Novel Manifestation of α-Clustering Structures: New “α+ ^{208} Pb” States in ^{212} Po Revealed by Their Enhanced E1 Decays

Author(s): A. Astier, P. Petkov, M.-G. Porquet, D. S. Delion, and P. SchuckExcited states in ^{212} Po were populated by α transfer using the ^{208} Pb( ^{18} O, ^{14} C) reaction, and their deexcitation γ rays were studied with the Euroball array. Several levels were found to decay by a unique E1 transition (E_{γ} <1  MeV) populating the yrast state with the same spin value. Their lifetimes were measured by the Doppler-shift attenuation method. The values, found in the range 0.1–1.4 ps, lead to very enhanced transitions, B(E1)=2×10^{-2} –1×10^{-3}   W.u. These results are discussed in terms of an α-cluster structure which gives rise to states with non-natural-parity values, provided that the composite system cannot rotate collectively, as expected in the “α+ ^{208} Pb” case. Such states due to the oscillatory motion of the α-core distance are observed for the first time.[Phys. Rev. Lett. 104, 042701] Published Mon Jan 25, 2010