Magnetization coils without iron core for high field intensities

A new theory of rectangular coils without an iron core is described which amends the old one of Fabry and Bitter. It enables us to compute field intensities in coils having very small openings, which the old theory could not do.

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, , , .

     

Double cascade transitions of gamma rays from radiative capture on Co59

Pairs of gamma quanta, giving a sum equal to the binding energy of the last neutron in a Co⁶⁰ isotope, were studied during radiation capture on a Co⁵⁹ nucleus. The energies of the gamma quanta giving such cascades were determined and an attempt was made to determine the relative intensities of the different cascades.

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- Co⁵⁹

Co⁵⁹ -, Co⁶⁰. -, , .

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In conclusion the authors thank J. Vávra for cooperation in the measurements.     

A remark on the third law of thermodynamics

It is shown that Falk's formulation of the third law of thermodynamics (when the energy has minimum value the entropy is also minimum) can be replaced by an equivalent assertion: the absolute minimum energy is unattainable with a finite number of processes.

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,

( , ) : .

     

Change in primary extinction of X-rays in solid solution of NaCl-CdCl2

The Suzuki model of regions with a hyperstructure was verified, the dependence of their size on the cooling rate was found and it was determined that they disappear at temperatures between 250° and 300°C according to their composition. Up to 1000 Å their structure is coherent with a matrix lattice and their formation is not accompanied by a decrease in the primary extinction. Regions above 1000 Å are partially incoherent and their formation and disappearance are apparent by a change in the primary extinction.

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NaCl-CdCl₂

, , , 250°–300°C . , 1000 Å, . , 1000 Å, .

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The author would like to thank I. Kunzlová, and M. Lébl for preparing the crystals of NaCl-CdCl₂ solid solution and Dr. Trnka for determining the cadmium Concentration in them.     

Change in primary extinction during decomposition of supersaturated solid solution II. Al-Cu 4% alloy-formation of G.P. zones

The change in integrated intensity of the (200) reflections of a solid solution during the formation of G.P. zones was measured and compared with the change in the character of the diffuse streaks corresponding to them. It was found that the. formation of G.P. zones does not lead to a decrease in primary extinction despite the great changes in the distribution of the copper atoms. It was shown that the formation of a precipitate accompanied by the formation of crystallographically incoherent boundaries greatly decreases the primary extinction.

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. II. 1-u 4%: [. . ]

(200) . . , . , . . , . , , , .

     

Elastic stress around linear dislocation in anisotropic medium

Relations are derived for the elastic stress field around a linear dislocation in an infinite medium with general anisotropy. The strongly deformed material around the core of the dislocation is cut out in the shape of an elliptic cylinder. The conditions of a free surface are used on the boundary thus formed. The calculation of the field around a crack in a crystal, the model of which was proposed by Fujita in [9], is given as an example.

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. , , , . , [9] .

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The author thanks Dr. F. Kroupa for valuable discussions and all-round help in solving the problem and Z. Hemanová for performing the numerical calculations.     

To the question of electron angular distribution at Μ-meson decay

The paper describes the measurement of the angular distribution of electrons at the decay of-mesons in a longitudinal magnetic field. The results of measurement indicate that electrons are emitted with preference not only in the direction parallel to the spin orientation of -meson but also in the antiparallel direction in disagreement with the angular distribution predicted by theory.

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- . , -, , , .

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The authors thank N. V. Rabin for irradiating the nuclear emulsions, Prof. Dr. V. Petrílka and M. Suk for mediating relations with the Joint Institute of Nuclear Research in Dubna and Dr. J. Pernegr for valuable discussions and remarks. Thanks also go to H. Koutová and H. Slámová for carefully scanning the nuclear emulsions.     

The distribution of neutron density in the vicinity of a partly inserted black rod in two-group approximation

The neutron density in the vicinity of a black cylindrical rod partly inserted in a bare reactor is calculated and illustrated by a numerical example. The starting point is a two-group diffusion theory approximation. While the dependence of the effect of the rod on the insertion depth can be calculated simply by means of perturbation theory, the question of the neutron density estimate in the vicinity of the rod is considerably more difficult and in some considerations the estimate of the neutron density caused by the presence of the rod is indispensable. The method makes it possible to determine the reactivity value of the rod in dependence on the insertion depth and especially the neutron density deformation in the vicinity of the rod.

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()

. , . , , . , . [1] . .

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In conclusion the author thanks J. Svato for help in carrying out the numerical calculations.     

The application of the thermodynamics of irreversible processes to welding arcs

The self-regulation of an inert gas shielded metal welding arc is dealt with briefly. A thermodynamic equation is derived for the self-regulation of such an arc.

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. .

     

Photo-piezoelectric effect in semiconductors

A new photo-voltaic effect was observed which is caused by inhomogeneous distribution of the pressure in a semiconductor. Its production can be explained by the dependence of the energy gap on the pressure.

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, . .

     

The propagation of excitation energy in perturbed crystals

The process of the propagation of excitation energy in perturbed dielectric crystals with a weak bond between the atoms having zero permanent dipole moment is studied. It is shown that on certain assumptions this process of propagation can be regarded as the motion of a Frenkel exciton in the electrostatic field of the defect. Frenkel's exciton can be characterized in this case as a neutral polarizable particle having induced dipole moment equal to the change in the induced dipole moment of the crystal during the excitation of one of its atoms.

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, . , . .

     

The effect of the orientation of zinc single crystals and of the rate of growth on the direction of cell substructure

The effect of the orientation of zinc single crystals and the rate of growth on the direction of the formation of cellular substructure is observed. A model accounting for the observed dependences is proposed.

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Anwendung der Hochfrequenzmessmethode für die Elektronenkonzentration zur Messung in der geschichteten positiven säule der Gleichstromglimmentladung

Zusammenfassung In der vorliegenden Arbeit werden Beziehungen abgeleitet, mit deren Hilfe es möglich ist, die Hochfrequenzresonanzmethode der Diagnostik des Plasmas zur Messung der Änderungen der Elektronenkonzentration in den laufenden Schichten in der positiven Säule der Glimmentladung zu verwenden. Ferner wird die Anwendung dieser Methode diskutiert, und zwar für den Fall, daß die Zusammenstoßfrequenz der Elektronen nicht von der Elektronengeschwindigkeit abhängt, und für den Fall, in dem die Zusammenstoßfrequenz der Elektronen eine Funktion der Elektronengeschwindigkeit ist.

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. , , , , .

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Abschließend dankt der Verfasser den Herren Prof. V. Kunzl und R. Bakule für ihre wertvollen Hinweise zu dieser Arbeit.     

Zur Frage derZ-Zentren bei der Exoelektronenemission aus Alkalihalogeniden

Zusammenfassung Es wurde das Maximum des Exoelektronenemissionsstroms untersucht, das an NaCl infolge Verunreinigung durch Kalzium auftritt, und die Möglichkeit, dieses Maximum denZ-Zentren zuzuordnen, diskutiert.

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Z-

, NaCl . Z-.

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Wir danken herzlichst Herrn Dr. A. Bohun für das gefällige überlassen des NaCl: Ca-Materials.     

New derivation of Bardeen-Shockley formula for mobility of electrons in homopolar semi-conductors

The Bardeen-Shockley formula for the mobility of an electron or hole in a homopolar semi-conductor is derived in a different way to that in which its authors obtained it. The interaction energy of the electron with the acoustic lattice oscillations is derived in an original way. A new possibility for determining the energy gap is given.

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- , , , . . .

     

The interaction of foils activated by thermal neutrons

The interaction of foils lying in a plane during their activation by thermal neutrons has been calculated. Numerical values of functions are listed, which can be used in calculations, especially for graphite. The interaction was measured in the graphite column of the VVR-S reactor.

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, , . , , . VVR-S.

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We thank J. Frytacký, T. Kania and V. ervenka for their help in the numerical calculations and measurements.     

Über den Einfluss von Stickstopf auf die Exoelektronenemission von Germanium

Zusammenfassung Es wurde der Einfluß eines Bombardements mit Stickstoffionen vor der Erregung untersucht und gezeigt, daß die Stiekstoffatome eine große Rolle bei der Entstehung des Emissionsmaximums bei 150° spielen.

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, 150°C.

     

The motion of 90° wedge domains in BaTiO3 in an alternating electric field

The paper deals with the motion of 90° wedge domains in BaTiO₃ in an alternating field of 50 c/s. The critical field, the positional hysteresis loops with double asymmetry, the production of wedges with polarization perpendicular to the field and 180° substructure in the wedges were studied. The differences between the behaviour of the wedges and the individual 90° walls are pointed out which are caused by differences in the energy balance of these formations and by different interactions with 180° processes. The upper limit of contribution of the wedge motion to the initial permittivity is estimated. The results are discussed from the phenomenological point of view.

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90° BaTiO₃

90° BaTiO₃ , 50 Hz. , , , , , , 180° . 90° , 180° . , . .

     

Zur Sichtbarmachung von Reptation-Erscheinungen an Rahmeneinkristallen

Zusammenfassung An einem Rahmeneinkristall wurde mit Hilfe der Kolloidmethode die Bewegung von BlochwÄnden infolge wiederholten Ein- und Ausschaltens eines konstanten FeldesH _A im Mikroskop beobachtet. Es zeigte sich, da\ es sich um Reptation-Erscheinungen im Sinne von Néel handelt. Diese mikroskopischen Reptation-Erscheinungen konnten nur in unmittelbarer NÄhe von Löchern im Kristall beobachtet werden, bei denen die Grundbereiche durch das wiederholte Ein- und Ausschalten des FeldesH _A geÄndert wurden.

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H _A . , . , H _A .

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Für die wertvolle Hilfe bei der Herstellung des Rahmeneinkristalls und der Me\-anordnung möchten wir an dieser Stelle besonders Herrn W. Schwab danken.