F. S. Dzheparov

Asymptotic behavior of neutron small-angle multiple scattering spectra

The asymptotic behavior of the spectra for large values of the scattering vector for the case of elastic multiple small-angle neutron scattering (SANS) is investigated theoretically and experimentally. An expansion of the spectrum in terms of the reciprocal of the magnitude of the momentum transfer is obtained taking account of the influence of the instrumental line. It is shown that, to within some factor, the leading term of the expansion is identical to the differential single-scattering cross section averaged over a statistical ensemble of particles; several subsequent terms in the expansion are calculated and the range of applicability of the resulting expressions is determined. The asymptotic behavior of the multiple SANS spectrum is measured, using a two-crystal neutron spectrometer, for samples of an HTSC ceramic, the alloy Fe-Ni, and Al powder. The agreement between the experimental results and the theoretical predictions is analyzed.

Interparticle Interference of Neutrons in Multiple Small-Angle Scattering by a Close-Packed Polydisperse System

Small-angle multiple neutron scattering by a disordered polydisperse system with various concentrations of scattering centers is studied experimentally and theoretically. The experiments show that, for high concentrations (specific volume of scatterers ≥30%), interparticle interference of neutron waves plays a significant role and strongly affects the angular distribution of scattered neutrons. The experimental results are qualitatively explained within the framework of the theory allowing for pair correlations in the spatial distribution of scatterers.

Effect of the concentration of inhomogeneities on the multiple small-angle neutron scattering

The interference effects manifested during multiple small-angle neutron scattering (MSANS) on a chaotically arranged close-packed ensemble of scatterers have been studied. MSANS measurements have been performed for mixtures of Al and Ti-Zr alloy powders. It is shown that the results can be satisfactorily described based on a theory that takes into account spatial correlations in the arrangement of powder grains.

Beta-NMR spectroscopy: Modern state and prospects

Fundamentals of the method of beta-NMR spectroscopy are outlined, and basic types of investigations performed thus far and possible new lines of investigations are surveyed.

Investigation of the external-magnetic-field dependence of polarization transfer in a 8Li-6Li disordered nuclear system

Random walks in disorderedmedia are studied by considering the example of the delocalization of nuclear polarization in an ensemble of 8Li beta-active nuclei produced in (n, γ) reactions induced by polarized thermal neutrons in LiF single crystals. The process is initiated by magnetic dipole-dipole interactions. It consists in polarization transfer from a primarily polarized 8Li nucleus to the closest (stable) 6Li nuclei and in subsequent polarizationmigration over 6Li nuclei, the return of the polarization in question to the 8Li nucleus being possible. In order to obtain information about the polarization of 8Li nuclei, the asymmetry of beta radiation from them was measured with respect to the external magnetic field H0. The process was studied until it reached the diffusion asymptotic regime. The concentration of 6Li was varied between 3% and 10%, while the field strength H0 was changed from 200 to 1200 G. It is shown that microscopic theory is in satisfactory agreement with the experimental results obtained in the way outlined above. A comparison with the investigation of the mathematically allied process of the Förster electricdipole transfer of localized excitons is performed.

Magnetic resonance in beta-active nuclei 8Li at the doubled larmor frequency in LiF polycrystals containing dislocations

The nuclear magnetic resonance in beta-active nuclei 8Li at the doubled Larmor frequency in LiF polycrystals is studied before and after treating these polycrystals with an external pressure. A quantitative approach is proposed that makes it possible to calculate the parameters of the resonance line-shape function versus the dislocation structure of crystallites. Data suggesting that the samples under investigation that were subjected to a treatment with an external pressure develop dislocations whose Burgers vectors are parallel are obtained.