Recent high-precision measurements of various types of particles in cosmic rays provide an unprecedented opportunity to study the structure of the galaxy. Radioactive cosmic-ray secondaries, such as beryllium-10 or aluminium-26, decay during propagation on a similar time scale to their escape time from the galaxy. As a result, the isotopic composition of these cosmic rays provides information about propagation time scales. We examined the energy dependence of cosmic-ray spectra and isotopic compositions, with a particular focus on the isotopes of beryllium. These data were considered in the context of a plain diffusion model with reacceleration effects, using a propagation code, GALPROP, to compute predicted elemental and isotopic spectra. The implications of the data on transport and source parameters in this model will be discussed. The impact of nuclear cross section uncertainties on these parameters will also be examined.