A new study for O-16(gamma,alpha)C-12 at the energies of nuclear astrophysics interest: The inverse of key nucleosynthesis reaction C-12(alpha,gamma)O-16

The key reaction C-12(alpha, gamma)O-16 in nuclear astrophysics is difficult to be performed experimentally at low energy because of the Coulomb barrier. But it is different if we use its inverse reaction O-16(gamma, alpha)C-12 because the cross-section of O-16(gamma, alpha)C-12 is almost 100 times larger than the cross-section of C-12(alpha, gamma)O-16 at the same center of mass energy (E-c.m.) based on our study. In the present work, we study the angular distributions and total cross-sections of O-16(gamma, alpha)C-12 which are induced by polarized photon using the resonance theory of low energy reaction. The differential cross-sections as well as E1 and E2 transition cross-sections at low nuclear astrophysics energies are also calculated. The feature of the future Shanghai Laser Electron Gamma Source (SLEGS) facility, a low energy gamma-ray beam line with a high photon flux, is presented. The experiments of O-16(gamma, alpha)C-12 are simulated with a time projection chamber (TPC) and a realistic SLEGS layout. The lowest (E-c.m.), which can be obtained from the simulation, is 0.8 MeV with the 20-30% uncertainty for the one-month beam time of SLEGS. The extracted S factors of C-12(alpha, gamma)O-16 and their statistical uncertainties from the simulation are compared with the existing data and some theoretical calculations. It is shown that the promising O-16(gamma, alpha)C-12 experiment at SLEGS can largely reduce the statistical uncertainties of the C-12(alpha, gamma)O-16 experiment at low energies. (c) 2007 Elsevier B.V. All rights reserved.