Search for the rare γ-decay mode in 12C

Excited states in 12C nuclei play a very important role in the nucleosynthesis in the universe. 12C nuclei are synthesized by the triple α reaction. Normally the triple α process proceeds via the state (Hoyle states) at Ex = 7.65 MeV in 12C. However, at high temperature T > 109, the highly excited 3α resonance states such as the state at Ex = 9.64 MeV might play a part of the triple α reaction. Unfortunately, the γ-decay probability of the state has not been determined, therefore we planned to measure 1H(12C, 12Cp) reaction without measuring γ-rays. The test experiment using the solid hydrogen target and GAGG(Gd3Al2Ga3O12) was recently carried out at the cyclotron facility in RCNP. The results of the test experiment are reported in this paper.