X-RAY BACKSCATTER IMAGING WITH A NOVEL TWISTED SLIT COLLIMATOR

No one less than Wilhelm Conrad Röntgen himself discovered X-ray backscatter radiation first when exploring the properties of the new kind of radiation he had discovered [1]. However, the predominant application of X-rays remained with the common radiology. To a lesser extend, Xrays have found their way into spectroscopic methods such as fluorescence or diffraction analysis, but within a considerable low energy range that is of limited use in the radiological field. From an energy level of some 100 keV on, the Compton Effect increasingly contributes to the absorption of X-ray. Concomitantly, the associated scatter radiation also increases which is regarded as a nuisance since it decreases the object contrast and may even blur sharp contours. Due to the lower capability to absorb X-rays lighter material consisting of low-Z-elements such material is preferentially prone to the Compton scatter effect. This also means that, if the scattered radiation would be visualised, the image would be dominated by the light materials, quite vice versa to the radiograph itself. Since this kind of view would be desirable in some applications, there should be a way to make a virtue out of necessity, i.e. utilising the X-ray backscatter effect for imaging. By any means, such an approach has to take into account that the scattered radiation is not directed, i.e. distributed into any spatial direction. This leaves an insurmountable problem in the beginning, there are no optical devices available as with the visible light, at least in the energy range relevant for Compton scattering. As a matter of fact, this is the reason why radiology only is handling shadow images in the first place.