Messung der von Elektronenlawinen erzeugten Raumladungsfelder mittels einer Sondenlawine

The electrical fields due to the space charge of positive ions in a plane-parallel discharge gap are measured by means of an electron avalanche. The measurements were made in a N₂-CH₄ gas mixture (5% CH₄) at a total pressure of 210 Torr (20 °C) in a 3 cm gap, at a voltage UD (static breakdown potential). The positive ions are produced by electron avalanches, which are released from a broad area by an UV flash at the cathode. The ions so produced drift towards the cathode with a drift velocity v₊. After a timeT the probe avalanche is started by a second UV flash in the symmetry axis of the charge distribution. From its temporal growth, which is given by the relation\(i_s (t) \sim \delta v\_\exp \left( {\int\limits_0^t {\alpha v\_dt} } \right)\), one can evaluate the space charge field E(z) of the positive ions. The measured fields are in good agreement with those predicted by calculations.     

Zur Theorie einer Klasse von Beugungsproblemen mittels singulärer Integralgleichungen. IV Hochfrequente Schallbeugung an der Kreisblende: numerische Ergebnisse

The six-term developments of the far-field amplitude and the transmission coefficient formerly given for the high-frequency diffraction of a plane sound wave by a circular aperture in an infinite plane sound-soft screen at normal incidence are corrected and numerically evaluated.     

Neue Aspekte der Phasenbestimmung an Festkörpern mittels Röntgenkleinwinkelstreuung

Recent developments in the field of the interpretion of small-angle X-ray scattering (SAXS) for solid two-phase samples are presented. It was found that a systematic alteration of three of the SAXS parameters which were chosen for theoretical reasons signalizes a well-defined change of the inhomogeneities (second phase) in the chemically or physically treated samples. Increasing and decreasing, crumbling or joining, change of the concentration and of the form of the inhomogeneities are calculated and discussed.

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Die kontinuierlichen Übergänge zwischen den Phasen bringen bei der Behandlung der zu besprechenden Probleme weitere theoretische Überlegungen mit sich, die wir hier aber nicht behandeln können     

Untersuchungen an der Mischkristallreihe Silber-Palladium mittels Halleffekt und elektrischer LeitfÄhigkeit

On the silver-palladium alloy system the Hall-constant and the specific electrical conductivity have been measured at room-temperature in different states. In addition, the change of these properties by thermal treatment (heating- and cooling-curves) was examined. The observed changes can be explained by the formation of a short-range order. A graphical analysis offers the possibility to establish the contribution of the electron in the 5s-band and the holes in the 4d-band to the observed effects.     

Zur Theorie einer Klasse von Beugungsproblemen mittels singulärer Integralgleichungen. V Hochfrequenz-Beugung ebener elektromagnetischer Wellen an einer ideal leitenden Kreisblende

The high-frequency diffraction of a plane electromagnetic wave by a circular aperture in a infinite plane conducting screen is considered at normal incidence. The asymptotic solution of the singular integral equation for the Fourier-transform of the current density on the screen is found by means of elementary function-theoretic methods. Five terms of the high-frequency development of the transmission coefficient are given.     

Theorie der Röntgenbeugung an einer planparallelen Platte mit idealem Gitter

Scattering of a plane wave (X-ray) by a plane parallel slab with perfect grating is treated by means of an integral equation. The formulas obtained include the cases of grazing incidence and grazing excidence which had to be excluded in the usual theory.     

Messungen des γi-Koeffizienten,der Zündspannung und des normalen Katodenfalls der Glimmentladung an gasbedeckten Mo- und Fe-Oberflächen in Edelgasen

Measurements of the γ_i-coefficient, the ignition voltage and the normal cathode fall of the glow discharge on gas-covered cathode surfaces for the combinations Mo—Ne⁺, Ar⁺, Kr⁺, Xe⁺ and Fe—Ne⁺ are described. H₂, N₂ and O₂ are used for covering the cathodes with a monomolecular adsorption layer. Measurements are carried out with a dynamic method according to VARNEY in the range 30 ? X/p₀ ? 400 V cm^?1 Torr^?1.     

Untersuchungen der Oxidbildung und Adsorption von Erdalkalien an einer sauerstoffvorbelegten Wolframoberfläche mit Hilfe der Oberflächenionisation

The surface ionization of alkaline-earth elements on tungsten has been studied in dependence on the temperature T and the surrounding oxygen partial pressure po₂; the values of the ionization efficiency β together with those of the change of the work function ΔΦ of the surface have been applied to get information about chemical reactions of the incident alkaline-earth atoms with adsorbed oxygen and about the adsorption of alkaline-earth elements on tungsten.Whereas in the high temperature range the tungsten surface is clean, towards lower temperatures (i.e. below ≈ 2500 K at po₂ = 1 × 10^?6 Torr or below ≈ 2000 K at po₂ = = 1 × 10^?9 Torr), an adsorption of oxygen increases the work function Φ and, consequently, the ionization efficiency β of incident metal atoms. A characteristic feature of the surface ionization of the alkaline-earth elements, however, is a rapid re-decrease of β with further decreasing temperature, which occurs at T ≈ 1400 K for Mg/W, T ≈ 1600 K for Ca/W, T ≈ 1800 K for Sr/W, and at T ≈ 2000 K for Ba/W. It is shown that this behaviour of β is caused by two different reasons: Whereas in the case of Mg/W a substantial Mg adsorption leading to a reduction of the work function is responsible for the decrease of β solely, the β values of Ca and Sr are additionally influenced by chemical reactions of the incident metal atoms with adsorbed oxygen resulting in an alkaline-earth oxide desorption. In the system $\text{Ba}\text{W}$ the decrease of the ionization efficiency β can be referred to BaO formation exclusively.Assuming a thermodynamic equilibrium between the different adparticles and using experimental values of the dissociation energy of the alkaline-earth oxides (in the gas phase), the results are in good agreement with theoretical calculations.     

Zur O2-Dissoziation in der Gleichstromglimmentladung. Teil I Bestimmung des Dissoziationsgrades mittels der O3-Bildung an gekühlten Oberflächen

The synthesis of ozone on the surface S cooled with liquid nitrogen O + O₂·S→O₃·S[1] was used to measure the concentration of atoms in a flow tube downstream of a d.c. discharge. The flow tube was constructed in the form of a U-tube. The ozone was deposited as a blue liquid film in the neighbourhood of the surface of the liquid nitrogen on the walls of the part of the U-tube, which was connected with the discharge tube. The oxygen atom decay in the U-tube was observed by measuring the production of ozone as the distance between the discharge tube (diameter: 5,2 cm) and the surface of the liquid nitrogen was varied. The decay is first order in atom concentration for the pressures p > 1 torr. But for the pressures below p = 1 torr near by the discharge tube we observed deviations from the law of decay In [O]₀/[O] = k·t for the currents of about i = 100 mA. This effect was attributed to the process From the extrapolation of an ozone production curve atom concentrations in the discharge have been obtained. The transition from the ?H”? form to the ?T”? form (striated, low average electric field) of the discharge [2] caused the dissociation to decrease rapidly. The highest dissociation (10%) was obtained in the ?H”? form at high currents (i = 120 mA) and low pressures (p = 0,60 torr). The yield of atomic oxygen per kilowatt hour of energy was measured as functions of pressure and gas flow rate for i = 100 mA and i = 50 mA.     

Die Störung der Resonanzstreuung von γ-Strahlung einer Kr79-Quelle an Br79 durch gaskinetische Stöße in der Quelle

γ-quanta emitted by gaseous Kr⁷⁹-sources were scattered resonantly from Br⁷⁹-nuclei. By increasing the density in the source the effective cross section for resonance scattering was influenced due to gaskinetic collisions of the recoiling Br⁷⁹-nuclei with atoms before emission of theγ-quantum. The cross section for gaskinetic collisions was determined to beσ _st=(12.0±1.8) 10^?16 cm² in agreement with the theoretical value obtained from a hard sphere model. This technique, similar to the usual “Doppler shift technique”, yields, if combined with the measurement of the absolute cross section for resonance scattering, spin and lifetime of the levels at 398 and 606 keV. The resonance scattering from the 834 keV level shows an unexpected behaviour in complete contradiction to the hard sphere model, indicating that the velocity of the recoiling nuclei is increased in a dense source atmosphere.