Spectra of He Isotopes and the 3He/4He Ratio

Abstract

Since its launch, the Alpha Magnetic Spectrometer-02 (AMS-02) has delivered outstanding quality measurements of the spectra of cosmic-ray (CR) species, e ^± , $\bar{p}$ , and nuclei (H–Si, S, Fe), which have resulted in a number of breakthroughs. Besides elemental spectra, AMS-02 also measures the spectra of light isotopes albeit within a smaller rigidity range. In this paper, we use the precise measurements of He isotopes and the ^3 He/ ^4 He ratio by AMS-02, together with Voyager 1 data, and investigate their origin. We show that there is an excess in ^3 He at higher energies compared to standard calculations assuming its fully secondary origin, which may indicate a source of primary ^3 He, or signify a change in the propagation parameters over the Galactic volume probed by the ^3 He/ ^4 He ratio. We provide updated local interstellar spectra (LIS) of ^3 He and ^4 He in the rigidity range from 2 to 40 GV. Our calculations employ the self-consistent G al P rop –H el M od framework that has proved to be a reliable tool in deriving the LIS of CR e ^− , $\bar{p}$ , and nuclei Z ≤ 28.

Keywords

• Galactic cosmic rays
• Secondary cosmic rays
• Heliosphere
• Cosmic rays