Superdeformation below N=73.

A decoupled rotational band with an average dynamical moment of inertia {ital J}{sup (2)} {approximately}55 {h_bar}{sup 2}/MeV has been observed to high spin in {ital N}=71 {sup 129}Ce. The measured quadrupole moment of {ital Q}{sub 0} = 6.3(4) eb is as large as that of the superdeformed band in {sup 131}Ce. The large deformation and decoupled character of the band suggests that the odd neutron occupies either the {ital h}{sub 9/2}/{ital f}{sub 7/2} [541] 1/2{sup {minus}} orbital or the {ital i}{sub 13/2} [660] 1/2{sup +} intruder orbital. This is the first example of a superdeformed band extending to high spin below {ital N}=73, a neutron number that has long been considered as the boundary for superdeformation in the {ital A}{approximately}130 mass region. {copyright} {ital 1996 The American Physical Society.}