Wigner effect

physics

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July 15, 2026

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The Wigner effect, also known as the "knock-on" process, describes the physical changes that occur in solid materials when they are irradiated by neutrons. When neutrons collide with atoms in a crystal lattice, they can dislodge these atoms from their normal positions, causing them to move and create vacancies and interstitial atoms. This process, named after physicist Eugene Wigner, can lead to significant structural damage within the material.123

The energy transferred during these collisions depends on the mass of the neutron and the atom it strikes. For instance, in graphite, a neutron can knock off many carbon atoms, causing substantial damage. This phenomenon is crucial in understanding radiation damage in materials, particularly in nuclear reactors, where it can lead to changes in material properties like expansion and increased hardness.2

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radiation
Neutrons
The phenomenon, known as the Wigner effect and sometimes as a “knock on” process, was actually discovered in 1943 by the American chemists Milton Burton and T.J. Neubert and found to have profound influences on graphite and other materials.
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The phenomenon, known as the Wigner effect and sometimes as a “knock on” process, was actually discovered in 1943 by the American chemists Milton Burton and T.J. Neubert and found to have profound influences on graphite and other materials.
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Sir Alan Cottrell
…was done to release the Wigner energy that had stored up in the graphite from the disruption of its atomic structure by neutron irradiation. Cottrell was placed in charge of the research program to better understand the release of Wigner energy, and by March 1958 the work of Cottrell’s team…
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…was done to release the Wigner energy that had stored up in the graphite from the disruption of its atomic structure by neutron irradiation. Cottrell was placed in charge of the research program to better understand the release of Wigner energy, and by March 1958 the work of Cottrell’s team…
Read More