[en] For the optimization of the stripper-foil application for ¹H, ²H, ¹⁶O, ³²S, ⁴⁰Ca, ⁵⁸Ni, ¹²⁷I, and ¹⁹⁷Au the transmissions through the Munich tandem accelerator in dependence on the stripper-foil thickness, the analyzed charge state, and different ion incidence conditions at 10 MeV terminal voltage were measured: For heavy ions (Z>15) the optimal carbon stripper thickness lies at 2 μg/cm², for light ions (Z<6) above 10 μg/cm², and for medium heavy ions at about 4 μg/cm². These data can be used for terminal voltages in the range from 8 to 13 MV. For some kinds of ions equilibrium charge distributions behind the stripper foils as well as charge-exchange cross sections were determined. The influence of the Coulomb explosion in the stripping of molecular ions on the transmission was exemplarically studied in the case of ⁴⁰CaF^-. The transmission of ⁴⁰Ca is thereby only little reduced. (orig.)

[en] Laser plasma ablation of spectroscopically pure graphite under UHV conditions is a well established method for the preparation of thin carbon stripper foils. Such foils with their structure of randomly oriented nanocrystallites can best withstand ion irradiation damage. Accelerator users around the world are interested in this type of carbon stripper foils due to a guaranteed reproducibility, quality, thickness and uniformity given by the procedure. In addition a high reproducible yield with a low effort for floating, mounting and slackening is desired. Users of high-energy accelerators want to profit from this development, but need stripper foils of up to 500 μg/cm² for the relevant charge state equilibrium whereas carbon foils of this type could only be prepared with an upper limit of 10 μg/cm² in the existing set up. The new design was aimed to overcome all thickness limitations. The crucial component of the laser plasma ablation technique is the laser entrance window which becomes opaque during carbon ablation. A new plant which overcomes this problem is being assembled. Due to a higher source-to-window distance and a better laser light transmission, caused by slightly changed laser plasma conditions, the life of the laser entrance window before exchange could be prolonged by a factor of five. Presumably, there are no thickness limitations anymore due to a vacuum interlock that permits the exchange of the entrance window without breaking the vacuum in the ablation-deposition chamber

[en] The aim to develop irradiation resistant carbon stripper foils for swift heavy ions led to the new technique of laser plasma ablation-deposition of carbon, in which a pulsed high power Nd:YAG laser induces a hot carbon plasma for deposition on suitable substrates in high vacuum. The essential physical property of the new technique is the ablation of monoatomic carbon with an average charge state of 4+ and a broad spectrum of energies of up to 1 keV of the monomers. These conditions influence the nucleation and growth of a carbon film in such a way that a nearly isotropic orientation of the nanocrystals in the condensed film is achieved. This results, as postulated, in a much better strength against irradiation damage caused by heavy ions, compared to all other types of stripper foils. (orig.)

[en] Aluminum oxide was deposited on arsenic doped silicon, using atomic layer deposition (ALD) with either a silicon oxide or a silicon nitride interface. The physical properties of these films were investigated by elastic-recoil-detection, X-ray-photoelectron-spectroscopy and transmission electron microscopy. Special focus was given to contamination of the film and the interface, crystallization and temperature effect on diffusion. The films remained stoichiometric and did not have Al-Al clusters, even post annealing steps. Evidence of diffusion of silicon and arsenic into the dielectric and of aluminum from the film was found. Carbon and hydrogen were seen in the film and at the interface as well, whereas hydrogen diffused out of the film to some extent due to anneal. Carbon content in the layer was reduced by using O₃ as oxidant. Grain size of crystalline Al₂O₃ films was in the order of film thickness

[en] The microscopic effects of the heavy ion irradiation on thin carbon foils is investigated. Direct knock on collisions of heavy ions with carbon atoms are responsible for the irradiation damage. Calculations of irradiation damage revealed that under normal irradiation conditions, each carbon atom is displaced about 5 times during the lifetime of a slackened carbon stripper foil. Electron microscopy investigations on carbon atoms displacements are carried out. It is suggested that carbon foils with no texture show better stripper performance

[en] Thickening and shrinkage are the well known macroscopic effects which can be observed on carbon stripper foils irradiated with heavy ions. Thickening reduces ion transmission due to larger small-angle scattering. Shrinkage finally results in the rupturing of the carbon foil. There is not much known about the microscopic effects which lead to the obvious macroscopic changes. Therefore slackened carbon stripper foils of about 4 μg/cm² thickness were investigated in order to get more information about the radiation damage. These carbon foils were produced by vacuum evaporation-condensation method and used for heavy ion stripping in a tandem accelerator. Direct knock on collisions of energetic, heavy ions with carbon atoms in the stripper foil are responsible for the radiation damage. Due to the repeated displacements of the carbon atoms, microscopic changes occur which were investigated by electron microscopy. The conclusion of these investigations is that carbon foils with no texture should show better stripper performance. This condition is partly fulfilled by carbon foils produced in a glow discharge process but their mechanical properties and stripper performance is still not good enough. (author)

[en] For the preparation of isotopic accelerator targets by means of an evaporation-condensation process, laser heating is a method with high efficiency and thus low consumption of expensive isotope materials. A Q-switched, pulsed Nd:YAG laser is utilized for the ablation of refractory metals, which are deposited on substrates in a vacuum of 10^-5 Pa. Even for metals with low vapor pressures at their melting points, high ablation rates nearly independent of the vapor pressure can be obtained with laser pulses of 300 mJ within 10 ns. With an average laser power of 3 W, deposition rates for various metals were measured. With a source to substrate distance of 5 cm, condensation rates varied only from 70-300 ng cm^-2s^-1 for the wide range of elements with lower vapor pressures from boron to uranium. (orig.)

[en] Elastic recoil detection analysis (ERD) with swift heavy ions has been improved in view of depth resolution. Profiles of light elements could be measured in carbon near the surface with single atomic layer resolution using ⁵⁸Ni, ¹²⁷I or ¹⁹⁷Au beams with energies between 0.5 A MeV and 1 A MeV and Q3D magnetic spectrograph. Due to the specific ion optical arrangement of the Q3D a relative energy resolution of about 7 x 10^-4 was achieved in ERD experiments although a large solid angle of 5 msr was used. This large acceptance guarantees good statistics even with low ion fluences. In this way the elemental concentration profiles are not essentially disturbed by irradiation damage effects and can be measured in the 0.1% level on an atomic depth scale. (orig.)

[en] Slackened carbon stripper foils of 3 to 5 μg/cm² produced by vacuum evaporation-condensation were graphitized by annealing at about 3300 K with a pulsed laser beam (1.06 μm). An average crystal size of 10 nm was measured by electron diffraction. The texture of the 002-plane is parallel to the surface of the foil as known from slightly annealed carbon foils. Radiation damages caused by high doses of heavy ions dramatically change the crystal structure. Electron diffraction patterns reveal newly formed graphite crystals with their 002-plane perpendicular to the texture. Compared to carbon foils of the same kind, but not graphitized, a lifetime prolongation of a factor of two was achieved for such foils tested in the terminal of the Munich MP tandem. The slope of the curve for heavy-ion transmission through carbon stripper foils varies for foils of the same kind and for different ion-beam conditions. (orig.)

[en] This work quantifies aluminium in thin surface and near surface layers. In one example, the layer overlies a thin gallium nitride layer on an aluminium oxide substrate and in a second example the aluminium exists just below the surface of an indium arsenide substrate. The technique of non-Rutherford elastic backscattering of protons was used for the samples where aluminum in the layer of interest needed to be resolved from aluminium in the sapphire substrate and the results were corroborated at the Technische Universitaet Muenchen using heavy ion elastic recoil detection analysis. In the second example, where it was unnecessary to isolate the signal of aluminium in the layer of interest (as the substrate contained no aluminium), then the ²⁷Al(d,p₀₁)²⁸ Al nuclear reaction was used. The elastic proton scattering cross section of aluminum was found to vary very rapidly over the energy range of interest