Structure of low-lying states of 9Ве nucleus

Abstract

Glauber's theory of multiple scattering is applied to the calculation of differential cross sections and polarization characteristics of particle scattering on light nuclei. All calculations were carried out within the framework of a reliable spectroscopic approach to nuclear reactions. Its essence consists in the use of nuclear models that reproduce practically all the spectroscopic characteristics of the nuclei under consideration. These include three-particle models of 6Li and 9Be nuclei, a many-particle shell model for nuclei with А = 6–14, and a particle-hole model of shells for nuclei with А = 15; three-body models for the 8Li and 9Li nuclei and a two-particle αt-model for the 7Li nucleus. As our experience shows, when implementing the spectroscopic approach, when the dominant mechanism of the process is also established, one can not only obtain a description of the main characteristics of the process, but also rely on the predictive nature of the theory. In the present work, the results obtained are supplemented by calculations of the structure of the low-lying 5/2+ and 5/2– levels. This allows us to draw a general conclusion: the negative parity levels in 9Be, in which the valence neutron is in the p state, do not have a halo structure; at the same time, low-lying levels of positive parity, in which the valence neutron passes into the next (2s-1d) shell, have such. A special place is occupied by our recent direct evidence of the halo structure of low-lying excited states of the 9Be nucleus with quantum numbers 1/2+ and 3/2+. Within the framework of the ααn model of the 9-Be nucleus, it was shown that a valence neutron with a high probability is located at 11 fm from the center of gravity of two α-particles, while in the 3/2- ground state this distance is several times smaller. The conclusions about the structure of low-lying levels of 9Be, obtained on the basis of the ααn model, are supported by calculations of p9Be scattering: only taking into account the halo structure makes it possible to reproduce the experimental data on inelastic scattering to positive parity levels.