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see [[http://www.nano-tera.ch/nanoterawiki/NEXRAY NEXRAY]]
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This project targets the development of novel pocket X-ray sources and X-ray direct detectors that will be combined in a distributed network to solve important tasks e.g. in the field of security. The miniaturised X-ray sources are based on multi-wall carbon nanotube (CNT) cold electron emitters and advanced microsystems technology. The electron field emission properties of CNTs with their high current densities make them prime candidates for cold emitter cathodes. Due to their small (nanometer) diameter and large aspect ratio, CNTs show a large electrical field enhancement factor and consequently a low threshold voltage for electron extraction. With using CNT cold electron emitters it will be possible to miniaturise the whole X-ray source to a volume of 1 cubic millimetre only. Additionally as opposed to classical thermionic emission, field electron emission of the CNT is voltage controlled which allows for high modulation frequencies up to GHz level. For modulations in the GHz level a additional grid will be required.
The X-ray direct detectors in turn are based on crystalline Germanium absorption layers grown directly on a pre-processed CMOS sensor chip yielding high resolution and high sensitivity X-ray detectors, targeting single photon detection and thus ensuring a significant improvement of throughput which is instrumental for applications in security and non destructive testing or a very significant reduction of applied dosis as critical to medical applications. Moreover radical new approaches to X-ray imaging will result and be addressed, respectively demonstrated including:
X-ray time-of-flight (xTOF) measurements based on Compton backscattering such that to probe the depth inside objects where scattering occurs can be precisely measured. This calls for an intensity modulated X-ray signal in the MHz range which is not possible with conventional X-ray sources but can be achieved with CNT based cold emitters, for which modulation frequencies up to the GHz level were already reported. In combination with dedicated CMOS image sensors and data-pre-processing already at the pixel level, potentially new 3D X-ray imaging instruments can be realized.
Tomographic imaging that exploits the fact that both the X-ray source and the X-ray detector are pixelated: the fact that a X-ray source is built as a matrix of micro X-ray sources that also can be addressed and controlled individually is very novel and the combination of pixelated X- ray sources and detectors brings up completely new imaging capabilities, in particular the possibility to do static tomographic imaging and further reduce the dose. This project is expected to set a novel technological base and platform which will lead to high benefits notably in the fields of security and health, contributing thus to the well being of human.
