We have performed detailed x-ray determinations of the crystal structure of Nb3Sn films as a function of 4He particle radiation damage. It is found that, in addition to antisite defects, substantial displacements (∼0.2 ») of both the Nb and Sn atoms must be invoked to explain the data. We suggest the data are consistent with a transition from covalent to metallic bonding along the Nb chains. © 1979 Plenum Publishing Corporation.