Rotational Quadrupole Moment of Thermally Excited High Spin States in 164Yb

The lifetime of the unresolved γ transitions forming the rotational quasicontinuum spectrum has been measured for 164 Yb using the Doppler shift attenuation technique. The fractional Doppler shifts of transitions along the diagonal valley of Eγ1×Eγ2 spectra are extracted for the first time using a new technique based on the fluctuation patterns of counts. The rotational collectivity was found to persist with full strength also when the rotational bands are strongly mixed. For the high spin (I>20ħ) and energy (0<2MeV) regions there is agreement between the discrete and the damped transitions and with Qt≈5.5eb.