Lifetime Measurements inXe120,122andBa126,128

The mean lifetime of a number of levels of the ground-state band in ${}_{}{}^{120,122}{}_{}{}^{}\mathrm{Xe}$ and the first $2^{+}$ states in ${}_{}{}^{126,128}{}_{}{}^{}\mathrm{Ba}$ have been measured with the recoil-distance Doppler-shift method. The nuclei were produced by (${}_{}{}^{16}{}_{}{}^{}\mathrm{O},4n$) reactions. The measured $E2\mathrm{}$ transition strengths which range from 50 to 100 Weisskopf units support the assumption of a transitional character for this neutron-deficient region. The deduced deformation parameters are found to be in rather good agreement with the predictions of theoretical calculations and the phenomenological variable-moment-of-inertia model.