Abundance measurements of Zn, Ga, Ge, & Se from the Cosmic Ray Isotope Spectrometer (Cris) experiment on the Advanced Composition Explorer (ACE) satellite

Abstract

The cosmic ray elemental abundances of _(30)Zn, _(31)Ga, _(32)Ge, and _(34)Se provide important tests of the model of the OB-association origin of galactic cosmic rays that has resulted from previous ACE measurements of the neon and iron isotopes and which appears to be confirmed by elemental abundances of Zn, Ga, Ge, and Se measured by the balloon-borne Trans-Iron Galactic Element Recorder (TIGER). These ultra-heavy (Z≥30) nuclei are very rare and require an instrument with a large product of geometrical factor and exposure time. We have measured these abundances using the CRIS instrument, which has a geometrical factor of about 250 cm^2sr, on the NASA-ACE spacecraft. Over the 11+ years since launch in 1997 we have collected ∼400 nuclei with Z≥30 over the energy range of ∼150 to 600 MeV/nucleon. These measured abundances relative to iron are presented and compared with those from the TIGER and HEAO-3 experiments. Our measurements are in reasonable agreement with the TIGER results and are consistent with an OB association origin of galactic cosmic rays.

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