ABSTRACT
Carbon burning is a key step in the evolution of massive stars, Type 1a supernovae and superbursts in x-ray binary systems. Determining the ^{12}C+^{12}C fusion cross section at relevant energies by extrapolation of direct measurements is challenging due to resonances at and below the Coulomb barrier. A study of the ^{24}Mg(α,α^{'})^{24}Mg reaction has identified several 0^{+} states in ^{24}Mg, close to the ^{12}C+^{12}C threshold, which predominantly decay to ^{20}Ne(ground state)+α. These states were not observed in ^{20}Ne(α,α_{0})^{20}Ne resonance scattering suggesting that they may have a dominant ^{12}C+^{12}C cluster structure. Given the very low angular momentum associated with sub-barrier fusion, these states may play a decisive role in ^{12}C+^{12}C fusion in analogy to the Hoyle state in helium burning. We present estimates of updated ^{12}C+^{12}C fusion reaction rates.
ABSTRACT
Angular distributions of the elastic, inelastic, and breakup cross sections of the halo nucleus ^{11}Be on ^{197}Au were measured at energies below (E_{lab}=31.9 MeV) and around (39.6 MeV) the Coulomb barrier. These three channels were unambiguously separated for the first time for reactions of ^{11}Be on a high-Z target at low energies. The experiment was performed at TRIUMF (Vancouver, Canada). The differential cross sections were compared with three different calculations: semiclassical, inert-core continuum-coupled-channels and continuum-coupled-channels ones with including core deformation. These results show conclusively that the elastic and inelastic differential cross sections can only be accounted for if core-excited admixtures are taken into account. The cross sections for these channels strongly depend on the B(E1) distribution in ^{11}Be, and the reaction mechanism is sensitive to the entanglement of core and halo degrees of freedom in ^{11}Be.
