Radiative proton capture to discrete states in 12C at 98 and 176 MeV

Abstract

A high-resolution magnetic pair spectrometer for medium energy photons has been used for studies of the exclusive (p, γ) reaction on 11B at 98 and 176 MeV. We present angular distributions of the differential cross section for transitions to the ground and first three excited states of 12C. The distributions from the three lowest lying states are compared with predictions from a microscopic continuum shell-model calculation using a realistic finite-ranged effective interaction with tensor components. Exchange current effects are examined in detail as both Δ(1232) isobar and pion exchange currents are rigorously included. In general, a good theoretical description of the data is obtained. The predominant reaction mechanism involves photon emission by the nucleonic one-body current.