Level lifetimes and the nuclear structure of $^{134,136}$Xe from inelastic neutron scattering*

The level structures of $^{134, 136}$Xe were studied with the inelastic neutron scattering reaction followed by $\gamma$-ray detection. Highly enriched solid XeF$_2$ samples were used in the measurements. A number of level lifetimes were determined for the first time with the Doppler-shift attenuation method, and the low-lying excited states were characterized from this new spectroscopic information. In $^{134}$Xe, the third excited state, a tentative $0^+$ level, was verified. The $3^-$ octupole phonon has been confirmed, and the complete negative-parity multiplet resulting from the $\nu (1h_{11/2}2d_{3/2})$ configuration has been tentatively identified for the first time in the $N = 80$ isotones. In $^{136}$Xe, a nucleus with a closed $N = 82$ neutron shell, several spins and parities of the states below 3 MeV in excitation energy have been firmly assigned for the first time, or have been re-assigned. New insights into the structures of these nuclei will be discussed.