6,272 research outputs found
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 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
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