Structure of the spatial periphery of the 11 Li and 11 Be isobars
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CLEI Theory
Structure of the Spatial Periphery of the
11
Li and
11
Bе Isobars
L. I. Galanina* and N. S. Zelenskaya Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, 119991 Russia Received January 21, 2016
Abstract—On the basis of the shell model with an extended basis, the structure of 9 Li–9 Bе to 11 Li– 11 Bе nuclei is examined with allowance for the competition of jj coupling and Majorana exchange forces via considering the sequential addition of neutrons, and the respective wave functions are determined. A formalism for calculating the spectroscopic factor for a dineutron and for individual neutrons in nuclei whose wave functions incorporate the mixing of shell configurations is developed. The reactions 9 Li(t, p)11 Li and 9 Bе(t, p)11 Bе treated with allowance for the mechanisms of dineutron stripping and a sequential transfer of two neutrons are considered as an indicator of the proposed structure of lithium and beryllium isotopes. The parameters of the optical potentials, the wave functions for the bound states of transferred particles, and the interaction potentials corresponding to them are determined from a comparison of the theoretical angular distribution of protons from the reaction 9 Bе(t, p)11 Bе with its experimental counterpart. It is shown that a dineutron periphery of size about 6.4 fm is present in the 11 Li nucleus and that a single-neutron periphery of size about 8 fm is present in the 11 Bе nucleus. DOI: 10.1134/S1063778816040098
1. INTRODUCTION The shell model of nuclei [1] is a commonly recognized tool for studying the structure of light nuclei. The residual interaction of nucleons belonging to the same shell configuration contains both jj-coupling forces and Majorana exchange forces. The coupling forces increase the binding energy of a nucleus and reduce its size. The Majorana forces, which split states of different isospin T , reduce the binding energy of nuclei and expel nucleons to distances in excess of R ∼ 1.3A1/3 . The construction of shell wave functions with allowance for their antisymmetrization in coordinate and spin–isospin spaces (Pauli exclusion principle) in terms of Young tableaux, which take directly into account the effect of Majorana exchange forces, reflects the virtual cluster structure of nuclei [2]. Via examining the filling of proton and neutron subshells on the basis of the shell model with allowance for the competition between jj-coupling forces and Majorana exchange forces, one can obtain deeper insight into the structure of various isotopes and isobars. In the present study, we analyze changes in the physical properties of lithium and beryllium nuclei in response to the sequential addition of neutrons. The ensuing exposition is organized as follows. In the next section, we give a characterization of the *
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shell structure of lithium and beryllium isotopes. In Section 3, we describe a formalism for calculating the spectroscopic factors for the dineutron and neutrons in nuclei whose wave functions include both p
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