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

Background: The gamma decay of C-12 levels above the particle emission threshold plays a crucial role in the production of C-12 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 gamma-decay widths of the 9.64-MeV state. The experiments were performed at Laboratori Nazionali del Sud of INFN (INFN-LNS), in Catania, using alpha and proton beams impinging on a carbon target.Methods: The method used consists in the detection of all charged products and gamma rays emitted in the reaction, in order to strongly reduce the background.Results: Few events of gamma decay of the 9.64-MeV level were observed in the reaction alpha + C-12. Also the decay yield of the Hoyle state was measured in both the measured reactions alpha + C-12 and p + C-1(2).Conclusions: The gamma decay of the 9.64-MeV level is, inside error bars, in reasonable agreement with the yield recently reported in literature by measuring the C-12 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.