THE CROSS-SECTION OF HE-3(HE-3,2P)HE-4 MEASURED AT SOLAR ENERGIES

We report on the status of the He-3(He-3,2p)He-4 experiment at the und erground accelerator facility LUNA (Gran Sasso). The lowest projectile energies for the measured cross section correspond already to energie s below the center of the solar Gamow peak (E-0=22 keV). The data prov ide no evidence for the existence of a hypothetical resonance in the e nergy range investigated. Although no extrapolation is needed anymore (except for energies at the low-energy tail of the Gamow peak), the da ta must be corrected for the effects of electron screening, clearly ob served the first time for the He-3(He-3,2p)He-4 reaction. The effects are however larger than expected and not understood, leading presently to the largest uncertainty on the quoted S(0) value for bare nuclides (=5.40 MeVb).