MEASUREMENTS OF THE COULOMB DISSOCIATION CROSS-SECTION OF 156 MEV LI-6 PROJECTILES AT EXTREMELY LOW RELATIVE FRAGMENT ENERGIES OF ASTROPHYSICAL INTEREST

Coulomb dissociation of light nuclear projectiles in the electric field of heavy target nuclei has been experimentally investigated as an alternative access to radiative capture cross sections at low relative energies of the fragments, which are of astrophysical interest. As a pilot experiment the breakup of 156 MeV Li-6 projectiles at Pb-208 with small emission angles of the alpha-particle and deuteron fragments has been studied. Both fragments were coincidentally detected in the focal plane of a magnetic spectrograph at several reaction angles well below the grazing angle and with relative angles between the fragments of 0-degrees-2-degrees. The experimental cross sections have been analyzed on the basis of the Coulomb breakup theory. The results for the resonant breakup give evidence for the strong dominance of the Coulomb dissociation mechanism and the absence of nuclear distortions, while the cross section for the nonresonant breakup follows theoretical predictions of the astrophysical S factor and extrapolations of corresponding radiative capture reaction cross section to very low c.m. energies of the alpha-particle and deuteron. Various implications of the approach are discussed.