Thermal excitation of electrons in energetic displacement cascades

A thermal description of the electron-ion interaction in the cooling phase of the displacement cascade in metals is given. Differential equations governing the transfer of heat between the two systems are derived and solved numerically using physically reasonable parameters for cascades in Cu and Ni. Large differences are found in the cooling rates of cascades in these two metals and the differences are shown to depend on the ratio of a parameter ${\mathit{T}}_0$, the temperature at which the electron-phonon mean free path reduces to the radius of the Wigner-Seitz sphere and ${\gamma }_{\mathit{e}}$, the coefficient of the electronic heat capacity. Simplified versions of the heat-transfer equations have been incorporated into a molecular-dynamics code in order to include the interaction in simulations of cascades in Cu. The net effect of including the interaction is to actually inhibit defect production in low-energy cascades (∼500 eV) by damping the ionic motion.