X-ray-based displacement measurement for hostile environments

A completely new method of noncontacting, hostile-environment displacement measurement based on the focus and scanning of X rays has been developed and shows promise of overcoming many of the limitations associated with available techniques. The chief advantage lies in the ability to make undisturbed measurements through stratified or flowing gases, smoke and flame.The system is based on the focus and scanning of lowenergy, hard X rays such as those emanating from copper or molybdenum sources. The X rays are focused into a narrow and intense line image which can be swept onto targets that fluoresce secondary X-ray radiation. This radiation is monitored and target-edge position can be determined by measuring the focused image position when the marker begins to fluoresce. The final goal for the system is to be able to conduct macroscopic strain measurement in hostile environments by utilizing two or more fluorescing targets. Current work has been limited to displacement measurement of a single target with a resolution of 0.5 micron. Tests have also been conducted at target temperatures of 1200°C, directly through an open flame. The main advantage of the technique lies in the penetrating nature of X rays, which are not affected by the presence of refracting gas layers, smoke, flame or intense thermal radiation, all of which could render conventional extensometry methods inoperative or greatly compromise their performance.