FIRST MEASUREMENT OF A P(N,Y)D REACTION CROSS-SECTION BETWEEN 10-KEV AND 80-KEV

For the first time we have successfully measured the important cross section of the p(n, gamma)d reaction at astrophysically relevant energies between 10 and 80 keV, where the difference in the cross section between old and new calculations is quite large. In the measurement we used a prompt gamma-ray detection method, combined with a pulsed neutron beam, which is crucial for determining the cross section accurately by discriminating small true signals from huge background signals; we also used a recently developed Monte Carlo code for correcting neutron multiple-scattering effects in a sample. The cross sections derived in the present experiment were 318 (25) mu b, 203 (19) mu b, and 151 (7) mu b at neutron energies of 20, 40, and 64 keV, respectively. They do not follow a simple 1/upsilon law and are in good agreement with new calculations. Regarding the primordial abundances of light elements, the present result supports a recent calculation by Smith et al. However, the discrepancy in the deuteron photodisintegration cross sections between the experimental values and a newly calculated one by Ohtsubo et al. remains to be explained.