X-ray induced pinhole closure in point-projection x-ray radiography

In pinhole-assisted point-projection x-ray radiography (or “backlighting”), pinholes are placed between the sample of interest and an x-ray source (or “backlighter”) to effectively limit the source size and hence improve the spatial resolution of the system. Pinholes are generally placed close to such x-ray backlighters to increase the field of view, leading to possible vaporization and pinhole closure due to x-ray driven ablation, thereby potentially limiting the usefulness of this method. An experimental study and modeling of time-dependent closure and resolution is presented. The pinhole closure time scale is studied for various pinhole sizes, pinhole-to-backlighter separations, and filtering conditions. In addition the time-dependent resolution is extracted from one-dimensional wire imaging prior to pinhole closure. Cylindrical hydrodynamic modeling of the pinhole closure shows reasonable agreement with data, giving us a predictive capability for pinhole closure in future experiments.