Coexistence of “ $ \alpha$ + 208Pb ” cluster structures and single-particle excitations in 212 84Po128

Abstract

Excited states in 212Po have been populated by $ \alpha$ transfer using the 208Pb(18O,14C) reaction at 85MeV beam energy and studied with the EUROBALL IV $ \gamma$ multi-detector array. The level scheme has been extended up to ∼ 3.2 MeV excitation energy from the triple- $ \gamma$ coincidence data. Spin and parity values of most of the observed states have been assigned from the $ \gamma$ angular distributions and $ \gamma$ - $ \gamma$ angular correlations. Several $ \gamma$ -lines with E γ < 1 MeV have been found to be shifted by the Doppler effect, allowing for the measurements of the associated lifetimes by the DSAM method. The values, found in the range [0.1-0.6]ps, lead to very enhanced E1 transitions. All the emitting states, which have non-natural parity values, are discussed in terms of $ \alpha$ - 208Pb structure. They are in the same excitation-energy range as the states issued from shell-model configurations.