Measurement of γ rays from giant resonances excited by the C12(p,p') reaction at 392 MeV and 0∘

We measured both the differential cross section (σp,p'=d2σ/dΩdEx) and the γ-ray emission probability [Rγ(Ex)=σp,p'γ/σp,p'] from the giant resonances excited by C12(p,p') reaction at 392 MeV and 0∘, using a magnetic spectrometer and an array of NaI(Tl) counters. The absolute value of Rγ(Ex) was calibrated by using the well-known γ-ray emission probability from C*12(15.11 MeV, 1+,T=1) and O*16(6.9 MeV, 2+,T=0) states within 5% uncertainty. We found that Rγ(Ex) starts from zero at Ex=16 MeV, increases to a maximum of 53.3±0.4±3.9% at Ex=27 MeV, and then decreases. We also compared the measured values of Rγ(Ex) with statistical model calculation based on the Hauser-Feshbach formalism in the energy region Ex=16-32 MeV and discussed the features of γ-ray emission probability quantitatively.