A satellite measurement of cosmic-ray abundances and spectra in the charge range 2 <= Z <= 10

Citation

Brown, James William (1974) A satellite measurement of cosmic-ray abundances and spectra in the charge range 2 <= Z <= 10. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/16Z7-5A26. https://resolver.caltech.edu/CaltechETD:etd-10282005-124729

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. The composition of the nuclear component of the cosmic radiation has been under study for some time, because it can yield information concerning the source, propagation, and confinement of cosmic rays within the galaxy. We present here the first comprehensive satellite measurement of cosmic-ray composition and spectra in the charge range 2 <= Z <= 10 using the geomagnetic field as a rigidity analyzer through the entire range of vertical cutoffs. The results indicate that the spectra of all the elements in the observed range are similar, and thus that various ratios of elemental abundances are nearly independent of rigidity over the range 2 <= P <= 15 GV. Calculations of the propagation of cosmic rays through the interstellar and interplanetary media predict that there should be a variation with rigidity of ratios of various elements, because of the charge-dependent effects of ionization of the interstellar gas by the cosmic rays. The absence of this variation can be explained by assuming a rigidity-dependent confinement of the cosmic rays in the galaxy. From the ratios Be/0 and B/0 we obtain a leakage mean free path decreasing from [...] at ~2 GV to [...] at 10-15 GV, assuming that the interstellar gas is composed of hydrogen and helium in a 10:1 ratio. Ratios of other cosmic-ray elements are consistent with such a decreasing path length. The confinement time of the cosmic rays in the galaxy can be estimated from the ratio Be/B, because of the radioactive decay of [...] to [...]. The data indicate a confinement time of [...] years, which may be rigidity-dependent.

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