Clustering in high-energy excited states of 16O probed by 3He+13C reactions at low energies

Abstract

High energy states in the self-conjugate 16O nucleus were investigated by analyzing 13C(3He,α)12C reactions in the bombarding energy range 1.4–2.2 MeV. Thanks to a low-threshold and high-resolution array, we succeed in measuring cross sections of the decay channel where an α particle is emitted in coincidence with a 12C nucleus in the Hoyle state, leading to 4α particles in the final channel. The analysis of angular distributions indicates the occurrence of two low-spin resonant states, respectively with Jπ=2+ and 3−, at energies of ≈ 24.1 and 24.5 MeV. In this energy window, the observed branching ratios for the transition involving the emission of the Hoyle state are well larger than calculations based on barrier penetration, signaling the possible occurrence of high-energy states in 16O with a large cluster component.

Keywords

• Clustering
• 16O
• Nuclear reactions
• Resonances