Intensity and Energy Spectrum of Fast Neutrons in Cosmic Radiation

Abstract

The intensity and the energy spectrum of low energy neutrons at Mt. Norikura (2740 m above sea level and 25°N geomagnetic latitude) were obtained by observing recoil protons with the randomly operated high pressure cloud chamber filled with hydrogen gas at the pressure of 92 atm. The differential energy spectrum for neutrons in the energy range from 1 Mev to 15 Mev was found to be expressed by
(1.2±40%)×10⁻³×E^{−1.25±0.10}cm⁻² sec⁻¹ sterad⁻¹ Mev⁻¹.
The neutron flux is in conformity with what one would expect from the density of thermal neutrons. Connecting the present data with the others which were obtained by many investigations in different energy ranges, the energy spectrum of neutrons ranging from 1 ev to 10 Bev are discussed.