Our vision is to provide a world leading 'designer' range of semiconductor materials suited for imaging applications in a diverse, dynamic and interdisciplinary scientific community. We will establish characterisation and fabrication facilities that will deliver devices for a wide range of applications from space science and medicine to homeland security. We will establish a network of end users who will very quickly be in a position to exploit these developments. It is our belief that this new and innovative technology coupled with our interdisciplinary applications network will give the UK a world lead in the field of high energy spectroscopic X-ray imaging. The aim of the project is to produce fully characterised detector grade cadmium zinc telluride (CZT) on a wafer scale that can be fabricated into a number of generic devices for use in high energy spectroscopic X-ray imaging. The new material will be grown by the Multi Tube Physical Vapour Transport (MTPVT) method that has been pioneered at Durham . The first major milestone will be the delivery of this fully characterised material on a wafer scale for detector manufacture. The project will enable the new material to be assembled into a number of detector types for uses in high energy colour X-ray imaging. The second major deliverable will be the fully fabricated devices. Finally a network of users with radically different applications will be established. If you are interested in receiving more information or have possible applications for these devices please register with our network.

High Energy X-Ray Imaging Examples: medicine In medicine multi-slice spiral CT scanners can currently produce a whole body image in a matter of seconds. However the standard systems still rely on X-ray absorption to produce the images and therefore have high dose consequences for the patient. We have demonstrated the advantages of employing mono-chromatic, X-rays for medical imaging using X-ray phase shift rather than the absorption leading to a far more sensitive way of obtaining morphological information. Phase contrast imaging is even more sensitive at high X-ray energies and will result in even lower doses. Figure a: shows an image of a human finger joint taken using a technique called Diffraction Enhanced Imaging (DEI). DEI was developed on synchrotron sources, and is currently being explored in the context of mammography, angiography, bronchography as well as the musculo-skeletal imaging shown here. The method is currently limited by the energy range of available detector materials. The developments proposed here would provide new materials to enable routine use of imaging systems delivering X-ray radiographs of this quality in a hospital environment.

Figure a: shows a human finger joint imaged using diffraction contrast X-ray imaging. Currently restricted to small samples because of the energy limitations of the detector. This project will enable the investigation of much larger medical subjects with the same spatial resolution and with lower X-ray doses.

The use of high energy X-rays has applications in the security industry most tangibly manifested by the ubiquitous baggage scanner of 21st century airports. Figure b shows an X-ray radiograph of a suitcase. The developments we propose here will not only image the contents of bags and other transport carriers but will allow the type of material to be identified through energy dispersive X-ray finger printing.

Figure b: shows an image of a suitcase produced by a conventional airport scanner. The TEDDI method at high energies will not only produce a 3D image but also the structure and chemistry of the object at each voxel point.

Conventional tomography will also benefit from being carried out at higher energy; the image of the casting in figure c was only made possible because of its light atom composition. The developments proposed here will enable heavy castings to be analysed. It has been shown that another tomographic method known as energy dispersive diffraction imaging (TEDDI) is capable of delivering 3-dimensional density contrast images as well as identifying the structure and chemistry of the object. This is particularly important for process engineering and materials science. The various TEDDI images can reveal complex flow patterns and alignment vortices inside steel vessels for instance. TEDDI is applicable in many situations however the images are constructed almost entirely from X-ray photons with energies above 30 keV, rendering conventional (silicon based) array detectors useless. Single crystal germanium detectors can be used to map a sample but the process is very slow (16 to 20 hours) even when carried out on a synchrotron source. Our developments will greatly facilitate rapid 3D measurements of large scale, as fabricated, engineering components.

Figure c: shows a tomographic reconstruction of a light alloy casting. The detector material we propose to develop will enable high density castings to be routinely examined at high speed.

In space and planetary science the study of high-energy emission mechanisms are vital to the understanding of stellar objects such as pulsars; binary stars; super novae; gamma ray bursts and active galactic nuclei. Currently only poor resolution images in the hard X-ray region are available (figure d). This image of the centre of the Milky Way has confirmed the presence of a black hole at the centre of our galaxy however the crude resolution makes proper interpretation of these images extremely difficult.

Figure d : shows an image of our galaxy produced by the state of the art high energy detector arrays. This project will deliver high energy arrays with much higher spatial resolution that will be used to make superb images of our universe.

The use of colour and higher energy X-rays would open up entirely new possibilities for a wide field including medical technology; security; defense, space science, oil and gas exploration; engineering; materials science; archaeology and chemical engineering.

The delivery of semiconductor sensors for high energy spectroscopic imaging requires the development of new high Z semiconductors such as CdTe and CdZnTe. The detection efficiency of direct-conversion silicon sensors for X-ray energies greater than 20 keV becomes negligible, as shown in figure 2. By contrast, the detection efficiency of 500 ?m thick CdTe/CdZnTe is >50% for 100 keV X-rays. CdZnTe is the optimum high-Z detector material, combining excellent detection efficiency with good charge transport properties and a high bulk resistivity (>1010 ?cm). CdTe has similar properties, however due to a slightly lower resistivity it does not provide the low dark current and the same excellent spectroscopic performance of CdZnTe. Progress in the development of commercial CdZnTe radiation detectors is currently prevented by the lack of availability of single-crystal high purity CdZnTe material.

Calculated X-ray detection efficiency (log scale) vs photon energy, for various semiconductors

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"X-ray refraction effects: application to the imaging of biological tissues." (2003) R. A. Lewis, C. J. Hall, et al.; British Journal of Radiology Br. J. Radiol. 76(905) : 301-308.

"Synchrotron radiation energy-dispersive diffraction tomography” (1998) C. Hall et al.; Nucl. Instrum. & Meth. in Phys. Res. B 140 , 253-257.

"Tomographic Energy-Dispersive Diffraction Imaging of Static and Dynamic Systems" (2001) P. Barnes et al; Nondestr. Test. & Eval. 17 , 143-167.

"Porosity Imaging in Porous Media using Synchrotron Tomographic Techniques" (2004) M.Betson et al.; Transport in Porous Media , 57(2) , 203-214.

“An in-process Tomographic Visualisation of Crystallisation and Polymorphism” (2005); S.D.M. Jacques et al.; Crystal Growth & Design , in press.

Unpublished results (2005) S.D.M. Jacques et al.