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Low-lying yrast states of 204 Po and 206 Po were investigated by the γ -γ fast timing technique with LaBr3(Ce) detectors. Excited states of these nuclei were populated in the 197 Au( 11 B,4n) 204 Po and the 198 Pt( 12 C,4n) 206 Po fusion-evaporation reactions, respectively. The beams were delivered by the FN-Tandem accelerator at the University of Cologne. The lifetimes of the 4 + 1 states of both nuclei were measured, along with an upper lifetime limit for the 2 + 1 state of 204 Po. A comparison between the derived B(E2; 4 + 1 → 2 + 1 ) values and results from simplified empirical two-state mixing calculations suggests that for the 4 + 1 states of even-even polonium isotopes the transition from single particle mode at N = 126 to collective mode, when reducing the number of neutrons, occurs above N = 122.

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