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

• DOI: 10.48550/arxiv.2502.01887
• Publication Date: 2025-02-28
• Authors: M. J. Boschini; S. Della Torre; M. Gervasi; D. Grandi; G. Jóhannesson; G. La Vacca; N. Masi; I. V. Moskalenko; S. Pensotti; T. A. Porter; L. Quadrani; P. G. Rancoita; D. Rozza; M. Tacconi
• Keywords: QB460-466; High Energy Astrophysical Phenomena (astro-ph.HE); Heliosphere; FOS: Physical sciences; Galactic cosmic rays; Secondary cosmic rays; Heliosphere; Cosmic rays; Galactic cosmic rays; Astrophysics; Astrophysics - High Energy Astrophysical Phenomena; Cosmic rays; Secondary cosmic rays

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 ±, 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 3He/4He ratio by AMS-02, together with Voyager 1 data, and investigate their origin. We show that there is an excess in 3He at higher energies compared to standard calculations assuming its fully secondary origin, which may indicate a source of primary 3He, or signify a change in the propagation parameters over the Galactic volume probed by the 3He/4He ratio. We provide updated local interstellar spectra (LIS) of 3He and 4He in the rigidity range from 2 to 40 GV. Our calculations employ the self-consistent GalProp–HelMod framework that has proved to be a reliable tool in deriving the LIS of CR e −, p ¯ , and nuclei Z ≤ 28.