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There is strong evidence that some states in 10Be exhibit molecular like α:2n:α configuration. Based on theoretical studies it appears that the 6:179 MeV 0+ state in 10Be has a pronounced α:2n:α configuration with an α-α inter-distance of 3:55 fm [1]. This is 1.8 times more than the corresponding value for the 10Be ground state. The 2+ at 7.542 MeV in 10Be is believed to be the next member of this rotational band. The state at 10.2 MeV was identified as a 4+ member in recent experiments. The algebraic model predicts that this band should also include the 6+ and 8+ states. We performed an experiment to search for the higher spin cluster states in the excitation function for 6He+α scattering. No evidence for the new states has been observed. [ABSTRACT FROM AUTHOR]

The total cross sections of the 12C+16O fusion have been experimentally determined at low energies to investigate the role of this reaction during late stellar evolution burning phases. A high-intensity oxygen beam was produced by the 5MV pelletron accelerator at the University of Notre Dame impinging on a thick ultra-pure graphite target. Protons and γ-rays were measured simultaneously in the center-of-mass energy range from 3.64 to 5.01 MeV, using strip silicon and HPGe detectors. Statistical model calculations were employed to interpret the experimental results. A new broad resonance-like structure is observed for the 12C+16O reaction, and a decreasing trend of its S-factor towards low energies is found. [ABSTRACT FROM AUTHOR]

The ratio of the reaction rates of the competing channels 17O(αγ)21Ne and 17O(α,n)20Ne determines the efficiency of 16O as a neutron poison in the s process in low metallicity rotating stars. It has a large impact on the element production, either producing elements to the mass range of A=90 in case of a significant poisoning effect or extending the mass range up to the region of A=150 if the γ channel is of negligible strength. We present an improved study of the reaction 17O(α,n)20Ne, including an independent measurement of the 17O(α,n1)20Ne channel. A simultaneous R-Matrix fit to both the n0 and the n1 channels has been performed. New reaction rates, including recent data on the 17O(α,γ)21Ne reaction, have been calculated and used as input for stellar network calculations and their impact on the s process in rotating massive stars is discussed. [ABSTRACT FROM AUTHOR]

The s process synthesizes the elements between Fe and Sr in massive stars during two major evolutionary stages, convective core He burning and C shell burning. This scenario implies fascinating consequences for the chemical evolution of the star. For instance, the neutron capture rate at each isotope can have a big influence on the production of many of the subsequent higher mass isotopes. Correspondingly, one needs to know the (n,γ) cross sections of the involved isotopes with high accuracy in order to determine the abundance pattern reliably and to obtain a consistent picture of this stage. This contribution gives an overview on recent and future experiments for the Fe/Ni nucleosynthesis in massive stars. New results on 60Fe, 62Ni and 64Ni are reported. 60Fe is mostly produced during the short convective C shell burning phase, where peak densities of ∼1011 cm-3 are reached, prior to the SN explosion. The stellar (n,γ) cross section of 60Fe could be measured with a 1 μg sample obtained at PSI (Switzerland), which was sufficient for an activation measurement using the intense, quasi-stellar neutron field for a thermal energy of 25 keV at the Karlsruhe Van de Graaff accelerator. The FZK accelerator was also used for an activation of 62Ni, whereas in this case, the number of 63Ni nuclei produced were determined via accelerator mass spectroscopy at the Maier-Leibnitz-Laboratorium in Garching/Munich. The (n,γ) cross section of 64Ni at a stellar temperature equivalent to 50 keV has been measured in a collaboration between FZK Karlsruhe and PTB Braunschweig. Finally, complementary time of flight measurements on the Fe and Ni isotopes over a broad energy range are planned at the white neutron source n_TOF of CERN for the future campaign in 2009. [ABSTRACT FROM AUTHOR]

The radiative thermal neutron capture cross section of the astrophysically important 22Ne nucleus has been measured at the guided cold neutron beam of the Budapest Research Reactor. High-pressure gas-bottles filled with mixtures of enriched 22Ne and CH4 were used. The cross section was determined by means of the comparator method, and an improved decay-scheme obtained in this work. The new value for the thermal neutron cross section is 52.7±0.7 mb, 18% larger than the accepted value. The influence of the new cross section on the astrophysical reaction rate is under investigation. [ABSTRACT FROM AUTHOR]

A new measurement of the 19F(p,γ)20Ne reaction has been made at the University of Notre Dame, covering proton energies from Ep=200–800 keV. Upper limits are placed on the strength of the Ep=224 keV and Ep=597 keV resonances. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]