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.

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[1] The cosmic ray decreases and interplanetary disturbances observed at 1 AU have been investigated by using some cosmic ray hourly intensities recorded with groundbased monitors at Alert, Deep River, and Mount Washington as well as the interplanetary magnetic field (IMF) and the solar wind plasma bulk speed, density, and temperature in the near-Earth space. We studied a two-step Forbush decrease (FD)-type, with large cosmic ray intensity decreases, on 29-30 September 1978, 24-26 April 1979, 27-28 August 1978, 30 January 1978, 13-15 January 1967, 3-5 January 1978, 28-29 November 1989, and 29-30 December 1989, each of which appears to be produced by the structure within the shock and sheath preceding the interplanetary coronal mass ejection (ICME). There is a sheath upstream of the ICME led by a fast forward shock. The sheath material is slow solar wind that has been swept up by the ICME and is not part of the ICME itself. The sheath material is hot, dense, and turbulent and is most probably produced by the shock. The large IMF variations in the shocked plasma scatter the galactic cosmic rays and thus sweep away the cosmic ray particles. When the IMF variations in the sheath become too feeble (the lull region), the scattering of the galactic cosmic rays ceases, corresponding to the recovery phase of the first step of the FD; the particle scattering resumes when the high IMF variations in the sheath resume and the onset of the second decrease starts. There is a second and rear region inside the interplanetary macrostructure, the ICME/ magnetic cloud, where the galactic cosmic rays are also scattered away from the high magnetic field pressure in the magnetic cloud. A data set with fine time resolution (less than an hour) and good statistics is needed to provide an exact timing of the various phenomena.

The atmospheric neutron leakage rate in the energy range 10−2 to 107 ev has been measured as a function of latitude, altitude, and time with a neutron detector on board the Ogo 6 satellite. The latitude dependence of the neutron leakage is in reasonable agreement with that predicted by R. E. Lingenfelter and E. S. Light et al. if the neutron energy spectrum has the shape calculated by L. L. Newkirk. The change in the neutron latitude dependence with the cosmic ray modulation agrees with the predictions of Lingenfelter and Light et al. For several solar proton events enhancements were observed in the neutron counting rates at λ ≥ 70°. Such events, however, provide an insignificant injection of protons at E ≤ 20 Mev into the radiation belts. An isotropic angular distribution of the neutron leakage in the energy range 0.1 kev to 10 Mev best fits the observed altitude dependence of the neutron leakage flux.

The cosmic‐ray neutron leakage flux and energy spectrum in the range 1–10 Mev were measured by a neutron detector on the Ogo 6 satellite from June 7 to September 30, 1969. The same detector simultaneously measured the total leakage flux, having 75% of its response to the leakage flux in the interval 1 kev to 1 Mev. For a neutron energy spectrum of the form AE−γ in the range 1–10 Mev, the upper limit to γ for polar regions (Pc⪕0.3 Gv) was found to be 1.0 and for the equatorial regions ( Pc⪖12 Gv) was 1.2. For the polar regions, the lower limit to γ was found to be 0.8. This energy spectrum at 1–10 Mev is slightly flatter than L. L. Newkirk predicted. The neutron fluxes at 1–10 Mev were 0.28±0.03 and 0.035±0.003 cm−2 sec−1 for Pc⪕0.3 and Pc⪖12 Gv, respectively. The ratios of the neutron flux at 1–10 Mev to the total neutron flux were 0.54±0.07 for Pc⪖0.3 Gv and 0.50±0.06 for Pc>12 Gv.