The influence of a preliminary deformation (the residual strain ε = 0.65%) and x-ray irradiation to exposure doses of 0-800 R on the frequency dependence of the sound velocity, v(f ), in LiF crystals in the frequency interval from 7.5 to 232.5 MHz and at room temperature has been studied using the pulsed technique. By extrapolating the results obtained for v(f ) to the low-frequency interval and using the well-known theoretical relations, the coefficient of dynamic viscosity B and the dislocation density Λ were found to be independent of the irradiation dose. At the same time, the absolute values of B were found to be lower and the values of Λ higher by an order of magnitude than the corresponding values obtained with the use of the most reliable techniques, such as the methods of high-frequency internal friction and etch pit counting, respectively.

the dynamics of dislocations using the method of amplitude-independent internal friction on different objects of studymetals and alkali-halide crystals was carried out. Revealed promising directions for further experimental work on this problematics. It can be stated that perspective directions for further work in this direction on ionic crystals are as follows. Firstly, it is conducting research on the influence of a magnetic field on the localization of frequency spectra of dislocation absorption of ultrasound in crystals. The presence of modern works convincingly indicates the high sensitivity of dislocation kinetics to the degree of magnetic processing of samples. The processing of the given experiment in the framework of the Granato-Lucke theory will allow us to determine the effect of magnetic processing on the dynamic and structural characteristics of the crystals, and the comparison in terms of the Alshits-Indenbom theory of the indicated data with those obtained earlier in the conditions of change in temperature, degree of pre-deformation and X-irradiation of samples will allow us to draw important conclusions about the activation of the process of dislocation motion by a magnetic field. Secondly, it is execution of thermoactivating analysis for unexplored ionic crystals, first of all, NaCl. Debye's low temperature for already studied crystals-CsJ, KBr, KCl allowed to study the processes of detachment at very high temperatures (up to 430 K). The transition to crystals with higher temperatures of the Debye will necessitate the modernization of experimental equipment for operation at higher temperatures. The relevance of further work in the direction of study of the processes of relaxation and dropping in crystals by the method of amplitude-independent internal friction also remains high.

The problem of diffraction of H-polarized light at normal incidence on an unlimited sequence of infinitely thin metallic strips is solved. A quantum-mechanical approach to the problem of diffraction is applied. Light wave is represented as a flow of particles-photons. Probability of a photon in front of and behind the grating is described by two-dimensional psi-function-single-valued, continuous and restricted, which satisfies the two-dimensional Schrödinger equation. A strict solution of the problem about determination of psi-function of a photon dissipated by the grating is led down to the boundary Riemann-Hilbert problem. The solution is obtained in the view of the convergent infinite system of linear algebraic equations. The system is suitable for any relation between the wavelength and the period of the structure and any relation between the width of a slit and the width of a strip and is convenient for numerical calculations with the help of PC. Analysis of the expressions obtained for psi-function gives the possibility to conclude the following. Photons passed through or reflected by the grating get the discrete values of momentum during the interaction with the grating and deviate at discrete angles which are determined by the obtained expressions. There are intensity maxima in the points where photons come and minima-in the points where photons do not come. As follows from the analysis of the values of the photon momentum, the possible values of the constituent of the photon momentum perpendicular to its initial direction of motion are determined by even values of the "quantum" of momentum which magnitude is determined by the grating period. This result may be examined as a rule of selection of possible values of the perpendicular constituent of the photon momentum. As follows from numerical calculations, the diffraction maxima are located in front of a slit and have some internal structure, depending on the relation between the wavelength and the grating period. When the ratio of the wavelength to the grating period decreases, the diffraction peak turns out to be slightly modulated. When the ratio of the wavelength to the grating period is more than one, the diffraction pattern vanishes and we have homogeneous illuminance.

The dependences of the absorption α and the ultrasound velocity in LiF single crystals with residual deformation ε = 0.65% at 300 K in the range of radiation doses 0...1057 R were studied using the acoustic pulse echo method at a frequency of 7.5 MHz. Based on the results of measurements of the acoustic characteristics, the absolute values of the parameters of the dislocation structure – the average effective length of the dislocation loop L and the dislocation density Λ and their dependences on the irradiation time are determined. The calculated characteristics are compared with the previously obtained results for the high-frequency branch of the damped dislocation resonance and using the selective etching method. The revealed noticeable discrepancy in the values of these parameters is explained by the impossibility of describing a single attenuation mechanism for acoustic measurements carried out in a wide frequency range.

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