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The Increase in the Primary Cosmic-Ray Intensity at High Latitudes, and the Non-Existence of a Detectable Permanent Solar Magnetic Field
Phys. Rev. 77, 830 – Published 15 March, 1950
DOI: https://doi.org/10.1103/PhysRev.77.830
Abstract
The primary cosmic-ray intensity at Churchill, Manitoba (geomagnetic latitude 69° N) has been compared directly with that at Swarthmore, Pennsylvania (geomagnetic latitude 52° N). The measurements, obtained with identical vertical quadruplecoincidence counter trains, have revealed an increase at the more northern station caused by the presence in the primary radiation of particles having energies below that which would have been permitted had the sun's magnetic field been effective to the extent previously assumed. The ratio of intensities is . Intensity vs. altitude curves were obtained with several different thicknesses of absorber interposed in the counter trains.
These experiments have revealed the absence of a sharp cut-off at the low energy end of the spectrum, imposed by a permanent solar dipole-moment having a magnitude consistent with certain controversial astrophysical determinations. Such a dipole-moment would have produced a knee in the latitude effect at about 50° N geomagnetic latitude. Furthermore, there is no indication of any diurnal variation which could be in conformity with the existence of a permanent dipole-moment at the sun.
The differential energy distribution at the low energy end of the primary cosmic-ray spectrum cannot be evaluated exactly because of absorption considerations, but it is doubtful that the exponent in an inverse power-law representation is as large as has usually been assumed heretofore.
Alternative explanations of the observed increase in counting rates, by invoking trapped orbit or re-entrant particle hypotheses, have been considered and rejected. It is concluded that the sun possesses no detectable permanent magnetic field and, on the basis of the present experiments, an upper limit of 0.6× gauss-, as compared with the previously quoted value of gauss-, may be assigned as a maximum possible value of the dipole-moment, if indeed it exists at all.
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