The purpose of this work is to resume investigation of Galactic thin disk dating using nucleocosmochronology with Th/Eu stellar abundance ratios , a theme absent from the literature since 1990 .
A stellar sample of 20 disk dwarfs/subgiants of F5 to G8 spectral types with -0.8 \leq \mathrm { [ Fe / H ] } \leq + 0.3 was selected .
In stars with such spectral types and luminosity classes , spectral synthesis techniques must be employed if we wish to achieve acceptably accurate results .
An homogeneous , self-consistent set of atmospheric parameters was determined .
Effective temperatures were determined from photometric calibrations and H \alpha profile fitting ; surface gravities were obtained from T _ { \mathrm { eff } } , stellar masses and luminosities ; microturbulence velocities and metallicities were obtained from detailed , differential spectroscopic analysis , relative to the Sun , using equivalent widths of \ion Fei and \ion Feii lines .
Chemical abundances of the elements that contaminate the Th and Eu spectral regions ( Ti , V , Cr , Mn , Co , Ni , Ce , Nd , and Sm ) were determined through spectroscopic analysis .
Abundance uncertainties were thoroughly scrutinised , their average value – ( 0.10 \pm 0.02 ) dex – being found to be satisfactorily low .
Eu and Th abundances were determined by spectral synthesis of one \ion Euii line ( 4129.72 Å ) and one \ion Thii line ( 4019.13 Å ) , taking into account the detailed hyperfine structures of contaminating Co lines , as well as the hyperfine structure and isotope shift of the Eu line .
Comparison of our abundances with literature data shows that our results exhibit a similar behaviour , but a considerably lower scatter ( 36 % lower for Eu , and 61 % lower for Th ) .
The [ Th/Eu ] abundance ratios thus obtained were used , in the second paper of this series , to determine the age of the Galactic disk .