Molecular orbital structures in Be-10 - art. no. 044306

The structure of Be-10 is investigated using a microscopic alpha + alpha n + n model based on the molecular orbit (MO) model. The low-lying states a re characterized by several configurations of valence neutrons, which are c onstructed as combinations of three basic orbits. The model space employed is extended from the traditional MO models, and the orbits are expressed as linear combinations of local Gaussians. Their positions are determined var iationally. Using this model, we reanalyze the structure of Be-9 and show t hat this extension enables us to use the original two-body spin-orbit inter action determined from a scattering phase-shift analysis of alpha-n. In Be- 10, all of the observed positive-parity bands and the negative-parity bands are described within the model. The 0(+) ground state of Be-10 is describe d by a dominant (3/2(-))(2) configuration. The state has a rather large bin ding energy (8.38 MeV from the alpha + alpha + n + n threshold experimental ly), and the mechanism leading to binding, such as a pairing effect and red uction of the kinetic energy between two clusters, is discussed in detail. In spite of this large binding, the a-a clustering in the ground state pers ists due to a coupling effect between the He-6 + alpha configuration and th e He-5 + He-5 configuration, which provides a smooth potential for the vale nce neutrons. The second 0(+) state of Be-10 has a large alpha-alpha struct ure with a (1/2(+))(2) configuration. An enlargement of the alpha-alpha dis tance due to two-valence neutrons along the alpha-alpha axis makes their wa ve function smooth and reduces the kinetic energy drastically. Furthermore, the contribution of the spinorbit interaction due to coupling between the S-z = 0 and the S-z = 1 configurations is important. We also show the media tion effect of two valence neutrons between two alpha clusters.