Deuteron Interaction Current in Thermaln−pCapture

The experimental cross section for radiative $n-p$ capture at thermal energies is 10% larger than the theoretical cross section calculated from the impulse terms (free-nucleon isovector magnetic moment). In the present work the pion-exchange contribution is evaluated using the Chew-Low static model amplitude for the photopion process. We demonstrate how the various pieces of the photopion amplitude contribute to the exchange current. The results for Hamada-Johnston, Reid-hard-, and soft-core potentials are 10.5, 10.9, and 11.5% increases, respectively, to the impulse cross section from pion processes. This work verifies the earlier paper of Riska and Brown demonstrating that the 10% discrepancy can be accounted for as a one-pion-interaction effect.