The Structure of 9Be Nucleus by a Molecular Model. I

Abstract

The nucleus 'Be is investigated by an extended molecular-orbital model and by the generator coordinate method in the simple LCAO approximation. The Hartree-Fock calculations show that a-cluster structures are stable in intrinsic states and the degree of clustering depends crucially on motions of the valence neutron. The generator coordinate calculations give good descriptions of the energy level structures of normal and non-normal parity states in terms of rotational bands. Energy spectra of 'B are given as well. A K"=1/2-band is also predicted. The ground state properties, that is, r.m.s.-radius, Q-moment and .a-moment are reproduced as quite well as electric transitions and charge form factors for the members of the ground rotational band. It is concluded that the molecular model admirably succeeds in systematic explanation of the low energy properties of 'Be. Comparisons are made with the simple shell model and the projected Hartree-Fock calculation by Bouten et al. § I. IntroductionIn the last 15 years, investigations of the cluster structures in light nuclei have been developed st'eadily from molecular viewpoints. It is found that a number of states in the light 4N-selfconjugate nuclei, which include both normal and anomalous states in the shell model versions up to rather high excitation energies, can be successfully explained as some modes of cluster motions."a> Compared with 4N-nuclei, odd-A and odd-odd nuclei have not been studied so well. 2 b> Especially as for 4N + 1-nuclei, a problem of the coupling of a valence nucleon to the motions of clusters has never been fully discussed in any nuclei_ In this and forthcoming papers, 9 Be nucleus is taken up as a typical example in order to study the probelm, because the a-cluster structure of 8 Be is well established_ The experimental data on this nucleus have been accumulated, 3 > not only about nuclear levels but also form factors for electron scattering which are able to give a definite test of model wave functions.As shown in the middle column of Fig. 4, this nucleus has a clear ground rotational band and the moment of inertia is very close to that of 8 Be nucleus (h 2 /2J' =0.49 MeV), which denotes a certain large deformation. Slight et al. 4 > used an extended Nilsson model, which includes major shell mixings up to N + 6, to analyze electromagnetic properties_ They obtained a good fit to the ground n The preliminary results were reported at

Investigation ofBe9from a nonlocalized clustering concept

“…This distribution, in which the extra neutron cannot stay along the z-axis, originates from the restriction of rotational symmetry by the phase factor e iφ Rn . However, this restriction is reasonable because similar distribution has been given by previous GCM calculations [11,17]. The distribution of the extra nucleon spreads more than 6 fm in z direction, which is about double the size of each α cluster.…”

Impurity effects of theΛparticle on the2αcluster states ofBe9andIsaka1, Kimura2 2015Phys. Rev. C22190View full textAdd to dashboardCite

“…From the above point of view, structure of Be hyperisotopes is particularly of interest, since Be isotopes have 2α cluster core surrounded by valence neutrons [25][26][27][28][29][30]. For example, in 9 Be, the first excited state 1/2 + is considered to have 8 Be(0 + ) + n(s 1/2 ) configuration, which can be regarded as a Hoyle analogue state with the replacement of a α particle by a neutron, while the ground state has a relatively compact structure with 8 Be(0 + ) + n(p 3/2 ) configuration.…”

6He-triton cluster states in9Li

“…Many of low-lying states of Be isotopes are understood in a molecular orbital picture where a Be nucleus is considered to consist of 2 α's and valence neutron(s) in molecular orbitals around the 2α core [1][2][3][4][5][6][7][8][9][10][11][12][13]. In highly excited states near the He+He threshold energy of 10 Be and 12 Be, well-developed cluster states have been suggested experimentally and theoretically [7,[12][13][14][15][16][17][18][19][20].…”