Shape-driving effects in the triaxial nucleus, Xe128

An extended decay scheme for Xe128 has been constructed by using data from the Sn124(Be9, 5n)Xe128 reaction at a beam energy of 58 MeV. Bands have been identified as being built on several intrinsic states, including a proposed 9/2-[514]-1/2+[400] two-quasineutron configuration that forms the Kπ=5- intrinsic state at 2228 keV, and on a previously assigned Kπ=8- intrinsic state at 2786 keV. A half-life of 73(3) ns has been measured for the latter. Theoretical calculations have been performed by using the configuration- constrained blocking method based on a nonaxial Woods-Saxon potential. Large γ deformation and γ softness are predicted for the ground state and the Kπ=5- intrinsic state, whereas a nearly axially symmetric shape is predicted for the Kπ=8- two-quasiparticle configuration. The low value of the hindrance factor for the E1 transition depopulating the Kπ=8- intrinsic state is discussed in the context of analogous transitions in neighbouring N=74 isotones.