Wigner effect

To create the Wigner effect, neutrons that collide with the atoms in a crystal structure must have enough energy to displace them from the lattice.

This is known as the Wigner effect, after its discoverer, the Manhattan Project scientist Eugene Wigner.

Any solid can be affected by the Wigner effect, but the effect is of most concern in neutron moderators, such as graphite, that are used to slow down fast neutrons.

The Wigner effect (named for its discoverer, E. P. Wigner), also known as the discomposition effect, is the displacement of atoms in a solid caused by neutron radiation.

It was suggested that neutrons from fission would displace atoms from their lattice sites by momentum transfer with effects on most of the properties of graphite, which has become known as the Wigner effect.

Graphite moderator blocks are especially susceptible to this effect, known as Wigner effect, and have to be annealed periodically; the well-known Windscale fire was caused by a mishap during such an annealing operation.

At Hanford, plutonium production fell off as Reactors B, D and F wore out, "poisoned" by fission products and swelling of the graphite moderator known as the Wigner effect.

Creation of large amounts of interstitials in a solid can lead to a significant energy buildup, which on release can even lead to severe accidents in certain old types of nuclear reactors (Wigner effect).