Isovector Quadrupole Resonance in ¹³C(γ,n) Reaction

Abstract

The photoneutron cross section for ¹³C was measured in the tagged photon energy range E_γ=17–70 MeV. Substantial forward to backward asymmetry was observed above the giant dipole resonance region. The observed asymmetries were analyzed by the direct and semi-direct model, assuming two isovector E2 resonances, which locate at E_x=30.9±1.5 MeV with Γ=8±6 MeV and E_x=43.2±1.8 MeV with Γ=13±6 MeV. They are identified as the T_< and T_> isospin components of the isovector quadrupole strengths, which exhaust most of the sum rule.