Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

T. Gregory Guzik


The CRRES satellite was in service from July 1990 to October 1991, during a period of high solar modulation and solar activity. The ONR-604 experiment aboard CRRES measured helium with isotopic resolution in the energy range 38--110 MeV/nucleon, and heavy ions through iron at 200--500 MeV/nucleon. Although solar modulation was high throughout the CRRES mission, the mission included periods of solar quiescence as well as a number of large solar flares and associated solar energetic particle events. Measurements were made of helium and heavy ions during both the quiet times and the flare periods. A study was made to search for anomalous component helium in the Earth's magnetosphere using the magnetic field as a rigidity filter. This effort was inconclusive due to background in the outer electron radiation belt. During the solar quiet times, the helium spectrum above 60 MeV/nucleon is consistent with the galactic cosmic rays. Below that energy, a separate component appears early in the mission and rises in prominence over the course of the mission, dominating over the galactic cosmic rays below 60 MeV/nucleon. The distinctness of this component is seen both in the helium spectra and the 3He/4He ratio. An association of this component with interplanetary shocks driven by coronal mass ejections is suggested. During the March and June 1991 flare periods, helium spectral characteristics and isotopic ratios are measured. The results are compared to related diagnostic phenomena of gradual and impulsive solar energetic particle acceleration. The average 3He/4He ratio in both periods is enriched relative to the solar wind; 0.01 in June 1991 and 0.07 in March. The March period contains spikes in the isotopic ratio rising to 0.22. Signatures of known solar phenomena are compared to attempt to identify the predominant acceleration mechanism of each major flare. The development of the CRRES/SPACERAD Heavy Ion Model of the Environment (CHIME) is described and the results presented.