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 ≤En <18 MeV, 1.5 × 10−3 from 18 ≤En <30 MeV, and 9.5 × 10−4 neutron/cm² s MeV from 30 ≤En ≤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.

Measurements have been made of the neutron intensities above the atmosphere at rocket altitudes with a moderated He³ neutron detector. The He³ proportional counter was encased in a polyethylene moderator, and the moderator and neutron detector were surrounded by a ring of charged particle counters to discriminate against neutrons produced in the detector assembly by galactic and solar cosmic rays. Flights were made from 1965–1967 at 0°, 20°, 50°, and 70° geomagnetic latitudes (λ). The neutron counting rates at these latitudes are 0.3, <0.7, 1.7, and 3.0 sec−1, respectively. These counting rates can be converted to a neutron leakage flux in the energy range 10 to 5 × 106 ev by using the neutron detector calibration curve and Lingenfelter's calculated neutron energy spectrums at different latitudes. The neutron leakage flux is 0.08 ± 0.02 and 0.80 ± 0.10 neutrons/cm² sec at λ = 0° and λ = 70°, respectively. This latitude effect is about 10/1, less than the 13/1 ratio calculated by Lingenfelter in 1963. For λ < 50°, the measured and the calculated neutron fluxes agree.

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/cm 2 over Palestine, Texas (X = .42øN). Two cylindrical liquid.scintilla,tors of dimensions 5 cm x 5 cm and 12.5 cm x 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 E• = 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 -'-8ñø-' neutron/cm 2 s MeV, and at 20, 30, 50, and 75 MeV the leakage rates are (1.6 + 0.4) X 10 -3, (1.15 +_0ø:•) X 10 -3, (8.0_+•:•) X 10 -4, and (6.3 ñ 1.3) X 10 -4 neutron/cm 2 s MeV, respectively.

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The flux and energy spectrum of fast neutrons (3 < E < 20 Mev) and γ rays (1 ≤ E ≤ 10 Mev) near the top of the atmosphere have been measured with an organic liquid scintillator. For a power law description of the omnidirectional neutron energy spectrum N(E) = AE−β(E) from 3 to 20 Mev at 3.5 g/cm² over Palestine, Texas (Pc = 4.4 Gv), the spectral index β depends strongly upon E. It changes from 1.8 ± 0.2 in the range 3 ≤ E ≤ 10 Mev to 0.3−0.4+0.1 for 15 ≤ E ≤ 20 Mev. From 20 to 50 Mev the neutron energy spectrum must be at least as flat as from 15–20 Mev to yield the observed proton recoil spectrum from 10 to 18 Mev, assuming that the neutron spectrum above 50 Mev varies as E−2. The neutron energy spectrum had essentially the same shape at Ft. Churchill, Canada (Pc = 0.3 Gv). The neutron leakage current at Pc = 4.4 Gv from 3 to 10 Mev at solar minimum was 0.089 neutron/cm² sec and from 3 to 20 Mev was 0.12 neutron/cm² sec. The measurements reported here agree with recent calculations by Armstrong and Chandler and by Merker but exceed Lingenfelter's predictions by factors ranging from 2 to ∼10. Assuming a power law description of the 1‐ to 10‐Mev atmospheric γ ray energy spectrum, we find β = 2.2 ± 0.3 for 1 ≤ E ≤ 4 Mev and β = 1.6 ± 0.3 for 4 ≤ E ≤ 10 Mev for a partially unfolded count rate spectrum with a total flux of 0.66 photon/cm² sec at 3.5 g/cm² at λ = 42°N. Essentially the same spectral shape was found at Ft. Churchill, Canada.