The energy spectrum of the heavy primary cosmic rays

Abstract

The magnetic rigidity spectrum of primary cosmic rays with Z ≥ 6, in the rigidity interval 2·5 to 16·0 GV, has been determined by means of a Cerenkov counter carried in the satellite Ariel. The integral spectrum shows a well-defined change in slope near 8·5 GV, indicating that this is probably the upper limit to the solar modulation process at this time (May and June 1962). In the rigidity interval covered by these measurements the integral spectrum is adequately represented by a power law with an exponent ca . 1.2 below 8.5 GV and ca . 1.5 above this rigidity. Under the plausible assumption that the integral galactic spectrum of these particles is represented by a power law with exponent 1·5, it follows that the solar modulation process in the 2·5 to 8·5 GV region is of the form J E = J ∞ [p/p o ] 0·3 , where J E is the intensity at the Earth of particles with rigidity greater than p , where p is in GV, J ∞ is the corresponding intensity outside the solar system, and p 0 ~ 8·5.