Cosmic-Ray Neutrons near the Earth

The altitude distribution of cosmic-ray neutrons has been measured from ground level up to 1175 ft using BF₃ detectors on a television antenna tower. Neutrons of about 1-keV energy were measured by surrounding the BF₃ counters with cadmium-coated polyethylene cylinders. The flux near the earth was found to depend strongly on the soil water content. The distribution of neutrons below 1 eV was found from the difference in count rates of bare and cadmium-covered detectors and agrees with the result of a diffusion calculation. The neutron energy spectrum was investigated at the 45-and 1175-ft levels by counting with varying thicknesses of polyethylene surrounding the detectors, but little difference between the spectra for the two levels was discernible.