  We report on measurements performed on silicon pixel sensor prototypes
exposed to a 200 MeV proton beam at the Indiana University Cyclotron Facility.
The sensors are of n+/n/p+ type with multi-guard ring structures on the p+-side
and p-stop electrode isolation on the n+-side. Electrical characterization of
the devices was performed before and after irradiation up to a proton fluence
of 4E14 p/cm2. We tested pixel sensors fabricated from normal and
oxygen-enriched silicon wafers and with two different p-stop isolation layouts:
common p-stop and individual p-stop.
