AMS-02 is a high-energy particle physics magnetic spectrometer installed
on the International Space Station since May 2011, and operating continuously
since then. By means of the simultaneous use of the Silicon Tracker,
the AMS-02 RICH is able to investigate the isotopic composition of cosmic
rays (CRs) in the kinetic energy range from few GeV/n to ~10 GeV/n
for elements with charge |Z| up to 4 with unprecedented statistics.
The isotopes of light nuclei provide a unique tool to constrain the
free parameters in the models for CR propagation in our Galaxy.
The performance of the AMS-02 RICH for the first 5 years of AMS operation
in space will be shown. The long term stability of the system and the effect
of varying environmental conditions will be addressed. The calibration procedures
as well as the offline reconstruction of the velocity and charge will be described.
Finally, examples of the use of the RICH for the CRs isotopic composition
measurement will be shown. The excellent simulation of the AMS detector provides
the precise description needed for this analysis. Moreover, the use of the
geomagnetic field for selecting control samples of CRs with enhanced abundances
of heavy isotopes provides an independent tool for the study of the light nuclei
isotopic composition with AMS.