The radiation annealing of frenkel pairs and the rate of the point defect accumulation in neutron irradiation

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Abstract
In neutron irradiation the primary knock-out atom, when producing secondary defects and slowing down, releases its energy in the cascade zone which, being heated up to a temperature higher than the ambient, provides the migration of the Frenkel pairs and their annihilation (radiation annealing). The system of equations which is presented describes the diffusion and annihilation of the defects and the cooling of the cascade zone resulting from the lattice and electron heat transfer. The solution of the system, using simplifying assumptions, brings one to the conclusion that the effectiveness of the Frenkel pair production, by the primary knocked-out atoms with an energy lower than a certain boundary energy, decreases because the atom dissipates its energy in a region of smaller dimensions, which is heated to higher temperature and, thus, the more incisive radiation annealing of the Frenkel pairs is provided. In accordance with this the number of secondary knocked-out atoms at energies lower than the boundary energy is small, and is described with the power dependence where the power is about three. The formulas are derived for the number of secondary knocked-out atoms in metals and dielectrics with allowance for the temperature of the material under irradiation. Taking into account radiation annealing, agreement can be reached between the experimental and theoretical values for the initial rate of the defect accumulation in neutron irradiation of the materials.