Absolute alpha decay width of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">Po</mml:mi></mml:mrow><mml:mprescripts/><mml:mrow/><mml:mrow><mml:mn>212</mml:mn></mml:mrow><mml:mrow/><mml:mrow/></mml:mmultiscripts></mml:mrow></mml:math>in a combined shell and cluster model

We give a parameter-free microscopic description of the \ensuremath{\alpha} decay of the ground state of $^{212}\mathrm{Po}$ by expanding the parent wave function over a basis containing shell-model- as well as cluster-model-type elements. The resulting decay width agrees with experiment well within the range of the uncertainty inherent in the input of the model. The amount of core +\ensuremath{\alpha} clustering in the parent state is found much higher (30%) than former microscopic estimates (\ensuremath{\sim}1%), which shows the soundness of assuming the existence of preformed \ensuremath{\alpha} particles with appreciable probability in the initial state.