Earth Albedo Neutrons from 10 to 100 MeV

Abstract

We report the measurement of the energy and angular distributions of Earth albedo neutrons from 10 to 100 MeV at 40\ifmmode^\circ\else\textdegree\fi{} N geomagnetic latitude from a balloon at 120 000 ft, below 4.65 g/${\mathrm{cm}}^{2}$. The albedo-neutron omnidirectional energy distribution is flat to 50 MeV, then decreases with energy. The absolute neutron energy distribution is of the correct strength and shape for the albedo neutrons to be the source of the protons trapped in Earth's inner radiation belt.