Changes in the near-surface region of V-5Fe alloy after irradiation at room temperature with 50 keV V+ions to fluences in the range from 1019to 1021ion/m2have been investigated. Radiation-induced segregation profiles were measured by means of XPS with ion sputtering. Calculations of the segregation profiles were performed using diffusion equations modified for the case of ion irradiation at temperatures where the vacancies are immobile. The difference in the interstitial diffusion coefficients of alloy components were considered as the main driving force for the component redistribution. By fitting the experimental data the ratio of iron to vanadium interstitial diffusion coefficients δihas been evaluated. Assuming the equality of the pre-exponential factors in the diffusion coefficients, a temperature dependence of δihas been found. An analytical expression for δihas been derived.