title: Origin of low-lying enhanced E1 strength in rare-Earth nuclei.
abstract: The experimental E1 strength distribution below 4 MeV in rare-earth nuclei suggests a local breaking of isospin symmetry. In addition to the octupole states, additional J^{π}=1^{-} states with enhanced E1 strength have been observed in rare-earth nuclei by means of (γ,γ') experiments. By reproducing the experimental results, the spdf interacting boson model calculations provide further evidence for the formation of an α cluster in medium-mass nuclei and might provide a new understanding of the origin of low-lying E1 strength.
authors.affiliation: Institut für Kernphysik, Universität zu Köln, Zülpicher Straße 77, D-50937 Köln, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Spieker
authors.affiliation: Institut für Kernphysik, Universität zu Köln, Zülpicher Straße 77, D-50937 Köln, Germany.|National Institute for Physics and Nuclear Engineering, R-77125 Bucharest-Magurele, Romania.
authors.forename: S
authors.initials: S
authors.lastname: Pascu
authors.affiliation: Institut für Kernphysik, Universität zu Köln, Zülpicher Straße 77, D-50937 Köln, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Zilges
authors.affiliation: Center for Theoretical Physics, Sloane Physics Laboratory, Yale University, New Haven, Connecticut 06520-8120, USA.
authors.forename: F
authors.initials: F
authors.lastname: Iachello