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The results of a high-altitude balloon measurement of the primary-proton spectrum at energies between 57 and 77 MeV are reported. It is concluded that the primary flux of these low-energy protons at Churchill is negligible, both as compared to the atmospheric secondary contribution and as compared to the primary flux at higher ({~}1 BeV) energies. A statistical upper limit of dJ/dE<0.49 protons/m²-sr-sec-MeV at E67 MeV is obtained.
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K. A. Brunstein (1964) studied this question.
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