Protons in the outer zone of the radiation belt

The trapped protons in the outer zone of the Van Allen radiation belt were measured on October 4, 1960, by means of a Scout rocket payload containing a two-crystal scintillation spectrometer. Protons with energies above 1 Mev were detected, the intensity rising above background at an altitude of 1200 km. Representative intensities for 1≤Ep≤0 Mev at 2, 3, 4, and 5 times; 03 km, through a range of 42°N to 30°N geomagnetic latitudes, were 0.27, 0.90, 2.02, and 4.56 times; 05 protons/cm2 sec ster. These intensities are averages for protons having pitch angles between 90° and ∼60°. The proton energy spectrum at 5000 km is J(E) = 2.0 × 106E−5.2 protons/cm2 sec ster Mev for 1.02≤Ep≤2.24 Mev, and J(E) = 0.71 × 106E−3.9 for 2.24≤Ep≤7.3 Mev. The pitch angle distributions for altitudes of 4600 km and 5150 km were also obtained for angles between 90° and 58°. There was no evidence for a proton intensity maximum coincident with the E2 maximum.