Coincidence recoil-distance Doppler-shift lifetime measurements in129,130Bawith EUROBALL Ge cluster detectors

Abstract

Picosecond lifetimes in ${}^{129,130}\mathrm{Ba}$ were determined using the recoil distance technique with a plunger device coupled to an array of EUROBALL-cluster-detectors for the first time. The differential decay curve method in coincidence mode was employed to derive lifetimes for six states in ${}^{129}\mathrm{Ba}$ and twelve states in ${}^{130}\mathrm{Ba}.$ The resulting $B(E2)$ values are compared with triaxial rotor plus particle calculations for ${}^{129}\mathrm{Ba}$ and, in ${}^{130}\mathrm{Ba},$ to the predictions of the general collective model, the interacting boson model, as well as to the symmetric and asymmetric rotor models. In ${}^{130}\mathrm{Ba},$ the transitional quadrupole moment in the ground state band is remarkably constant before and after the backbend. With this data the two-quasiparticle negative parity band in ${}^{130}\mathrm{Ba}$ was confirmed to be based on a $\ensuremath{\pi}{(h}_{11/2}\ensuremath{\bigotimes}{d}_{5/2}{/g}_{7/2})$ configuration.