THE ONR-602 EXPERIMENT AND INVESTIGATION OF PARTICLE-PRECIPITATION NEAR THE EQUATOR

The ONR-602 experiment on board the S81-1 US Air Force mission was used, as one of its objectives, to investigate the global precipitation of radiation belt particles at low altitude. The experiment consisted of two particle telescopes-the main telescope and the monitor telescope. The main telescope performed Pulse-Height Analysis (PHA) on a priority basis set by the triggering of specific logical combinations of detectors to determine the charge, mass and energy of events, and returned detector coincidence and singles counting rates. Detector coincidence counting rates were formed by various logical combinations of the detectors, and singles counting rates were simply individual detector's counting rates. The monitor telescope had a fully depleted Si detector, and was designed to return only high counting rates of protons (0.6-9 MeV), alpha particles (0.8-4.5 MeV/n), and Z > 2 particles (1.1-11 MeV/n). The three rates were corresponding to the three discriminator thresholds-ML (0.36 MeV), MM (2.80 MeV), and MH (10.50 MeV) for the pulse height analyzer of the single Si detector. The monitor had the peak efficiency of detecting particles of approximately 90-degrees pitch angle near the equator, and due to the wide opening angle of 75-degrees it could detect quasitrapped particles of all pitch angles satisfying the energy thresholds in the altitude of interest. The high energy cosmic ray background count by the monitor was very insignificant. The procedures of handling data for the equatorial zone (+/- 30-degrees geomagnetic latitude) has been presented. Careful separation of particle precipitation data during geomagnetic average condition for the equatorial zone from other zones, and subsequent analysis show that ML rates were almost entirely due to protons.