Alpha scattering and capture reactions in the A=7 system at low energies.

Differential cross sections for [sup 3]He-[alpha] scattering were measured in the energy range up to 3 MeV. These data together with other available experimental results for [sup 3]He+[alpha] and [sup 3]H+[alpha] scattering were analyzed in the framework of the optical model using double-folded potentials. The optical potentials obtained were used to calculate the astrophysical [ital S] factors of the capture reactions [sup 3]He([alpha],[gamma])[sup 7]Be and [sup 3]H([alpha],[gamma])[sup 7]Li, and the branching ratios for the transitions into the two final [sup 7]Be and [sup 7]Li bound states, respectively. For [sup 3]He([alpha],[gamma])[sup 7]Be excellent agreement between calculated and experimental data is obtained. For [sup 3]H([alpha],[gamma])[sup 7]Li an [ital S](0) value has been found which is a factor of about 1.5 larger than the adopted value. For both capture reactions a similar branching ratio of [ital R]=[sigma]([gamma][sub 1])/[sigma]([gamma][sub 0])[approx]0.43 has been obtained.