We summarize and critically evaluate the available data on nuclear fusion cross sections important to energy generation in the Sun and other hydrogen-burning stars and to solar neutrino production. Recommended values and uncertainties are provided for key cross sections, and a recommended spectrum is given for 8 B solar neutrinos. We also discuss opportunities for further increasing the precision of key rates, including new facilities, new experimental techniques, and improvements in theory. This review, which summarizes the conclusions of a workshop held at the Institute for Nuclear Theory, Seattle, in January 2009, is intended as a 10-year update and supplement to Reviews of Modern Physics 70 (1998) 1265.

The production of the 26 Al radioisotope in astrophysical environments is not understood, in part, because of large uncertainties in key nuclear reaction rates. The 25 Al(p,␥) 26 Si reaction is one of the most important, but its rate is very uncertain as a result of the lack of information on the 26 Si level structure above the proton threshold. To reduce these uncertainties, we have measured differential cross sections for the 28 Si(p,t) 26 Si reaction and determined excitation energies for states in 26 Si. A total of 21 states in 26 Si were observed, including ten above the proton threshold. One new state at 7019 keV was observed, the excitation energies of several states were corrected, and the uncertainties in the excitation energies of other states were significantly reduced. Spins and parities of several states above the proton threshold were determined for the first time through a distorted-wave Born approximation analysis of the angular distributions. These results substantially clarify the level structure of 26 Si.

The fusion reactions 6Li (p, cQ3He, 6Li(d,~)4He, and 7Li(p, c~)4He have been studied over the c.m. energy range E = 10 to 1450 keV. Each reaction involved the use of hydrogen projectiles and LiF solid targets as well as Li projectiles and hydrogen molecular gas targets. In all cases the effects of electron screening on the low-energy fusion cross sections (exponential enhancement) have been observed; the effects are somewhat stronger in the case of atomic p or d projectiles compared to the case of molecular H 2 or D2 gas targets. If isotopic effects on electron screening are negligible, all three reactions should exhibit the same enhancements for each set of experimental techniques. The measurements confirmed this expectation to a large extent.

Abstract. The d(d,n)3He and d(d,p)t fusion reactionshave been studied at center-of-mass energies E = 1.6 to 130 keV using intense beam currents from 30, 100, and 450 kV accelerators in combination with detectors in close and far geometry. The cross sesction ratio, (d,p), approaches unity (within 2%) at low energies; thus there is no experimental evidence for the Oppenheimer-Phillips effect at subcoulomb energies. R(E)=a(d,n)/cr The cross sections of d(d,p)t at E<10 keV show clearevidence for electron screening effects. However, the observed cross section enhancement is significantly larger than can be accounted for from available atomic physics models.