||Electropolishing is presently
accepted like most efficient surface treatment obtaining high gradients
in niobium RF cavities. This treatment seems to introduce more hydrogen
in niobium than chemical etching . We shall investigate hydrogen
contamination changes in various electrochemical conditions (like
anodic protection) during chemical etching and electropolishing, and
other conditions like hot water rinsing, hydrofluoric acid rinsing,
etc... Hydrogen contamination near the surface is analyzed with HFS
(hydrogen forward scattering). This technique allows exploring 200 to
300 nm of the surface (i.e. little bit more than the field penetration
depth) and it is used to monitor the hydrogen up-take inside niobium in
various electrochemical conditions.  Higuchi, T., K. Saito, et al.
(2001). 10th Workshop on RF Superconductivity.