A novel manifestation of α clustering in 212Po: Pure α-208Pb states revealed by their enhanced E1 decays

Excited states in Po-212 have been populated by a transfer using the Pb-208(O-18,C-14) reaction and studied with the Euroball gamma multidetector array. The level scheme of Po-212 has been extended up to similar to 3.2 MeV excitation energy. Spin and parity values have been assigned thanks to the measurements of gamma angular distributions and gamma-gamma angular correlations. Several gamma lines 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 [0.1-1.4] ps range, lead to very enhanced E1 transitions. The emitting states, which have non-natural parity values, are the fingerprints of the "alpha-Pb-208" structure present in Po-212. They are in the same excitation-energy range as the states issued from shell-model configurations.