What specific unit do engineers use to count the total number of times every atom in a metal's crystal structure has been knocked out of its original spot by radiation?

Engineers use the specific unit displacements per atom, often abbreviated as dpa, to count the total number of times every atom in a metal's crystal structure has been knocked out of its original spot by radiation. To fully understand dpa, it is essential to first grasp what happens at the atomic level. A metal's crystal structure refers to the highly ordered, repeating arrangement of its atoms in specific, fixed positions known as lattice sites. When this metal is exposed to radiation – which comprises energetic particles like neutrons, ions, or high-energy electrons – these particles can collide with the metal's atoms. If an incident radiation particle transfers sufficient energy to a metal atom, that atom can be violently ejected from its stable lattice site. This event is termed an atomic displaceme....