Carbon and something radioactive, not originally in bone (7)
I believe the answer is:
cranium
'bone' is the definition.
(I know that cranium is a type of bone)
'carbon and something radioactive not originally' is the wordplay.
I cannot really understand how this works, but
'carbon' could be 'c' (chemical symbol) and 'c' is present in the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is found in the answer.
'something radioactive' could be 'u' (chemical symbol for uranium) and 'u' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'in' is the link.
Can you help me to learn more?
(Other definitions for cranium that I've seen before include "Brainpan" , "Part of the skull" , "Brainbox" , "Skull, bones enclosing brain" , "Skull that encloses the brain" .)