Properties of Cosmic Helium Isotopes Measured by the Alpha Magnetic Spectrometer

Creative Commons License

Aguilar M., Cavasonza L. A., Ambrosi G., Arruda L., Attig N., Bachlechner A., ...More

PHYSICAL REVIEW LETTERS, vol.123, no.18, 2019 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 123 Issue: 18
  • Publication Date: 2019
  • Doi Number: 10.1103/physrevlett.123.181102
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Middle East Technical University Affiliated: Yes


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