Observation of 38-334-keV Interplanetary Protons during Solar Quiet Times

Abstract

We present the first observations of quiet-time interplanetary protons in the energy range 38 to 334 keV from the Apollo 16 subsatellite. These proton fluxes vary by a factor of ∼ 5 over a six-month period. Their spectrum can be represented by a power law $\frac{\mathrm{dJ}}{\mathrm{dE}}=5.6\mathrm{}{E}^{-1.3\mathrm{}}$ ${\left({\mathrm{cm}}^2\mathrm{s}\mathrm{e}\mathrm{c}\mathrm{s}\mathrm{t}\mathrm{e}\mathrm{r}\mathrm{k}\mathrm{e}\mathrm{V}\right)}^{-1\mathrm{}}$ from 38 to 334 keV during May 1972.