Collective-coupling analysis of spectra of mass-7 isobars: ^7He, ^7Li, ^7Be, ^7B

A nucleon-nucleus interaction model has been applied to ascertain the underlying character of the negative-parity spectra of four isobars of mass seven, from neutron-- to proton--emitter driplines. With one single nuclear potential defined by a simple coupled-channel model, a multichannel algebraic scattering approach (MCAS) has been used to determine the bound and resonant spectra of the four nuclides, of which ^7He and ^7B are particle unstable. Incorporation of Pauli blocking in the model enables a description of all known spin-parity states of the mass-7 isobars. We have also obtained spectra of similar quality by using a large space no-core shell model. Additionally, we have studied ^7Li and ^7Be using a dicluster model. We have found a dicluster-model potential that can reproduce the lowest four states of the two nuclei, as well as the relevant low-energy elastic scattering cross sections. But, with this model, the rest of the energy spectra cannot be obtained.Comment: Extended version published in Phys. Rev. C, 16 pages and 5 figure

Role of the Pauli principle in collective-model coupled-channels calculations

A multi-channel algebraic scattering theory, to find solutions of coupled-channel scattering problems with interactions determined by collective models, has been structured to ensure that the Pauli principle is not violated. By tracking the results in the zero coupling limit, a correct interpretation of the sub-threshold and resonant spectra of the compound system can be made. As an example, the neutron-12C system is studied defining properties of 13C to 10 MeV excitation. Accounting for the Pauli principle in collective coupled-channels models is crucial to the outcome.Comment: 4 pages, 1 figure, version appearing in Phys. Rev. Let

Non-localities in nucleon-nucleus potentials

Two causes of non-locality inherent in nucleon-nucleus scattering are considered. They are the results of two-nucleon antisymmetry of the projectile with each nucleon in the nucleus and the dynamic polarization potential representation of channel coupling. For energies $\sim 40 - 300$ MeV, a g-folding model of the optical potential is used to show the influence of the knock-out process that is a result of the two-nucleon antisymmetry. To explore the dynamic polarization potential caused by channel coupling, a multichannel algebraic scattering model has been used for low-energy scattering.Comment: 12 pages, 11 figures, submitted to EPJ

Particle-unstable light nuclei with a Sturmian approach that preserves the Pauli principle

Sturmian theory for nucleon-nucleus scattering is discussed in the presence of all the phenomenological ingredients necessary for the description of weakly-bound (or particle-unstable) light nuclear systems. Currently, we use a macroscopic potential model of collective nature. The analysis shows that the couplings to low-energy collective-core excitations are fundamental but they are physically meaningful only if the constraints introduced by the Pauli principle are taken into account. The formalism leads one to discuss a new concept, Pauli hindrance, which appears to be important to understand the structure of weakly-bound and unbound systems.Comment: 5 pages, 2 figures, 1 table, contribution to proceedings of "18th International IUPAP Conference on Few-Body Problems in Physics," Santos, Brazil, August 21-26, 200

Compound and quasi-compound states in low-energy scattering of nucleons from 12C

A multi-channel algebraic scattering theory has been used to study the properties of nucleon scattering from 12C and of the sub-threshold compound nuclear states, accounting for properties in the compound nuclei to ~10 MeV. All compound and quasi-compound resonances observed in total cross-section data are matched, and on seeking solutions of the method at negative energies, all sub-threshold states in 13C and 13N are predicted with the correct spin-parities and with reasonable values for their energies. A collective-model prescription has been used to define the initiating nucleon-12C interactions and via use of orthogonalizing pseudo-potentials, account is made of the Pauli principle. Information is extracted on the underlying structure of each state in the compound systems by investigating the zero-deformation limit of the results.Comment: 21 pages, 12 figures, 7 table