Measurement of the (n,H3) Cross Section in Nitrogen and Its Relationship to the Tritium Production in the Atmosphere

Nitrogen gas is irradiated by fast neutrons from a ${\mathrm{U}}^{235}$ fission plate and tritium is produced. The tritium is identified and counted by two different methods: (1) The gas is put into a cloud chamber where the ${\mathrm{H}}^3$ electrons are identified by their range and counted; (2) hydrogen is separated from nitrogen by its passage through palladium and is then counted in a Geiger counter. The average cross section for fission neutrons with energy sufficient to make the reaction proceed [4.4 Mev is (11±2)×${10}^{-27\mathrm{}}$ ${\mathrm{cm}}^2$].