Author/Authors :
N.E. Yanasak، نويسنده , , M.E. Wiedenbeck، نويسنده , , W.R. Binns، نويسنده , , E.R. Christian، نويسنده , , A.C. Cummings، نويسنده , , A.J. Davis، نويسنده , , J.S. George، نويسنده , , P.L. Hink، نويسنده , , M.H. Israel، نويسنده , , R.A. Leske، نويسنده , , M. Lijowski، نويسنده , , R.A Mewaldt، نويسنده , , E.C. Stone، نويسنده , , T.T. von Rosenvinge، نويسنده ,
Abstract :
Radionuclides in the galactic cosmic rays serve as chronometers for measuring the characteristic time of physical processes affecting cosmic ray energy spectra and composition. The radionuclide 59Ni, present in the ejecta of supernovae, will decay to 59Co via electron-capture with a halflife of T12 = 7.6 × 104 yr. However, if the cosmic ray acceleration time scale is shorter than the decay halflife, 59Ni will become fully-stripped of electrons and will be present in the cosmic rays. Abundances of cosmic ray 59Ni and 59Co measured with the Cosmic Ray Isotope Spectrometer (CRIS) are consistent with the decay of all source 59Ni, implying an acceleration time delay > 105 yr. Abundances of the β-decay radioactive secondaries, produced by fragmentation of the cosmic rays during transport in the interstellar medium (ISM), depend on the time scales for spallation and escape from the Galaxy. Consequently, measurement of these abundances can be used to derive the galactic confinement time, τesc, for cosmic rays. Using the abundances of the β-decay species 10Be, 26Al, 36Cl, and 54Mn measured by CRIS, we find a confinement time τesc ∼ 15 Myr.
