  We reassess the problem of the production and evolution of the light elements
Li, Be and B and of their isotopes in the Milky Way, in the light of new
observational and theoretical developments. The main novelty is the
introduction of a new scheme for the origin of Galactic cosmic rays (GCR),
which for the first time enables a self-consistent calculation of their
composition during galactic evolution. The scheme accounts for key features of
the present-day GCR source composition, it is based on the wind yields of the
Geneva models of rotating, mass losing stars and it is fully coupled to a
detailed galactic chemical evolution code. We find that the adopted GCR source
composition accounts naturally for the observations of primary Be and helps
understanding why Be follows closer Fe than O. We find that GCR produce ~70% of
the solar B11/B10 isotopic ratio; the remaining 30% of B11 presumably result
from neutrino-nucleosynthesis in massive star explosions. We find that GCR and
primordial nucleosynthesis can make at most 30% of solar Li. At least half of
solar Li has to originate in low-mass stellar sources (red giants, asymptotic
giant branch stars or novae), but the required average yields of those sources
are found to be much larger than obtained in current models of stellar
nucleosynthesis. We also present radial profiles of LiBeB elemental and
isotopic abundances in the Milky Way disc. We argue that the shape of those
profiles - and the late evolution of LiBeB in general - reveals important
features of the production of those light elements through primary and
secondary processes.
