- © The Mineralogical Society Of America
In radiographic methods, the attenuation of an incident beam on passing through an object is used to study the internal structure of this object. The availability of techniques to “look inside” large, optically intransparent objects without having to destroy them is obviously appealing and has had a profound impact in many fields, most clearly in medicine, but also in condensed matter studies. The development of radiography started with Röntgen’s discovery of X-rays in 1895, where the absorption of X-rays by bones were demonstrated publicly in 1896 by obtaining a radiograph of a hand. The medical applications were obvious, and already in World War I, mobile X-ray units were routinely deployed. The main shortcoming of X-ray radiography in early medical applications is that often it cannot be used to distinguish different kinds of soft tissue and that the two dimensional projections are sometimes difficult to interpret. This changed dramatically with the development of “computerized axial tomography” for which the Nobel prize was awarded in 1979 to Hounsfield and Cormack. Computed tomography, as it is now frequently called, is the three-dimensional reconstruction of the interior of an object from many radiographs taken at different angles, and this combination of data sets enables to distinguish between different soft tissues, such as kidneys and liver.
Medical computed X-ray tomography scanners were used soon afterwards to investigate minerals and rocks, for example in an early study of chondritic meteorites (Arnold et al. 1983). These had a comparatively poor spatial resolution of ~1 mm. As there is no need for low radiation doses in material science studies, and as the penetrating power of high energy X-rays is larger and higher spatial resolutions can be obtained, dedicated scanners for material science have been developed. Commercially available “table top” scanners now offer spatial resolution of less than 1 …