Real problem around small beam (5)
I believe the answer is:
laser
'beam' is the definition.
(laser beam is a kind of beam)
'real problem around small' is the wordplay.
'problem' indicates an anagram.
'around' indicates putting letters inside.
'small' becomes 's' (abbreviation - e.g. clothes size).
'real' is an anagram of 'laer'.
'laer' placed around 's' is 'LASER'.
(Other definitions for laser that I've seen before include "Device that produces an intense beam of light" , "Source of intense beam" , "Device producing an intense light beam - kind of sailing dinghy" , "E.g. surgical light-beam" , "Coherent light-beam" .)