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We present a high-resolution spectroscopic analysis of the bright (V=11.7),extreme halo giant CS31082-001 ([Fe/H] = -2.9), obtained in an ESO-VLT LargeProgramme dedicated to very metal-poor stars. We find CS31082-001 to beextremely rich in r-process elements, comparable in this respect only to thesimilarly metal-poor, but carbon-enriched, giant CS22892-052. As a result ofthe extreme overabundance of the heaviest r-process elements, and negligibleblending from CH and CN molecular lines, a reliable measurement is obtained ofthe U II line at 386 nm, for the first time in a halo star, along with numerouslines of Th II, as well as lines of 25 other r-process elements. Abundanceestimates for a total of 43 elements are reported in CS31082-001, almost halfof the entire periodic table. All elements with 56 \leq Z \leq 72 follow theSolar r-element pattern, reduced by about 1.25 dex ([r/Fe]=+1.7 dex, a factor50). Pb, in contrast, seems to be below the shifted Solar r-processdistribution, possibly indicating an error in the latter, while thorium is moreenhanced than the lighter nuclides. Thus, while a universal production ratiofor the r-process elements seems to hold in the interval 56 \leq Z \leq 72, itbreaks down in the actinide region. When available, the U/Th is thus preferableto Th/Eu for radioactive dating: (i) because of its faster decay rate andsmaller sensitivity to observational errors, and (ii) because the initalproduction ratio of the neighboring nuclides 238U and 232Th is more robustlypredicted than the 151Eu/232Th ratio. Our current best estimate for the age ofCS31082-001 is 14.0+/-2.4 Gyr.Comment: 20 pages, Latex, A&A style (aa.cls), Accepted for publication in A&

First stars. I. The extremer-element rich, iron-poor halo giant CS 31082-001