Acad Sinica, Inst High Energy Phys, Beijing 100039, Peoples R China
; Hiroshima Univ, Grad Sch Sci, Hiroshima 7398526, Japan
The cosmic-ray He-3/He-4 ratios from 0.09 to 1.2 GeV per nucleon are measured by Alpha Magnetic Spectrometer (AMS) at its precursor mission on board the space shuttle Discovery during the flight STS-91 in June 1998. Taking unique advantage of AXIS data collected from a large region covering the earth equator, we also studied the magnetic latitude effect on the ratios. Our analysis shows that the relative abundances of He-3 and He-4 in cosmic rays depend weakly on the magnetic latitude, and given present uncertainties, the observed isotopic composition is generally consistent with the predictions of the standard propagation model of cosmic rays.