The Intensity of Neutrons of Thermal Energy in the Atmosphere at Sea Level

The number of alpha-particles released in the disintegration of boron by neutrons in the atmosphere was measured in an ionization chamber filled with boron trifluoride. Assuming a cross section for the $n-\alpha$ reaction of 3×${10}^{-21\mathrm{}}$ ${\mathrm{cm}}^2$, the flux of neutrons of thermal energy was found to be 0.091±0.007 per square centimeter per minute, or one thermal neutron for every 16 ionizing cosmic rays. The consequences of the formation and absorption of this intensity of neutrons are discussed.