  We derive the mixture of odd to even barium isotopes in the atmosphere of the
metal-poor subgiant HD140283 from the analysis of the Ba II transition at 455.4
nm in a high-resolution high signal-to-noise spectrum of the star. The detailed
shape of this spectral line depends on the relative contributions of odd and
even isotopes via isotopic and hyperfine splitting. We measure the fractional
abundance of odd Ba isotopes by modelling the formation of the Ba II 455.4 nm
line profile with the use of both a classical 1D hydrostatic and a 3D
hydrodynamical model atmosphere of HD140283. We interpret the results in terms
of contributions by the slow (s-) and rapid (r-) neutron-capture processes to
the isotopic mix. While the result of the 1D analysis of the Ba II feature
indicates a (64 +/- 36)% contribution of the r-process to the isotopic mix, the
3D analysis points toward a mere (15 +/- 34)% contribution from this process,
that is consistent with a solar-like mixture of barium isotopes.
