The (n, α) reaction measurements on143Nd and180Hf with thermal neutrons

The thermal neutron cross sections for several-transitions of the¹⁴³Nd(n,) reaction have been measured using a semiconductor surface barrier telescope. The¹⁴³Nd(n, ) reaction has been observed. The¹⁸⁰Hf(n,) cross section estimation is given.The authors are in lebted to Mrs. M.Pospíilová, Mr. J.Baura and Mr. J.Novotný for their assistance during the experiment and Dr. K.Konený for the neutron capture gamma rays analysis.     

Some properties of the gas discharge in a magnetron geometry

The discharge in a magnetron geometry was experimentally investigated. At pressures less than 10^–2torr a high-voltage discharge (similar to corona discharge) burns, which discontinuously turns into glow discharge when the pressure is rising. Magnetic field changes the glow discharge in a similar way as the rising of pressure does (the cathode regions are getting shorter, etc.). The pressures and magnetic fields were found in which the positive column occupies 3/4 of the discharge space (gap distance 4 cm) and where an electric field 100 V/cm can be measured.The authors wish to thank Dr. P.unka and Dr. V.Kopecký for a valuable discussion and J.Dvoák and A.Kapar for technical assistance throughout the measurement.     

Thermal conductivity of semiconducting amorphous CdGeAs2

The thermal conductivity of amorphous semiconducting CdGeAs₂ was studied between 100 and 300°K. The Debye model was used for the calculation of the mean free path of phonons which was found to be 10 Å at 300°K and was related to the basic structure units of amorphous CdGeAs₂.Thanks are due to Mrs. J. Beránková, Mr. J. Kapar and Mrs. J. Trepeová for the preparation of the amorphous CdGeAs₂ used in this work and for the measurements of the thermal parameters, and to Dr. J. urek and Dr. S. Kolník from the College of Transport Engineering, ilina, for the sound velocity measurements.     

The effect of the time of flight of neutrons on the decay constant measurements by the pulse method

The effect of the time of flight of neutrons escaping from the moderator on the measured time dependence of the neutron density, which in turn serves for determining the decay constant , has been analyzed. The measured values of a have been found to vary considerably with the distance of the detector from the moderator and also with its size described by the bucklingB ². Measurement with light water and loose diphenyl has shown that the deviation in depends also on the type of moderator.The authors would like to thank Mr. J. Jirou and Mr. J. Jadavan for their collaboration in the measurements and for maintaining the electronic apparatus and the accelerator as well. The authors also acknowledge the help of Dr. M. Nepraová in preparing the computer programme.     

On the effect of trapped particles in the regime of cyclotron resonance

The motion of particles in a finite amplitude wave, propagating obliquely to the homogeneous magnetostatic field is discussed. As follows from simple integral properties, in the neighbourhood of Doppler-shifted cyclotron resonance similar trapping effects appear as in a plasma without magnetostatic field. Consequences of this trapping are discussed, in particular, the possibility of a strong absorption of the wave, and the origin of stochastic instabilities caused by the perturbation of an effective trapping potential and leading to the acceleration of particles.The author is indebted to Dr. R.Klíma, Dr. J.Lacina and Dr. P.unka for interesting discussions and to Dr. .Körbel, Mrs. P.Jaroová and Mrs. A.Harmáková for numerical calculations.     

Experimental study of ternary fission of U235 with thermal and resonance neutrons

The alpha particle spectra from ternary fission of U²³⁵ have been investigated in the thermal and the resonance neutron energy regions. The resonance neutrons have been obtained by passing the reactor neutron flux through a boron filter. A silicon surface barrier detector telescope technique for alpha particle detection has been used. In the resonance neutron energy region the ratio _f / _f has been found to be 1·02 ± 0·2 times the value of _f / _f in the thermal region. The non-gaussian tail of the LRA energy distribution has been observed.The authors are indebted to Dr. I.Wilhelm, Mrs. M.Pospíilová, Mr. J.vanda for their kindly help in the experimental data handling and to Mr. V.Kvítek for his assistance during the experiment.     

The effective mass of holes in CdSb from reflectivity measurements

From the measured reflectivity near the plasma edge the effective mass of free holes in Ag-doped CdSb was determined. In the studied concentration rangem _b ^* >m _a ^* >m _c ^* is valid. The dependence of the effective mass on the concentration of free holes indicates a strong non-parabolicity of the bands.The authors wish to thank Dr. B. Rheinländer for discussions and information about his results before publication. Mrs. D. Vaková carried out the measurements on UR-10 Zeiss, Mrs. V. Míková prepared the single crystals, Mr. J. Kapar oriented them by X-ray diffraction and Dr. L. Satoura determinedN and. The authors thank them for their help.     

On path integrals and relativistic quantum mechanics

A proposal for formulation of relativistic quantum mechanics in terms of path integrals is presented.We are deeply indebted to Dr. M.Petrá for many stimulating discussions.     

Influence of Ge and Ag impurities on the thermal conductivity of semiconducting amorphous As2Se3

The thermal conductivity of amorphous semiconducting As₂Se₃ is studied in the temperature range from 100 to 300°K and the influence of germanium and silver impurities is shown. The mean free path of phonons is determined and the observed change of the thermal conductivity is explained by the change of the velocity of sound in amorphous As₂Se₂ containing germanium.Presented by L. toura at the Meeting on Electronic Structure, Optical and Transport Effects in Amorphous and Liquid Semiconductors, Prague, May 1965.The authors are indebted to Dr. J. urek and Ing. I. Turek from the Department of Technical Physics of the College of Transport Engineering in ilina for measuring the velocity of sound in the investigated materials and to Mrs M. Kaparová and J. Trepeová for their help in the experimental work.     

Dispersion relations for forward pion-pion scattering and their consistency with Wolf pion-pion phase shifts

It is shown that the Wolf pion-pion phase shifts are in reasonable agreement with dispersion relations for forward scattering. The extent to which the inaccuracies of the experimental data might modify this agreement is examined.At attempt is made to explain some discrepancies which arise probably from too broad a -meson peak.The author is indebted to Dr. M. Petrá for valuable discussions, to P. Bóna for help with some calculations and to Dr. J. Mikloko from the Computing Centre of the Slovak Academy of Sciences for programming and computation. He is also indebted to Dr. G. Wolf and to Dr. F. Meiere for sending a copy of their papers prior to publication.     

A computational method of determination of constants of spin Hamiltonian of fine structure ESR spectra

In the case of strong electric crystal fields one cannot use the well-known method of determination of constants of the spin Hamiltonian based on the perturbation theory. This method results in less accurate values of determined constants. In the paper is presented a new method which uses exact numerical diagonalization of the matrix of spin Hamiltonian for determination of constants. The constants determined by this method satisfy the exact solution of the equations for the resonance transitions. This method causes practically no error in the determined constants.The autor would like to thank to Prof. Ing. M.Ráko, Dr. Sc. and Ing. O.Bartko for discussions, and to A.Kotuliaková and G.Petrá for help with the construction of the program.     

The electron paramagnetic resonance in reduced BaTiO3 crystals

The electrcn-spin resonance of reduced BaTiO₃ crystals, which was studied by Z. roubek and K. d'ánský [Czech. J. Phys.B 13 (1963), 309], is interpreted as the resonance of the Ti³⁺ ion. The facts which favour this interpretation are discussed. The distortion of the oxygen ions surrounding the Ti³⁺ ion has been taken into account in order to explain the measured electron paramagnetic resonance spectrum. Considering the crystal-field model of C_4v point-group symmetry, the Stark energy-level separations of the Ti³⁺ ion and the values of theg factors are calculated.The authors would like to thank Dr. E. imánek for many very helpful discussions and Dr. H. Arend for helpful comments.     

Evaluation of positron annihilation angular correlation curves and line profiles of compton scattering in noble metals

Angular correlation curveN () as well as the Compton line profile I() of Cu, Ag, Au and Pt have been calculated by the assumption, that the coincidence counting rate and Compton line shift intensity are proportional to the area of cuts through the body defined by the Fermi surface. Parametrical expression of the Fermi surface were employed and the results were used to fit some measured curves on Cu, Ag and Au.The authors are indebted to Prof. P.Ry and Dr. I.Volf for enabling the work, Dr. A. íek for supplying the experimental data for Au, Ag and Cu and J. Sedláek for assistance by programming of numerical evaluations.     

Microhardness and structure transformations of Al-15 at.% Zn alloy aged at elevated temperatures

The microhardness changes on ageing in single crystals of the Al-15 at.% Zn alloy at the temperatures of 201 °C and 222.5 °C are presented in this paper. The gradual decomposition of the solid solution was simultaneously studied from X-ray diffraction measurements. The results reveal the mutual correlation between the individual structural stages and the microhardness of this alloy.Cukrovarnická 10, Praha 6, Czechoslovakia.In conclusion the authors wish to express their thanks to Doc. Dr. V. Syneek CSc. for many stimulating discussions, to Ing. J. Laek CSc. for the careful chemical analyses of the investigated alloy and to Ing. P. Bartuka CSc. for the private communication of his results from the electron-microscopic study. Our thanks are also due to Mr. Z. iký and Mr. J. Bauer for assistance in measurements.     

The transport phenomena of pure and doped p-type ZnSb

The electrical conductivity, the Hall effect and the thermoelectric power in thec andb crystallo-graphic directions as a function of temperature on pure and doped ZnSb single crystals with hole conductivity were studied.The anisotropy of the hole mobility was explained on the basis of the anisotropy of the effective mass of holes in the crystallographic directions and the assumption of isotropic relaxation time. A model of the ZnSb valency band with two equivalent extremes was proposed which made it possible to explain the studied transport phenomena.The authors thank Mrs. V. Míková for preparing the ZnSb single crystals, Mr. J. Kapar for the crystallographic orientation and Mrs. J. Trepeová for her help in the experimental work.     

Localization of a high-power microwaves absorption in the cylindrical plasma column at ωLH ≪ ω ≪ ωce

This paper describes experiments which make it possible to determine the place of the absorption of electromagnetic waves in a cold (T _e=5–10eV) not fully ionized plasma column at _ce/=1 and _ce/> 1.The authors wish to thank L.Bárdo for helping with the experiments.     

A study of the plasma column with attention to the region near the wall

The ambipolar diffusion problem in a positive column is studied when charged particle inertia, heating and the mobility variation of positive ions in the radial electric field are taken into consideration. The atomic ion motion in their respective parent gases is approximated by the hard sphere model. The problem was also solved by approximate methods and compared with the precision numerical calculations. A simple formula for number density of charged particles at the boundary plasma-sheath was found.The authors would like to thank Professor .Veis for the support of this work. We are also grateful to Dr. I.Koinár and Dr. V.Jukl for their guidance in computer programming.     

A Metallografic study of the homogeneization quenching of copper

During homogeneization quenching the dislocation density in copper grows up to saturation and the dislocation structure becomes stabilized. This process is realized on quenching into gases and liquids, i.e. at both lower and higher quenching rates. Grain growth is also observed. The dislocation structure formed by cold-working is removed by annealing at temperatures near to the melting point in a time interval shorter than 30 minutes and the dislocation density reaches a stable value, growing with decreasing thickness of the specimen.The authors would like to thank Dr. K. Míek, CSc. (Institute of Solid State Physics, Czechosl. Acad. Sci., Prague) for his comments, Dr. J. Kuera CSc. and Dr. P. Luká, CSc. (Institute of Metallurgy, Czechosl. Acad. Sci., Brno) for critical remarks on the paper and Mrs. J. Zoubková for assistance with the experiments.     

Microprocessing of superconducting Nb3Sn tapes by electron-beam microetching

The unsuitable mechanical properties of Nb₃Sn (its brittleness) make the production of a conductor in the required shape and dimensions very difficult. A method has been proposed and experimentally investigated by which the existing superconducting Nb₃Sn tape could be modified to obtain intrinsically stable superconductor. The required filamentation of commercial Nb3Sn conductor is manageable by electron-beam microetching. The achieved results could serve as a starting point for the construction of a special electron-beam machine. Such device may work in connection with the Nb₃Sn producing apparatus.The authors are grateful to I.Hlásnik for the encouraging discussions, to V.ernuko for providing us with the Nb₃Sn vapour deposited tape and to S.Koina for performing the microanalysis.     

A resistometric investigation of the decomposition kinetics of Al-21·8 at.% Zn solid solution at 276 °C

Under the condition of nearly equilibrium concentration of vacancies, time dependence of the amount of isothermal transformation given byy=R/R _f was investigated whereR _f is the total structural change of resistivity on completion of the whole process andR is the measured resistivity change. The investigation was done on the 21·8 at.% (40·3wt.%) Zn alloy under the condition of relatively low supersaturation of a few degrees centigrade below the metastable _R solvus line. The total transformation involves four kinetic stages: the first two stages correspond probably to diffusion-controlled growth of the _R particles from the supersaturated solid solution and to the ripening of these particles till their conversion to the cubic phase takes place. The last two kinetic stages account analogously for the particles growth and ripening. Both _R and phases were identified by the transmission electron microscopy. When separating the individual stages, the approximation byy=1–exp [–(mt) ⁿ] of the amount of transformationy was used. The approximation allowed to get the starting values of both the time and the change of the structural part of the electrical resistance for individual stages and also to derive the parametersm _i, n_i which had to be redetermined for the individual separated stages. These data made it possible to synthetize the experimental curves ofR andy vs. time for the total transformation.It is a pleasure to thank Doc. Dr. V.Syneek CSc. for stimulating the author's interest in this problem and for providing helpful discussions. I also would like to express my thanks to Ing. P.Bartuka CSc. for the transmission electron microscopic study carried out to identify the particular phases. The author is indebted to Ing.V. íma for the preparation of the investigated alloy and to Mrs. A.Mendlová and Mr. P.Vyhlídka for technical assistance.