A new X-ray backscatter imaging technique for non-destructive testing of aerospace materials

• A new single-sided access method for quantitative imaging of aerospace materials.
• High-energy X-ray backscatter imaging based on a novel twisted-slit collimator.
• First system with variable irradiation geometry facilitates imaging internal sections of the stringers.
• Real-time measurement of backscatter signals based on high-resolution digital detector arrays.
• The effect of X-ray source energy and the slit width of the camera on the backscatter image are investigated.

This paper presents a new X-ray backscatter technique (XBT) for non-destructive imaging of aerospace materials with only a single-sided access. It uses a special twisted slit collimator to inspect the whole object by changing the viewing direction of the X-ray backscatter camera. For the first time, the X-ray backscatter measurements were conducted using high-energy (>500 keV) X-ray sources. Experiments were performed on thick complex structured aluminium components, stringers and honeycomb structures to validate the applicability of the present technique to image small changes in the material properties and also to detect low-density material inclusions. In order to reduce the inspection time from hours to several seconds and to improve the image quality of the X-ray backscatter image, the backscattered signals were measured using a digital detector array with high spatial resolution (200 µm). The influence of the energy of the X-ray source and the slit width of the camera on the X-ray backscatter image were also investigated. In the proposed technique, the whole object is irradiated by an un-collimated X-ray beam resulting in a low image acquisition time of 3 min that facilitates the use of XBT for the real time NDT&E of aerospace materials.