title: Stabilization of nuclear isovector valence-shell excitations.
abstract: Excited states in 138Ce have been studied via the 12C(138Ce, 138Ce*) Coulomb excitation reaction at 480 MeV. Relative cross sections have been determined from the gamma-ray yields observed with Gammasphere. The E2 and M1 strength distributions between the lowest six 2+ states up to 2.7 MeV enables us to identify the 2(4)+ state in 138Ce as the dominant fragment of the one-phonon 2(1,ms)+ mixed-symmetry state. Mixing between this level and a nearby isoscalar state is observed and is more than 4 times larger than in the neighboring isotone 136Ba. This is direct evidence that the stability of mixed-symmetry states strongly depends on the underlying subshell structure.
authors.affiliation: Department of Physics and Astronomy, SUNY at Stony Brook, Stony Brook, New York 11794-3800, USA.
authors.forename: G
authors.initials: G
authors.lastname: Rainovski
authors.forename: N
authors.initials: N
authors.lastname: Pietralla
authors.forename: T
authors.initials: T
authors.lastname: Ahn
authors.forename: C J
authors.initials: CJ
authors.lastname: Lister
authors.forename: R V F
authors.initials: RV
authors.lastname: Janssens
authors.forename: M P
authors.initials: MP
authors.lastname: Carpenter
authors.forename: S
authors.initials: S
authors.lastname: Zhu
authors.forename: C J
authors.initials: CJ
authors.lastname: Barton