Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...497l..85s&link_type=abstract
Astrophysical Journal Letters v.497, p.L85
Astronomy and Astrophysics
Astronomy
34
Ism: Cosmic Rays, Nuclear Reactions, Nucleosynthesis, Abundances, Ism: Abundances, Galaxy: Halo
Scientific paper
Radioactive 26 Al ( tau _{1/2}=8.7x105 yr) has been resolved from stable 27 Al in the cosmic radiation for the first time using the high mass resolution, charged particle telescope on the Ulysses spacecraft. The average density of the interstellar medium through which the cosmic radiation propagates was determined within the framework of a homogeneous propagation model, where all 26 Al is of cosmic-ray spallation origin. Heliospheric modulation of the two isotopes was included. The derived ratio 26Al/27Al = 0.061+/-0.007 yields an average interstellar medium density rho = 0.26^{+0.05}_{-0.04} atoms cm ^{-3} and a Galactic confinement time of 19+/-3 million years. These values agree with the results from radioactive 10 Be analysis and indicate that the cosmic radiation may spend part of its confinement time in a Galactic magnetic halo. The implications of the observed 1.809 MeV gamma -rays from 26 Al decay to 26 Mg throughout the Galaxy are discussed with respect to 26 Al, 27 Al, and 26 Mg in the cosmic radiation and their injection into the interstellar medium from nucleosynthesis in supernovae, novae, and red giant stars.
Connell James J.
Simpson André J.
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