The origin of the spectral intensities of cosmic-ray positrons

We present a straightforward model of cosmic-ray propagation in the Galaxy that can account for the observed cosmic-ray positrons entirely as secondary products of cosmic-ray interactions with the interstellar medium. In addition to accounting for the observed energy dependence of the ratio of positrons to total electrons, this model can accommodate both the observed energy dependence of secondary to primary nuclei, like boron/carbon, and the observed bounds on the anisotropy of cosmic rays. This model also predicts the energy dependence of the positron fraction at energies higher than those measured to date, with the ratio rising to ∼0.7 at very high energies. The model presented in this paper arises as a natural extension of the widely used current models and allows one to include the spatial and temporal discreteness of the sources of cosmic rays.