E 1 and E 2 cross sections of the C 12 ( α , γ 0 ) O 16 reaction using pulsed α beams

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