Photonuclear reaction data and γ-ray sources for astrophysics

Direct determination of photoneutron cross sections of astrophysical importance has recently become possible with use of quasi-monochromatic γ beams from laser Compton scattering (LCS) by relativistic electrons at AIST. The astrophysics to be discussed are both stellar and big bang nucleosynthesis: (a) the p-process; (b) the s-process; and (c) radiative capture for light nuclei. The topic (a) is directly related to photonuclear reactions. In the topic (b) for heavy nuclei with high level densities, photoneutron reactions are translated to neutron capture by the statistical model, whereas they are converted to radiative capture by the reciprocity theorem in the topic (c) for light nuclei with low level densities. A new photon source that is ideally suited to the p-process study is under development at SPring-8. A beam of 8 GeV electrons passing through a 10 Tesla superconducting wiggler (SCW) produces high-energy synchrotron radiations with energy spectra equivalent to the Planck distribution at a few billions of Kelvin. This SCW radiation can be used to determine photoreaction rates not only for (γ,n) but for (γ,α) reactions. This paper covers results of the cross section determination experiments with the LCS photons and a prospect of the study of photoreaction rates with the SCW photons. (author)