Proposed a method for calculating the rate of formation of unstable Frenkel pairs (UFP) accounting for the effect of screening. First  systematic data on cross section and concentration of UFP for various materials: Al, Cu, Ag, Pt, Au, etc is received. The ratio of the number of NFP to the number of stable defects is 10 ^ 6 for heavy nuclei. It is shown that the contribution of UFP in the radiation-stimulated processes can be significant.