J. P. Svenne

Collective-coupling analysis of spectra of mass-7 isobars : 7He, 7Li, 7Be, and 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.

Two causes of nonlocalities in nucleon-nucleus potentials and their effects in nucleon-nucleus scattering

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

Linking the exotic structure of 17C to its unbound mirror 17Na

\sim 40 - 300

Compound and quasicompound states in low-energy scattering of nucleons from {sup 12}C

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.

Low-energy neutron-{sup 12}C analyzing powers: Results from a multichannel algebraic scattering theory

Abstract The structure of 17C is used to define a nuclear interaction that, when used in a multichannel algebraic scattering theory for the n + C 16 system, gives a credible definition of the (compound) excitation spectra. When couplings to the low-lying collective excitations of the 16C-core are taken into account, both sub-threshold and resonant states about the n + C 16 threshold are found. Adding Coulomb potentials to that nuclear interaction, the method is used for the mirror system of p + Ne 16 to specify the low excitation spectrum of the particle unstable 17Na. We compare the results with those of a microscopic cluster model. A spectrum of low excitation resonant states in 17Na is found with some differences to that given by the microscopic cluster model. The calculated resonance half-widths (for proton emission) range from ∼2 to ∼ 672 keV .

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

A multichannel algebraic scattering theory has been used to study the properties of nucleon scattering from {sup 12}C and of the subthreshold compound nuclear states. The theory accounts for properties in the compound nuclei to {approx}10 MeV. All compound and quasicompound resonances observed in total cross-section data are matched, and, on seeking solutions of the method at negative energies, all subthreshold states in {sup 13}C and {sup 13}N 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-{sup 12}C interactions and, via use of orthogonalizing pseudopotentials, 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.

Weakly-bound rare isotopes with a coupled-channel approach that includes resonant levels

Analyzing powers in low-energy neutron scattering from {sup 12}C are calculated in an algebraic momentum-space coupled-channel formalism, that is, a multichannel algebraic scattering (MCAS) theory. The results are compared with recently obtained experimental data. The channel-coupling potentials have been defined previously to reproduce the total cross section and subthreshold bound states of the compound system. Without further adjustment, good agreement with data for the analyzing powers is obtained.

Isospin mixing of hartree-fock solutions

The fundamental ingredients of the MCAS (multi-channel algebraic scattering) method are discussed. The main feature, namely the application of the sturmian theory for nucleon-nucleus scattering, allows solution of the scattering problem given the phenomenological ingredients necessary for the description of weakly-bound (or particle-unstable) light nuclear systems. Currently, to describe these systems, we use a macroscopic, collective model. Analyses show 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. For this we introduce in the nucleon-nucleus system the Orthogonalizing Pseudo-Potential formalism, extended to collective excitations of the core. The formalism leads one to discuss a new concept, Pauli hindrance, which appears to be important especially to understand the structure of weakly-bound and unbound systems.

Low energy nuclear scattering and sub‐threshold spectra from a multi‐channel algebraic scattering theory

The question of how the scattering cross section changes when the spectra of the colliding nuclei have low-excitation particle-emitting resonances is explored using a multichannel algebraic scattering (MCAS) method. As a test case, the light-mass nuclear target Be, being particle-unstable, has been considered. Nucleon-nucleus scattering cross sections, as well as the spectra of the compound nuclei formed, have been determined from calculations that do, and do not, consider particle emission widths of the target nuclear states. The resonant character of the unstable excited states introduces a problem because the low-energy tails of these resonances can intrude into the sub-threshold, bound-state region. This unphysical behaviour needs to be corrected by modifying, in an energy-dependent way, the shape of the target resonances from the usual Lorentzian one. The resonance function must smoothly reach zero at the elastic threshold. Ways of achieving this condition are explored in this paper.

Linking nuclear masses with nucleon-removal thresholds and the mass of the proton-emitter 17Na

Abstract For nuclei with N > Z isobaric spin invariance is broken in the Hartree-Fock approximation even in the absence of charge dependent forces. A small modification of the usual Hartree-Fock procedure restores this symmetry. The modified procedure (constrained Hartree-Fock) is used to investigate isospin impurities due to the Coulomb interaction.