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Radiation Belts - Read More Print
PAMELA is studying the radiation environment along the orbit with a good accuracy. Due to the precession of the satellite elliptical orbit, in its six years of operation PAMELA performed a detailed 3-dimensional (latitude, longitude, altitude) mapping of the Van Allen Belts between 350 and 610 km, showing spectral and geometrical features. 

The map of the sky: in Figure 1  a map of the measured radiation environment is shown. The high latitude electron radiation belt and the proton belt in the South Atlantic Anomaly (SAA) are clearly visible. The particle flux measured at di fferent latitudes, expressed in GV, is shown in Figure 2, where the contribution of the galactic proton cosmic rays and the contribution of protons produced in the interaction of primary particles with the atmosphere (sub-cutoff protons) are clearly distinguished. 

Discovery of an antiproton radiation belt: PAMELA has discovered an antiproton radiation belt around the Earth. Figure 3 shows the energy spectrum of trapped antiprotons measured in the SAA region for a kinetic energy range between 60 MeV and 750 MeV. The measurement of the atmospheric, not trapped, subcutoff antiproton spectrum and of galactic antiproton spectra is also reported for comparison. The magnetospheric antiproton flux in the SAA exceeds the cosmic ray antiproton flux by three orders of magnitude at the present solar minimum, and exceeds the subcutoff , not trapped, antiproton flux outside radiation belts by four orders of magnitude. This antiproton belt constitutes the most abundant source of hadronic antimatter orbiting around the Earth. Figure 4 reports the geomagnetically trapped antiproton to proton ratio measured in the SAA. 

Figure 5  shows the quasi-trapped positron to electron ratio measured between 80 MeV and 8 GeV (L shell < 1.2, B > 0.23 G). The large value for the e+/e-  flux ratio observed for energies from 300 to 800 MeV can be explained by an East-West asymmetry of the geomagnetic cutoff .


Edited by Laura Marcelli