3He+4He→7Be astrophysical S factor

We present precision measurements of the He-3+He-4 -> Be-7 reaction in the range E-c.m.=0.33 to 1.23 MeV using a small gas cell and detection of both prompt gamma rays and Be-7 activity. Our prompt and activity measurements are in good agreement within the experimental uncertainty of several percent. We find S(0)=0.595 +/- 0.018 keV b from fits of the Kajino theory to our data. We compare our results with published measurements, and we discuss the consequences for Big Bang Nucleosynthesis and for solar neutrino flux calculations.