Structure of the spatial periphery of the isotopes 9,11 Li
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CLEI Theory
Structure of the Spatial Periphery of the Isotopes
9,11
Li
L. I. Galanina* and N. S. Zelenskaya Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, 119991 Received November 20, 2014
Abstract—The cross sections for the (t, p) reactions on the lithium isotopes 9,11 Li were calculated within a theoretical approach based on employing integral equations of the four-body problem in the Alt– Grassberger–Sandhas formalism and the multiparticle shell model. This made it possible to determine the wave functions for the relative motion of various clusters and the nuclear core and to calculate, on their basis, the root-mean-square radii of nuclei of the isotopes 9,11 Li and the spatial structure of their neutron periphery. It is shown that the 9 Li nucleus has virtually no neutron halo. The 11 Li nucleus is a Borromean halo nucleus. The two-neutron periphery of this nucleus manifests itself in both spatial configurations, a dineutron and a cigar one, the respective root-mean-square radii being large (about 6.5 to 6.9 fm). DOI: 10.1134/S1063778815050063
1. INTRODUCTION In [1], we showed that investigation of lithium isotopes in nuclear reactions at moderate energies permits in principle tracing the change in the structure of their neutron periphery and in its size (both in the dineutron and in the cigar configuration [2–4]) upon the sequential addition of neutrons. We found that the size of the neutron periphery changes sharply upon going over from 6 Li(0+ ) (isobaric analog of the 6 Не nucleus) to the Borromean [4, 5] nucleus 11 Li. This change is due primarily to the difference in the binding energy of extra neutrons owing to the effect of Majorana exchange forces [6], which form virtual nucleon clusters in light nuclei. The difference in the structure of the neutron periphery of the 9 Li and 11 Li nuclei is of greatest interest. These two nuclei are both neutron-rich: in relation to the most abundant isotope 7 Li, 9 Li has two extra neutrons, while 11 Li has four extra neutrons. In the ground state, the 9 Li nucleus features five nucleons in the 1p3/2 subshell, so that its total angular momentum is J = 3/2; its isospin is T = 3/2; its Young tableau is f = [432]; and L = 1, 2. The binding energy of one neutron in 9 Li is about 4 MeV; the binding energy of two neutrons is about 6 MeV, which is commensurate with the neutron binding energy in 7 Li (7.25 MeV). The matter radius of R9mLi = 2.31 fm [7] is smaller than R7mLi = 2.41 fm [7, 8]; that is, the 9 Li nucleus is quite a compact system despite the excess of neutrons. *
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The 11 Li nucleus differs sharply from the nucleus of the isotope 9 Li. The former has a low binding energy with respect to decay to 9 Li and two neutrons (it is as low as about 0.38 MeV) and undergoes breakup into three fragments upon excitation, and its m matter radius R11 Li is anomalously large; as determined by various authors, the values of this radius exceed substantially R9mLi and differ significantly from one another. In the following, we wil
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