The nucleus is investigated in the three-cluster generator coordinate method, involving several +n+n configurations. The core nucleus is described in the harmonic oscillator model with all possible configurations in the p shell. We present the theoretical energy spectrum of up to 5 MeV excitation energy, and show that the matter densities support a halo structure of the ground state. A strong enhancement of the rms radius with respect to the core is obtained, in agreement with experiment. Our calculation indicates that the (g.s.)+n+n configuration represents 66% only of the total wave function, and that core excitations cannot be neglected. A comparative study of the , , and nuclei is performed with identical conditions of calculation. We also analyze dipole and quadrupole excitations of the ground state, and show that a significant part of the sum rules for soft modes is exhausted at low excitation energies.
- Received 23 February 1995
- Published in the issue dated August 1995
© 1995 The American Physical Society