We present the first measurement of cosmic-ray fluxes of ⁶ Li and ⁷ Li isotopes in the rigidity range from 1. 9 to 25 GV. The measurements are based on 9. 7×10⁵ ⁶ Li and 1. 04 ×10⁶ ⁷ Li nuclei collected by the Alpha Magnetic Spectrometer on the International Space Station from May 2011 to October 2023. We observe that over the entire rigidity range the ⁶ Li and ⁷ Li fluxes exhibit nearly identical time variations and, above ∼4 GV, the time variations of ⁶ Li, ⁷ Li, He, Be, B, C, N, and O fluxes are identical. Above ∼7 GV, we find an identical rigidity dependence of the ⁶ Li and ⁷ Li fluxes. This shows that they are both produced by collisions of heavier cosmic-ray nuclei with the interstellar medium and, in particular, excludes the existence of a sizable primary component in the ⁷ Li flux.
Aguilar et al. (Wed,) studied this question.