The Wigner effect (named for its discoverer, Eugene Wigner),[1] also known as the discomposition effect or Wigner's disease,[2] is the displacement of atoms in a solid caused by neutron radiation.
Any solid can display the Wigner effect. The effect is of most concern in neutron moderators, such as graphite, intended to reduce the speed of fast neutrons, thereby turning them into thermal neutrons capable of sustaining a nuclear chain reaction involving uranium-235.