Observations of protons not exceeding 1 MeV/nuc and ions during the September 1974 series of flares

Results are presented on observations of energetic particles made during an active solar period in September 1974, concentrating in particular on an ESP (Energetic Storm Particle) event observed in association with an interplanetary shock wave on 21 September. It is shown that the observed variations in the proton to alpha particle ratios and spectral indices can be explained either by pile-up or by acceleration models of ESP events.