  The isotopic composition of beryllium nuclei and its energy dependence encode
information of fundamental importance about the propagation of cosmic rays in
the Galaxy. The effects of decay on the spectrum of the unstable beryllium--10
isotope can be described introducing the average survival probability $P_{\rm
surv} (E_0)$ that can inferred from measurements of the isotopic ratio Be10/Be9
if one has sufficiently good knowledge of the nuclear fragmentation cross
sections that determine the isotopic composition of beryllium nuclei at
injection. The average survival probability can then be interpreted in terms of
propagation parameters, such as the cosmic ray average age, adopting a
theoretical framework for Galactic propagation. Recently the AMS02
Collaboration has presented preliminary measurements of the beryllium isotopic
composition that extend the observations to a broad energy range ($E_0 \simeq
0.7$-12 GeV/n) with small errors. In this work we discuss the average survival
probability that can be inferred from the preliminary AMS02 data, adopting
publically available models of the nuclear fragmentation cross sections, and
interpret the results in the framework of a simple diffusion model, This study
shows that the effects of decay decrease more slowly than the predictions,
resulting in an average cosmic ray age that increases with energy. An
alternative possibility is that the cosmic ray age distribution is broader than
in the models that are now commonly accepted, suggesting that the Galactic
confinement volume has a non trivial structure and is formed by an inner halo
contained in an extended one.
