Abstract. The lifetimes of the 2

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

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The lifetime of the 2 + 1 state of 212 Po has been measured in the 208 Pb( 12 C, 8 Be) 212 Po transfer reaction by γ-ray spectroscopy employing the Recoil Distance Doppler Shift (RDDS) method. The derived absolute B(E2) value of 2.6(3) W.u. indicates a low collectivity and contradicts previous claims of α-cluster components in the structure of the 2 + 1 state. It is demonstrated that a consistent description of the properties of the 2 + 1 − 4 + 1 − 6 + 1 − 8 + 1 sequence in 212 Po cannot be achieved in the framework of a single-j shell-model calculation, either. This puzzle is traced to the properties of the seniority-2 configurations in 210 Pb and 210 Po.