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.
The VSOP mission is a Japanese-led project to image radio sources with sub-milliarcsec resolution by correlating the signal from the orbiting 8-m telescope, HALCA, with a global array of telescopes. Twenty-five percent of the scientific time of this mission is devoted to a survey of 402 bright, small-diameter extra-galactic radio sources at 5 GHz. The major goals of the VSOP Survey are statistical in nature: to determine the brightness temperature and approximate structure; to provide a source list for use with future space VLBI missions; and to compare radio properties with other data throughout the EM spectrum. This paper describes: the compilation of a complete list of radio sources associated with active galactic nuclei (AGN); the selection of the subsample of sources to be observed with VSOP; the extensive ground resources used for the Survey; the status of the observations as of 2000 July; the data-analysis methods; and several examples of results from the VSOP Survey. More detailed results from the full sample will be given in future papers.
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.
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