Energetic Heavy Ion Beams Research Articles

Erratum: Shock compression of condensed matter using intense beams of energetic heavy ions [Phys. Rev. E61, 1975 (2000)

Erratum: Shock compression of condensed matter using intense beams of energetic heavy ions [Phys. Rev. E<b>61</b>, 1975 (2000)

Hydrogen metallization in heavy-ion imploded multi-layered targets

This paper shows with the help of numerical simulations that one may be able to achieve physical conditions necessary for hydrogen metallization by imploding appropriately designed multi-layered targets that are irradiated by intense beams of energetic heavy ions. In these calculations we consider the beam parameters that will be available at the GSI accelerator facility by the end of the year 2001 when the upgrade of the present facility will be completed.

Shock compression of condensed matter using intense beams of energetic heavy ions

In this paper is presented, with the help of sophisticated two-dimensional hydrodynamic simulations, a suitable design with optimized parameters for a heavy-ion beam-matter interaction experiment that will be carried out at the Gesellschaft fur Schwerionenforschung (GSI) Darmstadt by the end of the year 2001 when the upgrade of the existing accelerator facility will be completed. Our simulations show that this upgraded heavy-ion beam is capable of generating strong shocks in solid targets that compress the target material to supersolid densities and generate multi-mbar pressures. This will open up, at the GSI, the possibility of investigation of the equation-of-state properties of matter under such extreme conditions. Numerical simulations can predict the experimental results with reasonable accuracy, which is helpful in designing the diagnostic tools for the experiment.

Elemental Analysis On Group-Hi Nitrides Using Heavy Ion Erd

AbstractElastic recoil detection (ERD) using energetic heavy ion beams (e.g. 170 MeV 127I) is a suitable method to measure depth profiles of light and medium heavy elements in thin films. The main advantages of ERD, which makes it favorable over many other techniques for elemental analysis, is the possibility to obtain reliable and quantitative results, a sensitivity in the ppm region or a depth resolution even better than 1 nm.ERD analysis was employed to obtain quantitative information about the aluminium content x in MBE grown AlxGa1−xN layers on Al2O3 substrates. Using this stoichiometry information and the lattice constants obtained from high resolution X-ray diffraction, Vegard's law could be confirmed with high accuracy. Secondly, nitridation of heated Al2O3 substrates in NH3 atmosphere was investigated using high resolution ERD. A substantial nitrogen content on the surface of the substrate was detected which means a nearly complete AIN layer grown on the Al2O3 surface by a heat treatment only. Such a nitridation layer can be the base for further growth of nitrides on Al2O3 surfaces. As a third, the impurity content of group III nitrides was investigated in dependence on deposition conditions for both, MBE and MOCVD grown samples. In all samples investigated an oxygen concentration larger than 100 ppm was detected which is much higher than the intrinsic charge carrier density of these samples. In addition it is shown that the efficiency of p-doping by Mg may not only be hindered by hydrogen but also by carbon impurities.

Elastic recoil detection analysis with heavy ions

Detection of elastically scattered recoils instead of projectiles offers the possibility to unambiguously identify sample components and is still a quantitative method for materials analysis. Large electrostatic accelerators delivering high energetic heavy ion beams of excellent quality and large area ionization detectors with particle and position resolution are shown to be a very suited combination to fully utilize the potential of the ERDA method. Using 170 MeV I or 200 MeV Au beams a sensitivity below 10 14atoms/cm 2 and depth resolution below 10 nm were obtained with 7.5 msr detector solid angle. The position resolution enables the correction of kinematic energy shifts and, in addition, the observation of blocking patterns from single crystalline materials.

Pulsed, high-current and iron-free ion optical systems for beam transport in ICF driver accelerators

To drive ICF implosion targets, pulsed ion beams will be used. Therefore the corresponding beam guiding systems do not have to provide the magnetic flux density in a d.c. mode, but only in a pulsed mode on a short time scale. The operation of steady-state magnetic fields in accelerator-based ICF driver scenarios as outlinede.g. in the HIBALL reactor study would lead to a waste of a significant fraction of the produced electrical energy. We suggest making use of pulsed, high-current and iron-free magnetic lenses for this purpose. In a number of experiments at the UNILAC accelerator at GSI-Darmstadt, pulsed quadrupole lenses have already proven their ability and reliability to focus and transport highly energetic heavy-ion beams.

Strong perturbation of ferromagnetic solids by heavy ion tracks of transient nature

Measurements of transient magnetic fields on different probe ions exhibit strong attenuations in magnetized solids of Fe and Gd when these materials are subjected to energetic heavy ion beams. The magnitude of the dynamic perturbations observed is correlated with the energy loss of the beam ions in the ferromagnet. There is further evidence that for the average field inner-shell electrons are more sensitively affected by the perturbations than electrons of higher orbitals. The time of recovery of the ferromagnetic state is found to be considerably longer than 10 -12 s.

Heavy-ion induced adhesion of thin gold films to oxidized substrates of tantalum and silicon

Energetic heavy ion beams are capable of enhancing the adhesion of metallic films to a variety of substrates. Gold films (200–600 Å) evaporated onto substrates of tantalum and silicon (with native oxides) were bombarded with ions of 12C, 16O, 28Si, 35Cl and 58Ni at 2.85 MeV/nucleon. The threshold dose required to produce a peel strength greater than the Scotch-tape peel strength for a gold surface was measured as a function of ion species and angle of incidence. We observed the threshold dose to vary as the cosine of the angle with respect to normal incidence. The dependence on particle type for the AuTa system (with approximately 40 Å native oxide) was found tobe D th(cm −2) = 10 17( dE dx ) Au −3.0±0.2 for all particle beams where ( dE dx ) Au is the (MeV cm 2/mg) of the ion in gold. A substrate of 6000 Å of tantalum oxide gave identical results. The value of the exponent, −3.0±0.2, differs significantly from the value −1.6±0.2 reported earlier by Tombrello et al. for AuTa. The AuSi system is described by D th = 6 × 10 18( dE dx ) Au −4.1±0.3 . Auger analysis of the AuTa interface suggests a migration of the nativ result of ion bombardment. For the AuTa system, some irradiated regions that passed the Scotch-tape test just after bombardment were observed to fail when the test was repeated a few days later. Thicker gold films and higher doses resulted in longer adhesion times. These and other observations suggest that the post-irradiation decline of adhesion for AuTa is caused by diffusion of ambient atoms through the gold film rather than by an intrinsic time dependence of the adhesive forces.

Secondary reactions as a tool to produce exotic nuclei

The possibility of using secondary reactions as a tool to produce new isotopes is considered. This question is renewed with the emergence of intense beams of energetic heavy ions in the range of 20 to 100 MeV/nucleon. Three different methods are considered. They involve either the in situ production of a secondary radioactive target, which interacts with the primary beam, or the production of a radioactive secondary beam by an inverse fusion or a fragmentation process. Very heavy or very neutron deficient isotopes can be produced by these methods.

Contributions to Fusion Research from Studies of Foil-Excited Heavy Ion Beams

XUV spectra in the wavelength region from 5-55 nm have been measured at Brookhaven National Laboratory for foil-excited ion beams of Au, W, Zr, Mo, Fe, and Ti. These atoms are of particular interest in fusion research. In sharp contrast to the wide-ranging time-dependent charge state evolution of heavy ions in a plasma discharge, foil excitation of a heavy ion beam produces relatively well-defined narrow charge-state distributions. Existing accelerators, such as the Brookhaven MP tandems, can produce sufficiently energetic heavy ion beams to span the range of charge states found in present-day tokamaks. The comparison of spectra from beam-foil excitation and tokamak plasmas can therefore be used to infer the average ion and charge state makeup of the plasma discharge. Such comparisons with Au, W, and Mo features in tokamak spectra are discussed and spectra for Zr and Fe (which are expected contaminants in new tokamaks) are presented. Additional contributions to fusion research from beam-foil experiments are demonstrated. These include: wavelengths and identifications for lines which can be resolved in plasma spectra and direct determinations of radiative lifetimes and absorption oscillator strengths for these transitions which are used to determine impurity concentrations in plasmas.

Heavy Ion Beam Model for Radiobiology

An ad hoc model of energetic heavy ion beams, including secondary and tertiary particles, has been constructed for predicting radiobiological experiments. While the beam model is relatively primitive, it yields depth-dose and depth-radiobiological calculations in good agreement with experiment upstream of the Bragg peak. Beyond the peak the model is somewhat coarse grained and seems to underestimate low-LET fragment production. These defects can be repaired at some cost in computer time. Presently a complete set of depth-dose and radiobiological results (RBE, OER, aerobic and hypoxic survival) is obtained in 4 to 8 min, for a single beam, at a cost of $10. The model can be extended to mixed radiation fields, or to explore the design of ridge filters. These predictions are based on cellular radiosensitivity parameters extracted from track-segment irradiations at about 8 MeV/amu. Their success implies that no new radiobiological results arise from irradiation with beams at 500 MeV/amu.

Heavy ion beam model for radiobiology

An ad hoc model of energetic heavy ion beams, including secondary and tertiary particles, has been constructed for predicting radiobiological experiments. While the beam model is relatively primitive, it yields depth-dose and depth-radiobiological calculations in good agreement with experiment upstream of the Bragg peak. Beyond the peak the model is somewhat coarse grained and seems to underestimate low-LET fragment production. These defects can be repaired at some cost in computer time. Presently a complete set of depth-dose and radiobiological results (RBE, OER, aerobic and hypoxic survival) is obtained in 4 to 8 min, for a single beam, at a cost of $10. The model can be extended to mixed radiation fields, or to explore the design of ridge filters. These predictions are based on cellular radiosensitivity parameters extracted from track-segment irradiations at about 8 MeV/amu. Their success implies that no new radiobiological results arise from irradiation with beams at 500 MeV/amu.

Large Tandem Accelerators

The increasing importance of energetic heavy ion beams in the study of atomic physics, nuclear physics, and materials science has partially or wholly motivated the construction of a new generation of tandem accelerators designed to operate at maximum terminal potentials in the range 14 to 30 MV. In addition, a number of older tandem accelerators are now being significantly upgraded to improve their heavy ion performance. Both of these developments have reemphasized the importance of negative heavy ion sources. The new large tandem accelerators are described, and the requirements placed on negative heavy ion source technology by these and other tandem accelerators used for the acceleration of heavy ions are discussed. First, a brief description is given of the large tandem accelerators which have been completed recently, are under construction, or are funded for construction, second, the motivation for construction of these accelerators is discussed, and last, criteria for negative ion sources for use with these accelerators are presented.