Shell-model study of boron, carbon, nitrogen and oxygen isotopes based on monopole-based-universal interaction

Abstract

We study boron, carbon, nitrogen and oxygen isotopes with a newly constructed shell-model Hamiltonian developed from monopole-based-universal interaction ($V_{MU}$). The present Hamiltonian can reproduce well the ground-state energies, energy levels, electric quadrupole properties and spin properties of these nuclei in full psd model space including $(0-3)\hbarω$ excitations. Especially, it correctly describes the drip lines of carbon and oxygen isotopes and the spins of the ground states of $^{10}$B and $^{18}$N while some former interactions such as WBP and WBT fail. We point out that the inclusion of $2\hbarω$ excitations is important in reproducing some of these properties. In the present $(0+2)\hbarω$ calculations small but constant E2 effective charges appear to work quite well. As the inclusion of the $2\hbarω$ model space makes rather minor change, this seems to be related to the smallness of $^{4}$He core. Similarly, the spin g factors are very close to free values. The applicability of tensor and spin-orbit forces in free space, which are taken in the present Hamiltonian, is examined in shell model calculations.