Abstract
We present the first ab initio structure investigation of the loosely bound nucleus, together with a study of the lighter isotope . The nuclear structure of these isotopes is particularly interesting because of the appearance of a parity-inverted ground state in . Our study is performed in the framework of the ab initio no-core shell model. Results obtained using four different, high-precision two-nucleon interactions, in model spaces up to , are shown. For both nuclei, and all potentials, we reach convergence in the level ordering of positive- and negative-parity spectra separately. Concerning their relative position, the positive-parity states are always too high in excitation energy, but a fast drop with respect to the negative-parity spectrum is observed when the model space is increased. This behavior is most dramatic for . In the largest model space we were able to reach, the level has dropped down to become either the first or the second excited state, depending on which interaction we use. We also observe a contrasting behavior in the convergence patterns for different two-nucleon potentials and argue that a three-nucleon interaction is needed to explain the parity inversion. Furthermore, large-basis calculations of and are performed. This allows us to study the systematics of the position of the first unnatural-parity state in the isotone and the isobar. The run in the model space involves a matrix with dimension exceeding , and is our largest calculation so far. We present results on binding energies, excitation spectra, level configurations, radii, electromagnetic observables, and overlap functions.
5 More- Received 10 December 2004
DOI:https://doi.org/10.1103/PhysRevC.71.044312
©2005 American Physical Society