Critical examination of the nested leaky box model for Galactic cosmic ray transport

We revisit the predictions of the nested leaky box model in detail, in terms of both primary cosmic-ray spectra, spectra of stable and unstable nuclei, and antimatter production (positrons and antiprotons). We conclude that the model is in direct conflict with several observational facts and at least in its vanilla version should be considered as ruled out by current data. We also speculate on some possibly interesting implications of the idea that at least a fraction of Galactic grammage may not be accumulated in the journey of cosmic rays in the interstellar medium but rather inside the sources or in regions around them. These speculations will become increasingly more relevant with the higher precision data becoming available at high energies.