Energy spectrum and flux of high-energy neutrons at balloon altitudes

Abstract

The energy spectrum and flux of neutrons from En ≃ 2 MeV to En ≃ 75 MeV were measured with organic liquid scintillators near the top of the atmosphere during a balloon flight in 1973 at 4.2–2.9 g/cm² over Palestine, Texas (λ = 42°N). Two cylindrical liquid scintillators of dimensions 5 cm × 5 cm and 12.5 cm × 12.5 cm filled with NE 213 were used to cover the neutron energy range from 2 to 75 MeV. Pulse shape discrimination on each detector separated the protons and alphas produced within the scintillator by neutron interactions from the electrons produced by gamma rays. The response functions for monoenergetic neutrons up to En = 75 MeV were determined from acclerator calibrations. The neutron leakage current from 2 to 10 MeV is given by R = (0.25 ± 0.05)E−1.8±0.1 neutron/cm² s MeV, and at 20, 30, 50, and 75 MeV the leakage rates are (1.6 ± 0.4) × 10−3, (1.15 +0.20−0.25) × 10−3, (8.0+2.0−1.4) × 10−4, and (6.3 ± 1.3) × 10−4 neutron/cm² s MeV, respectively.