We report the properties of sodium (Na) and aluminum (Al) cosmic rays in the rigidity range 2.15 GV to 3.0 TV based on 0.46 million sodium and 0.51 million aluminum nuclei collected by the Alpha Magnetic Spectrometer experiment on the International Space Station. We found that Na and Al, together with nitrogen (N), belong to a distinct cosmic ray group. In this group, we observe that, similar to the N flux, both the Na flux and Al flux are well described by the sums of a primary cosmic ray component (proportional to the silicon flux) and a secondary cosmic ray component (proportional to the fluorine flux). The fraction of the primary component increases with rigidity for the N, Na, and Al fluxes and becomes dominant at the highest rigidities. The $\mathrm{Na}/\mathrm{Si}$ and $\mathrm{Al}/\mathrm{Si}$ abundance ratios at the source, $0.036\pm 0.003$ for $\mathrm{Na}/\mathrm{Si}$ and $0.103\pm 0.004$ for $\mathrm{Al}/\mathrm{Si}$, are determined independent of cosmic ray propagation.

• Received 3 March 2021
• Revised 30 April 2021
• Accepted 1 June 2021

DOI:https://doi.org/10.1103/PhysRevLett.127.021101

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Published by the American Physical Society