Interplanetary cosmic ray intensity: 1972--1984 and out to 32 AU

Journal Article · Fri Feb 01 04:00:00 EST 1985 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JA090iA02p01399· OSTI ID:5887533

Van Allen, J A; Randall, B A

Using counting rates of a number of Geiger-Mueller tubes in the University of Iowa instruments of Pioneer 10 (P10) and Pioneer 11 (P11), we have measured the interplanetary intensity of cosmic rays (E/sub p/>80 MeV) over a complete solar activity cycle and out to a heliocentric distance of over 32 AU. Reliable free-space values of the background corrections due to the radioisotope thermal generators were determined during passage of Pioneer 11 under the rings of Saturn and in to 1.34 R/sub S/ (planetary radii) during the Septmber 1, 1979 encounter. These improved corrections and ones inferred therefrom for Pioneer 10 have supplanted earlier estimates and have been applied to all data. During the period 1972--1984, intensity vs. time curves have a flat, more-or-less constant maximum during 1975, 1976, and 1977; a brief (approx.8 months) minimum in mid-1981; and another brief minimum centered around early January 1983. The ratio of maximum to minimum intensity (normalized to the same radial distance) for the solar activity cycle is roughly-equal2.7. The temporal correlation of intensity at P10 with that at P11 is good, after allowance for propagation delay, as is that with data from the Deep River Neutron Monitor. The max/min intensity ratio for the latter is roughly-equal1.25. As noted by us and others in previous studies, the decline in intensity after the prolonged maximum occurred primarily by an irregular succession of stepwise decreases with subsequent slow recovery such that successive decreases overlapped cumulatively. The logarithms of the ratios of the counting rates of a GM tube on P10 to that of a matched Gm tube on P11 (after allowance for propagation delay) were plotted against the differences in heliocentric radial distance ..delta..r.

• Research Organization: Department of Physics and Astronomy, University of Iowa, Iowa City
• OSTI ID: 5887533
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 90:A2; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

640101* -- Astrophysics & Cosmology-- Cosmic Radiation
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COSMIC RADIATION
COSMIC RAY FLUX
INTERPLANETARY SPACE
IONIZING RADIATIONS
PIONEER SPACE PROBES
PLANETS
RADIATION FLUX
RADIATIONS
SATURN PLANET
SOLAR CYCLE
SPACE
SPACE VEHICLES
VARIATIONS
VEHICLES