Separating the size distributions for interstitial- and vacancy-type dislocation loops using integral X-ray diffuse scattering

A rigorous integral X-ray diffuse scattering (XRDS) method has been developed to experimentally determine separate densities and size distributions for interstitial- and vacancy-type dislocation loops in irradiated materials. Direct numerical calculations of the integral XRDS intensities for prismatic a 0 /2{111}-type dislocation loops around the tungsten (W) 110 Bragg reflection show for the first time that the opposite signs of the displacement fields surrounding interstitial and vacancy loops generate sufficiently asymmetric rocking curve intensity profiles to separate the size distributions of the two loop types. This capability is demonstrated using measurements of single-crystalline W after irradiation with 10.8 MeV self-ions near room temperature to 0.008 and 0.02 displacements per atom. Distinct size distributions are shown for interstitial and vacancy loops at both irradiation doses, and the densities of both loop types are shown to increase with higher dose. The comprehensive computational methods presented in this study enable integral XRDS intensity calculations to be rigorously tailored to specific measurement conditions and geometries. Moreover, these calculations can be applied to nearly any type of irradiation-induced defect cluster provided accurate modeling of the defect-induced strain field and atomic structure of the cluster is utilized. Combined with the new capability of distinguishing the interstitial/vacancy nature of dislocation loops presented in this study, these critical developments expand the utility of the technique significantly and establish a rigorous methodology for performing detailed studies of irradiation-induced defects using integral XRDS measurements.