Spatial measure of reaction size in proton scattering

We introduce a scattering radius, which characterizes a spatial size of the scattering area, from partial wave decompositions of a cross section for a nucleon-nucleus scattering. The coupled-channel calculations of the p + 12 C scattering are performed in the range of E lab = 29.95 MeV to 65 MeV, and the scattering radii for the elastic scattering and the various inelastic channels, which involve the rotational or vibrational excitations and the 3 α excitations in 12 C, are derived from the partial wave decomposition. We found that the scattering radii for the inelastic channels with a well developed 3 a structure are strongly enhanced in comparison to the scattering radius for the elastic and collective channels. This enhancement of the scattering radius for the 3 α channel strongly suggests that the scattering radius is sensitive to a size of the intrinsic structure of the finally excited state in the scattering process.