Cosmic ray propagation time scales: lessons from radioactive nuclei and positron data

Understand

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, using decaying charge to decayed charge ratios -- the only directly relevant data available at relativistic energies -- we show that a rigidity independent residence time is consistent with observations.
• The data for all nuclei can be described by f_{s,i}=(t_i/100 Myr)^{0.7}, where f_{s,i} is the suppression of the flux due to decay and t_i is the observer frame lifetime for nucleus specie i.