  A discussion on the nature of the 0+ states in 68Ni (Z=28, N=40) is presented
and a comparison is made with its valence counterpart 90Zr (Z=40, N=50).
Evidence is given for a 0+ proton intruder state at only ~2.2 MeV excitation
energy in 68Ni, while the analogous neutron intruder states in 90Zr reside at
4126 keV and 5441 keV. The application of a shell-model description of 0+
intruder states reveals that many pair-scattered neutrons across N=40 have to
be involved to explain the low excitation energy of the proton-intruder
configuration in 68Ni.
