Low-lying bound states of the neutron-rich boron isotopes, ${}^{15}\mathrm{B}$ and ${}^{17}\mathrm{B}$, have been investigated using the ${}^{15,17}\mathrm{B}+{}^{12}\mathrm{C}$ inelastic scatterings at approximately 70 MeV/nucleon. In-beam γ-ray spectroscopy was used to determine the energy levels of the excited states, and the angular distribution of the particle in the inelastic channel populating each state was measured. Two bound states were observed for ${}^{15}\mathrm{B}$, while a new bound excited state was found for ${}^{17}\mathrm{B}$ at $E_x=1.07(1)\hspace{1em}\mathrm{MeV}$ very close to the neutron emission threshold $(S_{2n}=1.39\hspace{1em}\mathrm{MeV})$. The angular distributions for the transitions to these states are well reproduced with $\Delta L^{\pi }=2^{+}$ diffraction patterns. The energy levels and $\Delta L^{\pi }=2^{+}$ are consistent with shell model predictions. The quadrupole deformation lengths for the transitions extracted from the differential cross sections are compared to the shell model, suggesting a strong quenching of the neutron effective charge both for ${}^{15}\mathrm{B}$ and ${}^{17}\mathrm{B}$.

• Received 3 September 2004

DOI:https://doi.org/10.1103/PhysRevC.71.044611