Nuclear astrophysics with radioactive beams at TAMU

A major contribution in nuclear astrophysics is expected now and in the nea r future from the use of radioactive beams. This paper presents an indirect method utilizing radioactive beams to determine the astrophysical S-factor at the very low energies relevant in stellar processes (tens and hundreds of keV) from measurements at energies more common to the nuclear physics la boratories (10 MeV/nucleon). The Asymptotic Normalization Coefficient (ANC) method consists of the determination from peripheral transfer reactions of the single particle wave function of the outermost charged particle (proto n or alpha particle) around a core in its asymptotic region only, as this i s the part contributing to nuclear reactions at very low energies. It can be applied to the study of radiative proton or alpha capture reactio ns, a very important class of stellar reactions. The method is briefly pres ented along with our recent results in the determination of the astrophysic al factor for the proton capture reactions Be-7(p, gamma)B-8 and C-11 (p ga mma)N-12. The first reaction is crucial for the understanding of the solar neutrino production, the second is a reaction that would bypass the mass A = 8 gap in the hot pp chains. Our study was done at tile K500 superconducti ng cyclotron of Texas A&M University (TAMU). Proton transfer reactions with radioactive beams Be-7 and C-11 produced with MARS were measured, as well as proton transfer reactions involving stable partners. We present the expe riments, then discuss the results and the uncertainties arising from the us e of calculated optical potentials between loosely bound radioactive nuclei .