[en] He-nozzle beams were scattered on a stepped Pt(997) surface. Diffraction peaks up to the 6th order are clearly resolved. For incident angles < 65⁰, the diffraction patterns are very similar to the patterns obtained by light scattering on echelette gratings. An elementary model based upon this analogy fits the results fairly well. The deviations observed for glancing angles of incidence are interpreted as an evidence for an upward bending of the interaction potential on the terrace in the vicinity of the downward step. (Auth.)

[en] The cross sections for proton elastic recoil of 0.6-5.0 MeV ⁴He ions have been measured at recoil angles of 10 deg., 15 deg., 20 deg., 25 deg., 30 deg., 35 deg. and 40 deg. with the target set for transmission geometry. Thin melamine (C₃H₆N₆) foils (10-25 μg/cm²) were used as the hydrogen target. By bombarding the ⁴He ions normal to the target, backscattered ⁴He ions from nitrogen and recoil protons at forward angles were detected. Hence the proton recoil cross section was determined by normalizing to the scattering cross section of ⁴He ions backscattered from nitrogen to 165 deg. [Y. Feng, Z. Zhou, G. Zhao, F. Yang, Nucl. Instr. and Meth. B 94 (1994) 11]. The measured cross sectional data are reviewed and compared with calculations for the kinematic inverse reaction ⁴He(p,p)⁴He, and with the measured results of the proton recoil cross section reported up to now. In order to simplify the application of these results for ERD analysis, an arbitrary polynomial is derived by fitting the cross sectional data from this study

[en] The energy deposited by MeV ions in a solid may create a cylindrical energised region expanding radially in the bulk and leading to an ejection of matter out from the bombarded surface. Here, simple description of matter ejection by MeV ⁴He⁺ ions is given by considering the material alteration process. To describe the mechanisms by which atoms or molecules are released under ion bombardment, it is necessary to take into account the time dependent nature of the process and consider the whole history of the target produced during the slowing down of the projectile. As a means of acquiring more experimental data, we investigated the material structure dependence of the polymer targets sputtering yield. The evolution of the ejected species as a function of the projectile dose and beam intensity is analysed and correlated to the changes of the target structure. The process by which these effects occur is discussed in terms of latent tracks density. It is shown that atoms and/or molecules ejection can be described by two different mechanisms: a prompt emission and a thermal ejection process

[en] We report a study on electronic distributions obtained from a CTMC treatment of the He²⁺ + H reaction, which may be used as criteria to improve the quality of pseudostates within the framework of close-coupling molecular methods. By using the concept of molecular energy of classical electrons, an analysis of the mechanism at intermediate energies confirms that at low nuclear velocities a sizeable part of the ionizing cloud could be transiently described by bound molecular wavefunctions, at small internuclear distances. However, the description of the ionization process is incomplete and worsens considerably at velocities larger than the maximum of the ionization cross section. Hence, pseudostates are indispensable for representing the evolution of the ionizing cloud, for the whole energy range. The dominant mechanisms in the classical description of ionization are illustrated at velocities close to the maximum of the cross section. The so-called saddle-point ionization mechanism is seen to correspond to the threshold behaviour of the so-called soft electrons in high-energy treatments. From a study of our data, some desirable (and unusual) general properties of the pseudostates are obtained. (Author)

[en] The effect of RF sputter etching and ion milling on the (111) surface of silicon is studied by Rutherford backscattering analysis with 1.5-2MeV He⁺ beam. In all cases, three phenomena are observed: argon trapping, silicon amorphization and metallic impurities incorporation. The experimental results are discussed and compared with the previously published models

[en] The ion channeling technique has been applied to study the stacking defects in heteroepitaxially grown silicon. He ion backscattering experiments were performed on 0.4 μm Si layers grown on sapphire at a beam energy of 1.5 MeV and crystal axes of (100), (110), and (111). A comparison with a single crystal Si wafer developed comparative data which was subsequently used to analyze the depth profile of the density of imperfections. The calculation of dechanneling cross section is based upon the model of 'parallel shift of equipotential contours'. (orig.)

[en] PIXE (Particle Induced X-ray Emission analysis) has been established as a method of trace element analysis. This work compares the detection limits using 2.13 and 2.55 MeV protons with those attainable using ⁴He²+ -ions of energies 6.07, 7.00, 8.52 and 9.12 MeV as projectile. This comparison was carried out using three common aerosol substrates: Kimfol, Nuclepore and Teflon. The detection limits using protons or ⁴He²+ -ions were of the same order but the lower detection limits with ⁴He²+ -ions according to theory were not observed, largely due to a higher intensity of gamma-quanta being Compton-scatterd in the Si(Li) detector. An improvement of the experimental chamber making it more suitable for ⁴He²+ -ions should lower the detection limits using ⁴He²+ as projectile. (author)

[en] Short communication. 3 refs., 1 tab

[en] Wear at supporting flanks of a splined shaft joint can be determined by using thin-layer activation in assembled state of the mechanism. Prerequisites to using this method are suitable parameters for exposure as to measuring problem as well as the knowledge of adequate dependence of activity decrease on the rate of wear. (author)

[en] Electronic orientation is produced via second order Stark effect by applying an oblique electric field on excited atomic levels previously aligned by beam-foil interaction. Frequencies of alignment and orientation modulations are measured in helium as a function of the applied electric field strength. The deduced tensor polarizabilities of the ⁴He (n ¹D, n = 3, 4, 5) levels are compared with theoretical values