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.E. Niebur
	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.