  Our sample of cool dwarf stars from previous papers is extended in this study
including 15 moderately metal-deficient stars. The samples of halo and thick
disk stars have overlapping metallicities with [Fe/H] in the region from -0.9
to -1.5, and we first compare chemical properties of these two kinematically
different stellar populations independent on their metallicity. We present
barium, europium and magnesium abundances for the new sample of stars. The
results are based on NLTE line formation obtained in differential model
atmosphere analyses of high resolution spectra observed mainly using the UVES
spectrogragh at the VLT of ESO. We confirm the overabundance of Eu relative to
Mg in the halo stars. Eight halo stars show the [Eu/Mg] ratios between 0.23 and
0.41, whereas stars in the thick and thin disk display a solar Eu to Mg ratio.
The [Eu/Ba] values found in the thick disk stars to lie between 0.35 and 0.57
suggest that during the thick disk formation evolved low-mass stars started to
enrich the interstellar gas by s-nuclei of Ba, and the s-process contribution
to Ba varies from 30% to 50%. Based on these results, and using the chemical
evolution calculations by Travaglio et al. (1999), we estimate that the thick
disk stellar population formed on a timescale from 1.1 to 1.6 Gyr from the
beginning of the protogalactic collapse. In the halo stars the [Eu/Ba] ratios
are found mostly between 0.40 and 0.67, which suggests a duration of the halo
formation of about 1.5 Gyr. For the whole sample of stars we present the
even-to-odd Ba isotope ratios as determined from hyperfine structure seen in
the Ba II resonance line lambda4554. Based on these data we deduce for the
thick disk stars the ratio of the s/r-process contribution to barium as 30 : 70
(+- 30%), in agreement with the results obtained from the [Eu/Ba] ratios.
