Primary Cosmic-Ray and Solar Protons

A study of the low-energy portion of the primary cosmic-ray proton spectrum has been made in August and September, 1960. We detected a significant flux of primary protons with energies below 500 Mev, which previously had been considered absent. This result is of importance to astrophysical considerations as it imposes restraints upon possible modulation mechanisms should these particles be of galactic origin. The alternate possibility, namely of solar origin of these particles is also discussed. The observations were made in three high altitude balloon flights at geomagnetic latitudes $\lambda \ge 73°$ N. The results show that the low energy proton spectrum observed on quiet days may be represented by $\frac{\mathrm{dJ}}{\mathrm{dE}}=2.3\mathrm{}\times {10}^4\times E^{-2\mathrm{}}$ protons/${\mathrm{m}}^2$ sec-sr-Mev for $78\le E\le 200$ Mev and flattens between 200 and 350 Mev. On September 8, 1960, the observed proton flux between 70 and 350 Mev was several times larger than on quiet days. These protons are believed to have been produced by a class 3 flare on September 3, 1960. Their energy spectrum has been measured.