Atmospheric neutron and gamma ray fluxes and energy spectra

Abstract

The energy spectra and fluxes of atmospheric neutrons and gamma rays from 8 to 60 MeV and from 2 to 10 MeV, respectively, have been measured with a time‐of‐flight (TOF) system using organic liquid scintillators at balloon altitudes (3–5 g/cm²) over Palestine, Texas (λ=42°N). The TOF detector consisted of two banks of six cylindrical NE213 liquid scintillators, each being 7.5 cm in diameter by 7.5 cm long, separated by 0.75 m. A TOF system was used to measure upward and downward moving neutrons and gamma rays. Pulse shape discrimination is included on each NE213 scintillator to discriminate between neutrons and gamma rays. The measured neutron leakage current is 1.9 × 10 −3 from 8 ≤E n <18 MeV, 1.5 × 10 −3 from 18 ≤E n <30 MeV, and 9.5 × 10 −4 neutron/cm² s MeV from 30 ≤E n ≤60 MeV. The total downward gamma ray flux from 2 to 6 MeV at 3.5 g cm −2 is given by 0.012E −1.5 photon/cm² s sr MeV. The upward moving gamma ray flux at 4 g cm −2 from 2 to 10 MeV is 0.063E −1.8 photon/cm² s sr Mev.