The atmospheric and leakage flux of neutrons produced in the atmosphere by cosmic ray interactions

Abstract

The curve of the integrated neutron flux in the “thermal” to 20 MeV energy range, as a function of the atmospheric depth from sea level up to 0.1 mbar, has been determined, assuming as energy spectrum that predicted by Newkirk. The instrument employed is a combination of a hydrogeneous moderator with a slow neutron detector, with anticoincidence rejection of background events. Four balloon flights have been carried out in March 1966; one rocket flight in July 1966. With this flight the curve has been extended to 0.1 mbar from 6 mbar, attained with the balloon flights. The neutron flux as a function of the atmospheric depth is given, at 5.3 GV geomagnetic rigidity, in quiet Sun conditions. The albedo neutron flux has been measured: (0.42 ± 0.04) neutrons cm −2 sec −1. The mean free path for absorption in the atmosphere is: L = (165 ± 5)g cm −2. The maximum intensity has been found at (90 ± 10) g cm −2 residual pressure.