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

We report on the results of the He-3(He-4,2p)He-4 experiment at the un derground accelerator facility LUNA (Gran Sasso). For the first time t he lowest projectile energies utilized for the cross section measureme nt correspond to energies below the center of the solar Gamow peak (E- o=22 keV). The data provide no evidence for the existence of a hypothe tical resonance in the energy range investigated. Although no extrapol ation is needed anymore (except for energies at the low-energy tail of the Gamow peak), the data must be corrected for the effects of electr on screening, clearly observed the first time for the He-3(He-3,2p)He- 4 reaction. The effects are, however, larger than expected and not und erstood, leading presently to the largest uncertainty on the quoted S- b(0) value for bare nuclides (=5.40 MeV b). [S0556-2813(98)04505-1].