Investigating γ -ray decay of excited C 12 levels with a multifold coincidence analysis

Background: The γ decay of C12 levels above the particle emission threshold plays a crucial role in the production of C12 in astrophysical environments. The Hoyle state is fundamental in the helium-burning phase of red giant stars, while the 9.64-MeV level can be involved in higher temperature explosive environments. Purpose: The aim of this work was to explore the feasibility of measuring the γ-decay widths of the 9.64-MeV state. The experiments were performed at Laboratori Nazionali del Sud of INFN (INFN-LNS), in Catania, using α and proton beams impinging on a carbon target. Methods: The method used consists in the detection of all charged products and γ rays emitted in the reaction, in order to strongly reduce the background. Results: Few events of γ decay of the 9.64-MeV level were observed in the reaction α+C12. Also the decay yield of the Hoyle state was measured in both the measured reactions α+C12 and p+C12. Conclusions: The γ decay of the 9.64-MeV level is, inside error bars, in reasonable agreement with the yield recently reported in literature by measuring the C12 residue. The observed yield is larger than previously accepted lower limit. Also, the decay yield of the Hoyle state seems larger than the one reported in literature, even if the limited statistics do not allow a definite conclusion.