Compound and quasicompound states in low-energy scattering of nucleons from C12

Abstract

A multi-channel algebraic scattering theory has been used to study the properties of nucleon scattering from 12 C 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 13 C and 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-12 C 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.

Comparison between two methods of solution of coupled equations for low-energy scattering

“…With the test model, set so that a direct comparison between two methods of solving coupled channels problems can be made, we show in Table I, the full spectra that have been obtained using MCAS with and without the OPP and in the zero deformation limit. This table is similar to that given previously [11] and which was found with a matrix of interaction potentials that gave an excellent fit to data. However, it is important to present these values, not only as they are specifically those from the test model we have used, but also as some of the values bear upon conclusions to be drawn from the results shown in Fig.…”

“…The prime effect of including the Pauli principle is to remove numerous spurious states from the spectrum. However, it also changes the underlying structure of what states remain [11]. In that reference, the tracking of states and resonances as deformation is decreased to zero revealed the basic origin of each state and resonance.…”

“…Doing that in a previous study [11] emphasized the need for their elimination from the coupled-channel dynamics.…”

COUPLED-CHANNEL CALCULATION OF BOUND AND RESONANT SPECTRA OF $^9_\Lambda{\rm Be}$ AND $^{13}_\Lambda\rm C$ HYPERNUCLEI

“…When the effects of the Pauli principle were incorporated in nucleon-nucleus dynamics, the method has been shown to describe, consistently, the bound and resonant spectra of normal (zero-strangeness) light mass nuclei. [22][23][24][25] Starting with the properties of spectra of nonstrange nuclei, we consider the modifications to the Hamiltonians in MCAS that are required to describe hyperon-nucleus dynamics. In particular, we analyze lowlying level structures of two p-shell Λ-hypernuclei with regards to the structure of the hypernuclear doublet levels.…”

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

“…12 C As a first application, we considered the scattering of neutrons off 12 C, coupling the ground state of the target to the first two low-lying excitations 2 + 1 (4.43 MeV) 0 + 2 (7.63 MeV), and searched parameters to obtain a description of the resonant spectra and scattering cross sections [ 2,3,4]. However, many deeply-bound spurious states occurred in the bound spectrum, and it was not possible to obtain a consistent description of both bound structure and scattering data with the same CC Hamiltonian.…”