  We report the results from resistivity and magnetic measurements on
polycrystalline Ce oxypnictide (CeFeAsO1-xFx) samples where x spans from 0.13
to 0.25. We find that the orbital limiting field is as high as 150 T and it
systematically decreases with increasing doping. The Maki parameter is greater
than one across the phase diagram and the large Maki parameter suggests that
orbital and Pauli limiting effects contribute to the upper critical field. The
broadening of the superconducting transition in the resistivity data was
interpreted using the thermally activated flux flow (TAFF) model where we find
that the TAFF activation energy, U0(B), is proportional to B^{-(gamma)} from 1
T to high fields, and (gamma) does not significantly change with doping.
However, U0 and the superconducting critical current, Jc, are peaked in the
mid-doping region (x = 0.15 to x = 0.20), and not in the low (x < 0.15) or high
doping (x > 0.20) regions. Furthermore, U0 is correlated with Jc and follows
the two fluid model for granular samples.
