Detection of an intense flux of low-energy protons or ions trapped in the inner radiation zone

Employing a set of CdS crystal energy-flux detectors flown in satellite Injun I, we have observed an energy flux in excess of 50 ergs/cm2 sec sterad at approximately 1000 km altitude in the inner Van Allen zone. Through discrimination by magnetic rigidity and with the help of data from other on-board detectors, it was found that the flux is comprised of protons of energy 0.5 kev ≲E≲1 Mev and/or other heavy ions, apparently trapped in the geomagnetic field. So large a flux of low-energy heavy particles seems to be markedly inconsistent with prevailing ideas of the source function and/or the trapped lifetime of such particles.