Analysis of states in 13C and their cluster structure

Abstract

Accurate studies on 13C spectroscopy have great impact in the present understanding of the role played by extra-neutrons in stabilizing α-cluster structures formed in light nuclei. Carbon-13 is in fact the simplest systems that can be formed by adding a neutron to make a triple-α molecular-like structure. The accurate spectroscopy of excited states at energies above the α emission threshold is fundamental to benchmark the calculations of theoretical models aiming to describe clustering in light nuclei.To improve our knowledge of 13C structure, we performed a comprehensive R-matrix fit of α+9Be elastic and inelastic scattering data in the energy region Eα ≈ 3:510 MeV at several backward polar angles. To carefully determine the partial decay widths of states above the α-decay threshold we included in the fit also 9Be(α n)12C cross section data taken from the literature. This analysis allows to improve the (poorly known) spectroscopy of excited states in 13C in the Ex ≈ 12-17 MeV region, and tentatively suggests the presence of a large-deformation negative-parity molecular band.