Discrepancy In Doubly Radiative Neutron-Proton Capture

In the present paper we reinvestigate the theoretical cross-section for the doubly radiative n-p capture at thermal energies. We find the upper limit of the ratio R of the two photon emission cross-section to the one photon emission cross-section to be R ⩽ 10−7. This limit is 3 orders of magnitudes larger than a previous calculation, however, still four orders of magnitudes too small compared to a recent experiment which thus remains to be explained.