Neutron measurements at balloon altitudes using organic scintillators and application for gamma ray measurements

The neutron differential energy spectrum at altitudes from 4.2 g/cm2 to 2.9 g/cm2 has been measured by two liquid organic cylindrical scintillators (NE213) during a balloon flight at Palestine, Texas, lambda = 420N on June 22, 1973. These detectors were calibrated at the University of New Hampshire Van de Graaff accelerator and at the Michigan State University cyclotron. Experimental response functions from calibrations are used to unfold the observed neutron spectrum. The neutron leakage current spectrum measured in this flight normalized to sunspot minimum at E/sub n/ = 2 MeV is 0.065/sub -0.012//sup +0.14/ neutrons/cm2-sec-MeV, and at E/sub n/ = 10 MeV is 3.1 x 10-3/sub -7.2 x 10-4//sup +7.5 x 10-4/ neutrons/cm2-sec-MeV. From E/sub n/ = 2 MeV to E/sub n/ = 10 MeV the spectrum can be described by a power law energy spectrum with an index of --1.9. From 10 MeV to 75 MeV the spectrum required to fit the data must be much flatter. At E/sub n/ = 50 MeV the leakage current is 7.1 x 10-3/sub -1.3 x 10-3//sup +2.3 x 10-3/ neutrons/cm2-sec-MeV. Between 20 MeV and 50 MeV the neutron leakage current spectrum from the measurement is approximately a factor of 3 lower than the measurement of White et al. (1972), but about a factor of 8 higher than the calculations of Lingenfelter (1963b) at 50 MeV. A computer program using the Monte Carlo technique to unfold the measured gamma ray spectrum was developed and applied to the gamma ray data obtained. A prototype neutron-gamma ray telescope system was also included which incorporated a time of flight system between the two detectors and used the double scattering technique to measure the directional fluxes and energy spectra of neutrons and gamma rays