  The discovery of a single anti-helium nucleus in the cosmic ray flux would
definitely point toward the existence of stars and even of entire galaxies made
of anti-matter. The presence of anti-nuclei in cosmic rays has actually
profound implications on the fundamental question of the baryon asymmetry of
the universe. It is therefore crucial to determine the amount of anti-matter
which our own galaxy already produces through the spallation of high-energy
protons on the interstellar gas of the galactic disk. We have used here a
coalescence model to assess the amount of anti-deuterium and anti-helium 3
present in cosmic rays together with anti-protons. The propagation of cosmic
rays in the galaxy is described through a two-zone diffusion model which
correctly describes the observed abundances. We find that the
antideuterium/proton ratio exceeds $10^{-9}$ above a momentum per anti-nucleon
of about 4 GeV/c. Would the universe be purely made of matter, the AMS
collaboration should be able to detect a few anti-deuterons during the space
station stage of the experiment. However, the antihelium3/proton abundance does
not exceed $4 10^{-13}$. Heavier anti-nuclei are even further suppressed.
