  We study a mixture of s-bosons and like-nucleon pairs with the standard
pairing interaction outside a inert core. Competition between the nucleon-pairs
and s-bosons is investigated in this scenario. The robustness of the BCS-BEC
coexistence and crossover phenomena is examined through an analysis of pf-shell
nuclei with realistic single-particle energies in which two configurations with
Pauli blocking of nucleon-pair orbits due to the formation of the s-bosons is
taken into account. When the nucleon-pair orbits are considered to be
independent of the s-bosons, the BCS-BEC crossover becomes smooth with the
number of the s-bosons noticeably more than that of the nucleonpairs near the
half-shell point, a feature that is demonstrated in the pf-shell for several
values of the standard pairing interaction strength. As a further test of the
robustness of the BCS-BEC coexistence and crossover phenomena in nuclei,
results are given for B(E2; 0^{+}_{g}->2^{+}_1) values of even-even 102-130Sn
with 100Sn taken as a core and valence neutron pairs confined within the 1d5/2,
0g7/2, 1d3/2, 2s1/2, 1h11/2 orbits in the nucleon-pair orbit and the s-boson
independent approximation. The results indicate that the B(E2) values are well
reproduced.
