  The Alpha Magnetic Spectrometer (AMS) to be installed on the International
Space Station (ISS) will be equipped with a proximity focusing Ring Imaging
Cerenkov detector (RICH). Reconstruction of the Cerenkov angle and the electric
charge with RICH are discussed. A likelihood method for the Cerenkov angle
reconstruction was applied leading to a velocity determination for protons with
a resolution around 0.1%. The electric charge reconstruction is based on the
counting of the number of photoelectrons and on an overall efficiency
estimation on an event-by-event basis. The isotopic mass separation of helium
and beryllium is presented.
