The result of heaps of work by nuclear scientists, no doubt (6,4)
I believe the answer is:
atomic pile
'scientists no doubt' is the definition.
I can't tell whether this defines the answer.
'the result of heaps of work by nuclear' is the wordplay.
'the result of heaps of work' becomes 'pile' (I can't explain this - if you can you should believe this answer much more).
'by' means one lot of letters go next to another.
'nuclear' becomes 'atomic' (synonyms).
'pile' after 'atomic' is 'ATOMIC PILE'.
Can you help me to learn more?
(Another definition for atomic pile that I've seen is " Old name for nuclear reactor".)