E. D. Johnson

Molecular Structures in T = 1 states of

Multi-center (molecular) structures can play an important role in light nuclei. The highly deformed rotational band in 10Be with band head at 6.179 MeV has been observed recently and suggested to have an exotic alpha:2n:alpha configuration. A search for states with alpha:pn:alpha two-center molecular configurations in 10B that are analogous to the states with alpha:2n:alpha structure in 10Be has been performed. The T=1 isobaric analog states in 10B were studied in the excitation energy range of E=8.7-12.1 MeV using the reaction 1H(9Be,alpha)6Li*(T=1, 0+, 3.56 MeV). An R-matrix analysis was used to extract parameters for the states observed in the (p,alpha) excitation function. Five T=1 states in 10B have been identified. The known 2+ and 3- states at 8.9 MeV have been observed and their partial widths have been measured. The spin-parities and partial widths for three higher lying states were determined. Our data support theoretical predictions that the 2+ state at 8.9 MeV (isobaric analog of the 7.54 MeV state in 10Be) is a highly clustered state and can be identified as a member of the alpha:np:alpha rotational band. The next member of this band, the 4+ state, has not been found. A very broad 0+ state at 11 MeV that corresponds to pure alpha+6Li(0+,T=1) configuration is suggested and it might be related to similar structures found in 12C, 18O and 20Ne.

^{10}

Resonances in atomic nuclei play a vital role in determining rates of astrophysically important nuclear reactions. Efficient experimental technique, Thick Target Inverse Kinematics method, which allows to study properties of resonances in exotic nuclei with radioactive beams using resonance elastic scattering is discussed. Various extensions of this technique for measurements of inelastic excitation functions and application of one of these methods for 7Be(p,p’)7Be* (0.43 MeV) reaction is considered.The astrophysical rates of some (α, γ), (α, n), (α, p) reactions are often determined by the near α‐threshold resonances. Application of sub‐Coulomb α‐transfer reactions (7Li,t) and (6Li,d) allow to determine α‐particle Asymptotic Normalization Coefficients of these resonances with minimal dependance on model parameters. The 14C(α,γ) reaction is considered as an example for application of this approach.

B

We address two important indirect techniques, the asymptotic normalization coefficient (ANC) and the Trojan Horse (TH) methods. We discuss the application of the ANC technique to determine the astrophysical factor for the 13 C( α , n ) 16 O reaction which is one of the neutron generators for the s processes in AGB stars. The TH method is a unique indirect technique allowing one to measure astrophysical S factors for rearrangement reactions down to astrophysically relevant energies. We derive equations connecting the cross sections for the binary direct and resonant reactions determined from the indirect TH reactions to direct cross sections measurements.

Resonance scattering and α‐transfer reactions for nuclear astrophysics

V.Z. Goldberg, M. Avila, S. Cherubini, G.V. Rogachev, M. Gulino, E.D. Johnson, A.N. Kuchera, M. La Cognata, L. Lamia, S. Romano, L.E. Miller, R.G. Pizzone, G.G. Rapisarda, M.L. Sergi, C. Spitaleri, R.E. Tribble, W.H. Trzaska, A. Tumino Department of Physics, Florida State University, Tallahassee, Florida Istituto Nazionale di Fisica NucleareLaboratori Nazionali del Sud, Catania, Italy Physics Department, University of Jyvaskyla, Jyvaskyla, Finland

Indirect Techniques in Nuclear Astrophysics. Asymptotic Normalization Coefficient and Trojan Horse

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 Non-Self-Conjugate Nuclei

Motivation: Detailed experimental knowledge of the level structure of light weakly bound nuclei is necessary to guide the development of new theoretical approaches that combine nuclear structure with reaction dynamics. Purpose: The resonant structure of 8 B is studied in this work. Method: Excitation functions for elastic and inelastic 7 Be+p scattering were measured using a 7 Be rare isotope beam. Excitation energies ranging between 1.6 and 3.4 MeV were investigated. An R-matrix analysis of the excitation functions was performed. Results: New low-lying resonances at 1.9, 2.5, and 3.3 MeV in 8 B are reported with spin-parity assignment 0 + , 2 + , and 1 + , respectively. Comparison to the Time Dependent Continuum Shell (TDCSM) model and ab initio no-core shell model/resonating-group method (NCSM/RGM) calculations is performed. This work is a more detailed analysis of the data first published as a Rapid Communication. [J.P. Mitchell, et al, Phys. Rev. C 82, 011601(R) (2010)] Conclusions: Identification of the 0 + , 2 + , 1 + states that were predicted by some models at relatively low energy but never observed experimentally is an important step toward understanding the structure of 8 B. Their identification was aided by having both elastic and inelastic scattering data. Direct comparison of the cross sections and phase shifts predicted by the TDCSM and ab initio No Core Shell Model coupled with the resonating group method is of particular interest and provides a good test for these theoretical approaches.

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

Motivation: Detailed experimental knowledge of the level structure of light weakly bound nuclei is necessary to guide the development of new theoretical approaches that combine nuclear structure with reaction dynamics. Purpose: The resonant structure of 8 B is studied in this work. Method: Excitation functions for elastic and inelastic 7 Be+p scattering were measured using a 7 Be rare isotope beam. Excitation energies ranging between 1.6 and 3.4 MeV were investigated. An R-matrix analysis of the excitation functions was performed. Results: New low-lying resonances at 1.9, 2.5, and 3.3 MeV in 8 B are reported with spin-parity assignment 0 + , 2 + , and 1 + , respectively. Comparison to the Time Dependent Continuum Shell (TDCSM) model and ab initio no-core shell model/resonating-group method (NCSM/RGM) calculations is performed. This work is a more detailed analysis of the data first published as a Rapid Communication. [J.P. Mitchell, et al, Phys. Rev. C 82, 011601(R) (2010)] Conclusions: Identification of the 0 + , 2 + , 1 + states that were predicted by some models at relatively low energy but never observed experimentally is an important step toward understanding the structure of 8 B. Their identification was aided by having both elastic and inelastic scattering data. Direct comparison of the cross sections and phase shifts predicted by the TDCSM and ab initio No Core Shell Model coupled with the resonating group method is of particular interest and provides a good test for these theoretical approaches.

Structure of 8 B from elastic and inelastic 7 Be+ p scattering

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.

Structure of8B from elastic and inelastic7Be+pscattering

Resonance scattering with rare isotope beams provides direct access to continuum properties of exotic nuclei and can serve as a stringent test for modern theoretical approaches. Properties of neutron deficient isotope 8B, that were studied using resonance scattering of protons of 7Be, are discussed and compared to the predictions of the ab initio theories. New experimental data on clustering in 10Be studied using 6He+α resonance elastic scattering is presented.

Clustering in A=10 nuclei

We report on the study of a new nuclide, 14F, and on the idea of an experiment to solve the structure mystery of nuclei in the region around 9He.