  Alpha clustering in nuclei is considered with the quartet model (QM) where
four valence nucleons (the quartet) move on the top of the core (daughter)
nucleus. In the QM approach, it is assumed that the intrinsic wave function of
the quartet is changed from the pure cluster configuration to the shell-model
configuration when it crosses some critical radius and enters into the core
nucleus. The QM approach could give not only the level scheme, the
electromagnetic transition, the nuclear radius, but also the alpha-cluster
formation probability. Numerical results are calculated for ${}^{20}$Ne,
${}^{44}$Ti, and ${}^{212}$Po, where a quartet moves on top of a double magic
nucleus. Good agreement with experimental data and previous theoretical studies
is obtained. The QM approach is a useful complement to the present
phenomenological and microscopic models and could help deepen our understanding
of alpha clustering across the nuclide chart.
