Bestimmung der Hochfeldgrenze der dynamischen Kernpolarisation aus der Dispersion der Kernrelaxation

The dynamic nuclear polarisation arising from dipolar interactions between unpaired electrons and protons in liquids decreases with increasing magnetic fieldH ₀. Since the polarisation involves the same electron-proton flip-flop processes which are responsible for nuclear magnetic relaxation, we were able to determine the maximum possible enhancement factorV _max of the protons in paramagnetic solutions as a function of the applied magnetic field from the dispersion of nuclear magnetic relaxation. The measurements of the frequency dependence of nuclear magnetic relaxation in the field range of 33 to 38000 Gauss show thatV _max drops to one half of its low field value in fields of 2000 to 6000 Gauss depending on the solvent and on the temperature. An appreciable enhancement of the order of 50 or more seems to be possible in magnetic fields up to 30 or 40 kG.     

Messung der Anisotropie der van der Waals-Kraft

As is well known, van der Waals forces between two atoms (not both in an S-state) have no spherical symmetry. We report on an experiment, which verifies this anisotropy by measuring it. The experiment consists in comparing the total scattering cross sections of Ga atoms in selected magnetic substatesm _J=1/2 and 3/2 of the upper (² P _3/2) level of the ground state doublet of Ga. Rare gases are used as the scatterer. The relative total cross section difference in units of 10^?4 is 94.9±4.3 for Xe, 79.4±6.6 for Ar, and 195±5 for He as the scattering gas. In addition, measurements of the total scattering cross sections of Na and Ga on various gases have been made. The apparatus uses an atomic beam with magnetic selection, a common geometry, and a common detecting scheme for both states, which are compared in short intervalls by merely switching the selecting magnet's current. By converting the beam intensity to a pulse rate and summing the numbers of pulses in scalers, the sequence of alternate measurements could be automatized. In that way a comparison could be made every second, thus largely eliminating most drifts, which otherwise would have made impossible an intensity measurement of that accuracy. A theoretical estimate of the experimental results has been made on the following basis: 1. Only van der Waals forces are taken into account. 2. Matrix element sums in the expression for the van der Waals potential are approximately reduced to terms involving only the polarizability of the rare gases and matrix elements of Ga, which can be calculated from Hartree-Fock functions. 3. The Schiff approximation is used to calculate the scattering cross section. The calculations are in rough agreement with experiments, and errors are discussed.     

Anvendung und Perspektiven der Strahlungsvernetzung in der Volkswirtschaft der DDR

Zum angegebenen Thema wurde vom Zentralinstitut für Festkörperphysik und Werkstofforschung der Akademie der Wissenschaften der DDR (ZfFW) gemeinsam mit dem Bezirksvorstand Dresden der Kammer der Technik am 9. 10. 1975 ein Tageskolloquium veranstaltet. Es wurden 100 Teil-nehmer registriert, wobci Kombinate und Betriebe zur Anwendung von Plasten und Elasten stark vertreten waren.     

Deutung der optischen Absorptionsspektren der Übergangselemente der Eisenreihe,insbesondere der des Rubins

Crystal field, ligand field and molecular orbital theories have been used to explain the optical spectra of transition elements. It is shown an additional possibility to explain the absorption bands of the transition elements, especially those of ruby, as transitions not between the nonbondingt _2g and the antibondinge _g ^* but between the bondinga _1g and the nonbondingt _2g.