Stellar neutron sources and s-Process in Massive Stars

Potential stellar neutron sources for the s-process in massive stars are associated with $\alpha $-capture reactions on light nuclei. The capture-reaction rates provide the reaction flow for the buildup of the neutron sources $^{22}$Ne, and $^{26}$Mg during the helium-burning phase in stars. A critical influence on these reactions is expected to come from low-energy resonances at stellar energies between 300 keV and 1500 keV. It is possible that these resonances are suspected to correspond to pronounced cluster structures near the $\alpha $-threshold. Direct measurements of capture reactions to study these cluster states are handicapped by the Coulomb barrier and limited detector resolutions. Hence, inelastic $\alpha $-scattering on these nuclei has been used as an alternative tool to probe into the level structure. Also $\alpha $-transfer technique has been used to extract $\alpha $-strength information. In reference to this, the experiments performed using the Grand Raiden Spectrometer at RCNP, Osaka will be discussed and preliminary results will be presented.