Analysis of states in 13C and their cluster structure

Accurate studies on 13 C 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 13 C structure, we performed a comprehensive R -matrix fit of α + 9 Be elastic and inelastic scattering data in the energy region E α ≈ 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 9 Be( α n ) 12 C cross section data taken from the literature. This analysis allows to improve the (poorly known) spectroscopy of excited states in 13 C in the E x ≈ 12-17 MeV region, and tentatively suggests the presence of a large-deformation negative-parity molecular band.