  The behavior of spin propagation in metals in various measurement schemes is
shown to be qualitatively different than a simple exponential decay - due to
the backflow effect on spin diffusion in the presence of interfaces. To probe
this effect we utilize the spin sensitivity of an Andreev contact between gold
films of variable thickness deposited on top of a spin injector,
Co$_{2}$Mn$_{0.5}$Fe$_{0.5}$Si, with the spin polarization of approximately
45\%, and Nb superconducting tip. While the results are consistent with
gradually decaying spin polarization as the film thickness increases, the spin
diffusion length in Au found to be 285 nm, is more than two times larger that
one would have obtained without taking the backflow effect into account.
