The Collaborative International Dictionary of English v.0.48:

Nuclear physics \Nu"cle*ar phys"ics\, n.
   That branch of physics which studies the structure of and
   phenomena observed in atomic nuclei.
   [PJC]

WordNet (r) 3.0 (2006):

nuclear physics
    n 1: the branch of physics that studies the internal structure
         of atomic nuclei [syn: nuclear physics, atomic physics,
         nucleonics]

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "nuclear physics":
   Newtonian physics, acoustics, aerophysics, applied physics,
   astrophysics, atomic science, atomics, atomistics, atomology,
   basic conductor physics, biophysics, chemical physics, cryogenics,
   crystallography, cytophysics, electron physics, electronics,
   electrophysics, geophysics, macrophysics, mass spectrography,
   mass spectrometry, mathematical physics, mechanics, medicophysics,
   microphysics, molecular physics, natural philosophy,
   natural science, nuclear chemistry, optics, philosophy, physic,
   physical chemistry, physical science, physicochemistry,
   physicomathematics, physics, psychophysics, quantum mechanics,
   radiation physics, radiology, radionics, solar physics,
   solid-state physics, statics, stereophysics, theoretical physics,
   thermionics, thermodynamics, wave mechanics, zoophysics