Threshold Displacement Energy - Relation To Higher-energy Damage Production

Relation To Higher-energy Damage Production

The threshold displacement energy is often used to estimate the total amount of defects produced by higher energy irradiation using the Kinchin-Pease or NRT equations which says that the number of Frenkel pairs produced for a nuclear deposited energy of is

for any nuclear deposited energy above .

However, this equation should be used with great caution for several reasons. For instance, it does not account for any thermally activated recombination of damage, nor the well known fact that in metals the damage production is for high energies only something like 20% of the Kinchin-Pease prediction.

The threshold displacement energy is also often used in binary collision approximation computer codes such as SRIM to estimate damage. However, the same caveats as for the Kinchin-Pease equation also apply for these codes (unless they are extended with a damage recombination model).

Moreover, neither the Kinchin-Pease equation nor SRIM take in any way account of ion channeling, which may in crystalline or polycrystalline materials reduce the nuclear deposited energy and thus the damage production dramatically for some ion-target combinations. For instance, keV ion implantation into the Si 110 crystal direction leads to massive channeling and thus reductions in stopping power. Similarly, light ion like He irradiation of a BCC metal like Fe leads to massive channeling even in a randomly selected crystal direction.