ANISOTROPIC PHONON SYSTEMS IN SUPERFLUID HELIUM

I.N. Adamenko, Yu.A. Kitsenko, K.E. Nemchenko, V.A. Slipko and A.F.G. Wyatt

Full Text :  (1260 kB, Rus.)

Abstract
In the paper a number of remarkable phenomena, which have been recently discovered in anisotropic phonon systems of superfluid ⁴He, are considered. They are the phenomenon of high energy phonon creation by low energy phonon pulse, suprathermal distribution of high energy phonons in long phonon pulses and formation of hot line, which arises in colliding of phonon pulses. Three phonon processes in isotropic and anisotropic phonon systems of superfluid helium at different pressures are investigated. The dependence of three phonon rate on angle, temperature, measure of anisotropy of phonon pulse and pressure is found, what allowed to analyze the interaction picture of two phonon pulses at different intersection angles and pressures. The rate of four phonon interaction in anisotropic phonon systems at arbitrary angles, which determines the creation and decay rates of high energy phonons in the pulse of low energy phonons, is calculated. This allowed to account for the phenomena observed experimentally.

KEY WORDS: phonon, anisotropic system, distribution function, phonon-phonon interaction, relaxation rate.

POLARIZATION OBSERVABLES IN REACTIONS ⁹Be(d,p_o)¹⁰Be AND ⁹Be(d,t_o)⁸Be AT THE LOW DEUTERON ENERGIES AND CONTRIBUTION OF THE DIRECT NEUTRON-TRANSFER MECHANISM

V.D. Sarana, N.A. Shlyahov, U.V. Lyashko

Full Text :  (1350 kB, Rus.)

Abstract
The possibility of the description of the previously obtained experimental data for angular distributions of the differential cross sections and VAP of the reactions ⁹Ве(d,p_o) and ⁹Ве(d,t_o), induced by vector-polarized deuterons with energie from 2,0 to 2,8 MeV, in the framework of DWBA with "measured" optical model parameters in entrance and exit channels without additional variations is considered. Pairs of the optical potential parameter sets, allowing simultaneously reproduce basic tendency in behaviour pattern of cross section and VAP angular distributions for ⁹Ве(d,t_o) and, in addition, proton polarization in ⁹Ве(d,p_o) reactions are discovered. Role of the cut-off in radial integrals and influence of nonlocality and finite range corrections are clarified. It is demonstrated, that predominant mode of these reactions are direct neutron pick-up and stripping. It is possible that characteristic features of the direct process at the low deuteron energies are determined by peculiarities of the low bounded interacting particles in region of influence of their disintegration thresholds.

KEY WORDS: nuclear reaction, beryllium, deuteron, stripping, pick-up, cross section, VAP, proton polarization, DWBA, optical potentials.

INFLUENCE OF CRYSTALS MOSAICITY ON CHARACTERISTICS OF PARAMETRIC X-RAY RADIATION

A.N. Baldin, I.E. Vnukov, D.A. Nechaenko, R.A. Shatokhin

Full Text :  (600 kB, Rus.)

Abstract
The main lack of mosaic crystals in comparison with perfect ones for their using as radiators for generation of parametrical x-ray radiation is the large width of a spectral line. At the same time mosaic crystals provide significant increasing of the radiation observed due to real photons diffraction. The diamond crystal with mosaic factor σ_m~ 0,2 mrad provided almost quadruple gain of the radiation yield obtained at tomsk synchrotron "Sirius". It is shown that mosaic structure weakly affects on the monochromaticity of the radiation if the mosaic factor is less than the collimation angle. Advantages of mosaic crystals for generation of intensive X-ray beams are discussed.

KEY WORDS: parametric X-ray radiation, electron, crystal, mosaicity, radiation yield, diffracted bremsstrahlung, diffraction.

SIMULATION OF NUCLEAR TRANSMUTATION EFFECTS AND THEIR INFLUENCE ON THE INTERMETALLIDE COMPOSITION IN ZIRCONIUM ALLOYS

V.G. Kirichenko, A.I. Kirdin

Full Text :  (700 kB, Rus.)

Abstract
The results of physical metallurgy simulation of nuclear transmutation effects in zirconium alloys are stated. The source materials were the zirconium-based alloys produced by electron-beam melting with additions of iron, niobium and chromium, molybdenum, vanadium, copper and tantalum. The research of model alloys structure and phase composition was carried out with the use of nuclear gamma-resonance spectroscopy. It was found that the microstructure of ternary alloys, in which the transmutation effects were simulated, differs from microstructure of source materials and it is determined by crystallization modes of zirconium binary and ternary alloys and phase formation peculiarities. It was shown that possible modes of phase formation in the modified alloys and the microstructure evolution of such alloys lead (in comparison with source alloys) to irregular and heterogeneous formation of phase precipitates with different composition and structure. In Zr-Fe alloys the main part of iron atoms is bounded in Zr₃Fe and Zr₂Fe phases. In Zr-Fe-V and Zr-Fe-Cr alloys it is bounded accordingly in Zr(Fe,V)₂ and Zr(Fe,Cr)₂ mixed phases. In Zr-Fe-Mo alloys it is bounded in (Zr,Mo)₂Fe and (Zr,Mo)Fe₂ phases. In Zr-Fe-Nb alloys it is bounded in (Zr,Nb)₂Fe and (Zr,Nb)Fe₂ phases. In Zr-Fe-Та alloys it is bounded in (Zr,Та)₂Fe and (Zr,Ta)Fe₂ phases. The crystalline structure and type of the starting intermetallides and those formed after transmutation are different. The ensembles of both kinds of intermetallic particles are characterized by different type of bounding with the zirconium matrix.

KEY WORDS: zirconium alloys, nuclear transmutation, physical metallurgy simulation, evolution of microstructure, phase transformation, intermetallides.

CONSISTENT MODEL FOR INTERACTION OF HIGH-SPIN BOSON AND TWO SPINLESS PARTICLES

E.V. Rybachuk

Full Text :  (340 kB, Rus.)

Abstract
The currents for the interaction of the massive high-spin boson (J ³ 1) with two spinless particles are proposed in a consistent model. The current tensors are derived for the spin J = 1,2,3,4 explicitly. The consistency of the model is determined by two theorems. According to one of them the derived current tensors must be traceless and conserved as well as the field tensors for high-spin boson (HSB). Therefore the equation systems for the components of HSB fields are consistent. According to the second theorem the currents must include the scalar function, which provides the convergence of the double integrals with respect to the HSB momentum components. The integrands are the modulus of the products of the current tensors and the HSB momentum components. It is shown that the scalar function of any one variable (from three possible scalar variables) leads to the divergence of such integrals.

KEY WORDS: higher spin, boson, integral, convergence, interaction, current, consistensy.

MODEL-FREE DETERMINATION OF THE FIELD OF ORDER PARAMETER WITH HELP OF EVOLUTIONARY ALGORITHM

V.Yu. Korda, A.S. Molev, L.P. Korda

Full Text :  (350 kB, Rus.)

Abstract
A new method is proposed to solve the variation problem of searching for the spatially modulated distribution of the field of order parameter, which gives minimum to the extended free energy functional of Ginzburg-Landau type. The method is based on the application of the evolutionary algorithm which provides for evolving the population of the equilibrium order parameter distributions via their smooth deformation. It is shown that the method developed is independent of the a priori model assumptions on the shapes of distributions in question and allows finding the solution of variation problem which gives deeper minimum to the free energy functional than the most successful analytical solutions do.

KEY WORDS: phase transition, order parameter, free energy, evolutionary algorithm.

SIMULATION OF THE GEV ELECTRONS COHERENT RADIATION IN ORIENTED CRYSTALS

V.B. Ganenko, A.A. Greenenko, N.F. Shul’ga, V.I. Truten’

Full Text :  (320 kB, Eng.)

Abstract
It is proposed a method of numerical simulation of the coherent radiation of electrons with energy ~GeV in oriented crystals. The method is based on semi-classical approximation of quantum electrodynamics and dipole approximation, and takes into account both coherent and incoherent effects at the particles scattering, effects of dechanneling and rechanneling at the particles passage through the crystal. The simulation results are in a good agreement with experimental data on radiation spectra of the electrons with energy ~GeV in silicon and diamond crystals for a wide range of the particles angles to the crystal axes.

KEY WORDS: simulation, oriented crystals, coherent radiation, semi classical model, dipole approximation, radiation spectra.

EFFECT OF OXYGEN DEFICIT ON ANISOTROPY OF NORMAL TRANSPORT IN YВa₂Сu₃О_7-x SINGLE CRYSTALS

R.V. Vovk, M.A. Obolenskii, A.A. Zavgorodny, A.V. Bondarenko, M.G. Revyakina, N.N. Chebotaev

Full Text :  (500 kB, Ukr.)

Abstract
The temperature dependence of the longitudinal and transversal electrical resistivity of YВа₂Сu₃О_7-х single crystals have been investigated on a step-by-step decrease in the oxygen contents in the process of thermal treatment. It is found that the anisotropy of the normal electric resistance ρc/ρ_ab(Т) is well described by the universal "law ½" of the thermally activated hopping conduction. The conception dependence of the activation energy has been obtained, which increases as the oxygen contents decrease.

KEY WORDS: anisotropy, YВа₂Сu₃О_7-х single crystals, activation energy, longitudinal and transversal conductivities.

ENERGY DISTRIBUTIONS OF BACKWARD He⁺ INDUCED SECONDARY ELECTRON EMISSION FROM SOME METALS

V. Zhurenko, S. Kononenko, O. Kalantaryan, V. Kolesnik, V. Muratov, V. Filipenko

Full Text :  (360 kB, Rus)

Abstract
Backward electron emission induced by 1-2 MeV He⁺ beams from the surfaces of some metals has been experimentally studied. The following targets were used: silver and titanium foils, massive stainless steel sample. Angle-integrated energy distributions were measured in the energy range of 0-100 eV by means of quasispherical electrostatic retarding field energy analyzer. The distributions are well approximated by piecewise power-law functions: two power-law intervals with junction point energy near 20-35 eV. Power index of the first energy interval is found to depend on ion energy. Consequently, the shape of the distribution changes and mean energy of emission electrons grows as the ion energy increases. At the same time the junction point of piecewise power-law distribution function tends to move to higher energy of secondary electrons.

KEY WORDS: secondary ion-induced electron emission, energy distribution of electrons, energyanalyzer.

THE FEATURES OF AN ELECTROACOUSTICAL CONTROL OF POWER ENERGY DEVICES

S.I. Ivanov

Full Text :  (180 kB, Rus.)

Abstract
The absorption of energy of the powerful current impulses in constructional elements of energy devices gives infringements in their operation down to melting and mechanical fracture. The ultrasonic radiation incipient in the pre-critical situation carries over the information on features of an energy deposition in constructional elements of the device, allowing protecting it from fracture. The making of an ultrasonic protection system demands the registration of features of excitation, propagation and recording of ultrasonic waves raised in this situation. In the represented paper the results of model operation of such case for a reactor on hydrogen fuel are given. The deuterated target was irradiated by powerful low energy electron beams of a field emission. The beginning of fracture of the irradiated target is accompanied by excitation, except thermoelastic stresses, mechanical stresses, connected with emerging of macro defects on a surface of the target. Also, it is pointed out that extra contribution to a filed acoustic emission can be given by reactions of nuclear fusion of deuterium.

KEY WORDS: acoustic radiation, electro acoustical conversion, power energy devices.