Galactic Cosmic-Ray Confinement Time: [ITAL]Ulysses[/ITAL] High Energy Telescope Measurements of the Secondary Radionuclide [TSUP]10[/TSUP]B[CLC]e[/CLC]

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Abstract
We report new measurements of the isotopic abundances of the Galactic cosmic-ray isotopes 7Be,9Be, and radioactive 10Be. 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. 10Be, with its long lifetime (τ½=1.6 × 106 yr by β− decay) and pure secondary origin, is particularly well suited to this purpose. The HET measurement yields a density of ρ=0.19 ± 0.03 atoms cm-3, corresponding to a confinement time of 26+ 4−5 Myr. Measurements of the shorter lived cosmic-ray radioisotopes 26Al and 36Cl, including the results from the HET reported elsewhere (by Connell and coworkers), complement these 10Be results and provide a broader view of cosmic-ray propagation.