BSTRACTThe sizes of defect clusters

produced in materials by energetic ion or neutron impacts

are critically important input for models describing microstructural evolution of irradiated materials. We propose a model for the distribution of sizes of vacancy and self-interstitial defect clusters formed by high-energy impacts in tungsten

and provide new data from

in situ

ion irradiation experiments to validate the model. The model predicts the statistics of sub-cascade splitting and the resulting distribution of primary defects extending over the entire range of cluster sizes

and is able to provide initial conditions for quantitative multi-scale simulations of microstructural evolution.