Eine neue Methode zur Messung von Korrelationszeiten mit Hilfe von NMR-Impulsverfahren

We demonstrate a new method for the determination of correlation times. This method is based on examining the temperature dependence of coherent pulse averaging effects. We derive formulas for the temperature dependence of the decay time T_2eff of the transverse magnetization in the so called WHH and MW cases. As application of this method we measured T_2eff for OH-protons on a decationated Y-zeolite.     

Elektroneninterferometer mit Feldemissionskathode zur Messung von Kontaktpotentialdifferenzen im Ultrahochvakuum

Two-beam electron-interferences have been applied to measure contact potential differences (CPD) between polycristalline metal surfaces. Highly coherent and intense electron waves are produced using a field emission source. The materials under investigation are evaporated in situ in a bakeable oilfree vacuumsystem with an ultimate pressure of 5 · 10^?10 Torr. Gold is used as a reference element, as its work function is almost unaffected by residual gas. The accuracy of this method is ± 0.01 V. CPD values of different films of the same material combination vary by ± 0.05 V. The CPD between gold and copper is 0.45 ± 0.05 V, and between gold and aluminium 1.10 ± 0.05 V, gold being negative. The CPD of the clean Al-surface increases under prolonged influence of residual gas by an amount of 0.85 ± 0.05 V. Adsorption measurements show that this increase is mainly due to water vapour and not to oxygen.     

Zur Erzeugung von Impulszügen im Farbstofflaser mit sättigbarem Absorber

Generation of Pulse Trains in a Dye Laser with Saturable Absorber The evolution of a pulse in a ring resonator containing a continuously pumped amplifier and a saturable absorber is investigated, assuming the transversal relaxation times are very short and the longitudinal relaxation times are very long with respect to the pulse duration. Expressions for high and low steady-state energies and conditions for the single pulse regime are given. From these conditions a maximum resonator length can be calculated. An analogous length of the linear resonator is deduced. Moreover, we determine the halfwidth and the steepening of the edges of pulses which are unchanged after a resonator round trip. In the last part we consider the pulse compression.     

Eine Methode zur Erzeugung von Strahlen negativer Ionen

A new method for the production of beams of negative ions to be injected into a tandem Van de Graaff accelerator is presented. Negative ions of a desired species are produced by impact of noble gas ions with molecules of a gas containing this element, and are then collected and bent into a beam with high efficiency. For example, a beam of negative fluorine ions has been obtained by bombardment of boron fluoride with 30 keV krypton ions, resulting in a current of 0·5 μA of F⁺⁺⁺⁺ at the target. The original ion source of the tandem has been used with this modified procedure. The krypton gas has been fed into the duoplasmatron and the boron fluoride into the charge exchange channel. No damage to the ion source system has been observed, even in this case. This method has also been applied to nitrogen and oxygen with good results. Some measurements are reported, and a brief discussion of the basic process of the method is given.     

Die Erzeugung von negativen polarisierten Deuteriumionen aus metastabilen Deuteriumatomen im 2S 1/2-Zustand

An experimental method to produce polarized negative hydrogen ions is discussed and compared with other methods. The method makes use of the different lifetimes of the metastable 2S 1/2 state and the 2P 1/2 state of the hydrogen atom. Polarized ion beams are obtained by using a selective quenching process followed by selective ionisation. Experimental results are given for the intensity and polarization of the polarized negative ion beam of deuterons. These results were obtained as a function of the quenching-field, the magnetic field in the argon-cell and the density of argon and cesium. The yield of negative ions can be expressed by the cross sections for the different charge exchange reactions in argon. The measured tensorpolarisationP ₃₃ can be interpreted as a function of the cross sections, the argon-density and the magnetic field along the beam axis. Beams of 50 nA intensity were produced with a polarization ofP ³³=?0.250±0.006. The main advantage of this method is a low beam emittance, values of 0.7 cm rad eV^1/2 were achieved. The production of a polarized positive deuteron beam seems to be possible.     

Untersuchungen zur Zeeman-Spektroskopie mit Hilfe nichtlinearer Resonanzen eines Multimoden-Lasers

Intensity dips in the output power of a multimode He/Ne-Laser as a function of an axial magnetic field have been measured up to a field strength of 600 Gauß. These intensity dips are appearing if the Zeeman-splitting is equal to the frequency separation of different modes. The effect is used for Zeeman-spectroscopy. A discussion of the observed phenomena is given based on Lamb's Theorie. The measured value for the Landé-Factor of the 2p ₄ Ne-level isg _j (2p ₄)=1.3005 (±0.2%).     

Methode zur biochemischen Untersuchung des Proteinstoffwechsels mit Hilfe der Doppelmarkierungstechnik

Die ³H/¹⁴C-Doppelmarkierungstechnik wird zu Proteinstoffwechseluntersuchungen eingesetzt. Dabei treten Probleme der Optimierung des Meßverfahrens sowie einer rationellen und Fehlerquellen erfassenden Auswertung auf. Eine für biochemische Untersuchungen des Proteinstoffwechsels anwendbare Methodik wird beschrieben.     

Zur Untersuchung des reziproken Gitters von Einkristallen mit Hilfe von Kikuchi-Diagrammen

A new method has been developed for the examination of the reciprocal lattice of single crystals by means of Kikuchi patterns. The Kikuchi bands belonging to a zone axis may be used to locate the lattice points lying within the reciprocal lattice plane, which is orthogonal to this axis and passes through the origin. For the investigation of the whole reciprocal lattice, a series of reflection patterns is taken at different orientations of the specimen. Each group of Kikuchi bands belonging to a zone axis is used to locate the reciprocal lattice points in a section orthogonal to the respective zone axis. The angles between the section planes are obtained by recording the angle of rotation between successive exposures and by considering the inclinations of the zone axes relative to the primary beam. In a perspective drawing the reciprocal lattice region near the origin is then composed of these sections.     

Die dekorationstechnik zur untersuchung des mischzustandes von typ-II-supraleitern mit höheren Ginzburg-Landau-parametern

We show that the Ising model hamiltonian is a special case of a matrix Toda lattice hamiltonian with operator variables from a Clifford algebra of dimension equal to the size of the lattice.     

Gitterpositionsbestimmung von Fremdatomen in Granaten mit Hilfe des Channeling

Foreign Atom Location in Garnets Using the Channeling Technique Using the particle channeling technique the lattice sites of Magnesium and Zircon (octahedral sites) in Gadolinium Gallium Garnet (GGG) and the lattice sites of Bismuth and Lead (dodecahedral sites) in Bi-substituted Yttrium Iron Garnet (YIG) were determined. In comparison the channeling behavior of protons in undoped GGG has been investigated.     

Untersuchungen zur Struktur des Triglycinsulfats mit Hilfe der hochauflösenden magnetischen Kernresonanzspektroskopie im Festkörper

Investigations of the Structure of Triglycinsulfate by High Resolution Magnetic Resonance in Solids Measurements were performed in the ferroelectric and paraelectric phase of TGS monocrystals with the aid of multiple pulse experiments for high resolution magnetic proton resonance in solids. The contributions to the spectra, which are to be expected theoretically from the different proton groups (NH₃, CH₂, OH), were calculated and compared with the corresponding experimental results. Splittings are discussed, which occur as a consequence of the ¹⁴N? ¹H-interaction and indicate changes at the phase transition point. The anisotropy of the effective chemical shift tensor caused by the rotation of NH₃-groups and the anisotropy of the chemical shift tensor of OH-groups were determined.     

Bestimmung von Verunreinigungen in Silizium mit Hilfe der Aktivierungsanalyse

Mittels Aktivierungsanalyse wurde der Gehalt an Arsen, Antimon, Kupfer, Phosphor und Zink in Halbleitersilizium bestimmt. Die Methode besteht aus zwei Schritten:

1. Gruppentrennung durch Anionenaustausch mit einem Gemisch von Salz- und Fluorwasserstoffsäure,

2. Selektive substöchiometrische Extraktion von Arsen und Kupfer mit Diäthyldithiocarbamat, von Antimon mit Cupferron und von Zink mit Dithizon. Phosphor wurde extraktiv als Phosphomolybdat abgetrennt.     

Zur Untersuchung von Versetzungen mit Hilfe der magnetischen Kernresonanz

The line width of the nmr signal is obtained for a statistical distribution of distances and orientations of dislocations as a function of the dislocation density. The quadrupolar part of the line width increases proportional to the root of the dislocation density in the case of first order distortion but is proportional to the dislocation density itself in the case of second order distortion. The total line width passes through a maximum within the range of first order distortion and approaches the value of the undistorted central line which arises from magnetic dipole interaction when the dislocation density becomes sufficiently large. The intensity decay of the nmr signal connected with this line width behaviour will also be presented. In the range of second order distortion the total line width is determined by the constant dipole interaction and the quadrupole interaction of the central line which depends on the dislocation density. Under the assumption of a Gaussian distribution for the line shape a simple expression for this width can be obtained. The calculations are checked for the case of first order distortion by measurements on the Na²³ and Cl³⁵ nmr signals of NaCl single crystals and for the case of second order distortion by measurements on the J¹²⁷ signal of KJ single crystals.