Latitude and altitude dependence of the cosmic ray albedo neutron flux

Abstract

Preliminary measurements of the cosmic ray albedo neutron flux above 400 km are reported for the period June 7 to 17, 1969. The measurements were made with a detector on board the Ogo 6 satellite that responds primarily to neutrons in the energy range 104 to 106 ev. The latitude variation of the counting rate was found to be 7.4/1 between 90° and 0°, similar to that predicted by Lingenfelter (1963). The neutron counting rate near the poles was found to decrease by 26±5% between 450 and 950 km altitude, corresponding to a R−4.2±0.9 dependence, where R is the distance from the center of the earth. This large altitude dependence excludes any angular distributions of neutron flux at the top of the atmosphere that are more peaked toward the vertical than cos θ (where θ is the angle from the vertical), but it is not in disagreement with an isotropic neutron flux. The total neutron leakage flux found by assuming isotropy was about 0.7 times that predicted by Lingenfelter (1963). The neutron leakage flux values obtained from the Ogo 6 experiment agree with those estimated from other experiments with a similar neutron energy response, if the same angular distribution is used. Estimates of the total neutron leakage flux, deduced from experiments responsive only to neutrons above 1 Mev by using the Lingenfelter (1963) and Newkirk (1963) energy spectra of leakage neutrons, show agreement with the lower energy results when the Newkirk spectrum is used but are up to twice as great as the lower energy results when the Lingenfelter spectrum is applied.

Upper limit to the 1?20 MeV solar neutron flux

“…No correction was made for background events in the He 3 counter because differences in counting rates rather than absolute counting rates were used. In any case this background rate was only about 3% at the equator (Jenkins et a/.,] 1970. Any contributions from locally produced neutrons in the OGO-6 spacecraft were calculated to be less than 0.3%.…”

“…The neutron detector efficiency for events in the He 3 counter as a function of energy for an isotropic neutron flux is shown in Figure 2. The details of the detector calibration have been presented (Jenkins et al, 1970). The variation of the detector efficiency with the incident angle of the neutron flux was determined at neutron energies of 0.3 MeV and 14 MeV.…”

“…For this spectrum r is estimated to be 5 < r < 10% (Lingenfelter, 1963). Taking the smallest value of n = 1 to yield the highest upper limit to F D, a=0.25.…”

Atmospheric Neutrons and Their Contributions to the Earth's Radiation Belts.

“…1. Comparison of the observed trapped proton flux at L=1.5 (FREDEN et at., 1965;FILLius and MCILWAI`N, 1964;VALOT, 1972) with that predicted by GRAND using the recent cosmic ray albedo neutron measurements (JENKINS et at., 1970(JENKINS et at., , 1971LocKwooD et at., 1973LocKwooD et at., , 1976IFEDILI 1972IFEDILI ,1982WHITE et at., 1972;KANBACH et at., 1974;PRESZLER et at., 1976). …”

A search for solar neutrons during solar flares

“…The details of the detector assembly and calibration have been presented (Jenkins et al, 1970(Jenkins et al, , 1971Ifedili, , 1972.…”