Distribution of Neutrons in the Atmosphere

Measurements on the distribution of neutrons in the atmosphere have been made to an altitude of 36,600 feet. Observations were made with counters filled with boron trifluoride containing 82 percent of B¹⁰. Information concerning the spectral distribution of the neutrons was obtained by using the counters in various shielding geometries. Counters were used bare (no shielding), cadmium-covered, boron-covered, and surrounded with a layer of paraffin. The counting rates of all counters varied in the same way with altitude in the pressure range from 20 to 50 cm Hg. Within this pressure range the intensity I is given quite accurately by the relation I=I₀e^-0.083p, where p is expressed in cm of Hg. The counting equipment was carried in a B-29 type aircraft.