Institute for Advanced Study Informal Astrophysics Seminar - SPECIAL DAY

ABSTRACT: We take a fresh look at high energy radioactive nuclei data reported in the 90's and at the positron data recently reported by PAMELA. Our aim is to study the model independent implications of these data for the propagation time scales of cosmic rays in the Galaxy. Considering radioactive nuclei, in contrast to previous analyses we adopt an empiric approach, enabling us to draw general conclusions regarding the energy dependence of the cosmic ray residence time and the suppression of the flux due to decay. Using decaying charge to decayed charge ratios -- the only directly relevant data available to relativistic energies -- we show that the data for all nuclei species is consistent with a simple scaling relation as a function of the observer frame lifetime of the nuclei. Considering positron measurements, we argue that the positron flux is consistent with a secondary origin. Relating the positron data with radioactive nuclei at the same energy range, we derive constraints on the cooling time of the positrons. These constraints can be used to test the secondary origin hypothesis for the positrons in detail.