Angular distribution and altitude dependence of atmospheric neutrons from 10 to 100 MeV

The altitude dependence of atmospheric neutrons from ground level to 5 g/cm² of residual atmosphere at neutron energies of 10–100 MeV is reported. Ground level measurements were taken at Cape Girardeau, Missouri, on September 18, 1972. The other measurements were made during ascent and float on launch from Palestine, Texas, on September 26, 1971. The intensity of both the downward- and the upward-moving neutrons is maximum at about 100 g/cm² of residual atmosphere. Neutron angular distributions are reported from 20° to 80° and 100° to 160° for 10- to 100-MeV neutrons. Omnidirectional fluxes at altitudes of 5, 50, 100, and 200 g/cm² of residual atmosphere are in good agreement with recent theoretical calculations of Armstrong et al. in the three energy intervals of 10–30, 30–50, and 50–100 MeV.