Understanding the lithium-7(d,n)beryllium-8 reaction at very low energies

The 7Li(d, n)8Be reaction was studied at energies between Ed = 45 keV and 160 keV at Triangle Universities Nuclear Laboratory (TUNL) using the polarized ion source and stopping the beam in the target. The differential cross section, vector analyzing power iT11(theta), and tensor analyzing powers T20(theta), T21(theta), and T22(theta) were measured for the 7Li( d&ar; , n0)8Be and 7Li( d&ar; , n1)8Be reactions at beam energies of E d = 80 keV, 130 keV, and 160 keV. The polarization observables were compared with Distorted Wave Born Approximation (DWBA) and coupled reaction channels calculations. In addition, the Transition Matrix Elements (TMEs) were extracted from the data and compared with the coupled reaction channels predictions. The absolute cross section and astrophysical S factor were also measured for the 7Li(d, n0)8Be and 7Li(d, n1)8Be reactions at beam energies of Ed = 45 keV, 60 keV, and 80 keV. The results of these measurements were compared with previous measurements and the predictions of the DWBA and coupled channels models.;The TME analysis of the polarization data revealed unique solutions for both neutron states, both solutions being dominated by p-waves in the entrance channel. Although DWBA calculations failed to reproduce the data, the coupled reaction channels model using the code FRESCO was able to qualitatively reproduce the data once a large target spin-orbit potential and coupling to the first excited state of the target were included in the calculation. However, the TME solution produced by the FRESCO calculations consisted of predominantly d-waves in the entrance channel for the n0 state and p-waves for the n1 state.;The absolute cross section and S factor measurements confirmed that for the 7Li(d, n0 + n1)8Be reaction, the astrophysical S factor in the low energy region relevant to Big Bang Nucleosynthesis models has zero slope, as assumed by Boyd, et al., with a value of 4 x 103 (+/- 1 x 103) keV b. The average DWBA value of 340 keV b for the n0 state is in good agreement with the measured value of 430 +/- 120 keV b. The FRESCO code predicted an S factor with a positive slope and possibly some higher-order energy dependence in this energy region for the 7Li(d, n0)8Be and 7Li(d, n1)8Be reactions, which does not agree with the experimental results. The S factor results and the TME solution from FRESCO indicate that a more sophisticated theory is necessary to fully explain the data.