Speaker
Description
We present the measurements of cosmic H, He, Li and Be isotopes based on AMS data. We observed that over the entire rigidity range D exhibits nearly identical time variations with p, $^3$He, and $^4$He fluxes. Above 4.5 GV, the D/$^4$He flux ratio is time independent and its rigidity dependence is well described by a single power law $\propto$ R$^\Delta$ with $\Delta^4$D/$^4$He = $−0.108 \pm 0.005$. This is in contrast with the $^3$He/$^4$He flux ratio for which we find $∆_{^3\mathrm{He}/^4\mathrm{He}} = −0.289 \pm 0.003$. The significance of $\Delta^4$D/$^4$He > $∆_{^3\mathrm{He}/^4\mathrm{He}}$ exceeds $10\sigma$. In addition, we found that above $\sim$13 GV the rigidity dependence of D and p fluxes is identical with a D/p flux ratio of $0.027 \pm 0.001$. These unexpected observations indicate that contrary to expectations, cosmic deuterons have a sizeable primary component. The Li and Be isotopic compositions provide crucial complementary information on cosmic ray propagation and sources. The $^7$Li/$^6$Li ratio tests the origin of Li nuclei in cosmic rays. As the radioactive isotope $^{10}$Be decays to $^{10}$B with a half-life comparable to the cosmic-ray residence time in the Galaxy, the $^{10}$Be/$^9$Be ratio can be used to measure the cosmic-ray propagation volume. Current measurements of the $^7$Li/$^6$Li, and $^{10}$Be/$^9$Be ratios are limited to energies below 2 GeV/n and are affected by large uncertainties. We present the measurement of the $^6$Li and $^7$Li fluxes and their ratio, and of the $^7$Be, $^9$Be, $^{10}$Be fluxes and their ratios in the energy region ranging from 0.6 GeV/n to 12 GeV/n.
