Polar-cap measurements of solar-flare protons with energies down to 12.4 keV

Solar protons with energies down to 12.4 kev were measured over the polar caps by instruments aboard the OV 1–17 satellite. The observations were made following the March 21, 1969, solar-particle event. The polar-cap differential fluxes measured by OV 1–17 and Injun 5 from 0.012 Mev to 1.1 Mev are well represented by a single power law. Over a 22-hour period the spectral index changed from 1.7 to 1.9. Temporal and spatial comparisons were made with data from the Explorer 35 and Injun 5 spacecraft. Good agreement is found at energies (>300 kev) where a comparison can be made.