We report thorium abundances for 77 metal-poor stars in the metallicity range of -3.5 < \mathrm { [ Fe / H ] } < -1.0 , based on “ snapshot ” spectra obtained with VLT-UT2/UVES during the HERES Survey .
We were able to determine the thorium abundances with better than 1 \sigma confidence for 17 stars , while for 60 stars we derived upper limits .
For five stars common with previous studies , our results were in good agreement with the literature results .
The thorium abundances span a wide range of about 4.0 dex , and scatter exists in the distribution of log ( Th/Eu ) ratios for lower metallicity stars , supporting previous studies suggesting the r-process is not universal .
We derived ages from the log ( Th/Eu ) ratios for 12 stars , resulting in large scattered ages , and two stars with significant enhancement of Th relative to Eu are found , indicating the “ actinide boost ” does not seem to be a rare phenomenon and thus highlighting the risk in using log ( Th/Eu ) to derive stellar ages .