Volume 22, Issue 6

The electric current density in a superconductor is calculated up to second order in the pair potential. The current density can be formulated in terms of the classical distribution function in phase space which was introduced in previous papers. The resulting expression is specialized both to the Ginzburg-Landau approximation and to the diffusion approximation. Finally, we discuss the current distribution at the critical fields H c2 and H c3

By comparing theory and experiment we try to find out, if the effective Spin-Hamiltonian (2) is applicable for a metal like Nickel. We get no contradictions.

Energy eigenvalues and transition-probabilities for the anharmonic oscillator are calculated by evaluating functional integrals in a lattice-space and reordering infinite series in summable series. The results are compared with the known values.

The selfconsistent field equation (VLASOV equation) is derived for the one-particle WIGNER function of a relativistic electron-positron gas. From the linearized form we obtain the dispersion relation for any quasi-equilibrium state, which for the special case of thermal equilibrium has already been derived by TSYTOVICH 1 .

Dc and ac currents to a rf resonance probe were investigated experimentally in the frequency range from 1 to 100 Mc/s in a quiescent Cesium plasma. The measurements in the plasma are explained by calculations and measurements with a lumped-constant equivalent network (“plasma simulator”). It is shown that the ac current to the probe is strongly influenced by the capacitance of the cable leading to the probe. A device to compensate this cable-capacitance is developed and used. Furthermore, it is shown for the first time that the double (or devided) main resonance maximum, occurring frequently with dc and ac currents to the resonance probe, is generally due to the influence of a second reference electrode. A simple and direct (“focus”) method for very precise plasma density determination (from the intersection point of the rf-current-vs.-frequency curves with probe voltage as parameter) is developed and compared with ac transmission current and LANGMUIR probe measurements at plasma densities between 2 × 10 6 and 3 × 10 7 cm –3 . Agreement is obtained between these three experimental methods within their margins of error. The comparison leads to a better understanding of the measured LANGMUIR characteristic and of the Cs-plasma of the “Alma I” device.

Electrical conductivities and densities of molten (Na—Tl)NO 3 mixtures have been measured in the temperature range between 192°C and 400°C. At all compositions the specific conductivities appear to be linear functions of the temperature. While the equivalent conductivities of the mixtures deviate negatively from additivity, the apparent activation energies ΔΕ (from the relation Λ =Λ 0 · exp(—ΔE/R T) exhibit positive deviations from additivity. This behavior is similar to that of other univalent binary systems with a common anion and seems to indicate that the polarization of the nitrate ion due to different cation sizes is the main cause of the additional hindrance to the electrical transport in mixtures.

The growth rate of ice in supercooled water and in dilute aqueous solutions of various salts which dissociate in water into univalent ions was studied. The solutions contained in polyethylene tubes of small bore had concentrations between 10 -6 and 10 -1 moles liter -1 and were investigated at bath supercoolings between 1° and 15°C. The growth rate of ice which in pure water was found to vary approximately with the square of the bath supercooling was affected in a systematic manner by the type and concentration of the salt in solution. At salt concentrations smaller than 5 × 10 -2 moles liter -1 most salts did not affect the growth rate. However, the fluorides were found to increase the growth rate over and above the one in pure water. At concentrations larger than 5 × 10 -2 moles liter -1 all the salts reduced the growth rate of ice below the one in pure water. By comparing solutions of salts with common anion it was found that at a particular bath supercooling and salt concentration the growth rate of ice was reduced most in lithium solutions and least in cesium and ammonium solutions. By comparing solutions of salts with common cation it was found that the growth rate of ice was reduced most in fluoride solutions and least in bromide solutions. It was concluded that in solutions with salt concentrations larger than 5 × 10 -2 moles liter -1 the rate of dissipation of latent heat which controls the growth rate of ice is affected in a systematic manner by the freezing point lowering effects which result from pure mass transfer conditions prevailing at the ice-solution interface of a stagnant system. Some features of the observed growth rates are discussed in terms of the effect of dissolved salts on the growth forms of ice in aqueous solutions.

In the present paper a method is described, which permits the measurement of the crystal misorientation in thin films by means of electron diffraction. In some special cases it was possible to make use of other techniques to determine the degree of misorientation and to compare the values obtained by the different methods. The result of this comparison is a consistency of the measuring values within the limits of about 10%.

The temperature dependence of the photoconductivity and the luminescence of ZnS-single crystals containing Α-centers were investigated. The results are discussed using the model first suggested by PRENER and WILLIAMS.

Der Temperaturgradient in kontinuierlich und quasikontinuierlich betriebenen Festkörperlasern wird abgeschätzt. Die Strahlengänge im thermisch geschichteten Medium und die thermische Krümmung der Endflächen werden berechnet und durch äquivalente Brennweiten berücksichtigt. So ergeben sich Korrekturmöglichkeiten für verschiedene Resonatortypen. Es zeigt sich, daß ein mit einfachen Mitteln korigierbarer optischer Resonator dann möglich ist, wenn das Pumplicht den Kristall homogen ausleuchtet. Die stark vereinfachten Überlegungen ergeben eine gute Übereinstimmung mit früheren Messungen an kontinuierlichen Rubinlasern.

In all dynamic nuclear polarisation (DNP) experiments in liquids carried out so far the electronic spin belonged to the paramagnetic molecule while the proton was part of the diamagnetic solvent molecule. In this paper the relaxation and DNP of protons inside free radicals in protonfree solvents is studied. A calculation of the DNP coupling parameter ξ is given for mixed scalar and dipolar intramolecular interaction with simultaneous time dependences by electron spin relaxation, electron spin exchange and molecular motion on the basis of the formalism of ABRAGAM and SOLOMON. Experimental results at 12.5 kGauß were obtained for the t-butyl-protons in the three radicals tri-t-butyl-phenoxyl (TBP), COPPINGER'S Radical (CR) or Galvinoxyl and di-t-butyl-nitroxide (DBNO). The experimental technique differs from the usual NMR-detection in the use of pulse technique and of a dielectric resonator in the microwave equipment. DNP enhancements from high positive to high negative values could be observed corresponding to mixed proton-electron-coupling from dominantly scalar to dominantly dipolar interaction. All results can be at least qualitatively explained by the theory of the intramolecular interaction since the essential parameters and constants of the interaction can be measured with other independent methods.

The isotropic hfs splitting constants of the radical ions of 6 nonalternant hydrocarbons have been related to MO calculations of spin and charge densities of the π systems. MO calculations were performed with and without including π electron correlation (HÜCKEL, MCLACHLAN, and AMOS-SNYDER). Also bond length alternation has been considered with the aid of a bond order-bond length relation. It turns out that for non-AH’s the full SCF method of AMOS-SNYDER with annihilation of spin quartet states gives the best description of the π electron distribution. The mean deviation between theoretical and experimental splitting constants is still 35% and much higher than in alternant systems. In the case of the dibiphenylene ethylene cation consideration of steric hindrance results in a significant improvement. For the anion of this molecule an oxidation to fluorenone during electrolytic reduction has been observed.

The microwave rotational spectrum of toluene has been investigated in the region from 8 to 23 GHz. The three types of absorption lines to be expected in the case of a molecule of this symmetry with a very low sixfold barrier hindering internal rotation of the methyl top have been found: m=0; |m|≠ 0, 3 n; | m | = 3 n. From the lines m= 0 the rotational constants and the dipole moment (0.375 ± 0.01 D) have been determined; from the lines 1 |m|=3 the internal rotation barrier could be calculated as V 6 0 = (13.94 ± 0.1) cal/mole. This value is discussed and compared with the very much larger value derived from solid-phase heat capacity data.

The previous M.O. treatment of unsubstituted hexahalides has been modified, taking the results on Faraday effect obtained at the University of Virginia into account. The absorption spectra previously measured of the complexes (M=Os, Ir) trans-MCl 4 Br 2 — and trans-MCl 2 Br 4 — are interpreted by a M.O. treatment for the symmetry D 4h as electron transfer transitions, including a first-order relativistic (spin-orbit coupling) correction. The concept of holohedrized symmetry is sufficiently valid to allow a description of MCl 5 Br — and MClBr 5 — as if they were tetragonal with centre of inversion and ƒac-(or cis-)MCl 3 Br 3 — as if they were cubic. It is shown that the ligand-ligand antibonding effects have the same order of magnitude as the moderate difference in optical electronegativity between Cl - and Br - .

The radiation chemistry of liquid carbon monoxide at —196°C and mixtures of CO with various gases has been investigated. In the γ-radiolysis of pure CO CO 2 is formed with G(CO 2 ) =0.18. The addition of CH 4 , C 2 H 4 , O 2 , and NO leads to the formation of C 3 O 2 which is not observed in the γ-radiolysis of pure CO. In the case of CO—CH 4 mixtures the following reacting products were identified: C 2 H 6 , C 2 H 2 , H 2 CO, H 2 C 2 O (Ketene), CO 2 and C 3 O 2 . Results of experiments with CO —CH 4 —13 CH 4 and CO—CH 4 —CD 4 mixtures and measurements of the dependence of G(CO 2 ), G(C 3 O 2 ), G(C 2 H 2 ) and G (C 2 H 6 ) on the concentration of CH 4 have shown that ethane is formed by energy transfer from CO to CH 4 or by reaction of CH 4 with excited CO and that C 3 O 2 and C 2 H 2 are formed by reaction of free carbon atoms which are formed in the presence of methane.

Fast reactions of 0 - with water, various alcohols, diethylether, acetone, c-hexane, c-hexene, benzene and toluene have been observed. The following types of reactions which often compete in these systems have been found: a) Η-atom transfer (such as CH 3 OD+O - → OH - +CH 2 +CH 2 OD), b) Proton (deuteron) transfer (such as CH 3 OH+O - → CH 3 O – +OH, and CH 3 OD+O - → CH 3 O - +OD), c) H 2 + -transfer [such as (CH 3 3) 2 CO+O - → C 3 H 4 O - +H 2 O], d) dissociative proton transfer (such as i-C 3 H 7 OH+O - → C 2 H 3 O - +OH+CH 4 or C 3 H 5 O - +OH+H 2 ), e) dissociative addition (such as C 6 H 6 → C 6 H 5 O - +H).

The release of tritium from single crystalline quartz and from fused silica has been measured following 40 keV ion bombardment to a dose of 4 × 10 11 ions/cm 2 . The release can be explained by normal volume diffusion with D 0 =10 1±1 cm 2 sec -1 for both materials and activation enthalpies of (42 ± 5) kcal/mole for quartz and (52 ± 5) kcal/mole for fused silica. Release from quartz is faster than release from fused silica. This latter diffusion process, however, is essentially slower than diffusion of hydrogen during permeation. Possible reasons for this discrepancy are the existence of radiation damage due to the ion bombardment or the chemical state of hydrogen which cause a different elementary process for mass transport: Hydrogen diffuses in molecular form during permeation whereas probably tritium atoms or ions will diffuse following ion bombardment.

The relative abundances of the isotopes of terrestrial xenon were re-determined using a large quadrupole spectrometer. All 11 measured isotopic ratios are in good agreement with the 1950 results of Nier. However, within the error limits a small, but systematic enrichment of the lighter isotopes is noticed in our data compared to Nier's.

A semiempirical formula σ(ΔA, E 0 , A 0 ), giving the sum of the spallation cross sections of the products of an isobar as a function of the mass loss Δ A, the primary energy E 0 of the irradiating particle and the atomic mass number A 0 of the target nucleus is deduced. The formula is intended to be used for the interpretation of the spallation product distribution in meteorites, in the atmosphere of the earth and hopefully in cosmic dust and lunar surface samples.