RadiativenpCapture and Meson Exchange Currents

The experimental cross section for radiative $\mathrm{np}$ capture is 334.2±0.5 mb. Theoretical calculations to date yield a result about 10% lower. In this work we calculate a number of mesonic exchange currents, using a simple phenomenological method and nonrelativistic wave functions. We obtain an increase of about 2-3%, almost entirely due to $\pi$ exchange. Since this is numerically too small to resolve the discrepancy, we discuss other possible contributions to the cross sections. A review section is included in which we discuss previous work on the impulse approximation and the meson exchange effect; no discrepancies remain between the numerically accurate theoretical treatments, and the errors in the remaining treatments are discussed.