Yu. G. Abov

Dynamical neutron diffraction on perfect crystals

The theory of phenomena occurring in the interaction of a thermal-neutron beam with a regular periodic set of nuclei, which represents a perfect crystal, and the results of relevant experimental investigations of such phenomena are described. The development of studies in these realms has led to the emergence of new fields of investigations in neutron optics, such as neutron interferometry and neutron topography. Neutron crystal spectrometers that possess a high angular and a high energy resolution and which serve for studying small-angle and diffuse scattering have been created. The possibilities for developing new theoretical descriptions of dynamical neutron diffraction and for performing new experiments with neutron beams are discussed.

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.

On the history of the institute of theoretical and experimental physics (ITEP, Moscow)

A survey of investigations performed at the Institute of Theoretical and Experimental Physics (ITEP, Moscow) in the realms of low-energy physics from the foundation of the institute to the present time is given.

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.

Investigation of multiple ultrasmall-angle neutron scattering with the aid of a double-crystal diffractometer

A method of multiple small-angle neutron scattering (MSANS), used to obtain information about inhomogeneities of substances, is considered. Experimental schemes and theory of a double-crystal diffractometer intended for measuring multiple small-angle neutron scattering are described. Methods used to approximate MSANS angular distributions at a low concentration of inhomogeneities and based on Moliére’s theory are reviewed. Their applicability is demonstrated for the examples ofMSANS spectra of samples from ferromagnetic iron-nickel alloys, aluminum powders, and high-Tc superconductor ceramic materials. Theoretical and experimental investigations of interference effects that manifest themselves in multiple small-angle neutron scattering on systems containing high concentrations of scatterers are reported.

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.

Neutron Storage in a Magnetic Field

The motion of neutrons in magnetic traps is considered for various cases of neutron polarization. The results of implementing such traps in practice and special features of experiments studying magnetic neutron storage are discussed. The problem of neutron losses during injection via magnetic valves can be solved by conjoining a magnetic trap with a converter of cold neutrons into ultracold ones or with a source of ultracold neutrons. Prospects for expanding neutron-storage experiments by invoking a correlation analysis of neutron decay and by using the transport properties of charged particles in a nonuniform magnetic field are analyzed. In such an investigation, the recording of the storage time of neutrons proper can be supplemented with the detection of decay protons and electrons and with a parallel measurement of the asymmetries of proton and electron emission with respect to the magnetic field. A set of relative measurements permits improving the accuracy of an experimental determination of the neutron lifetime and combining this determination with the determination of correlation coefficients. On this basis, it is possible to find directly the ratio of the weak-interaction constants and the constants themselves. The application of the most advanced reactor and accelerator technologies to subcritical electric nuclear devices optimized for generating cold and ultracold neutrons, along with the use of solid deuterium and superfluid helium, creates preconditions for developing a neutron plant and for launching neutron studies at accelerators. Thus, the work that has been done as a development of V.V. Vladimirskys proposals on magnetic neutron storage is analyzed, and the potential of a further use of ultracold neutrons and magnetic devices for deploying a full-scale precision experiment to study the beta decay of polarized neutrons is demonstrated.