Band 24, Heft 10

A partial differential equation for the electric potential in an arc with an applied axial magnetic field is derived by using Ohm's law and the equations ∇·j=0 and ∇XE=0. To clarify the physics the potential equation is solved for two simple cases where the plasma is assumed to be homogeneous. The solutions reveal that the Hall parameter ω e τ e and the arc length strongly influence the potential distribution. The dependence of the potential on the axial and radial temperature profiles is studied numerically by relaxation methods.

In continuation of the work on interaction between shock waves and magnetic fields 1,2 the experiments reported here measured the atomic and electron densities in the interaction region by means of an interferometric and a spectroscopic method. The transient atomic density was also calculated using a one-dimensional theory based on the work of Johnson 3 , but modified to give an improved physical model. The experimental results were compared with the theoretical predictions.

Stark broadening of spectral lines is considered as a semi-classical many-body problem. Starting from a Liouville equation for a distribution function depending on the atomic Hilbert space vector and the coordinates and velocities of the classical plasma particles, BBGKY hierarchy techniques are used to derive a complete line profile for the electron contribution. The line shape formula is expressed in terms of the atomic time evolution operator for a collision with a single plasma electron. This operator is approximated by a strictly unitary exponential expression, yielding more accuracy than second order perturbation theory and being valid also in the quasi-static limit. The resulting line shape expression covers the whole frequency domain from the impact regime to the quasi-static regime. The results of the impact and quasi-static approximations are recovered as special cases for small and large distances from the line center. A numerical application to Lyman - α shows very good agreement with an experiment of Boldt and Cooper.

In a cylindrical arc without external magnetic field the radius of the discharge current is identi-cal with that of the conductive plasma column. It is shown here that, in general, this is not the case in an arc with superposed magnetic field. Instead, the current is limited by the magnetic flux tube whose cross section is governed by that of the electrodes. This is still true if the radius of the conductive plasma column is much larger than that of the flux tube. In this case electromotive forces prevent radial expansion of the current carrying region and form a potential distribution in keeping with the current density distribution.

By solving the coupled system of collisional-radiative rate equations for a homogeneous and steady-state plasma as a function of the radiative excitation rates one obtains the population densities of the ground and of the excited levels for any given degree of reabsorption. One finds that in hydrogen plasmas which are completely optically opaque towards all Lyman lines and partially optically opaque towards H α the equilibrium populations will not be established for electron densities below 1X10 16 cm -3 .

The shift of the resonant frequency of microwave cavities excited in TM 0m0 (m=1, 2, 3), TM l10 (l=1, 2), TE 01n (n>0 integer) modes under the influence of a plasma is calculated for arbitrary radii of plasma and cavity for Bessel profile and common parabolic profiles. In measuring the frequency shift for two of the cited cavity mode types an approximate electron density profile can be determined from the submitted diagrams.

There are two kinds of water in CuSO 4· 5H 2 O differing by their binding in the crystal. The oxygen of four water molecules is bonded to the copper ion, that of the fifth molecule is hydrogen bonded. It is shown that the D/H ratios of these two kinds of water differ by 5.7%, the light isotope being enriched in the water molecules coordinated with the copper ion. The results show that there is no exchange of the hydrogen isotopes during the time needed for dehydration at room temperature which takes several days. The assumption has been confirmed that the water coordinated with the copper ion leaves the crystal first on dehydration at temperatures below 50 °C. Additional measurements of the separation factor for the hydrogen isotopes between water vapor and copper sulfate solutions allow conclusions on the fractionation of the hydrogen isotopes between bulk water and hydration water in aqueous solutions.

The kinetics of Na + -isotopic exchange in zeolite A has been measured with a new experimental method at 21 °C. The exchange rate does not fit the classical function for the time-dependence of an ideal diffusion process. This confirms what had been observed earlier for the isotopic exchange of Rb-and Cs-ions 1 . It is assumed that, on the average, the initial by stronger bound cations start diffusing later than the other cations. Further it is assumed hat the distribution over the different lattice sites is temperature dependent. The solution of the appropriate diffusion equation yields the diffusion constant D along with the fraction of stronger bound cations and the probability b (sec -1 ) of escape of these cations from their lattice sites. In the case of the Cs + -isotopic exchange the agreement between calculated and measured exchange curves is excellent. The results of this investigation show that the method of isotopic exchange between solid and solution as carefully investigated by Zimen 2 can be used to determine the distribution of exchangeable cations over different sites.

The ESR-powder-spectra of the perovskite-mixed-crystals M 2 II (CuxZn 1 -x W)O 6 [M II =Sr, Ba] and Sr 2 (Cu x Zn 1 -x Te)O 6 , which have been investigated by means of conventional X-ray-techniques and ligand-field-spectroscopy 1,2 , are described and the results extensively discussed. The conclusions can be summarized as follows: (a) At very low x-values isolated, dynamically Jahn-Teller-distorted CuO 6 -octahedra are present in the cubic matrices, which can be frozen into tetragonally elongated polyhedra at 4.2 °K; (b) At high x-values the CuO 6 -entities are statically JT-distorted with the long axes lined up along the c-axis of the macroscopically tetragonal phases; (c) The ESR-spectra around the cubic-tetragonal phase-transition are complex, containing signals of obviously magnetically coupled Cu 2+ -ions; (d) The g-values "follow" the ligand-field-parameters quantitatively. Comparative data of some other compounds are given.

The relaxation of nuclear dipolar energy to the lattice has been measured in three different organic solids (benzene, cyclohexane and hexamethylbenzene) as a function of temperature. In the cases of C 6 H 8 and C 6 (CH 3 ) 6 very slow motions associated with rather high activation energy were detected near the melting point. They are thought to be thermally activated rotations of the molecules about axes other than the hexad axis. In the case of cyclohexane the activation energy for the process of molecular diffusion was determined directly from the experimental results without the need of a model for vacancy diffusion. A maximum in dipolar relaxation rate was always observed for correlation times of the order of the rigid lattice line width i. e. in the temperature region where the lines narrow.

In order to produce high proton polarizations, several organic hydrocarbons have been doped with stable free radical molecules. Through the "solid state effect" a part of the electronic polarization in a magnetic field has been transferred to the protons of these materials. For this purpose, the "forbidden electronic transitions" of the combined electron-proton system have been saturated at about 37 GHz. The enhancement factor of the dynamic proton polarization was measured by pulsed NMR at 56 MHz. In phenanthrene with about 4 w.% bis-diphenylen-phenylallyl (BPA) a maximum polarization of 10.5% has been obtained at 1.5 °K and 13 200 gauss. This value may be increased by extending the temperature and magnetic field range. Systematic investigations in numerous organic systems have been carried out and have particularly yielded data on the frequency dependence and on the saturation behaviour of the enhancement curves. - Spin temperature theories of dynamic polarization have been considered to explain the results and to find possibilities for improving the polarization. In particular, the exchange interaction of the radicals and the distinction between relaxing and polarizing paramagnetic centres had to be taken into account.

Nuclear interactions of cosmic rays under paraffin and lead have been studied by means of a counter controlled multiplate cloud chamber. The lead plates inside the chamber served as producer and analyser. A search has been made for the possible transition effect of nuclear interaction in lighter elements using charged components for triggering and to compare it with a previously observed apparent transition effect in graphite for neutron shower using coincidence of neutron counters. The results show a continuous increase of nuclear interaction with increasing thickness of paraffin absorber up to 30.4 gcm -2 . A similar rise is also observed under 11.3 gem -2 of Pb.

Beim Chloroform und einigen Chloroform-Lösungen wurden die differentiellen Intensitäten und Profile der Raman-Linien und ihre Verschiebungen gegenüber den Linien des reinen Chloroforms untersucht und daraus Schlüsse bezüglich der Änderung der Polarisierbarkeit und der Bindungsmomente des Chloroforms durch die zwischenmolekularen Wechselwirkungen gezogen.

Laser emission has been obtained from coronene in methyl-cyclohexane/isopentane (MCH/IP) at 100 °K with a wavelength of 4439 Å (22 522 cm -1 ). It is remarkable for its very low value of threshold energy (≦ 50 Ws) and its very shot relaxation oscillations (τ ½ ~ 10-20 ns). The theoretrical considerations for a laser with aromatic hydrocarbons are compared with our practical results.

Measurements of the energy distributions of emitted electrons from Si, GaP, and ZnS allowed the determination of the relative positions of some core levels of these materials and the optical density of states of the valence band in Si. These energy levels were determined relative to the Fermi level. The electron emission was induced by monochromatic X-rays (AlKα). These results are compared with values obtained from OPW calculations for the valence bands and selfconsistent Hartree-Fock-Slater calculations for the core states.

Electrical sparks are studied which occur when ferroelectric TGS crystals are heated through the Curie point. The light comes from electrical discharges into the surrounding atmosphere. A rough surface of the crystal and the configuration of the domains have a very strong influence on this effect. Similar sparks are found at the edge of the electrode when the polarization is reversed by an electrical voltage being greater than a certain critical value. A mechanism is proposed which describes these phenomena.

Antistokes fluorescence in the green and blue region, excited by infrared radiation (λ=0.97μm) is observed with a relatively high efficiency in substances which contain not only a luminescent activator (Er 3+ or Tm 3+ ), but also a sensitizer which has a strong infrared absorption (Yb 3+ ). Polycrystalline mixed tungstates and germanate glasses have been studied. The green fluorescence of Er 3+ increases as a square-law function of the excitation intensity, the blue fluorescence of Tm 3+ as a cubic function. This effect has been used to build an optical amplifier which has served to measure the excitation spectra. The mechanism of excitation is the following: Absorption of the infrared radiation by the sensitizer, followed by energy transfers to the luminescent activator, which is excited stepwise up to the initial level of luminescence. Oscillator strengths for some transitions between excited levels have been calculated.

Al-ZnS-Al cells withstanding fields of 10 6 V cm -1 were studied; their resistivity being of 10 14 Ω • cm. The induced conductibility is related to Makhov's law of the absorption of the electronic flux. The distribution of the secondary charge carriers and the electric field inside of the layer are given. The experimental results agree with Makhov's law. It is possible therefore to express the dependence of the range in the thin ZnS layer upon the energy of the bombarding electrons: R = 95 E 0 1,8 , where R is expressed in Å and E 0 in kV. The optimal conditions for the gain as a function of the energy of the electronic flux, the thickness, and the quality of the layer are given.

Starting from a master equation for a physical system consisting of mutually non-interacting Brownian particles in a dilute gas and using the collision model of hard spheres we obtain a coupled system of equations of motion for the Brownian distribution function F (R,V; t) and the (single-particle) distribution function f(r,v;t) of the gas. For these equations, assumed to form a "dynamical system", a "H-Theorem" yields asymptotic Lyapunov stability in the large relative to total (Maxwell) equilibrium ("tendency to equilibrium"). For example we investigate approximately the system influenced initially by a sound field (phenomenological coefficients of the equation for F, Fokker-Planck approximation, BGK model for the f-equation).

A non-stationary technique of e.m.f. measurements after polarization of solid galvanic cells, previously applied to the determination of the standard free energy of formation of metal oxides, has been extended to intermetallic phases. The chief condition of applicability of this technique to intermetallic compounds is that the rates of recombination of the cathodic reduction products to yield the stable intermetallic phase be high as compared with that of chemical oxidation at the interface with the solid intermediate electrolyte, due to oxygen impurities in the gas phase. In particular, the solid electrolytic cell: (y values expressing the ε-phase iron-rich boundary compositions according to different authors investigations) was examined. Values of the standard free energy of formation of Fe 7 -y Nb 2 from the elements, ranging between -3.77+0.72-10 -3 T and -5.66+1.09 · 10 -3 T kcal/atom were found.

Es wurden zonengeschmolzene Mischkristalle besonders der Zusammensetzung Zn 0.75 Cd 0.25 Sb hergestellt und der Einfluß der Dotierung mit den als Donatoren wirkenden Elementen In und Te untersucht. Für In-dotierte Proben wurde die Temperaturabhängigkeit der elektrischen Transport-größen (elektrische Leitfähigkeit, Hall-Effekt, Thermokraft und transversaler Nernst-Ettingshausen-Effekt) im Temperaturbereich von etwa 80 bis 300 °K gemessen. Bei Zimmertemperatur n-leitende Proben zeigen bei tiefen Temperaturen p-Ueitung. Die verschiedenen Vorstellungen über dieses eigenartige Verhalten werden diskutiert.

Durch Zonenschmelzen wurden Kristalle der halbleitenden Legierung Bi 88 Sb 12 hergestellt. Die Ladungsträgerkonzentrationen und der Leitungstyp wurden variiert durch Zugabe von Te als Donator und von Sn und Ga als Akzeptoren. Der elektrische Widerstand, die magnetische Widerstandsänderung, der Hall-Effekt, die Thermokraft sowie ihre Änderung im Magnetfeld wurden im Temperaturbereich von 5 bis 300 °K gemessen. Die elektrischen Transportgrößen, die Probleme der Invertierung und der ΔE-Bestimmung werden diskutiert.

Diffusion processes were investigated by means of quantitative electron-probe microanalysis in the systems Mo-Al, Nb-Al and Mo-Nb. With the system Mo -Nb the annealing temperature amounted to 980 °C and a smooth run of concentration versus distance was obtained. The diffusion coefficient was dependent on concentration and amounted to 0.7-3.0·10 -14 cm 2 sec -1 . In the case of Mo-Al the diffusion zone was composed of the phases Al 8 Mo 3 , Al 4 Mo and Al 12 MO. The breadth of these phases is discussed in dependence on annealing-temperature and -time. Occurrence of volume diffusion could be confirmed. Within the phase Al 8 Mo 3 after annealing at 525 °C a concentration gradient was obtained, which yielded a diffusion coefficient of 8.47 · 10 -6 cm 2 sec -1 . In the case of Nb -Al the diffusion zone consists of the intermetallic compound NbAl 3 .

In äquiatomaren Cu -Ni-Legierungen werden durch Elektronenbestrahlung Frenkel-Defekte erzeugt, die den Diffusionskoeffizienten erhöhen. Dadurch wachsen durch Cu-Diffusion ferromagnetische nickelreiche Bereiche, während der Paramagnetismus der Matrix abnimmt. Damit ist das Vor-handensein der Mischungslücke auch in kompaktem Material nachgewiesen. Die kritische Mischungs-temperatur ist zwischen 270 und 300 °C zu suchen.

Die geometrischen Strukturparameter und Schwingungsamplituden des Dimethylsulfodiimins wurden durch Elektronenbeugung an Gasen bestimmt. Das Ergebnis zeigt, daß S-N-Doppelbin-dungen vorliegen und daß das Schwefelatom und die beiden Stickstoffatome keinen Dreiring bilden. Folgende Werte wurden für die geometrischen Parameter gefunden: S-N=1,533±0.002 Å, S-C=1,791±0.002 Å, C-H=1,085 ±0,008 Å, N-H=1,022±0,018 Å, ∢NSN = 135,0±1,2°, ∢CSC=101,2±1,4°, ∢SNH i =114,1±2,4°, ∢H m CH m =108,2±1,1° (Hm = Methylwasserstoff, H i =Iminwasserstoff).

Unter Verwendung eines erweiterten Valenzkraftmodells werden Normalkoordinatenanalysen an Cyclopropenylium-Ionen C 3 X 3 + (X=Cl, Br, C 6 H 5 ), Tetrahalogencyclopropenen C 3 X 4 (X=Cl, Br) sowie 16 O-und 18 O-Cyclopropenonen (R=CH 3 , C 6 H 5 ) durchgeführt. Es werden Kraftkonstanten erhalten, die folgende Aussagen zulassen: Im Cyclopropenyliumsystem sind die Valenzkraftkonstanten der Bindungen im und am Ring größer als bei analogen Benzolderivaten. Bei den Cyclopropenonen sind die Kraftkonstanten der Doppelbindungen gegenüber den Werten in nichtkonjugierten Olefinen und Ketonen erniedrigt, diejenigen der Einfachbindungen erhöht. Daraus folgt, daß die Betain-Struktur am Grundzustand beteiligt ist. Die Potentialenergieverteilungen und Eigenvektoren zeigen eine starke Mischung der verschiedenen inneren Koordinaten des Moleküls an.

Die Lichtablenkung durch eine elastisch beanspruchte homogene isotrope Scheibe wird sowohl für den ebenen als auch für den nichtebenen Spannungszustand auf die Dicken-und Dichteänderung bzw. Brechungsindexänderung zurückgeführt. Die theoretischen Zusammenhänge werden für den Fall der Belastung mit Ultraschalldehnungswellen hergeleitet. Mit Hilfe einer schlierenoptischen Anlage werden Querkontraktion, Schubwellengeschwindigkeit und dynamischer Elastizitätsmodul und mit Hilfe eines punktförmigen Abtastverfahrens (Lichtwegänderungen von 10 -5 mm werden aufgelöst) die Anteile der Dicken-und Brechungsindexänderung zur Lichtablenkung bestimmt. Für dünne Scheiben sind Dicken-und Dichteänderung einander proportional, für dicke Scheiben ergibt sich, daß bei Dickenvergrößerung der Scheibe in deren Innern die mittlere Dichte abnimmt.

The number of neutrons per discharge which are emitted during the collapse of a hollow D-T-z-pinch is calculated. In the system of differential equations describing the radial acceleration of the cylinder by Lorentz-forces the internal pressure of the sheath is incorporated. Due to the pressure-term it is possible to calculate the time dependance of density, temperature and reactionrate within the sheath. Using a capacitor bank of 200 kJoule at 100 kV and a hollow cylinder of 30 cm initial radius and 10 cm height the emission of 3·10 13 neutrons is expected during the implosion phase, lasting a few nsec. The optimization of the experimental parameters for maximum neutron emission is given.

The paper presents a study of the effect of a high frequency stochastic field on particles contained in a magnetic mirror system. The r.f. field is assumed to be excited by an external source and to penetrate from one side through the mirror to only those locations in which the rf field is in resonance with the cyclotron frequency. The rf field is further assumed to have a specified correlation, and to be unaffected by changes in the particle distribution function brought about by heating. The case in which it is possible merely to consider the effect of the perpendicular component Eτ+(νxB rf )τ was studied separately from the case in which both components of E+(νB rf ) are to be taken into consideration simultaneously; E and B rf are here the electric and magnetic components of the rf field. The absorption by a small group of particles the distribution function of which has the form of a δ-function is examined. The solution is performed in one-particle approximation. As the solution implies, in a configuration of this kind transverse heating is accompanied by diffusion of particles through the mirrors as well as by a transformation of a portion of transverse energy into longitudinal (resulting from both the transformation due to the magnetostatic field inhomogeneity and the effect of B rf ).

The probability of magnetic and nuclear magnetic recoilless spin-flip scattering in magnetic crystals is calculated as a function of temperature. This is an elastic spin-flip scattering process in which the angular momentum is absorbed by the whole crystal. The probability of elastic scat-tering in a ferromagnet is proportional to the squared magnetization and plays the same part as the Debye-Waller factor in the Mössbauer effect.

Using the Fourier convolution theorem GELLER 1 has given analytical results for the two-center integrals

ESR-spectra of Cr 3+ -ions on orthorhombic lattice sites in single crystals of SrTiO 3 were observed at room temperature. The following constants were found: g z =1.9783±0,0005 , gx=9y=1.9761±0,0005 , | D | = (0.464±0.002) cm -1 , | E | = (0.272±0.005) cm -1 , | A | = (16.2±0.3) 10 -4 cm -1 .

The Raman spectrum of Na3[Co(NO,)8] has been mea-sured in the range from 2000 to 50 cm 1 and the vibrational frequencies and their assignment are compared with infrared data already obtained. The force constants are calculated in the valence force field. With respect to vibrational spectro-scopy the CoN6-octaeder and the N02-group are assumed to be approximately two separate units. The justification of this approximation is discussed on the basis of the Raman spec-trum and the selection rules for the Symmetrie point group S6 of Na3 [Co (N02) 6]. Gefärbte Substanzen mit Absorptionsbanden im kurzwelligen sichtbaren Spektralbereich eignen sich vorzüglich für die Aufnahme des Raman-Spektrums, wenn man einen He —Ne-Laser mit seinem relativ lang-welligen Erregerlicht einsetzt 1 . Ein Molekül mit

Zeigt der elektrische Widerstand eines Körpers zeit-liche Schwankungen um seinen Mittelwert, so tritt bei Belastung mit einem Gleichstrom zusätzlich zum ther-mischen Gleichgewichtsrauschen ein "Stromrauschen'' auf, dessen totales mittleres Spannungsquadrat durch das totale mittlere Quadrat der relativen Widerstands-schwankung und die am Meßobjekt liegende Gleich-spannung gegeben ist Phasenübergänge erster Ord-nung sind durch Instabilitäten gegenüber Fluktuatio-nen der extensiven Parameter gekennzeichnet 2 . Es wurde daher das Stromrauschen von flüssigem und Sonderdruckanforderungen erbeten an: Dr. J.

In der V. Mitteilung 1 war über die Kinetik des Alkali-Isotopenaustausches in Zeolith A zwischen 0 °C und 30 °C, in der VI. Mitteilung 2 über die Kinetik des Ba-Isotopenaustausches zwischen 20 und 140 °C berich-tet worden. Beide Untersuchungen hatten ergeben, daß die ge-messenen Umsatzkurven formal als Summe von zwei Diffusionsprozessen dargestellt werden können, die un-abhängig voneinander mit unterschiedlicher Geschwin-digkeit nebeneinander ablaufen, wobei der Anteil des langsamen Teilprozesses mit steigender Temperatur ab-nimmt. Beim Ba war allerdings die Uneinheitlichkeit nur wenig ausgeprägt und verschwand oberhalb 85 C ganz.