Abundances of the Cosmic Ray Beta-decay Secondaries and Implications for
Cosmic Ray Transport
N.E. Yanasak, M.E. Wiedenbeck
Jet Propulsion Laboratory, Pasadena, California, USA
A.C. Cummings, J.S. George, R.A. Leske, R.A. Mewaldt, E.C. Stone
California Institute of Technology, Pasadena, California, USA
E.R. Christian, T.T. von Rosenvinge
Goddard Space Flight Center, Greenbelt, Maryland, USA
W.R. Binns, P.L. Hink, J. Klarmann, M. Lijowski, S.M. Mahan
Washington University, St. Louis, Missouri
Galactic cosmic rays (GCR) pass through the interstellar medium (ISM) and
interact to produce secondary fragments during transport. Measurement of
the stable GCR secondary abundances provides information about the amount of
ISM material traversed by the cosmic rays to produce the observed fragments.
The abundances of radioactive secondary species will depend on the average ISM
density traversed during the lifetime of the species against decay or escape
from the galaxy. Considering the amount of ISM material indicated by stable
secondaries, abundance measurements of long-lived species such as Be-10,
Al-26, Cl-36, and Mn-54 can be used to derive a galactic
confinement time for cosmic rays. These species allow a comparison of
propagation histories for different parent nuclei. Collectively, their
different decay lifetimes provide a sensitivity to the ISM matter distribution
over a range of propagation volumes around the Earth. Abundances for these
species have been measured in the energy range 100-500 MeV/nuc during the
past two years, using the Cosmic Ray Isotope Spectrometer (CRIS) aboard the
Advanced Composition Explorer (ACE) spacecraft. To interpret the data we have
modeled the production and propagation of the radioactive secondaries, taking
into account recently published isotopic production cross-sections. Taking
advantage of the high statistical significance of the CRIS data, we present the
radioactive secondary abundances at different energies, testing the predicted
energy dependence of these abundances within our model. We discuss the
implications for GCR transport.