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

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

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 multi-channel algebraic scattering (MCAS) method. As a test case, the light-mass nuclear target ⁸Be, 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 the exotic structure of 17{}^{17}C to its unbound mirror 17{}^{17}Na

The structure of ${}^{17}$C is used to define a nuclear interaction that, when used in a multichannel algebraic scattering theory for the $n+{}^{16}$C system, gives a credible definition of the (compound) excitation spectra. When couplings to the low-lying collective excitations of the ${}^{16}$C-core are taken into account, both sub-threshold and resonant states about the $n+{}^{16}$C threshold are found. Adding Coulomb potentials to that nuclear interaction, the method is used for the mirror system of $p+{}^{16}$Ne to specify the low-excitation spectrum of the particle unstable $^{17}$Na. We compare the results with those of a microscopic cluster model. A spectrum of low excitation resonant states in ${}^{17}$Na is found with some differences to that given by the microscopic-cluster model. The calculated resonance half-widths (for proton emission) range from $\sim 2$ to $\sim 672$ keV.Comment: 13 pages, 5 figure

Extending MCAS to hypernuclei and radiative-capture reactions

Using a Multi-Channel Algebraic Scattering (MCAS) approach we have analyzed the spectra of two hypernuclear systems, 9ΛBe and 13ΛC. We have studied the splitting of the two odd-parity excited levels (1/2− and 3/2−) at 11 MeV excitation in 13ΛC, 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 9ΛBe and 13ΛC, 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 + 3He→7Be+γ

Re-evaluating low-energy neutron-deuteron elastic scattering using three-nucleon theory

Using a well-established nucleon-nucleon interaction that fits the NN scattering data (Bonn potential), and the AGS form of three-body theory, we perform precise calculations of low-energy neutron-deuteron scattering. There appear to be problems for this system in the ENDF/B-VI.8 (ENDF/B-VI.5 through VI.8) data library, which persist in the newest version, ENDF/B-VII.0. Supporting experimental data in this energy region are rather old (>25 years), sparse and often inconsistent. Our three-body results at low energies, 50 keV to 10 MeV are compared to the ENDF/B-VII.0 and JENDL-3.3 evaluated angular distributions. The impact of these results on calculated reactivity for various critical systems involving heavy water is shown

The spectra of exotic light mass nuclei determined with MCAS theory

A Multi-Channel Algebraic Scattering (MCAS) theory has been used to study the interaction of a nucleon with light-mass nuclei as a coupled-channel problem. The method can be solved for all energies so that bound states as well as resonances of the compound nucleus can be specified, even if the compound nucleus is nucleon unstable. A resonance finding prescription ensures that all resonances of the system can be found no matter how weak and/or narrow. Spectra of mass-7 nuclei and of the proton unstable 15F are discussed, the Coulomb displacement energy considered, and first results on using MCAS details in a radiative capture cross section calculation presented

TEST OF CHARGE SYMMETRY I N n-p ELASTIC SCATTERING AT 480 MeV+

L'expérience en cours à TRIUMF vise à mesurer la différence ƊA entre les puissances d'analyse des neutrons et des protons, An et Ap, en diffusion élastique n-p à 480 MeV.The experiment in progress at TRIUMF measures the difference ƊA between the neutron and proton analyzing powers An, and Ap in n-p elastic scattering at 480 MeV