Cosmic-ray 26Al and its decay in the galaxy

Radioactive Al-26 (tau(1/2) = 8.7 X 10(5) yr) has been resolved from stable Al-27 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 Al-26 is Of cosmic-ray spallation origin. Heliospheric modulation of the two isotopes was included. The derived ratio Al-26/Al-27 = 0.061 +/- 0.007 yields an average interstellar medium density rho = 0.26(-0.04)(+0.05) atoms cm(-3) and a Galactic confinement time of 19 +/- 3 million years. These values agree with the results from radioactive Be-10 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 Al-26 decay to Mg-26 throughout the Galaxy are discussed with respect to Al-26, Al-27, and Mg-26 in the cosmic radiation and their injection into the interstellar medium from nucleosynthesis in supernovae, novae, and red giant stars.