  The Alpha Magnetic Spectrometer (AMS), to be installed on the International
Space Station (ISS) in 2008, is a cosmic ray detector with several subsystems,
one of which is a proximity focusing Ring Imaging Cherenkov (RICH) detector.
This detector will be equipped with a dual radiator (aerogel+NaF), a lateral
conical mirror and a detection plane made of 680 photomultipliers and light
guides, enabling precise measurements of particle electric charge and velocity.
Combining velocity measurements with data on particle rigidity from the AMS
Tracker it is possible to obtain a measurement for particle mass, allowing the
separation of isotopes. A Monte Carlo simulation of the RICH detector, based on
realistic properties measured at ion beam tests, was performed to evaluate
isotope separation capabilities. Results for three elements -- H (Z=1), He
(Z=2) and Be (Z=4) -- are presented.
