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Register a new userAstrophysical S_{17}(0) factor from a measurement of d(7Be,8B)n reaction at E_{c.m.} = 4.5 MeV
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Angular distribution measurements of $^2$H($^7$Be,$^7$Be)$^2$H and $^2$H($^7$Be,$^8$B)$n$ reactions at $E_{c.m.}sim$~4.5 MeV were performed to extract the astrophysical $S_{17}(0)$ factor using the asymptotic normalization coefficient (ANC) method. For this purpose a pure, low emittance $^7$Be beam was separated from the primary $^7$Li beam by a recoil mass spectrometer operated in a novel mode. A beam stopper at 0$^{circ}$ allowed the use of a higher $^7$Be beam intensity. Measurement of the elastic scattering in the entrance channel using kinematic coincidence, facilitated the determination of the optical model parameters needed for the analysis of the transfer data. The present measurement significantly reduces errors in the extracted $^7$Be(p,$gamma$) cross section using the ANC method. We get $S_{17}$~(0)~=~20.7~$pm$~2.4 eV~b.
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We measured the 7Be(p,gamma)8B cross section from E_cm = 186 to 1200 keV, with a statistical-plus-systematic precision per point of better than +- 5%. All important systematic errors were measured including 8B backscattering losses. We obtain S_17(0) = 22.3 +- 0.7(expt) +- 0.5(theor) eV-b from our data at E_cm <= 300 keV and the theory of Descouvemont and Baye.
The $^{18}$Ne($alpha,p$)$^{21}$Na reaction plays a significant role in Type-I X-ray bursts. It is a major path in the breakout from the hot-CNO cycles to the synthesis of heavier elements in the $alpha p$-- and $rp$-processes. An experiment to determine the cross section of this reaction was performed with the ANASEN active-target detector system, determining the cross section at energies between 2.5 and 4 MeV in the center-of-mass frame. The measured cross sections for reactions populating the ground state in $^{21}$Na are consistent with results obtained from the time-inverse reaction, but significantly lower than the previously published experimental data of direct measurements. The total cross sections are also compared with those derived from indirect methods and statistical-model calculations. This experiment establishes a new experimental data set on the excitation function of the $^{18}$Ne($alpha,p$)$^{21}$Na reaction, revealing the significance of the excited states contributions to the total reaction cross section and allowing to separate the contribution of the $(alpha,2p)$ reaction. The impact of the measured cross section on thermal reaction rates is discussed.
We investigate the ground state structure of $^8$B within the Skyrme Hartree-Fock framework where spin-orbit part of the effective interaction is adjusted to reproduce the one-proton separation energy of this nucleus. Using same set of force parameters, binding energies and root mean square radii of other light p-shell unstable nuclei, $^8$Li, $^7$B,$^7$Be, and $^9$C, have been calculated where a good agreement with corresponding experimental data is obtained. The overlap integral of $^8$B and $^7$Be wave functions has been used to determine the root mean square radius of the single proton in a particular orbit and also the astrophysical S factor ($S_{17}$) for the $^{7}$Be($p, gamma)^{8}$B radiative capture reaction. It is found that the asymptotic region (distances beyond 4 fm) of the p-shell single proton wave function contributes more than half to the calculated value (4.93 fm) of the corresponding single particle root mean square radius. We determine a $S_{17}$ 21.1 eV.b which is in good agreement with the recommended value for near zero energy $S_{17}$ of $19.0^{+4.0}_{-1.0}$ eV.b.
The $^{14}textrm{N(p,}gammatextrm{)}^{15}textrm{O}$ reaction is the slowest reaction of the carbon-nitrogen cycle of hydrogen burning and thus determines its rate. The precise knowledge of its rate is required to correctly model hydrogen burning in asymptotic giant branch stars. In addition, it is a necessary ingredient for a possible solution of the solar abundance problem by using the solar $^{13}$N and $^{15}$O neutrino fluxes as probes of the carbon and nitrogen abundances in the solar core. After the downward revision of its cross section due to a much lower contribution by one particular transition, capture to the ground state in $^{15}$O, the evaluated total uncertainty is still 8%, in part due to an unsatisfactory knowledge of the excitation function over a wide energy range. The present work reports precise S-factor data at twelve energies between 0.357-1.292~MeV for the strongest transition, capture to the 6.79~MeV excited state in $^{15}$O, and at ten energies between 0.479-1.202~MeV for the second strongest transition, capture to the ground state in $^{15}$O. An R-matrix fit is performed to estimate the impact of the new data on astrophysical energies. The recently suggested slight enhancement of the 6.79~MeV transition at low energy could not be confirmed. The present extrapolated zero-energy S-factors are $S_{6.79}(0)$~=~1.24$pm$0.11~keV~barn and $S_{rm GS}(0)$~=~0.19$pm$0.05~keV~barn.
Final results from an exclusive measurement of the Coulomb breakup of 8B into 7Be+p at 254 A MeV are reported. Energy-differential Coulomb-breakup cross sections are analyzed using a potential model of 8B and first-order perturbation theory. The deduced astrophysical S_17 factors are in good agreement with the most recent direct 7Be(p,gamma)8B measurements and follow closely the energy dependence predicted by the cluster-model description of 8B by Descouvemont. We extract a zero-energy S_17 factor of 20.6 +- 0.8 (stat) +- 1.2 (syst) eV b.
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