A simple atom in favour of weight (6)

I believe the answer is:

proton

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'a simple atom' is the definition.
'proton' can be an answer for 'atom' (thesaurus). I'm unsure of the 'a simple' bit.

'in favour of weight' is the wordplay.
'in favour of' becomes 'pro' (I've seen this before).
'weight' becomes 'ton' (ton is a kind of weight).
'pro'+'ton'='PROTON'

Can you help me to learn more?

(Other definitions for proton that I've seen before include "Subatomic particle with positive charge" , "just a little bit" , "Positive nucleon" , "One charged" , "Tiny item charged" .)

I've seen this clue in the Sydney Morning Herald.

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