Galactic cosmic-ray confinement time:: Ulysses High Energy Telescope measurements of the secondary radionuclide 10Be

We report new measurements of the isotopic abundances of the Galactic cosmic-ray isotopes Be-7, Be-9, and radioactive Be-10. These measurements from the Ulysses High Energy Telescope (HET) combine exceptional mass resolution with superior statistics. Measurements of radioisotopes produced as secondaries during cosmic-ray propagation provide estimates of the average density of material traversed by the cosmic rays and, within the context of the "leaky box" model, the confinement time of cosmic rays in the Galaxy. Be-10, with its long lifetime (tau(1/2) = 1.6 x 10(6) yr by beta(-) decay) and pure secondary origin, is particularly well suited to this purpose. The HET measurement yields a density of rho = 0.19 +/- 0.03 atoms cm(-3), corresponding to a confinement time of 26(-5)(+4) Myr. Measurements of the shorter lived cosmic-ray radioisotopes Al-26 and Cl-36, including the results from the HET reported elsewhere (by Connell ansi coworkers), complement these Be-10 results and provide a broader view of cosmic-ray propagation.