E1 and E2 cross sections of the 12C(α,γ0)16O reaction using pulsed α beams

We measured the gamma-ray angular distribution from C-12(alpha,gamma(0))O-16 to the ground state of O-16 using a pulsed alpha beam at E-eff=1.6 and 1.4 MeV. True events of C-12(alpha,gamma(0))O-16 were discriminated from background events with a time-of-flight method because of neutrons from C-13(alpha,n)O-16. The obtained gamma-ray spectrum with anti-Compton NaI(Tl) spectrometers showed a characteristic line shape from C-12(alpha,gamma(0))O-16: the Doppler broadening and energy loss of alpha particles in C-12 targets. A Rutherford backscattering spectrum of alpha particles from enriched C-12 targets was measured during beam irradiation to obtain the target thickness and incident alpha-beam intensities. The astrophysical S factors for E1 and E2,S-E1(gamma(0):E-eff) and S-E2(gamma(0):E-eff), derived from the present cross sections are in excellent agreement with the values derived by R-matrix calculation of the beta-delayed alpha spectrum of N-16, and by using the asymptotic normalization constant in the R-matrix fit.