  The $\alpha$ particle preformation in the even-even nuclei from $^{108}$Te to
$^{294}$118 and the penetration probability have been studied. The isotopes
from Pb to U have been firstly investigated since the experimental data allow
us to extract the microscopic features for each element. The assault frequency
has been estimated using classical methods and the penetration probability from
tunneling through the Generalized Liquid Drop Model (GLDM) potential barrier.
The preformation factor has been extracted from experimental $\alpha$ decay
energies and half-lives. The shell closure effects play the key role in the
$\alpha$ preformation. The more the nucleon number is close to the magic
numbers, the more the formation of $\alpha$ cluster is difficult inside the
mother nucleus. The penetration probabilities reflect that 126 is a neutron
magic number. The penetration probability range is very large compared to that
of the preformation factor. The penetration probability determines mainly the
$\alpha$ decay half-life while the preformation factor allows us to obtain
information on the nuclear structure. The study has been extended to the newly
observed heaviest nuclei.
