Optical properties of GeO2 in the ultraviolet region

The optical constants of amorphous and crystalline GeO₂ were determined by measurements of reflectivity in the region of phonon energy 0·5–25 eV and subsequent use of Kramers-Kronig analysis. The differences between the spectra of GeO₂ and those of SiO₂ are shown and discussed.The author would like to express her gratitude to Prof. J. Tauc for his interest in this work, to Dr. Z. Trousil, J. Charvát, Dr. S. Koc, Mrs. V. Míková and Dr. Németh-Sallay for the preparation of the samples, to Dr. L. ervinka and Dr. M. Rozsival for the test of their structure and to Dr. M. Závtová and Dr. I. Gregora for kind cooperation in the index-of-refraction measurements. Very useful comments by Dr, J. Sak are gratefully acknowledged.It is also a pleasure to thank Dr. R. P. Madden for discussion on the later stage of this work.     

Mass resolved angular distribution in helium ion induced fission of233U

Mass resolved fission fragment angular distribution was measured in the 28.5 MeV alpha induced fission of²³³U using recoil catcher technique and direct gamma spectrometry. The angular distribution of 8 fission products were obtained. The angular anisotropies of asymmetric fission products were found to be higher than those of symmetric products indicating a correlation between the fragment angular distribution and the mass distribution.The authors are grateful to Dr. S.K. Kataria and Dr. T. Datta for fruitful discussions. We thank the operation crew of the variable energy cyclotron, Calcutta for their help in carrying out the irradiations. Thanks are due to Dr. P.R. Natarajan, Head of the Radiochemistry Division for his keen interest in the work.     

An improved analysis of temperature autostabilization of ferroelectrics

A graphical method is proposed which permits the investigation of the influence of the parameters of an electrical circuit on the temperature autostabilization of a ferroelectric capacitor connected in this circuit. The region of temperature autostabilization is defined more accurately, and the influence on the value of the temperature autostabilization factor is shown. The influence of the electric circuit must be taken into account when interpreting the experimental results of the study of the temperature autostabilization regime.The authors are indebted to Dr. V. Dvoák, Dr. Z. Málek, and Dr. Ing. J. Mastner for stimulating discussions, and to J. trajblová and other colleagues for friendly help. Special thanks are due to Dr. Ing. V. Zima for critical remarks.     

Ionization waves in nitrogen

The systematic study of the wave phenomena was performed in the nitrogen glow discharge at the pressures from 0·1 to 5 Torr and the currents from 0·1 to 40 mA. From the measurement of the phase and group velocities and Novák's potentials in dependence on pressure and current changes it was concluded, that at least three different varieties of ionization waves exist in this region and three independent dispersion curves were observed. Relations between various types and varieties of ionization waves and their connection with possible ionization processes were studied.The authors are indebted to Dr. O. Stirand for drawing their attention to this problem. Simultaneously they would like to thank Dr. L. Pekrek, Dr. V. Kreji and Dr. K. Maek for many helpful discussions and also Dr. T. Rfitik a for providing the programme for the computer Minsk.     

Positive muon spin precession in magnetic oxides MnO and V2O3; local fields and phase transition

Muon spin precession is observed in the ordered state of antiferromagnetic oxides MnO and V₂O₃. An anomalous temperature dependence of muon precession frequency and the absence of critical behavior atT _N are found in MnO and a hysterisis of the transition temperature is observed in V₂O₃. These results are explained in terras of the crystal distortion of these materials belowT _N.We would like to thank Dr. T. Suzuki, Dr. S. Takagi, Dr. Y. Kuno and Dr. C.Y. Huang for their help in the measurements, and Dr. K. Kosuge and Dr. S. Kachi for providing the specimen of V₂O₃. We are grateful to the financial support from Japan Society for Promotion of Science.     

Finite nuclei in many body theory

An exact method of solution of the Goldstone equation for reaction matrix for finite nuclei is presented. The method can be applied to any double-magic nucleus if the two-nucleon potential does not contain a hard core. The basic properties of the nucleus, i.e. binding energy, nucleon densities, r.m.s. and formfactor are expressed with the help of reaction matrix and certain auxiliary quantities and related to the centre of mass motion.The author would like to express his gratitude to the Rutherford High Energy Laboratory for the possibility to perform this study and especially to Dr G. H.Stafford, Dr G.Manning, Dr R. J. N.Phillips and Dr C. J.Batty for their encouraging interest.     

On ferromagnetic resonance damping in metals

The Landau-Lifshitz damping coefficient is defined in terms of spin-orbital torque correlations in the one-electron model and estimated as a function of the orbital collision frequency. The formal results are compared with previous studies and the results of a numerical calculation for nickel are compared with known experimental data.I would like to thank Dr. L.Hodges for a copy of his thesis and Dr. A. V.Gold, Dr. J. R.Anderson, Dr. V.Dvoák, Dr. Z.Frait and Mr. M.Kolá for valuable discussions at various stages of this work.     

Dynamic behaviour of electric arc gas discharge

The time-dependent energy and circuit equations are solved numerically to obtain temperature profiles, current-voltage characteristics and electric field strength vs axial temperature diagrams in the asymptotic region of a wall-stabilized electric arc operated in nitrogen. Dynamic current-voltage characteristics and transient phenomena of the formation of the stationary state during the spark ignition phase are studied. The arc timeconstant for free decay is computed and compared with approximate analytical results. It is found that for fixed initial conditions the arc response to the variable applied voltage is several times longer than the arc time-constant for free decay.The author is grateful to Dr. Z. Sedláek, Dr. M. Hrabovský and Dr. R. Klíma for their stimulating advices and helpful comments.     

Chemical aspects of muon spin rotation

High energy muons induce radiation damage when they interact with molecules or ions. The chemical reactions expected to occur are summarised, and attention is then given to events likely to give rise to radicals exhibiting muon-electron hyperfine coupling. Addition of muonium atoms to double or treble bonds, which is one example of the way this can occur is considered, and, in particular, the resulting proton-muon hyperfine isotope effect is discussed. Finally, possible chemical models for paramagnetic muon centres in carbon and silicon are outlined.I thank Dr. S. Cox and Dr. A. Hill for helpful discussions.     

Susceptibility of iron films near remanence

Susceptibility in the direction perpendicular to the average magnetization of a not completely saturated polycrystalline film is influenced by the magnetic anisotropy of the crystallites (or defects) and by the energy connected with the non-uniformity of magnetization.The results of measurements on iron films are compared with the simple theory of susceptibility [1] and with a further analysis of the role of anisotropy.The authors thank Dr. J. Kaczér and Dr. E. Feldtkeller for valuable discussions.     

Surface spin waves in ferromagnetic thin films

Surface spin-wave modes are calculated for (100) surface of simple cubic structure. An isotropic part as well as an anisotropic part are introduced in the spin Hamiltonian. The anisotropic factor is allowed to vary on the first two surface layers. Dispersion curves are derived by a Green function formalism.The authors are indebted to Dr A. P. Legrand for his help in numerical calculations and to Dr J. Korringa for his continuous encouragement and suggestions.     

A thermodynamic theory of the cubic-orthorhombic phase transition in boracites

A thermodynamic theory of the cubic-orthorhombic phase transition in boracites is developed. The temperature dependences of dielectric, piezoelectric and elastic constants near the phase transition temperature are derived. Since the parameter of the phase transition is not the polarization, the spontaneous strains and polarization are not related by electromechanical constants. Magnetic properties of boracites are not considered.It is a pleasure to acknowledge many helpful discussions with Dr. V. Janovec, as well as with Dr. J. Fousek, J. Petzelt and F. Smutný of the Institute of Physics of the Czechoslovak Academy of Sciences in Prague.     

Application of iterative deconvolution procedures for evaluation of boron depth profiles

The problem of evaluation of boron depth profiles from measured spectra of alpha particles in¹⁰B(n, alpha)⁷Li nuclear reaction is considered. Two iterative deconvolution procedures are examined which may be applied to profile reconstruction. Both techniques have been tested using artificial spectra and they were found to give satisfactory profile reconstruction. The performance of the deconvolution methods is demonstrated by comparison with the measured data.The authors are grateful to their colleagues Dr. J. Vacík and Dr. L. Jahoda for their help in the course of the measurement.     

A study of traps for current carriers in organic solids The effect of crystallinity on ethyl 2,5-di(anilino)-terephthalate and its oligomer

The dark electric conductivity, photoconductivity, thermostimulated currents (TSC) and space-charge-limited currents (SCLC) were measured on amorphous, polycrystalline and spherulitic layers of ethyl 2,5-di(anilino)terephthalate and of its oligomer. The electric behaviour is considerably influenced by processes of trapping of charge carriers. The activation energy of photoconductivity is determined by the trap depth. The crystalline and spherulitic domains in the amorphous phase form new traps, ca. 0·6 eV deep.The authors wish to thank Dr M. Tlust'áková for her assistance in the preparation of ethyl 2,5-di(anilino)terephthalate, Dr F. Lednický for the microscopic observations, Dr J. Holoubek for the light scattering investigations, Dr K. Ulbert and Dr I.Chudáek for the interest they have taken in this work.     

Thermodynamic theory of finite ferroelectric crystals with surface energy

The phenomenological Landau theory of phase transition is generalized to finite ferroelectric crystals with surface energy. Restrictions of the expansion imposed by the symmetry of the surface are considered, and further analysis is devoted to a special case. The solution in the approximation of constant polarization is discussed. Single domain states of a plate are analysed in greater detail.The authors are very grateful to Dr. V.Janovec and Dr. J.Fousek of the Czechoslovak Academy of Sciences for helpful discussions. Thanks are due to Prof. L.Valenta for the valuable discussions dealing with the magnetical analogical problem.     

Physical properties of sputtered amorphous Ge: The role of the deposition rate

The role of the deposition rate was studied on thin layers of amorphous germanium, prepared by cathode sputtering. Strong influence of this technological parameter on the density, electrical conductivity and optical absorption was found. The dependences observed are discussed in terms of the presence of voids, which influence the properties of a-Ge in their vicinity. The effect of argon and the traces of oxygen in argon is considered.We thank Dr. M. Rozsíval for testing our samples by the electron diffraction and Dr. B. Velický for his interest and helpful discussions.     

Luminescence of AgCl/Mn++ crystals

The temperature dependence of the luminescence spectra and kinetics, the excitation spectra, luminescence polarization, quantum yield of the integral luminescence and paramagnetic resonance of AgCl crystals doped with three concentrations of manganese ions at 77°K were measured and the results are discussed.The author expresses his gratitude to associate professor K. Vacek, Ph.D. for suggesting the work on the above problem and for his help. Thanks are also due to Dr. Krutina and Dr. Sroubek, of the Research Institute of Radio Engineering of the Czechoslovak Academy of Sciences, for enabling the measurement of the spectra of paramagnetic resonance to be carried out in their laboratory.     

The CNDO-MO study of oxygen impurity states in AlN crystal

Deep levels due to oxygen impurity have been theoretically studied by the quasimolecular approach. The calculation of the orbital spectra was performed using the CNDO/2 method. Some important quantities (transition energies, width of valence band, effective charges etc.) were estimated. The results obtained agree qualitatively well with experimental data but quantitatively are still about 20% in error. Some reasons for the above discrepancy are briefly discussed.The authors are very grateful to Dr. J.Kubátová and Dr. S.Paesová for helpful discussions of the experimental investigations of aluminum nitride and to Dr. J.Pastrák for his interest in this work and discussion of results.     

Kinetics of spinodal decomposition in Fe-Si alloys

The spinodal decomposition in the two-phase region of the phase diagram (B₂ + DO₃) of Fe-Si alloys is studied on the basis of the generalized diffusion equation. The configurational free energy is calculated in the Bragg-Williams-Gorsky approximation. The effect of the coherency strain energy is estimated. In the main part of the paper the Langer's method is applied in the investigation of the coarsening rate in Fe-Si system with a good agreement with experimental data in a broad range of annealing times. The limitations of such approach are discussed with respect to the Khachaturyan's theory of the periodic distributions of decomposition products.The author is grateful to Dr. F.Kroupa for his guidance and encouragement during the course of this work, to Dr. S.Libovický and Dr. A.Gemperle for discussions of their latest experimental results.     

The scattered radiation spectrum of a laser and the measurement of the electron concentration in a pulse plasma

The scattered radiation spectrum obtained in probing a high-frequency (hf) pulse plasma with a laser beam is discussed. The presence of satellites is attributed to Raman scattering at plasma vibrations occasioned by electron drift. The procedure, and results of measuring the electron density on the basis of the intensity of scattered radiation are described. Preliminary calibration of the apparatus was carried out by comparison with Rayleigh scattering in air and in argon.In conclusion we should iike to thank Dr. R. A. Demirkhanov for his interest in our study and Dr. I. A. Akhiezer for his useful comments on the results.