Low collectivity of the 21+ state of ²¹²Po

The lifetime of the 21+ state of ²¹²Po was measured in the ²08Pb(¹²C,8Be)²¹²Po transfer reaction by g-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 a-cluster components in the structure of the 21+ state. It is demonstrated that a consistent description of the properties of the 21+− 41+− 61+− 81+ sequence in ²¹²Po 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 ²¹0Pb and ²¹0Po.