α-Resonance structure in 11C studied via resonant scattering of 7Be+α and with the 7Be(α,p) reaction

Background: The resonance structure in 11C is of particular interest with regard to the astrophysical 7Be(α,γ) reaction, relevant at high temperature, and to the α-cluster structure in 11C. Purpose: The measurement was made to determine the unknown resonance parameters for the high excited states of 11C. In particular, the α-decay width can be useful information to discuss the α-cluster structure in 11C. Methods: New measurements of 7Be+α resonant scattering and the 7Be(α,p)10B reaction in inverse kinematics were performed for center-of-mass energy up to 5.5 MeV, and the resonances at excitation energies of 8.9-12.7 MeV in the compound 11C nucleus were studied. Inelastic scattering of 7Be+α and the 7Be(α,p¹)10B^* reaction were also studied with a simultaneous γ-ray measurement. The measurements were performed at the low-energy radioactive ion beam facility CRIB (CNS Radioactive Ion Beam separator) of the Center for Nuclear Study, the University of Tokyo. Results: We obtained excitation functions of 7Be(α,α₀)7Be (elastic scattering), 7Be(α,α₁)7Be^* (inelastic scattering), 7Be(α,p⁰)10B, and 7Be(α,p ¹)10B^*. Many resonances including a new one were observed and their parameters were determined by using an R-matrix analysis. Conclusions: The resonances we observed possibly enhance the 7Be(α,γ) reaction rate but with a smaller magnitude than the lower-lying resonances. A new negative-parity cluster band, similar to the one previously suggested in the mirror nucleus 11B, is proposed.