The production of an isolated displacement spike by a collision cascade in $\alpha$-iron, tungsten, and copper at 0°K and the annealing of displacement spikes in $\alpha$-iron at temperatures up to 250°C were studied using the computer-experiment (simulation) method. Collision-cascade simulation in the associated body-centered-cubic (bcc) and face-centered-cubic (fcc) arrays of atoms was based on the approximation of assuming a branching sequence of binary-collisions. The primary knock-on atom (PKA) displacement efficiency was found to be a decreasing function of PKA energy, in contrast to the constant displacement efficiency given by structureless solid models. This effect was caused predominantly by damage-production interference among different parts of the cascade. Long-range channeling (range ≥ 1000 Å) played a very minor role in the decrease of the PKA displacement efficiency with increasing PKA energy, in bcc metals and none at all in copper. Quasichanneling events were common and greatly influenced the development of a displacement spike along $〈110〉$ directions in bcc metals. In this regard, the dimensions of a cascade were determined by the ranges of quasichanneled higher order knock-on atoms in the cascade rather than by the PKA range. The preferred directions for long-range self-channeling were also $〈110〉$. The calculations suggest that in $\alpha$-iron and tungsten, only those displacement spikes that would contain clusters of ≥ 10 vacancies at an irradiation temperature of 0°K survive thermal annealing at room-temperature irradiation. Specifically, this means that only those spikes produced by PKA with energies above 3 keV in $\alpha$ iron and above 6 keV in tungsten would contribute surviving defects. The density of displacements in a spike produced at 0°K in $\alpha$ iron was saturated at all PKA energies considered (0.5-20 keV). The temperature dependence of the shape and size of the interstitial-vacancy recombination region in $\alpha$-iron was determined in part.

• Received 19 May 1966

DOI:https://doi.org/10.1103/PhysRev.150.470