In a previous paper we were able to measure the abundance of uranium and thorium in the very-metal poor halo giant BPS CS 31082-001 , but only obtained an upper limit for the abundance of lead ( Pb ) .
We have got from ESO 17 hours of additional exposure on this star in order to secure a detection of the minimum amount of lead expected to be present in CS 31082-001 , the amount arising from the decay of the original content of Th and U in the star .
We report here this successful detection .
We find an LTE abundance \log \mathrm { ( Pb / H ) } +12 = -0.55 \pm 0.15 dex , one dex below the upper limits given by other authors for the similar stars CS 22892-052 and BD +17° 3248 , also enhanced in r -process elements .
From the observed present abundances of Th and U in the star , the expected amount of Pb produced by the decay of ^ { 232 } Th , and ^ { 238 } U alone , over 12 – 15 Gyr is -0.73 \pm 0.17 dex .
The decay of ^ { 235 } U is more difficult to estimate , but is probably slightly below the contribution of ^ { 238 } U , making the contribution of the 3 actinides only slightly below , or even equal to , the measured abundance .
The contribution from the decay of ^ { 234 } U has was not included , for lack of published data .
In this sense our determination is a lower limit to the contribution of actinides to lead production .
We comment this result , and we note that if a NLTE analysis , not yet possible , doubles our observed abundance , the decay of the 3 actinides will still represent 50 per cent of the total lead , a proportion higher than the values considered so far in the literature .