  Results of low-temperature upper critical field measurements for
Nd$_{2-x}$Ce$_x$CuO$_{4+\delta}$ single crystals with various $x$ and
nonstoichiometric disorder ($\delta$) are presented. The coherence length of
pair correlation $\xi$ and the product $k_F$$\xi$, where $k_F$ is the Fermi
wave vector, are estimated. It is shown that for investigated single crystals
parameter $k_F$$\xi$ $\cong$ 100 and thus phenomenologically NdCeCuO - system
is in a range of Cooper-pair-based (BCS) superconductivity.
