  The B(E2:0_1^+ -> 2_1^+) values of the Ba isotopes (Z=56) exhibit a sharp
increase in deformation as the neutron numbers approach the mid-shell value of
N=66. This behavior is anomalous because the 2_1^+ level energies are very
similar to those of the neighboring isotopes. By means of the axially-symmetric
deformed Woods-Saxon (WS) hamiltonian plus the BCS method, we investigated the
systematics of B(E2) of the Ba isotopes. We showed that 15% of the B(E2) values
at N=66 was due to the level crossing, occurring at the deformation with beta
being nearly 0.3, between the proton orbits originating from the orbits
Omega=1/2^-(h11/2) and 9/2^+(g9/2) at zero deformation. The latter of these two
was an intruder orbit originating from below the energy gap at Z=50, rising
higher in energy with the deformation and intruding the Z=50-82 shell. These
two orbits have the largest magnitude of the quadrupole moment with a different
sign among the orbits near and below the Fermi surface. Occupancy and
non-occupancy of these orbits by protons thus affect B(E2:0_1^+ -> 2_1^+)
significantly.
