Quiet time observations of equatorially trapped megaelectronvolt radiation belt ions with nuclear charge Z ≧ 4


  • Walther N. Spjeldvik,

  • Theodore A. Fritz


The equatorial satellite Explorer 45 was equipped with a heavy ion solid state ion detector system in which four of the detector channels were sensitive to heavy ions like oxygen ions but not to protons or helium ions. Of these, only the lowest energy passband covering 1.82–4.8 MeV per ion for oxygen showed sufficiently high count rates to give meaningful statistics in a single satellite pass through the radiation belts. All measurements were carried out close to the equatorial plane, 1 ≤ B/B0 ≲ 1.4 at L shells below the spacecraft apogee of 5.24 RE, and the scope of this report is restricted to geomagnetically quiescent conditions during the period June 1–15, 1972. Fluxes of these ions are interpreted as oxygen ions and are found to maximize in the L shell range 3–3.5 with a peak equatorially mirroring flux of 0.38 ions/cm² s sr keV. This peak is not as sharply confined in L shell as the one previously reported for helium ions.