Elastic scattering of the proton drip-line nucleus F-17

Journals published by the American Physical Society can be found at http://publish.aps.org/Precision data have been obtained for the elastic scattering of F-17 on C-12 and N-14 at 10 MeV/nucleon to clarify the reaction mechanism for loosely bound nuclei at low energies and to assess the validity of a double-folding procedure to predict optical model potentials for use in indirect methods for nuclear astrophysics. The double-folding procedure incorporates density and energy-dependent effective nucleon-nucleon interactions with realistic densities consistent with experimentally determined asymptotic normalization coefficients. The derived potentials provide an excellent description of the data and point to a complete dominance of absorption at the barrier. A semiclassical analysis in terms of multireflection barrier-internal barrier series expansion of the scattering amplitude shows that only the barrier component survives in the scattering process, pointing to the peripheral character of the reactions

New limits for the F-18(p,alpha)O-15 rate in Novae

The degree to which the (p, gamma) and (p, alpha) reactions destroy F-18 at temperatures similar to 14x10(8) K is important for understanding the synthesis of nuclei in nova explosions and for using the long-lived radionuclide F-18, a target of gamma ray astronomy, as a diagnostic of nova mechanisms. The reactions are dominated by low-lying proton resonances near the F-18+p threshold (E-x=6.411 MeV in Ne-19). To gain further information about these resonances, we have used the d (F-18,p)F-19 neutron transfer reaction to selectively populate corresponding mirror states in F-19. The results would suggest F-18(p, gamma)Ne-19 and F-18(p, alpha)O-15 reaction rates that are 2-3 times lower than reported previously

New constraints on the F-18(p, alpha)O-15 rate in novae from the (d, p) reaction

The degree to which the (p, gamma) and (p, alpha) reactions destroy F-18 at temperatures (1-4) x 10(8) K is important for understanding the synthesis of nuclei in nova explosions and for using the long-lived radionuclide F-18, a target of gamma-ray astronomy, as a diagnostic of nova mechanisms. The reactions are dominated by low-lying proton resonances near the F-18+p threshold (E-x = 6.411 MeV in Ne-19). To gain further information about these resonances, we used a radioactive F-18 beam from the Holifield Radioactive Ion Beam Facility to selectively populate corresponding mirror states in F-19 via the inverse H-2((18)p)F-19 neutron transfer reaction. Neutron spectroscopic factors were measured for states in F-19 in the excitation energy range 0-9 MeV. Widths for corresponding proton resonances in Ne-19 were calculated using a Woods-Saxon potential. The results imply significantly lower F-18(p, gamma)Ne-19 and F-18(p, alpha)O-15 reaction rates than reported previously, thereby increasing the prospect of observing the 511 keV annihilation radiation associated with the decay of F-18 in the ashes ejected from novae

The F-17(p, gamma)Ne-18 direct capture cross section

The F-17(p,gamma)Ne-18 reaction is important for understanding nucleosynthesis in novae. This reaction rate is expected to be dominated by the unmeasured direct-capture cross section at nova temperatures. We have measured cross sections for the proton-transfer reaction N-14(F-17,Ne-18)C-13 to determine F-17+p asymptotic normalization coefficients for Ne-18 bound states and the F-17(p,gamma)Ne-18 direct-capture cross section. Elastic scattering cross sections for the N-14(F-17,F-17)N-14 and C-12(F-17,F-17)C-12 reactions were also measured and used to determine reliable optical-model parameters within the framework of a microscopic double-folding model. Here we present the technique and some preliminary results

The F-17(p, gamma)Ne-18 direct capture cross section

The F-17(p, gamma) Ne-18 direct capture cross section is important for understanding nucleosynthesis in novae. We have measured cross sections for the proton-transfer reaction N-14 (F-17, Ne-18) C-13 in order to determine asymptotic normalization coefficients for the F-17 + p system and hence the F-17(p, gamma) Ne-18 direct capture cross section. The technique and preliminary results are presented