  Possible reasons that confinement resonances are not observed in a recent
photoionization experiment on the endohedral fullerene Ce@C82+ are explored.
The effect of the polarization of the fullerene shell in response to the
ionization of the endohedrally encaged atom A@Cn, termed the "shielding"
effect, has been investigated and found to be relatively small; no more than a
20% effect near threshold, and much less at higher energies. It is argued that
most likely, the absence of confinement resonances in Ce@C82+ is due primarily
to the finite thickness of the carbon cage; the off-the-center position and
thermal vibration of the encaged atom, discussed elsewhere, further weaken the
resonances rendering them beyond the sensitivity of the experiment to detect,
in this case. For other situations/endohedrals, the confinement resonances
should well be observable, and Ne@C60 is suggested as an excellent candidate.
