Energy Spectrum of Fast Cosmic-Ray Neutrons near Sea Level

Measurement of the sea-level spectrum of cosmic-ray neutrons in the energy region 0.05-2.0 MeV has been carried out with $4\pi$ hydrogen-recoil proportional counters. Electronic pulse-shape discrimination has been utilized to reject meson- and photon-induced events. In general, the flux per unit energy decreases monotonically with increasing energy. The experimental data reveal some structure which may be due to scattering resonances in elements that dominate the environment. An integral flux of 2.3×${10}^{-3\mathrm{}}$ neutrons/${\mathrm{cm}}^2$ sec in the interval 0.05-2.0 MeV has been obtained for the air-land interface at the Argonne National Laboratory site (53° N geomagnetic latitude).