Absolute alpha decay width ofPo212in a combined shell and cluster model

We give a parameter-free microscopic description of the α 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 +α clustering in the parent state is found much higher (30%) than former microscopic estimates (∼1%), which shows the soundness of assuming the existence of preformed α particles with appreciable probability in the initial state.