Curie discovery (6)
I believe the answer is:
radium
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">curie discovery</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for radium that I've seen before include "Radioactive metallic element found in pitchblende" , "Chemical element, Ra" , "Metallic element discovered by the Curies" , "Curie-found element" , "Radioactive metal" .)