Isotopic analysis of high energy cosmic-ray nuclei

Abstract

The isotopic and chemical composition of primary cosmic-ray nuclei of a given magnetic rigidity does not change as the particles penetrate the magnetosphere. Their velocity spectra, however, are strongly modified. These modifications depend on the charge-to-mass ratio of each nuclear component. By comparing the velocity spectra of pairs of elements, their isotopic composition can be obtained. A detailed knowledge of geomagnetic cut-off values or of the transmission functions in the penumbra region is not required for such an analysis. The precision of isotopic composition analysis is limited by statistical fluctuation, nuclear interactions, and distortion of the velocity spectra by the measuring instruments. These effects have been evaluated. It is concluded that in the region of rigidities between 3 and 20 GV/c a reasonably dimensioned Cherenkov counter telescope in a near-earth orbit, making use of established techniques, can measure with considerable precision the isotopic composition of the most abundant elements in the primary cosmic radiation including many elements of special interest from the astrophysical point of view.