  The Alpha Magnetic Spectrometer (AMS) is a state of the art detector for the
extraterrestrial study of matter, antimatter and missing matter. During the ten
days long STS-91 precursor flight in may 1998 AMS collected nearly 100 millions
of Cosmic Rays on Low Earth Orbit, measuring with high accuracy their
composition. We present results on the flux of proton, electron, positron and
helium particles in the rigidity region 0.1 to 200 GV . Analysis of the under
cutoff spectra indicates the existence of a new type of belts containing high
energy particles and characterized by a dominance of positrons versus
electrons.
