We have applied the Transmission Function approach to evaluate the primary Helium CR spectrum inside the magnetosphere. We have evaluated the trajectories of simulated alpha particles through the Earth magnetic field by backtracing up to the magnetopause or down the atmosphere. In this way we have computed first the trasmission function for a particular position inside the magnetosphere; then we have evaluated the spectrum of primaries, propagating a energy population of GCR. The analysis has

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... en restricted to the geographic coverage of the AMS-01 detector (between 51.6 and -51.6 degrees) and altitude ( 400 km) and divided in geomagnetic zones. Finally we have compared our results with the measured data. * CILEA, Segrate (Mi), Italy