(γ, π) reaction in C-13

Recently, experimental research was carried out on the angular distribution of (γ, π+) reaction in p shell nuclei by Tohoku University group. Here, analysis is performed on C-13 (γ, π+) B-13 (gr). In the (γ, π+-) reaction, a Kroll-Ruderman term becomes the main term at low energy, and the reaction is a good probe for the research on nuclear structure by sigmatau type excitation. As the treatment of nuclear structure, the analysis of (γ, π) has been carried out, using the transient density adjusting electron scattering phenomenologically. However, all the transient density cannot be determined uniquely, rather (γ, π) reaction and electron scattering give the information on nuclear structure complementarily. Here, how the effect of core polarization studied in detail in electron scattering works in the (γ, π) reaction is investigated. The contribution of exchange current is small in both M1 and E2, and core polarization plays a main role in the region of the momentum transfer of high electromagnetic form factor. The effective Hamiltonian of (γ, π) and the nuclear model adopted are explained. To the angular distribution of C-13 (γ, π+) B-13 (gr), in the front part, M1, and in the back part, E2 contributed mainly. The effect of core polarization improved the difference in the back part by reducing E2. (Kako, I.)