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  • 1
    Electronic Resource
    Electronic Resource
    Investigation of phase transition thresholds by nonlinear transient laser gratings on silicon surfaces (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 3505-3510 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nonlinear transient laser gratings were excited by crossing two 180 ps Nd:YAG laser pulses (355 nm) at the silicon surface. The launched counterpropagating surface acoustic wave trains were detected outside the source with a cw laser probe-beam-deflection setup. Phase transitions occurring within the Gaussian fluence distribution of the grating induced characteristic changes in the amplitude of the corresponding grating oscillations involved and higher harmonics were found in the frequency spectrum. In the molten surface region, the amplitude decreased compared to the thermoelastic excitation, and second-harmonic generation was observed, whereas ablation generated an asymmetric profile with higher amplitudes and even the third harmonic could be detected. An accurate method is introduced to determine the ablation threshold (340 mJ/cm2 for silicon) from the transition of linear to nonlinear behavior in the distorted non-Gaussian amplitude distribution. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372373
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  • 2
    Electronic Resource
    Electronic Resource
    Excitation of higher harmonics in transient laser gratings by an ablative mechanism (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 1640-1642 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laser-induced transient gratings were excited at the surface of an aluminum film by picosecond laser pulses. The counterpropagating surface acoustic waves with a fundamental frequency of 70 MHz that were launched were monitored outside the source region by laser probe beam deflection. The second and third harmonics were observed for ablative interaction of the laser radiation with the aluminum surface. A simple model is presented that describes the effects on the basis of nonlinear photoacoustic signal generation at the source due to a nonsinusoidal driving force. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122231
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  • 3
    Electronic Resource
    Electronic Resource
    Anisotropic effects in surface acoustic wave propagation from a point source in a crystal (2003)
    Springer
    The European physical journal 35 (2003), S. 429-439 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. Strong anisotropic effects in the propagation of surface acoustic waves (SAWs) from a point-like source are studied experimentally and theoretically. Nanosecond SAW pulses are generated by focused laser pulses and detected with a cw probe laser beam at a large distance from the source compared to the SAW wavelength, which allows us to resolve fine intricate features in SAW wavefronts. In our theoretical model, we represent the laser excitation by a localized impulsive force acting on the sample surface and calculate the far-field surface response of an elastically anisotropic solid to such a force. The model simulates the measured SAW waveforms very well and accounts for all experimentally observed features. Using the data obtained for the (111) and (001) surfaces of GaAs, we describe a variety of effects encountered in the SAW propagation from a point source in crystals. The most interesting phenomenon is the existence of cuspidal structures in SAW wavefronts resulting in multiple SAW arrivals for certain ranges of the observation angle. Cuspidal edges correspond to the “phonon focusing” directions yielding sharp peaks in the SAW amplitude. A finite SAW wavelength results in “internal diffraction” whereby the SAW wavefront spreads beyond the group velocity cusps. Degeneration of a SAW into a transverse bulk wave is another strong effect influencing the anisotropy of the SAW amplitude and making whole sections of the SAW wavefront including some phonon focusing directions unobservable in the experiment. The propagation of a leaky SAW mode (pseudo-SAW) is affected by a specific additional effect i.e. anisotropic attenuation. We also demonstrate that many of the discussed features are reproduced in “powder patterns”, a simple technique developed by us earlier for visualization of SAW amplitude anisotropy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1140/epjb/e2003-00295-y
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  • 4
    Electronic Resource
    Electronic Resource
    Elastic scattering of low-energy electrons by a uranium atom: Reliability of theoretical predictions of based on a model description (1997)
    Springer
    Journal of experimental and theoretical physics 84 (1997), S. 669-677 
    Details
    ISSN: 1090-6509
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We used the method of phase functions to solve the radial relativistic Dirac equation and nonrelativistic Schroedinger equation. With these solutions, we investigated the elastic scattering of slow electrons by a uranium atom, and obtained numerical values for the total cross section and elastic scattering phases. In order to check the correctness of the results found from the method of phase functions, in all cases we also solved the Dirac and Schroedinger equations by direct numerical integration. Several types of polarization and exchange potentials were used to simulate the scattering process. We conclude that the strong dependence of the cross section for elastic scattering of an electron by uranium on the shape of the effective potential of the latter at small kinetic energies (E k〈5 eV) makes it impossible to predict the presence or absence of a Ramsauer effect reliably.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.558199
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  • 5
    Electronic Resource
    Electronic Resource
    Studying parity-nonconservation effect in the conversion transition between the levels of the (5/2)± doublet in the 229Pa nucleus (2000)
    Springer
    Physics of atomic nuclei 63 (2000), S. 365-372 
    Details
    ISSN: 1063-7788
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Effects of weak nucleon interaction are calculated for the ground-state doublet of 5/2± levels of the strongly deformed nucleus 229Pa91. A parity-nonconservation effect in the doublet states can be observed in the conversion spectrum for the isomeric transition between the doublet levels. By using a generalized model of the nucleus, the matrix element of the effective one-nucleon weak-interaction potential, which determines the weight of the opposite parity admixture in the doublet components is estimated in the single-particle approximation. The reduced probabilities of the E1 and M1 nuclear transitions between the doublet states are calculated within various models of the deformed nuclear potential. The effect of Coriolis forces on the dipole electric transition in question is considered. The lifetime of the upper doublet state is estimated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.855643
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  • 6
    Electronic Resource
    Electronic Resource
    Parity-nonconservation effect in the helicities of conversion electrons accompanying the (5/2)− → (5/2)+ nuclear transition in the 229Pa nucleus (2000)
    Springer
    Physics of atomic nuclei 63 (2000), S. 724-728 
    Details
    ISSN: 1063-7788
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The ground state of the 229Pa nucleus is a 5/2± doublet with a splitting energy of 220±50 eV. Such levels are peculiar to nuclei in the mass region around A=225 that are characterized by octupole deformations. A direct observation of P-odd effects in this system is of great interest because this can furnish information about the parity-nonconserving nucleon-nucleon potential. The transition between the two doublet states of opposite parities proceeds predominantly through internal conversion; therefore, P-odd mixing can be explored by studying the helicities of the conversion electron. It is shown that the helicities of the 6s 1/2, 6p 1/2, and 6p 3/2 conversion electrons are about 1%, which makes it possible to perform experiments aimed at determining the parameters of the effective parity-nonconserving nuclear potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.855698
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  • 7
    Electronic Resource
    Electronic Resource
    Specific features of the ionization of atmospheric air resulting from radioactive pollution (2000)
    Springer
    Technical physics 45 (2000), S. 137-140 
    Details
    ISSN: 1090-6525
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Specific features of inhomogeneous ionization resulting from radioactive pollution in the lower atmosphere are investigated. A model of track ionization of air is proposed that allows for such elementary processes as kinetics, molecular diffusion, and drift of ions in an electric field. The applicability limits of the model are determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1259585
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  • 8
    Electronic Resource
    Electronic Resource
    Solvent extraction for cleaning phosphoric acid in fertilizer production (1998)
    Springer
    Journal of radioanalytical and nuclear chemistry 229 (1998), S. 111 
    Details
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract Phosphorites of sedimentary origin utilized in manufacturing of fertilizer contain uranium, thorium and products of their radioactive decay, as well as health-endangering compounds of cadmium, arsenic and fluorides. Some of them may transit into the phosphoric acid, when breaking down the phosphorites with sulphuric, acid, and then into the fertilizer. The purpose of the phosphoric acid cleaning is its decontamination from uranium and thorium as well as the removal of toxic cadmium. The above task can be achieved by solvent extraction. The paper presents the results of the extraction of uranium and cadmium from phosphoric acid using polyalkyl phosphasene and trioctyl amine, respectively. The extraction kinetics, equilibrium distribution of uranium and cadmium within the phases, the effect of extractant concentrations and temperature of the process is also discussed. The technological schemes for cleaning phosphoric acid from uranium and cadmium are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02389457
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