Crossword clue: a highly unstable radioactive element (the heaviest of the halogen series); a decay product of uranium and thorium

The most common answer is astatine (8 letters).

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

Possible answers

astatine 8 letters wn-def

a highly unstable radioactive element (the heaviest of the halogen series); a decay product of uranium and thorium