Displacement Spikes

A displacement spike occurs while several atoms in a small area are displaced through a knock-on (or cascade of knock-ons).  A 1 MeV neutron might affect around 5000 atoms, making up one of these spikes.  The presence of several displacement spikes will modify the properties of the material being irradiated.  A displacement spike holds large numbers of lattice vacancies  and interstitials (referred  to  as  Frenkel  pairs  or  Frenkel  defects  when  considered  in  pairs).  The presence of huge numbers of vacancies and interstitials in the lattice of a metal will commonly increase hardness and reduce ductility. In several materials (for instance, graphite, uranium metal) bulk volume rise occur.