Large-basis shell-model calculations for p-shell nuclei

Results of large-basis shell-model calculations for nuclei with A=7-11 are presented. The effective interactions used in the study were derived microscopically from the Reid93 potential and take into account the Coulomb potential as well as the charge dependence of T=1 partial waves. For A=7, a $6\hbar\Omega$ model space was used, while for the rest of the studied nuclides, the calculations were performed in a $4\hbar\Omega$ model space. It is demonstrated that the shell model combined with microscopic effective interactions derived from modern nucleon-nucleon potentials is capable of providing good agreement with the experimental properties of the ground state as well as with those of the low-lying excited states.Comment: 17 pages. REVTEX. 16 PostScript figure

Three-body resonances in He-6, Li-6, and Be-6, and the soft dipole mode problem of neutron halo nuclei

Using the complex scaling method, the low-lying three-body resonances of $^6$He, $^6$Li, and $^6$Be are investigated in a parameter-free microscopic three-cluster model. In $^6$He a 2$^+$, in $^6$Li a 2$^+$ and a 1$^+$, and in $^6$Be the 0$^+$ ground state and a 2$^+$ excited state is found. The other experimentally known 2$^+$ state of $^6$Li cannot be localized by our present method. We have found no indication for the existence of the predicted 1$^-$ soft dipole state in $^6$He. We argue that the sequential decay mode of $^6$He through the resonant states of its two-body subsystem can lead to peaks in the excitation function. This process can explain the experimental results in the case of $^{11}$Li, too. We propose an experimental analysis, which can decide between the soft dipole mode and the sequential decay mode.Comment: REVTEX, Submitted to Phys. Rev. C, 12 pages, 2 postscript figures are available upon request. CALTECH, MAP-16