S. Karataglidis

Constraints on the spectra of 17,19C

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.

Microscopic model analyses of proton scattering from 12C, 20Ne, 24Mg, 28Si and 40Ca

Abstract Differential cross sections and analyzing powers for elastic proton scattering from, and for inelastic proton scattering to a set of 2 1 + states in, 12 C, 20 Ne, 24 Mg, 28 Si and 40 Ca, and for a set of energies between 35 to 250 MeV, have been analyzed. A g -folding model has been used to determine optical potentials and a microscopic distorted wave approximation taken to analyze the inelastic data. The effective nucleon–nucleon interactions used to specify the optical potentials have also been used as the transition operators in the inelastic scattering processes. Shell and large space Hartree–Fock models of structure have been used to describe the nuclear states. The calculations are in general agreement with the data when the cross sections are in excess of ∼ 1 mb / sr (elastic) and ∼ 0.1 mb / sr (inelastic, 2 1 + ), which suggests that other small effects (such as coupled-channel diagrams) are necessary before agreement between theory and data can be found at large scattering angles. However, the agreement found otherwise gives credibility to the models of structure considered.

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

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 excitation structure of 10B probed by scattering of electrons and of 197 MeV polarized protons

Abstract Differential cross section and analyzing power data from 197 MeV ( p → , p ′ ) scattering and longitudinal and transverse form factors for electron scattering to low lying states in 10B have been analyzed as tests of the structure of the nuclear states when they are described using a no-core ( 0 + 2 ) ℏ ω shell model. While the results obtained from the shell model clearly show the need of other elements, perhaps three-body forces, to explain the observed spectrum, the reasonable level of agreement obtained in the analyses of the scattering data suggest that the wave functions from our shell model with only a two-body potential are credible through the volume of the nucleus. Any changes to the wave functions with the introduction of additional terms in the shell model Hamiltonian, therefore should be relatively minor.

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

Radioactive ion beams of weakly bound nuclei are now being used to investigate properties of nuclear systems well off of the valley of stability. Those ions can and do have low excitation spectra that involve particle unstable resonances. We seek to describe the spectra of the compound systems formed, and the low energy nscattering cross sections for clusters formed coupling a nucleon or an

Very low-energy nucleon-16O coupled-channel scattering: Results with a phenomenological vibrational model

alpha

Coupling to two target-state bands in the study of the n+22 Ne system at low energy

-particle with such weakly bound systems.

Extending MCAS to hypernuclei and radiative-capture reactions

We employ a collective vibration coupled-channel model to describe the nucleon-16O cluster systems, obtaining low-excitation spectra for 17O and 17F. Bound and resonance states of the compound systems have been deduced, showing good agreement with experimental spectra. Low energy scattering cross sections of neutrons and protons from 16O also have been calculated and the results compare well with available experimental data.

MULTI-CHANNEL ALGEBRAIC SCATTERING THEORY AND THE STRUCTURE OF EXOTIC COMPOUND NUCLEI

One theoretical method for studying nuclear scattering and resonances is via the multi-channel algebraic scattering (MCAS) formalism. Studies to date with this method have used a simple collective-rotor prescription to model target states with which a nucleon couples. While generally these target states all belong to the same rotational band, for certain systems it is necessary to include coupling to states outside of that main band. Here, we extend MCAS to allow coupling of different strengths between such states and the rotor band. This is an essential consideration in studying the example examined herein, the scattering of neutrons from 22Ne.

A Predictive Model of Nucleon-Nucleus Scattering Cross Sections

Using a Multi-Channel Algebraic Scattering (MCAS) approach we have analyzed the spectra of two hypernuclear systems, 9 Λ Be and 13 Λ C. We have studied the splitting of the two odd-parity excited levels (1/2− and 3/2− ) at 11 MeV excitation in 13 Λ C, originated by the weak Λ -nucleus spin-orbit force. We have also considered the splittings of the 3/2+ and 5/2+ levels in both 9 Λ Be and 13 Λ C, finding how they originate from couplings to the collective 2 + states of the core nuclei. In both hypernuclei, we suggest that there could be additional low-lying resonant states in the Λ -nucleus continua. From the MCAS approach one can extract also the full coupled-channel scattering wavefunction to be used in the calculation of various transition matrix elements. As a first application, we have considered the EM-transition matrix elements for the capture reaction α + 3 He→7 Be+γ .