Rupture regularly found in noble gas particle (7)
I believe the answer is:
neutron
'particle' is the definition.
(neutron is a kind of particle)
'rupture regularly found in noble gas' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'found in' indicates putting letters inside.
'noble gas' becomes 'neon' (I've seen this before).
The alternating letters of 'rupture' are 'utr'.
'utr' inserted into 'neon' is 'NEUTRON'.
(Other definitions for neutron that I've seen before include "one isn't charged" , "On tuner (anag.)" , "Charged particle" , "Particle that decays when released" , "Elementary particle with zero charge" .)