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 ± , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>p</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> </mml:math> , 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 − , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>p</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> </mml:math> , and nuclei Z ≤ 28.