Volume 29, Issue 4, July 1998
The role of the spin and orbital components of the nuclear current in forming multipole resonances of light nuclei29(1998); http://dx.doi.org/10.1134/1.953082View Description Hide Description
A microscopic analysis is performed of the contributions of the orbital and spin currents to multipole 1ℏω resonances in the cross sections of excitations of - and -shell nuclei. The dependence of the transverse form factors and their spin and orbital components on the momentum transferred to the nucleus is traced for all single-particle transitions. Effects of the destructive interference of the spin and orbital components are revealed for several transitions from the and shells. A method is proposed for determining the configurational structure of the wave functions of multipole excited states. The dependence of the weighted mean energies of and resonances in the cross sections on the momentum transfer is interpreted as the result of the interplay of the orbital, spin-dipole, and spin-octupole modes in multipole excitations of light nuclei.
29(1998); http://dx.doi.org/10.1134/1.953083View Description Hide Description
This review is devoted to the properties of neutron-rich nuclei of light elements and the problems concerning them which have been of greatest interest in recent years. The reactions used to produce such nuclei are discussed. Special attention is paid to the multinucleon transfer mechanism, used successfully for spectroscopic studies of light exotic nuclei near the neutron drip line. The feasibility of studying the structure of exotic nuclei in reactions involving radioactive beams is discussed.
29(1998); http://dx.doi.org/10.1134/1.953084View Description Hide Description
We investigate how different magnetization distributions interact with an external electromagnetic field. Strong selectivity to the time dependence of the external electromagnetic field arises for particular magnetizations and suggests that it can be used for practical applications. We review the properties of the known charge–current radiationless configurations. The radiation field of toroidal-like time-dependent current configurations is investigated. Infinitesimal time-dependent configurations are found outside which the electromagnetic field strengths disappear but the potentials survive. For a number of time dependences, their finite radiationless counterparts can be found. In these cases topologically nontrivial (unremovable by a gauge transformation) electromagnetic potentials exist outside the sources. The well-defined rule obtained for constructing time-dependent infinitesimal sources suggests the existence of finite nontrivial radiationless sources with a rather arbitrary time dependence. The latter can be used to carry out time-dependent Aharonov–Bohm-like experiments. Examples are given of nonstatic current configurations generating the static electric field and adequately described by the electric vector potential rather than by the scalar one.
29(1998); http://dx.doi.org/10.1134/1.953080View Description Hide Description
The radiance generated in a medium composed of charged classical oscillators is calculated. It is shown that it is essentially collective in nature. The mechanism for the generation of coherent radiation is discussed. The important role of screening, which dramatically changes the nature of the superradiance, is studied. In particular, it is shown that in the well known Dicke limiting case the dipole–dipole interaction between atoms causes the medium to undergo a transition to a unique metastable nonradiating state with zero total dipole moment. In this case the active medium consists of individual localized excitations. It is shown that collective cyclotron radiation arises in a magnetized plasma, which might explain the experimentally observed anomalously large energy transport transverse to the magnetic field.
29(1998); http://dx.doi.org/10.1134/1.953081View Description Hide Description
Mechanisms of backward elastic scattering at energies of 0.5–2 GeV are studied using the 3-and 4-dimensional nonrelativistic diagrammatic technique. In the first step the structure of the nucleus is described using the approximation of the two-body configuration, and then the three-body 5-channel wave function from solving the Faddeev equations is used. It is shown that the inclusion of the three-particle properties of the structure is crucial. Relativistic effects are taken into account using the relativistic quantum mechanics of systems with fixed numbers of particles, and are found to be unimportant for the dominant mechanism. In addition to mechanisms containing information about the structure of the nucleus at small relative internucleon separations, special attention is paid to the mechanism of sequential -pair transfer. This mechanism in fact does not require high-momentum components of the nuclear wave functions in spite of the large momentum transfer, and it dominates under certain kinematical conditions. It is shown that when rescattering is taken into account, this mechanism allows the successful description of the available experimental data on the energy and angular dependence of the differential cross section at without the use of free parameters. The clearly manifested effects due to the component of the wave function of the nucleus and Glauber rescatterings in the initial and final states are displayed. The results of a low-energy analysis using the unitarized -matrix approach are also presented.