• Energy Research

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 8B 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. 54 pages, 20 figures, version to be published in Reviews of Modern Physics; various typos corrected and several updates made

Abstract The d( 3 He,p) 4 He cross section has been measured at E =4.2 to 13.8 keV using the LUNA underground accelerator facility. The experiment was performed to determine the magnitude of the atomic screening effect and to establish values for the energy loss used in data reduction. The observed stopping power of the 3 He ions in the D 2 target is in good agreement with the standard compilation. Using these stopping power values the data lead to an electron-screening potential energy U e = 132±9 eV, which is significantly higher than the estimated value of 65 eV from an atomic-physics model.

Luna is a pilot project initially focused on the 3He(3He, 2p)4He cross section measurement within the thermal energy region of the Sun (15–27 keV). A compact high current 50 kV ion accelerator facility including a windowless gas target system, a beam calorimeter and four detector telescopes has been built, tested and installed underground at Laboratori Nazionali del Gran Sasso. In these conditions, thanks to the cosmic ray suppression, we could attain a background level of less than 1 event per week, a rate similar to the one expected from 3He(3He, 2p)4He at the lower edge of the Sun thermal energy region.

Studies of the charge state distribution of low energy (<1.5 MeV/u), low Z (<13) heavy ions passing through hydrogen and helium gas of varying target pressure have been performed using separate windowless gas target systems at TRIUMF and the University of Naples. Semi-empirical relationships have been deduced to estimate the equilibrium charge state distributions as a function of beam energy. From these distributions, cross-sections for the relevant charge changing reactions have been deduced.