Awful strain besets atomic technician (7)
I believe the answer is:
artisan
'technician' is the definition.
(I've seen this before)
'awful strain besets atomic' is the wordplay.
'awful' is an anagram indicator.
'besets' indicates putting letters inside (beset can mean to surround).
'atomic' becomes 'a' (eg in A-test, atomic test).
'strain' with letters rearranged gives 'artisn'.
'artisn' placed around 'a' is 'ARTISAN'.
(Other definitions for artisan that I've seen before include "Sinatra (anag) -- skilled manual worker" , "Egypt peninsula; holy Mount" , "Tsarina (anag.)" , "craftsman of his trade" , "Skilled worker at craft or trade" .)