Stabilization of nuclear isovector valence-shell excitations.
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.
Rainovski
G
G
Department of Physics and Astronomy, SUNY at Stony Brook, Stony Brook, New York 11794-3800, USA.
Pietralla
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N
Ahn
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T
Lister
C J
CJ
Janssens
R V F
RV
Carpenter
M P
MP
Zhu
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S
Barton
C J
CJ