Diffusion von Tritonen in NH4F-dotierten Eis-Einkristallen

The diffusion coefficient of tritons in ice has been measured as a function of the concentration of NH₄F. The absolute value of the diffusion coefficient as well as the activation energy of diffusion were found to be independent of the doping within the error limits. The value found for the activation energy amounts toQ=14.5±1.0 kcal/mole.     

Diffusion von Protonen (Tritonen) in reinen und dotierten Eis-Einkristallen

The diffusion of tritium in HF doped ice was studied as a function of HF concentration ranging from 10^?5 to 5·10^?3 mol/l. The magnitude of the coefficient of diffusion as well as the activation energy of diffusion were found to be independent of HF concentration within this range. At a temperature of ?10°C an anisotropy in the diffusion coefficientD was observed in undoped monocrystalline ice samples. In the direction perpendicular to thec-axis,D exceeded by 10% the value found in the parallel direction. An interpretation of these observations is based on a mechanism involving only vacancies.     

Die elastischen Moduln von Eis-Einkristallen

The velocity of sound has been measured in ice with temperatures from the melting point to ?140°C, using two different supersonic pulse methods. The complete set of the five elastic moduli has been determined from the measurements for the above mentioned temperature range. To explain various results for piezoelectricity, density and elastic moduli a model of an aging process is discussed.     

Zur Verteilung von Fremdsubstanzen in Eis-Einkristallen

Single ice crystals of cylindrical shape were grown from water doped with HF and with NH₄F. In the obtained crystals the impurity concentration shows a marked gradient inradial direction.     

Untersuchung zur Segregation von Ammoniumfluorid bei Eis-Einkristallen

The composition of ice single crystals grown from dilute aqueous solutions of ammonium fluoride (concentrationsc ₀=4×10^?4...5×10^?2 mole/I) was investigated. The crystals were divided into parts, which were melted separately. Then the electrical conductivities and thepH-values of the melts were measured. A comparison of the measured values with those of the aqueous solutions of ammonium fluoride shows that the components of ammonium fluoride were not built into the ice in ratios corresponding to the stoichiometric composition of the NH₄F molecule. Therefore, it is impossible to describe the segregation with only one segregation coefficient. The acid components are predominating in the crystals. The deviation from the stoichiometric composition is largest in the initial parts of the crystals.     

The 5v 3 bands of 18O enriched ozone: line positions of 16O16O18O, 16O18O16O, 16O18O18O and 18O16O18O

The four 5v ₃ bands of ¹⁸O enriched ozone have been observed and analysed for the first time. Two species (¹⁶O¹⁸O¹⁶O and ¹⁸O¹⁶O¹⁸O) belong to the C_2v symmetry group and two other (¹⁸O¹⁸O¹⁶O and ¹⁶O¹⁶O¹⁸O) to the C_s symmetry group. They have been recorded at a resolution of 0.008 cm^?1 with a pathlength of 32.16 m. Despite the very weak absorptions observed, almost 250 energy levels have been derived for each of the 4 species, with J ? 35 and K _a ? 13, and suitable sets of Hamiltonian parameters have been determined. For 3 species it has been necessary to account for the resonance between the (005) and (311) states to correctly reproduce the spectra observed. These resonances, anharmonic for C_2v, and hybrid (both anhar-monic and Coriolis) for C_s symmetry confirm the accidentally extremely strong coupling between the (005) and (311) states for ¹⁶O₃, due in that case to the very close distance between unperturbed energy levels. This work also confirms the excellent prediction of band centres of these four species derived from the recently determined isotopically invariant molecular potential function.     

Zur protonischen Leitfähigkeit von Eis-Einkristallen bei tiefen Temperaturen und hohen Feldstärken

In the course of an investigation of the electrical conductivity of ice single crystals a technique was developed for achieving electric fields of 450 kV/cm at low temperatures. Protons were injected into the sample from specially designed Pd electrodes. TheI – V (current-voltage) characteristics were found to resemble those due to space-charge limited currents which are well known inelectronic semiconductors. The concentration and depth of proton-traps, and the temperature dependence of the proton mobility were studied over a temperature range with a lower limit of 77°K. On the basis of these observations a number of mechanisms are proposed which contribute to the proton conductivity.     

Die mechanische Dämpfung in Eis-Einkristallen

The attenuation of multiply reflected acoustic pulses has been measured in ice single crystals for longitudinal and transversal waves. The frequency range extended from 5 to 200 Mc/s, the temperature from the melting point to ?120 °C. The attenuation in the range mentioned above is caused by scattering at microcrystalline units in the hexagonal ice.     

Diffusion study of 18O implanted into α-Hf using the nuclear resonance technique

The diffusion of ¹⁸O in α-Hf was studied in the 723–923 K temperature range by using ion implantation and nuclear resonance techniques. The measurements show that the diffusion coefficients follows an Arrhenius behavior D(T)=D₀e^(-Q/RT), where D₀=(5±3)×10^-9 m²s^-1 and Q=162±5 kJ/mol. A comparison of the present results with previous ones is also done. PACS 66:30 Jt; 85:40 Ry     

Elastic and inelastic scattering of 18O by 16O and 18O

Angular distributions have been measured for the elastic and inelastic scattering of ¹⁸O by ¹⁶O and ¹⁸O at laboratory bombarding energies of 42 and 52 MeV. The inelastic scattering data are analyzed in terms of collective excitations using a coupled channel approach. Deformation parameters are obtained for the strongly excited states. The relationship between the strength of inelastic scattering and the amount of structure in the elastic scattering distributions is discussed.     

The 18O(18O, 16O)20O reaction at 52 MeV

The structure of the ²⁰O nucleus was studied by the ¹⁸O(¹⁸O, ¹⁶O)²⁰O reaction at E_1ab = 52 MeV. Angular distributions for the transitions to the lowest four states in ²⁰O were obtained and analyzed with finite-range DWBA calculations. Optical potential sets were used which fit the experimental elastic scattering differential cross sections over almost the whole angular range. The two L = 0 transitions to the ground state and the 4.45 MeV state of ²⁰O populated by the ¹⁸O(¹⁸O, ¹⁶O) reaction were analyzed with exact finite-range DWBA calculations using microscopic form factors. These calculations underestimate the absolute cross sections by a factor of 11. The relative strength of the two L = 0 transitions is well reproduced in the ¹⁸O(¹⁸O, ¹⁶O) reaction. However, DWBA calculations for the ¹⁸O(t, p)²⁰O reaction overestimated the relative cross sections for the excited 0⁺ state by a factor of 6. Several model wave functions were tested for the ground-state transition. It was found that the absolute cross sections of the (¹⁸O, ¹⁶O) reaction are very sensitive to the mixing of shell-model configurations. The angular distribution shapes are also slightly dependent on the mixing.     

18O(p,p)18O and18O(p,p′)18O1for E = 6.1−16.6 MeV

Angular distributions of cross sections and analyzing powers have been measured for ¹⁸O(p, p)¹⁸O and ¹⁸O(p, p₁)¹⁸O¹(1.98 MeV) for proton energies between 6.1 and 16.6 MeV. The measurement were crarried out in 25 keV intervals between 6.1 and 8.0 MeV, and in 100 keV intervals between 8.0 and 16.6 MeV. Although the general appearance of the angular distributions changes quite smoothly with energy above about 8 MeV, structure is evident in the backangle excitation functions up to 14 MeV. A phase-shift analysis of the elastic scattering data yielded resonance parameters for 25 levels in ¹⁹F in the excitation enrgy region 13.8?21.4 MeV. A large fraction of these levels have odd parity, and the energies of the $\text{1}\text{2}{}^{\mathrm{?}}$ and $\text{3}\text{2}{}^{\mathrm{?}}$ levels coincide closely with peaks seen in the ¹⁹F photonuclear yield curves. A simple model involving proton single-particle states coupled to the 2₁^+; and 3₁^? levels of ¹⁸O is able to account for some features of the observed structure. The energy-averaged elastic and inelastic scattering data for E_p > 12 MeV agree reasonably well with the spherical optical model and the DWBA, respectively, as well as with coupled-channels calculations.     

Autoradiographische Untersuchung der Diffusion von Zinn in Sinterbronzen

Zu Untersuchungen der Diffusion von Zinn in den Sinterbronzen wurde die Autoradiographie mit automatischer photometrischer Auswertung angewandt. Die Verwendung von Schrägschliffen (mit sehr kleinem Anschliffwinkel) ermöglicht es, bei kurzer Glühdauer die Diffusionskoeffizienten zu bestimmen. Es wurden die Reproduzierbarkeit der Ergebnisse bestimmt und Fehler der Methode geschähzt.     

Diffusion von Protonen (Tritonen) in Eiskristallen

The diffusion coefficient of tritons in ice crystals has been measured at different temperatures between 0°C and ?35°C. The applied method excludes any surface diffusion. The absolute value of the diffusion coefficient at ?7°C was determined as 2·10^?11 cm²/sec (±10%) and the activation energy as 13,5 kcal/mole (±8%). The activation energy of proton (triton)-diffusion is therefore consistent with the activation energy found for the dielectric and mechanical relaxation of protons in ice. The importance of this consistency relative to the diffusion mechanism is discussed.     

Structure calculations in18O nucleus

A multishell Hartree-Fock calculation for¹⁸O nucleus has been done with the Tabakin and Hamada-Johnston interactions followed by pairing correlations and angular momentum projection. TheB(E2) transition rates have been reproduced with an effective charge of 1.5e for protons and 0.5e for neutrons, but the fit to energy levels is poor. An approximate alternative formalism has then been developed which casts the eighteen-particle problem into a two-valence nucleon problem. The two valence nucleons interact through the RPA-type oscillation modes of the core. Calculations with the two interactions mentioned above have reproduced roughly the uncorrelated projected Hartree-Fock spectrum. Lastly, the excited band spectra of¹⁸O have been examined in the TDA approach followed by band mixing.