  The properties of loosely bound proton-rich nuclei around A = 20 are
investigated within the framework of nuclear shell model. In these nuclei, the
strength of the effective interactions involving the loosely bound proton s1=2
orbit are significantly reduced in comparison with those in their mirror
nuclei. We evaluate the reduction of the effective interaction by calculating
the monopole-baseduniversal interaction (VMU) in the Woods-Saxon basis. The
shell-model Hamiltonian in the sd shell, such as USD, can thus be modified to
reproduce the binding energies and energy levels of the weakly bound
proton-rich nuclei around A = 20. The effect of the reduction of the effective
interaction on the structure and decay properties of these nuclei is also
discussed.
