Rutherford backscattering channeling (RBS-C) spectra of ion-implanted Si are simulated according to an atomistic model of radiation damage which consists of a distribution of point defects (split- interstitials and vacancies) structurally relaxed by empirical potentials. This model, successfully used to reproduce multiaxial spectra of lightly damaged Si, is applied here to the case of a heavily damaged sample. As a consequence of the increasing strain generated by lattice relaxation, simulations predict a superlinear trend of RBS-C disorder versus defect concentration in the range of intermediate damage density. This contrasts with the linear trend obtained by the usual description of defects as atoms randomly displaced in a rigid lattice. The new approach represents an improvement in the physical description of ion irradiation disorder within RBS-C analysis; however simulation results are found to be in less …