[en] The previously developed Eikonal/Time-dependent Hartree-Fock method is applied to slow ionic and atomic collisions involving many active electrons. The electronic density matrix is written in a basis of traveling atomic orbitals including s, p, and d-type atomic basis functions. One- and two-electron integrals are calculated in a static basis and transformed to the traveling basis. Electronic orbital polarization parameters are calculated during the collision to determine the degree of electonic orientation and alignment as a function of time. This method is currently being applied to slow collisions of hydrogen, alkali, alkali earth and rare gas atoms and ions, to calculate the time evolution of electronic energy and charge transfer, as well as orbital polarization

[en] Slow ion-atom collisions can be described within a first-principles molecular dynamics based on eikonol wave functions for the nuclei and the time-dependent Hartree-Fock (TDHF) approximation for electrons that self-consistently couples the electronic and nuclear degrees of freedom. By expanding the molecular orbitals in traveling atomic orbitals containing electron translation factors, it is possible to eliminate spurious couplings between same-center orbitals at asymptotic distances, and this generates a term in the density matrix equations proportional to the nuclear accelerations. The authors examine the effect of this acceleration term on Loewdin atomic populations for H⁺ + H(1s) and He²⁺ + H(1s) collisions, for varying collision energies and impact parameters. They find significant increases in atomic populations for an intermediate range of energies going from several tens to several hundreds of electron volts, and for low impact parameters, in the case of the H⁺ + H(1s) collision

[en] A mathematical model has been suggested to predict the time-dependent accumulation of brine at nuclear waste packages emplaced in a rock salt repository owing to thermomigration of brine inclusions. The model is based mainly on a description of the migration rate as a function of the temperature, temperature gradient, inclusion size and gas/liquid ratio of inclusions. Other factors are treated merely as disturbing quantities with respect to the migration rate. (author)

[en] Particle detectors were made using semi-insulating 4H-SiC as the detection medium. Devices produced with this material have the possibility of being extremely radiation hard. For the purposes of building radiation hard detectors, the parameters of interest are the large band gap and low intrinsic carrier density which implies low leakage currents, the large resistivity that allows ohmic contacts to be used to sense the charge created during ionisation, the large breakdown voltage that gives stable operation, and the large cohesive energy and tightly bound structure which imply good radiation resistance. The investigated photoconductivity detectors are formed by ohmic contacts (Al) on the front- and back-side of a 310 μm thick semi-insulating 4H-SiC substrate from Cree. These structures of contacts are ranging from 1 - 3 mm in diameter and have a guard ring structure to prevent edge leakage currents. From the I-V characteristic a substrate resistivity of 5.1·10¹⁰ Ωcm was determined. The detectors respond to β-particles similar as detectors made of diamond. Signal heights of about 2000 e^- were achieved for quasi minimum ionising electrons. First radiation hardness tests shows an increase of the substrate resistivity by a factor three after a proton (8 GeV) fluence of 4.16·10¹⁴ cm^-2 and a reduction of the signal height of about 23%. The results indicate the feasibility of using silicon carbide as detection medium for particle detectors. Future developments of SiC-detectors with applications in particle physics experiments and other fields are discussed

[en] Revised and extended version of a paper presented during the Interregional Training Course on the Safe Transport of Radioactive Materials, organized by the IAEA, Harwell, May 1982, dealing with the test conditions for Type A and Type B packages as well as possible test methods, the performance of testing, and the assessmnt of test results

[en] The advent of the new generation of accelerators, LEP and HERA, requires a new quality of networks for the HEP community. Plans for the very high speed wide area network in Germany are presented. Modelled after the first 140 Mb/s pilot line, which currently connects the Ethernet LANs of the Karlsruhe and Stuttgart, this network includes CERN and DESY and a number of German HEP institutes and so constitutes a backbone for high speed telecommunication to be used by HEP and other scientists. We discuss the technology, architecture, protocols and operational aspects of this network. (orig.)

[en] A coupling of microprocessors to a modular high speed data path system permits large data interchange to take place in a short time. The data path system serves: the definition of a data acquisition structure; the data transmission between measuring and digitizing electronics on the one hand and microprocessors on the other. The microprocessors undertake: the control of the data flow over the data path system; a partial evaluation and reduction of the data for the delivery from the lowest to the next highest hierarchy level. (Auth./G.T.H.)

[en] A model for the electric field distribution beneath the Schottky contact in semi-insulating (SI) GaAs particle detectors is developed. The model is based on a field-enhanced electron capture of the EL2-defect. The influence of the compensation mechanism in SI-GaAs on the field distribution, leakage current density and charge collection properties of the detectors will be discussed. The detailed understanding allows then a device optimization. (author)

[en] A time-dependent molecular orbital approach has been developed for describing the dynamics of atomic and molecular interactions. Equations derived for the time-dependent electronic density matrices in the TDHF approximation are locally linearized in time with the use of a time-dependent reference density. It contains a time-dependent driving term due to the nuclear motions. Nuclear motions are obtained from the gradients of effective potentials which change with electronic states and account for couplings of nuclear and electronic motions. Results are presented for electron transfer in proton-hydrogen collisions, to compare to other calculations

No abstract available