Leptons with E>200 MeV trapped in the Earth's radiation belts

For the first time, accurate measurements of electron and positron fluxes in the energy range 0.2–10 GeV have been performed with the Alpha Magnetic Spectrometer (AMS) at altitudes of 370–390 km in the geographic latitude interval ±51.7°. We describe the observed under-cutoff lepton fluxes outside the region of the South Atlantic Anomaly. The separation in quasi-trapped, long-lifetime (O(10 s)), and albedo, short-lifetime (O(100 ms)), components is explained in terms of the drift shell populations observed by AMS. A significantly higher relative abundance of positrons with respect to electrons is seen in the quasi-trapped population. The flux maps as a function of the canonical adiabatic variables L, α0 are presented for the interval 0.95 < L < 3, 0° < α0 < 90° for electrons (E < 10 GeV) and positrons (E < 3 GeV). The results are compared to existing data at lower energies. The properties of the observed under-cutoff particles are also investigated in terms of their residence times and geographical origin.