Properties of Cosmic Helium Isotopes Measured by the Alpha Magnetic Spectrometer

This is the authors' abstract. We don't add key points for this paper.

Precision measurements by the Alpha Magnetic Spectrometer (AMS) on the International Space Station of ³He and ⁴He fluxes are presented. The measurements are based on 100 million ⁴He nuclei in the rigidity range from 2.1 to 21 GV and 18 million ³He from 1.9 to 15 GV collected from May 2011 to November 2017. We observed that the ³He and ⁴He fluxes exhibit nearly identical variations with time. The relative magnitude of the variations decreases with increasing rigidity. The rigidity dependence of the ³He/⁴He flux ratio is measured for the first time. Below 4 GV, the ³He/⁴He flux ratio was found to have a significant long-term time dependence. Above 4 GV, the ³He/⁴He flux ratio was found to be time independent, and its rigidity dependence is well described by a single power law ∝RΔ with Δ=-0.294±0.004. Unexpectedly, this value is in agreement with the B/O and B/C spectral indices at high energies.