We present the results from an experiment dedicated to measure the lifetime of the 2 + 2 state, candidate for the one-phonon mixed-symmetry state, of 208 Po. This nucleus was studied in the α-transfer reaction 204 Pb( 12 C, 8 Be) 208 Po and the lifetime of the 2 + 2 state was determined by utilizing the Doppler-shift attenuation method. The experimental data show that the 2 + 2 state decays with a sizable M 1 transition to the 2 + 1 state revealing its isovector nature. Keywords Lifetimes • Electromagnetic transitions • Transfer reactions • 190≤ A ≤219

The lifetimes of the 2 + 1 and 4 + 1 states of 208 Po were measured in the α-transfer reaction 204 Pb( 12 C, 8 Be) 208 Po by γ-ray spectroscopy utilizing the recoil distance Doppler Shift method. The newly extracted transition strengths alongside with ones of the decay of 2 + 2 state were compared to the results of large-scale shell-model calculations using an effective interaction derived from the realistic CD-Bonn nucleon-nucleon potential. The comparison indicates the importance of the quadrupole isovector excitations in the valence shell for a fine tuning of the two-body matrix elements of the shell-model interaction.

In this study we present the preliminary results about the lifetimes of the 2 2 + , 4 1 + states of 208Po and the upper limit of the lifetime of the 2 1 + state. For measuring the lifetimes of the 2 1 + and 4 1 + states the Recoil Distance Doppler Shift (RDDS) method and for the lifetime of the 2 2 + state the Doppler Shift Attenuation method (DSAM) were used. The resulting absolute transition strength B ( M 1 ; 2 2 + → 2 1 + ) ≥ 0.122 ( 20 ) μ N 2 reveals the predominant isovector nature of the 2 2 + state of 208Po.

Lifetimes of excited states of 124Ba were measured by the Recoil Distance Doppler Shift (RDDS) technique. The γ-ray coincidence data were analysed by the Differential Decay Curve method (DDCM). The trend of the experimentally deduced normalized B(E2) values reveals a drop at the 8+1 state, which may be caused by structural changes in the backbending region.