We review and analyze the available information on the nuclear-fusion cross sections that are most important for solar energy generation and solar neutrino production. We provide best values for the low-energy cross-section factors and, wherever possible, estimates of the uncertainties. We also describe the most important experiments and calculations that are required in order to improve our knowledge of solar fusion rates. [S0034-6861(98)00704-1]

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The He 3 (a,y)Be 7 reaction has been investigated using gaseous helium targets behind thin nickel foils and using monoenergetic alpha-particle beams with energies from 0.42 to 5.80 MeV. The prompt gamma rays were detected using Nal(Tl) scintillation spectrometers, and the resulting pulse-height spectra were analyzed to determine both the total capture cross section and the branching ratio between the cascade and the crossover transitions as functions of energy. These cross-section measurements have been used to obtain a new value for the zero-energy intercept of the cross-section factor S{E) for this reaction: ^0 = 0.47^0.05 keV-b, and (dS/dE) 0 = -2.8X10" 4 b.

The cross section and branching ratio for 3 He (a,y) 7 Be have been measured from E c#m# = 165 to 1170 keV by counting prompt y rays from a windowless, recirculating, 3 He gas target. Absolute cross sections were also measured at E CmTr)m = 945 and 1250 keV by measuring the 7 Be activity produced in a 3 He gas cell with a Ni entrance foil. The inferred zero-energy intercept is S M (Q) = 0.52± 0.03 keV b. The effect of this extrapolated value on the solar-neutrino problem is discussed.

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