Radiation left wolf with great metamorphoses (9)
I believe the answer is:
afterglow
'radiation left' is the definition.
(radiation left behind by something)
'wolf with great metamorphoses' is the wordplay.
'with' says to put letters next to each other.
'metamorphoses' indicates anagramming the letters (I've seen 'metamorphosis' mean this).
'wolf' after 'great' is 'greatwolf'.
'greatwolf' anagrammed gives 'AFTERGLOW'.
(Other definitions for afterglow that I've seen before include "residual light" , "Pleasure of remembering something nice" , "The satisfaction" , "Remaining light" , "following which gloom sets in?" .)