Heliocentric Radius of the Cosmic Ray Modulation Boundary.
IOWA UNIV IOWA CITY DEPT OF PHYSICS AND ASTRONOMY
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A semi-empirical analysis is made of our extensive body of observed cosmic ray intensity data from Pioneers 10 and 11 and related spectral information from other sources in order to infer the radius R of the modulation region surrounding the sun. During the period 1972-1985 the inferred values of R vary with the time systematically and in manner generally similar to that of sunspot numbers. The range of values of R is from 42 AU at the time of minimum solar activity about 1976 to 88 Au about 1.5 yr following the time of maximum solar activity about 1980. A specific, testable prediction is that Pioneer 10 will cross the modulation boundary in 1988 and will remain in its vicinity for several years thereafter.