P. R. Fraser

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

Coupled-channel evaluations of cross sections for scattering involving particle-unstable resonances.

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.

Constraints on the spectra of 17,19C

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 .

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

How does the scattering cross section change when the colliding bound-state fragments are allowed particle-emitting resonances? This question is explored in the framework of a multichannel algebraic scattering method of determining nucleon-nucleus cross sections at low energies. Two cases are examined, the first being a gedanken investigation in which n + 12C scattering is studied with the target states assigned artificial widths. The second is a study of neutron scattering from 8Be, a nucleus that is particle unstable. Resonance character of the target states markedly varies evaluated cross sections from those obtained assuming stability in the target spectrum.

Importance of resonance widths in low-energy scattering of weakly bound light-mass nuclei

Abstract Diverse means are used to investigate the spectra of the radioactive, exotic ions, 17,19 C. First, estimates have been made using a shell model for the systems. Information from those shell model studies were then used in evaluating cross sections of the scattering of 70 A MeV 17,19 C ions from hydrogen. Complementing those studies, a multichannel algebraic scattering (MCAS) theory for n + 16,18 C coupled-channel problems has been used to identify structures of the compound systems. The results show that the shell model structure assumed for these ions is reasonable with little need of effective charges. The conditions that two excited states exist within a few hundred keV of the ground state places some restriction upon the structure models. Other positive parity states are expected in the low-lying spectra of the two nuclei.

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.

Effective two-body model for spectra of clusters of H 2, H 3, He 3, and He 4 with He 4, and H 2 - He 4 scattering

What effect do particle-emitting resonances have on the scattering cross section? What physical considerations are necessary when modeling these resonances? These questions are important when theoretically describing scattering experiments with radioactive ion beams which investigate the frontiers of the table of nuclides, far from stability. Herein, a novel method is developed that describes resonant nuclear scattering from which centroids and widths in the compound nucleus are obtained when one of the interacting bodies has particle unstable resonances. The method gives cross sections without unphysical behavior that is found if simple Lorentzian forms are used to describe resonant target states. The resultant cross sections differ significantly from those obtained when the states in the coupled channel calculations are taken to have zero width, and compound-system resonances are better matched to observed values.

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

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. Positive (scattering) and negative (sub‐threshold) solutions can be found to predict both the compound nucleus sub‐threshold spectrum and all resonances due to coupled channel effects that occur on a smooth energy varying background.

Role of Target Resonances In Low-energy nucleon and α Interactions with Weakly-bound Nuclei

Four light-mass nuclei are considered by an effective two-body clusterisation method;