Enhancement of solar heavy nuclei at high energies in the 4 July 1974 event

Abstract

Relative abundances of energetic nuclei in the 4 July 1974 solar event are presented. The results show a marked enhancement of abundances that systematically increase with nuclear charge numbers in the range of the observation, 6 ≤ Z ≤ 26 for energies above 15 MeV nucl.−1 While such enhancements are commonly seen below 10 MeV nucl−1, most observations at higher energies are found to be consistent with solar system abundances. The energy spectrum of oxygen is observed to be significantly steeper than most other solar events studied in this energy region. It is proposed that these observations are characteristic of particle populations at energies ∼1 MeV nucl−1, and that the anomalous features observed here may be the result of the high energy extension of such a population that is commonly masked by other processes or populations that might occur in larger solar events.