Landscape of a preformation probability for even-even nuclei in medium mass region

The behavior of alpha cluster preformation probability, in a decay, is a rich source of the structural information, such as the clustering, pairing, and shell evolution in heavy nuclei. Meanwhile, the experimental alpha decay data have been very recently compiled in the newest table NUBASE2016. Through a least square fit to the available experimental data of nuclear charge radii plus the neutron skin thickness, we obtain a new set of parameters for the two-parameter Fermi nucleon density distributions in target nuclei. Subsequently, we make use of these refreshed inputs, involved in the density-dependent cluster model, to extract alpha preformation factor (P-alpha) for a large range of medium alpha emitters with N < 126 from the newest data table. Besides checking the supposed smooth pattern of P-alpha in the open-shell region, the special attention has been paid to those exotic alpha-decaying nuclei around the Z = 50 and N = 82 shell closures. Moreover, the correlation between the alpha preformation factor and the microscopic correction of nuclear mass, corresponding to the effect of shell and pairing plus deformation, is in particular investigated, to pursue the valuable knowledge of the P-alpha pattern over the nuclide chart. The feature of alpha preformation factor along with the neutron-proton asymmetry is then detected and discussed to some extent.