D. Santiago-Gonzalez

New measurement of the α asymptotic normalization coefficient of the 1 / 2 + state in O 17 at 6.356 MeV that dominates the C 13 ( α , n ) O 16 reaction rate at temperatures relevant for the s process

Background: Accurate knowledge of the 13C(α,n)16O reaction cross section is important for the understanding of the s-process in AGB stars, since it is considered to be the main source of neutrons. The sub-threshold 1/2+ state at excitation energy of 6.356 MeV in 17O has a strong influence on the reaction cross section at energies relevant for astrophysics. Several experiments have been performed to determine the contribution of this state to the 13C(α, n)16O reaction rate. Nevertheless, significant discrepancies between different measurements remain. Purpose: The aim of this work is to investigate these discrepancies. Method: An 8 MeV 13C beam (below the Coulomb barrier) was used to study the α-transfer reaction 6Li(13C,d)17O. Results: The squared Coulomb modified ANC of the 1/2+ state in 17O measured in this work is (C̃ 17O(1/2+) α−13C ) 2 = 3.6 ± 0.7 fm−1. Conclusions: Discrepancy between the results of α-transfer experiments have been resolved. However, some discrepancy with the most recent measurement using the Trojan Horse method

α -cluster asymptotic normalization coefficients for nuclear astrophysics

Background: Many important α-particle induced reactions for nuclear astrophysics may only be measured using indirect techniques due to small cross sections at the energy of interest. One of such indirect technique, is to determine the Asymptotic Normalization Coefficients (ANC) for near threshold resonances extracted from sub-Coulomb α-transfer reactions. This approach provides a very valuable tool for studies of astrophysically important reaction rates since the results are practically model independent. However, the validity of the method has not been directly verified. Purpose: The aim of this letter is to verify the technique using the 16O(6Li,d)20Ne reaction as a benchmark. The 20Ne nucleus has a well known 1− state at excitation energy of 5.79 MeV with a width of 28 eV. Reproducing the known value with this technique is an ideal opportunity to verify the method. Method: The 1− state at 5.79 MeV is studied using the α-transfer reaction 16O(6Li,d)20Ne at sub-Coulomb energies. Results: The partial α width for the 1− state at excitation energy of 5.79 MeV is extracted and compared with the known value, allowing the accuracy of the method to be evaluated. Conclusions: This study demonstrates that extracting the Asymptotic Normalization Coefficients using sub-Coulomb α-transfer reactions is a powerful tool that can be used to determine the partial α width of near threshold states that may dominate astrophysically important nuclear reaction

Clustering in non-self-conjugate nuclei 10Be and 18O

Clustering phenomena in 10Be and 18O were studied by means of resonance elastic scattering of α-particles on 6He and 14C. Excitation functions for α+6He and α+14C were measured and detailed R-matrix analyses of the excitation functions was performed. We compare the experimental results with the predictions of modern theoretical approaches and discuss properties of cluster rotational bands.

Clustering in A=10 nuclei

We discuss the identification and properties of the states that belong to the highly clustered rotational band in A=10 nuclei, 10Be, 10B(T=1) and 10C. The band is of interest because it may correspond to an exotic α:nn:α configuration.

Measurement of 17F + p reactions with ANASEN

Reactions involving radioactive nuclei play an important role in stellar explosions, but those reactions involving short-lived nuclei have only limited experimental information available due to currently limited beam intensities. Several facilities are aiming to provide greater access to these unstable isotopes at higher beam intensities, but more efficient and selective techniques and devices are needed to properly study these important reactions. The Array for Nuclear Astrophysics Studies with Exotic Nuclei (ANASEN), a charged particle detector designed by Louisiana State University (LSU) and Florida State University (FSU), was created for this purpose. ANASEN is used to study the reactions important in the αp- and rp- processes with proton-rich exotic nuclei, providing essentially complete solid angle coverage through an array of 40 silicon-strip detectors backed with CsI scintillators, covering an area of roughly 1300 cm2. ANASEN also includes an active gas target/detector in a position-sensitive annular gas proportional counter, which allows direct measurement of (α,p) reactions in inverse kinematics. The first in-beam measurements with a partial implementation of ANASEN were performed at the RESOLUT radioactive beam facility of FSU during the summer of 2011. They included stable beam experiments and measurements of the 17F(p,p)17F and 17F(p,α)14O reactions which are important to understanding the structure of 18Ne and the 14O(α,p)17F reaction rate. The performance of ANASEN and initial results from the 17F studies will be presented.