The proton-rich nucleus 23Al has a ground state just 123 keV below the proton drip-line, and as a result comparatively little is known experimentally about its properties, as with many such nuclei. Theoretical investigations have tended to model exclusively the ground and first one to three excited states known. In this paper, we theoretically model most of the known spectrum, and predict what states may as yet be unobserved. We use the multichannel algebraic scattering (MCAS) method to describe states as resonances of a valence proton coupled to a 22Mg rotor core. Six states with low-excitation energies and defined J are matched, and we make the first prediction of the properties of four others and propound the possible existence of several more. PACS numbers: 21.10.Ft, 21.60.Ev, 25.40.-h Submitted to: J. Phys. G: Nucl. Phys. Structure of Al from a multi-channel algebraic scattering model based on mirror symmetry 2

Recently, new high-precision data reconfirmed the existence of narrow resonances in the p+ 14 O cross section, first predicted by the multi-channel algebraic scattering (MCAS) theory of light-mass, low-energy scattering and later found by other experimental means. Prompted by this and a decade of extension to the method, we have updated the original MCAS study. Additionally, we use MCAS to interpret the low-energy spectrum of 19 F, which has an interesting structure that appears to stem from clusterisation, and we compare the results of several types. As only early, small-basis shell model investigations of this spectrum exist, we also perform a complete (0 + 2) ħω calculation. MCAS is well suited to these studies, having the advantage of accounting for the Pauli principle between the nucleons of the clusters, and so spurious states of the compound nucleus are removed.

In a previous letter (Phys. Rev. Lett. 96, 072502 (2006)), the multi-channel algebraic scattering (MCAS) technique was used to calculate spectral properties for proton-unstable $^{15}$F and its mirror, $^{15}$C. MCAS achieved a close match to the then-new data for $p+^{14}$O elastic scattering and predicted several unusually narrow resonances at higher energies. Subsequently, such narrow resonance states were found. New cross section data has been published characterising the shape of the $J^\pi =\frac{1}{2}^-$ resonance. Herein we update that first MCAS analysis and its predictions. We also study the spectra of the set of mass-15 isobars, ${}^{15}$C, ${}^{15}$N, ${}^{15}$O, and ${}^{15}$F, using the MCAS method and seeking a consistent Hamiltonian for clusterisation with a neutron and a proton, separately, coupled to core nuclei ${}^{14}$C and ${}^{14}$O.

A multi-channel algebraic scattering (MCAS) method has been used to solve coupled sets of Lippmann-Schwinger equations for the \( \alpha + {}^{6}{\rm He}\) cluster system, so finding a model spectrum for 10Be to more than 10MeV excitation. Three states of 6He were included and the resonance character of the two excited states taken into account in finding solutions. A model Hamiltonian has been found that gives very good agreement with the known bound states and with some low-lying resonances of 10Be . More resonance states are predicted than those which have been observed as yet. The method also yields S -matrices which we have used to evaluate low-energy 6He - \( \alpha\) scattering cross sections. Reasonable reproduction of low-energy differential cross sections and of energy variation of cross sections measured at fixed scattering angles have been found. Enlarging the channel space by including two higher energy states of 6He , assuming values for their spin-parities, leads to an enlarged spectrum for 10Be in which the number and distribution of resonances show similarity to the known spectrum.

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.

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.

The proton-rich nucleus 23Al has a ground state just 123 keV below the one-proton emission threshold, and as a result comparatively little is known experimentally about its properties, as with many such nuclei. Theoretical investigations have tended to model exclusively the ground and first one to three excited states known. In this paper, we theoretically model most of the known spectrum, and predict what states may as yet be unobserved. We use the multichannel algebraic scattering method to describe states as resonances of a valence proton coupled to a Mg-22 rotor core. Six states with low-excitation energies and defined J(pi) are matched, and we make the first prediction of the properties of four others and propound the possible existence of several more.

The spectra of nucleon-nucleus mirror systems allow examination of charge symmetry breaking in nucleon-nucleus interactions. To date, such examination has been performed with studies using microscopic models of structure. Herein we seek characterisation with a coupled-channel model in which the nucleon-nucleus interactions are described using a collective model prescription with the Pauli principle taken into account. The neutron-nucleus Hamiltonian is chosen to give the best match to the compound system spectrum, with emphasis on finding the correct ground state energy relative to the neutron-nucleus threshold. The Coulomb interactions for the proton-nucleus partner of a mirror pair are determined using charge distributions that match the root-mean-square charge radii of the nuclei in question. With the Coulomb interaction so defined modifying the neutron-nucleus Hamiltonian, we then predict a spectrum for the relevant proton-nucleus compound. Discrepancies in that resulting spectrum with measured values we tentatively ascribe to charge-symmetry breaking effects. We consider spectra obtained in this way for the mirror pairs 13C and 13N, 15C and 15F, and 15O and 15N, all to ∼ 10 MeV excitation.

The Multi-Channel Algebraic Scattering (MCAS) method for the description of nucleon-nucleus scattering has been used with a (collective) rotational model of structure describing the target. The success of that model, when incorporating the Pauli Principle in the interactions describing the scattering and the formation of the compound systems, has been quite good. We extend that method to include the vibrational model in describing the target states, and apply the method to the scattering of low-energy nucleons from oxygen isotopes. Preliminary results for neutron scattering from O-16, leading to states in O-17 will be reported.

A multi-channel algebraic scattering (MCAS) method has been used to obtain spectra of a number of light-mass nuclei, which are treated as a two-cluster system, here specifically a nucleon plus nucleus. To date, collective models have been used to specify the interactions between the nucleon and low-lying states of the nucleus that form the compound. For the case of the carbon isotopes, these studies have been complemented by sufficiently complex and complete shell-model calculations. Comparisons with the multi-ħω shell-model results provide new insights into the validity of those from MCAS.

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 multi-channel algebraic scattering (MCAS) method has been used to solve coupled sets of Lippmann-Schwinger equations for α+nucleus systems to find spectra of the compound systems. Low energy spectra for ^12C, ^16O, and ^20Ne are found with the systems considered as the coupling of an α particle with low-excitation states of the core nuclei, ^8Be, ^12C, and ^16O, respectively. Collective models have been used to define the matrices of interacting potentials. Quadrupole (and octupole when relevant) deformation is allowed and taken to second order. The calculations also require a small monopole interaction to provide an extra energy gap commensurate with an effect of strong pairing forces. The results compare reasonably well with known spectra given the simple collective model prescriptions taken for the coupled-channel interactions. Improvement of those interaction specifics in the approach will give spectra and wave functions suitable for use in analyses of cross sections for α scattering and capture by light-mass nuclei; reactions of great importance in nuclear astrophysics.

A multi-channel algebraic scattering (MCAS) method has been used to obtain spectra of a number of light-mass nuclei, which are treated as a two-cluster system, in these cases a nucleon plus nucleus. The MCAS method gives both sub-threshold and resonance states of the nuclei in question. To date, collective models have been used to specify the interactions between the nucleon and low-lying states of the nucleus that form the compound. For the case of the carbon isotopes, these studies have been complemented by sufficiently complex and complete shell-model calculations. Comparisons with the shell model results provide new insights into the validity of those from MCAS.

By performing studies of the structure of the spectra of mass-17 nuclei we discuss specific aspects of the Multi-Channel Algebraic Scattering (MCAS) method. We devote particular attention to the comparison with results from large-scale shell-model calculations, the treatment of Pauli-forbidden or -hindered states, and to the collective/coupled nature of the states obtained in our model. By using different shell-model spaces as platform to assess the MCAS method, we question statements raised recently about the validity of this method on the basis of a small-scale shell-model approach.

The structure of C-17 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 C-16-core are taken into account, both subthreshold 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 Na-17. We compare the results with those of a microscopic cluster model. A spectrum of low excitation resonant states in Na-17 is found with some differences to that given by the microscopic cluster model. The calculated resonance half-widths (for proton emission) range from similar to 2 to similar to 672 keV. (C) 2012 Elsevier B.V. All rights reserved.

With the growing interest in masses of nuclei near the drip lines, and especially for those beyond the drip lines, we take a survey of mirror systems near the drip lines, where one of the mirror pair is unbound. Various methods are followed by which their masses may be determined. As an example, we consider the mass of Na-17, and its energy relative to the p+Ne-16 threshold.