Structure of the mirror nuclei Be-9 and B-9 in a microscopic cluster model

The structure of the mirror nuclei Be-9 and B-9 is studied in a microscopic alpha + alpha + n and alpha + alpha + p three-cluster model using a fully antisymmetrized nine-nucleon wave function. The two-nucleon interaction includes central and spin-orbit components together with the Coulomb potential. The ground state of Be-9 is obtained accurately with the stochastic variational method, while several particle-unbound states of both Be-9 and B-9 are investigated with the complex scaling method. The calculation for Be-9 supports the recent identification for the existence of two broad states around 6.5 MeV, and predicts the 3/2(2)(-) and 5/2(2)(-) states at about 4.5 MeV and 8 MeV, respectively. The similarity of the calculated spectra of Be-9 and B-9 enables one to identify unknown spins and parities of the B-9 states. Available data on electromagnetic moments and elastic electron scatterings are reproduced very well. The enhancement of the El transition of the first excited state in Be-9 is well accounted for. The calculated density of Be-9 is found to reproduce the reaction cross section on a carbon target. The analysis of the beta decay of Li-9 to Be-9 clearly shows that the wave function of Be-9 must contain a small component that cannot be described by the simple alpha + alpha + n model. This small component can be well accounted for by extending a configuration space to include the distortion of the cu particle to t + p and h + n partitions.