam production

Abstract: The doubly achromatic spectrometer LISE installed at GANIL has been running since six years for the study of exotic nuclei and the production of secondary beams obtained by the interaction of high energy heavy ions (E/A i) The angle of entry of the primary beam with respect to the axis of the spectrometer has been made variable (0° to 3.5°). This allows the suppression of remaining incompletely stripped beam-charge-states in experiments with heavy beams (Z > 30). ii) A velocity filter based on an electrostatic field crossed with a magnetic one has been installed. This filter provides a third selection which is powerful in suppressing contaminants. Furthermore, the flight path between the target and the final focus is now increased to 43 m, which allows easy time-of-flight measurements also for heavy species. LISE 3 provides separated secondary beams of increased intensity and isotopic purity. We shall review the essential properties and present some recent experimental results for illustration.

Amorphization of zirconolite: alpha-decay event damage versus krypton ion irradiation

Abstract: Natural zirconolite (CaZrTi 2 O 7 ) can receive α-decay event doses of > 10 26 alpha-decay events/m 3 (~2 dpa), and can thus become amorphous (metamict) due to the radioactive decay of 238 U, 235 U and 232 Th and their daughter products which occur as substitutional impurities (the zirconolite contains approximately 20 wt% ThO 2 and is 550 million years old). In this study, the zirconolite sample was recrystallized by thermal annealing at 1130°C for 8 hours in air. Amorphization was induced with 1.5 MeV Kr + ions using the HVEM-Tandem Facility at Argonne National Laboratory. The Kr dose rate used during the irradiation was 3.4 × 10 11 ions/cm 2 s. which is a damage rate 2 × 10 12 times higher than that which has occurred in the natural sample due to decay of the actinides. In-situ transmission electron microscopy was completed during the ion irradiation. The recrystallized zirconolite also formed isolated thorianite (ThO 2 ) crystals, 25–100 nm in size, in the matrix of the polycrystalline zirconolite. After a Kr + dose of 4 × 10 14 ions/cm 2 (= 0.3 dpa ). the zirconolite grains were reamorphized: however, the thorianite grains remained crystalline even after a Kr + dose of 6 × 10 14 ions/cm 2 .

Endothelial cell adhesion to ion implanted polymers

Abstract: The biocompatibility of ion implanted polymers has been studied by means of adhesion measurements of bovine aorta endothelial cells in vitro. The specimens used were polystyrene (PS) and segmented polyurethane (SPU). Na+, N2+, O2+ and Kr+ ion implantations were performed at an energy of 150 keV with fluences ranging from 1 × 1015 to 3 × 1017 ions/cm2 at room temperature. The chemical and physical structures of ion-implanted polymers have been investigated in order to analyze their tissue compatibility such as improvement of endothelial cell adhesion. The ion implanted SPU have been found to exhibit remarkably higher adhesion and spreading of endothelial cells than unimplanted specimens. By contrast, ion implanted PS demonstrated a little improvement of adhesion of cells in this assay. Results of FT-IR-ATR showed that ion implantation broke the original chemical bond to form new radicals such as OH, z.lbond2;C=O, SiH and condensed rings. The results of Raman spectroscopy showed that ion implantation always produced a peak near 1500 cm−1, which indicated that these ion implanted PS and SPU had the same carbon structure. This structure is considered to bring the dramatic increase in the extent of cell adhesion and spreading to these ion implanted PS and SPU.

Statistical theory of charged-particle stopping and straggling in the presence of charge exchange

Abstract: General expressions have been derived for the mean energy loss and straggling of a heavy charged particle penetrating through a thin slice of matter. The main input parameter is a differential energy loss rate that allows for transitions within an arbitrary number of projectile states. Both spontaneous and collision-induced events are potentially induced, but different events are assumed statistically independent. Asymptotically, the mean energy loss is shown to approach a linear dependence on time or path length. The slope is given by the equilibrium energy loss rate, and the intercept at zero path length depends on the incident projectile state. Energy-loss straggling can be split into a collisional part and a contribution from variations in projectile state. The latter turns out to be related to the intercept in the mean energy loss for the pertinent projectile states. Previous results applying to a two-state system have been generalized to an arbitrary number of states. A full evaluation has been presented for a three-state system. A procedure is outlined that allows to empirically determine the magnitude of charge-exchange straggling.

RIKEN isotope separator on-line GARIS/IGISOL

Abstract: This paper describes the fabrication and the characteristics of an isotope separator on-line (ISOL) which was constructed at the RIKEN Ring Cyclotron Facility. The ISOL consists of a gas-filled recoil separator and an ion-guide isotope separator on-line. Because of this combination the ISOL enables us to study short-lived isotopes of almost all elements.

Mass measurements of exotic nuclei at the ESR

Abstract: We plan to measure masses of exotic nuclei far from the valley of β-stability using the Experimental Storage Ring (ESR) at GSI, Darmstadt, as a time-of-flight (TOF), multi-turn mass spectrometer. For this purpose the ring must be tuned to an isochronous mode, so that the flight time per turn of an ion depends only on its mass-to-charge ratio and not on its velocity spread. For these measurements the timing detector is planned to be placed directly in the ESR to record each circulating ion.

Progress report on Aramis, the 2 MV tandem at Orsay

Abstract: Aramis is a home built multipurpose 2 MV electrostatic tandem accelerator. A large variety of ions are available for high energy implantation. Characterization possibilities are also quite large in the Van de Graaff mode owing to the Penning positive ion source in the terminal. A second beam line is now available that sends the beam into the target chamber of the 200 kV medium current implanter. We will provide a progress report on the machine and present some results regarding in situ studies of multilayer mixing and implanted silicide layers

DATTPIXE, a computer package for TTPIXE data analysis

Abstract: Thick target PIXE (TTPIXE) data analysis requires the calculation of an integral (which we call penetration integral) which accounts for the various effects that take place during proton stopping in the target and lead to X-ray emission. This is done by numerical integration and in most TTPIXE work target homogeneity both along the surface and in depth is necessary. This reduces the applicability of the technique in cases as ion implanted, film coated, or other kinds of samples which are by their own nature nonhomogeneous in depth while preserving their surface homogeneity (we call them layered targets). The DATTPIXE main program, which enables the conversion of spectra peak area data into sample concentration values, is being developed so as to be able to face these kinds of problems. Secondary X-ray fluorescence is accounted for and the correction is calculated for each of the layers into which the target is divided for numerical integration. The program was tested by applying it to the analysis of three metal alloy certified reference materials from the British Chemical Standards. The need for secondary X-ray fluorescence corrections and the correctness of the method used are shown.

Optical fibres as radiation dosimeters

Abstract: The radiation induced transmission loss reduction of a phosphorus (P) containing gradient index fibre has been investigated with respect to the suitability for radiation dosimetry purposes. The emphasis was concentrated on the determination of linearity range, reproducibility, dose rate dependence, fading behaviour, and the useable temperature range.

Study of the ion beam induced amorphisation, bond breaking and optical gap change processes in PET

Abstract: Ion beam bombardment induced effects on the crystalline and chemical structures, as well as in the thermal, optical, and electrical properties of PET (Mylar) were studied. The induced modifications were followed by Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-VIS), X-ray diffractometry, differential scanning calorimetry (DSC), and electrical resistance measurements. The melting temperature and the crystalline fraction started to decrease at fluences where the chemical degradation was not significant. The hydrogen and oxygen losses led preferentially to new carbon-carbon bonds within the polymer chains and gradually increased the aliphatic and aromatic conjugation. Simultaneously, a decrease in the optical gap as function of the ion fluencc is observed. For 40Ar2+-bombarded samples the optical gap saturates around 0.7 eV lor f'luences of the order of 1015 cm−2, At those fluences the electrical resistivity is relatively high (τ ⪢ 10 6 Ω cm) , but for higher fluences it decreases by several orders of magnitude before saturation. The cross sections for the amorphisation, for the optical gap change and for the ester group bond reorganization processes were extracted.

Pair versus many-body potentials in atomic emission processes from a Cu surface

Abstract: Atom emission from the (100) surface of a Cu crystal is investigated using molecular dynamics simulation. Different potentials are employed: the Morse potential as an example of pair potentials, and many-body potentials of the EAM and the tight-binding type. Many-body potentials lead to a slightly smaller surface binding energy than pair potentials, when fitted to the same cohesive energy of the bulk crystal. Furthermore, many-body potentials lead to a stronger refraction of emitted atoms away from the surface normal. As a consequence, the maximum in the energy distribution of emitted particles is shifted to around 50% higher energies for many-body potentials, if compared to the prediction of the model of a planar surface barrier. These characteristic deviations between pair and many-body potentials are explained by using simple analytical reasoning.