Context : HD 140283 is a nearby ( V=7.7 ) subgiant metal-poor star , extensively analysed in the literature .
Although many spectra have been obtained for this star , none showed a signal-to-noise ( S/N ) ratio high enough to enable a very accurate derivation of abundances from weak lines .

Aims : The detection of europium proves that the neutron-capture elements in this star originate in the r-process , and not in the s-process , as recently claimed in the literature .

Methods : Based on the OSMARCS 1D LTE atmospheric model and with a consistent approach based on the spectrum synthesis code Turbospectrum , we measured the europium lines at 4129 Å and 4205 Å , taking into account the hyperfine structure of the transitions .
The spectrum , obtained with a long exposure time of seven hours at the Canada-France-Hawaii Telescope ( CFHT ) , has a resolving power of 81000 and a S/N ratio of 800 at 4100 Å .

Results : We were able to determine the abundance A ( Eu ) =-2.35 \pm 0.07 dex , compatible with the value predicted for the europium from the r-process .
The abundance ratio [ Eu/Ba ] =+0.58 \pm 0.15 dex agrees with the trend observed in metal-poor stars and is also compatible with a strong r-process contribution to the origin of the neutron-capture elements in HD 140283 .

Conclusions :