Abstract
Recent measurements of the charge and energy composition of cosmic rays have shown the energy spectra of secondary cosmic ray nuclei (Li, Be, B) to be steeper than those of the parent nuclei (C, O) indicating a decreasing path length for the particles with increasing energy. Differences also exist in the energy spectra of primary nuclei such as C, O and Fe. Of particular interest is the spectrum of Fe above 100 GeV. Measurements exist up to ∼1013eV (refs 1, 2), and these indicate that the spectrum of Fe is less steep than that of lighter nuclei including protons. If this trend were to continue to ⩾1015eV, Fe would then become the dominant constituent of cosmic rays. This conclusion is supported by results from air shower measurements at primary energies >1013eV (refs 3–5). However, air shower measurements suffer from the inherent uncertainty of having to extrapolate data from lower energy accelerator measurements for air shower modelling6. Thus these results need confirmation by direct measurements of Fe nuclei. We describe here results from such an experiment.
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Sood, R. Detection of 1014-eV iron nuclei in cosmic rays. Nature 301, 44–46 (1983). https://doi.org/10.1038/301044a0
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DOI: https://doi.org/10.1038/301044a0
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