Geomagnetically trapped protons with energies greater than 350 Mev

The intensity and pitch-angle distribution of geomagnetically trapped protons with energies greater than 350 Mev have been determined by means of data received from a Cerenkov detector on board Explorer 11. Analysis of the data reveals that the contours of constant counting rate rise more rapidly in altitude with increasing latitude than do the contours at a threshold energy of 43 Mev. The scale height of the high-energy protons along a magnetic field line is found to be significantly greater than the scale height of the lower-energy protons. The first of these results is consistent with a breakdown of the transverse adiabatic invariant J, which tends to steepen the proton energy spectrum with increasing geomagnetic latitude and altitude, assuming cosmic ray albedo neutrons to be the source of these protons. The assumptions concerning the breakdown of the invariance of J are justified through detailed numerical calculations of proton trajectories in both a dipole magnetic field and the Finch and Leaton approximation to the geomagnetic field. The second result is not consistent with the cutoff energy dependence obtained by trajectory calculations and the approximate constancy of the neutron albedo injection coefficient along a magnetic field line. The average atmospheric density ρ¯ and energy losses ( (dE/dt)¯) along a magnetic field line as a function of energy have been investigated. It is found that the variations of the scale heights of ρ¯ and ( (dE/dt)¯) are much less than the observed variation of the scale height of the radiation as a function of energy.