Some Measurements of Atmospheric Neutrons

Abstract

A series of airplane flights carrying neutron counters to an altitude of 700 g ${\mathrm{cm}}^{-2\mathrm{}}$ was made at 52°20′ north geomagnetic latitude in 1955. Enriched and normal B${\mathrm{F}}_3$ counters were covered with Cd, Sn, Pyrex, and lime-glass shields. The ratios of the counting rates of the variously shielded counters are compared with the ratios calculated theoretically on a thick-shield basis using the neutron energy distribution function derived by Freese and Meyer. The neutron-production data taken by Davis and by Staker with Pyrex-glass-envelope B${\mathrm{F}}_3$ counters are corrected for the absorption of neutrons by the boron in the Pyrex. The corrected neutron-production rates are recalculated to be 2.1±0.4 ${\mathrm{cm}}^{-2\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ and 0.9±0.2 ${\mathrm{cm}}^{-2\mathrm{}}$ ${\sec }^{-1\mathrm{}}$ at 54°36′ and 30°24′ north geomagnetic latitude, respectively, using recent values for the various neutron cross sections. These corrected rates agree, to within 5%, with the recent measurements reported by Soberman. The above energy distribution function was found, within the limited accuracy of the experiment, to describe the energy distribution of atmospheric neutrons.