Finite-range nucleon-nucleon interaction in the radiative capture of fast nucleons

Abstract

The direct-semidirect model for nucleon radiative capture has so far been formulated assuming a zero-range nucleon-nucleon interaction. An extension of the theory to finite-range forces is proposed here. The usual δ-function in the interaction is replaced by a range-dependent gaussian function and then the radial form factor in the particle-vibration coupling (responsible for excitation of the E1 and E2 giant resonance states) is derived. Calculations are performed for the 142(p, γ) reaction in the 5–30 MeV energy region. A detailed analysis provides indications on effects related to the interaction range as regards both the E1 and E2 integrated cross sections and the forward-backward asymmetry of the γ-ray angular distributions. Sensitivity to the interaction range shows connections with the proton final-level spin.