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Geoffrey Harding; 06 August 1948 – 14 September 2019 was an English physicist and inventor. He pioneered several X-ray based technologies like Monochromatic Fluorescence X-ray sources, Compton Backscattering Imaging for material inspection, Liquid Metal X-ray sources, Fluorescence Tomography, Coherent Scatter Tomography and X-ray diffraction imaging.

His greatest achievement was the invention of a technology for automatic identification of hidden explosives in airplane baggage using X-ray diffraction. His work on Compton backscattering was honored with the Röntgen-Plakette in 1995.

Geoffrey Harding held over 140 patents and published over 80 articles.

Life and scientific education
Geoffrey Harding was born in Gillingham, Kent, UK, 6 August 1948 and died on 14 September 2019 in Hamburg, Germany.

Following graduation with an honours physics degree from the University of Kent at Canterbury in 1969, he received the Ph. D. degree in 1974 for a thesis entitled 'Studies associated with the foil-excited beam spectroscopic source'.

He performed post-doctoral work, in association with Newcastle University UK (1974 - 1976), to investigate coherent optical processing in radiography.

Dr Harding had been visiting Professor to the Physics Department of the University of Surrey, U.K., from the beginning of 1995. He was also Visiting Professor to the University of Shenyang, commencing in 1995.

Professional Career
From 1976 to 2003 he was employed at the Philips Research Laboratories in Hamburg, Germany, holding the position of 'Research Fellow'. He initiated research projects on 'X ray scatter imaging' and supervised the various research activities which developed from it. These included Compton scatter imaging (industrial and defense applications), coherent scatter imaging (security, medical and industrial applications); and x ray generation (monochromatic radiation sources, transmission anodes, micro-focus x ray sources).

From 2003 to 2015 he held the position of Chief Scientist in Morpho Detection Germany GmbH. In this capacity he invented the general geometry of Morpho Detection’s XDI (x-ray diffraction imaging) technology.

Important work
Geoffrey Harding started his research work with basic investigations on X-ray inelastic (Compton) scatter and elastic (Rayleigh) scatter. Imaging was done via pencil-beam configuration in combination with samples mounted on a translation stage or being scanned by a scanning pencil beam arrangement, while in a second step sample rotation was added - ending up with a pencil beam based Computed Tomography (CT) set up (REF_1 - REF_4). In the early 2000’s he studied fan-beam CT configurations in combination with energy resolved scatter detection named “Coherent Scatter CT” (REF_5 - REF_7).

X-ray imaging in the medical as well as the industrial field was the goal. Special investigations of material mapping, such as of explosives, via Compton scatter were triggered (REF_8) or via elastic scatter were directly supported (REF_9). Also, the uasge of X-ray fluorescence for tomogrpahy was investigated (REF_10, REF_11).

Following the desaster of Lockerby, he got inspired to apply diffraction technology to identify explosives in airplane luggage, starting as a research project within Philips and eventually evolving into a product applied at airports, first marketed by the company Yxlon. The system employeed the patented cone-surface beam geometry. Together with a translation stage, this enable sensitive scanning of a full bag. The system was very accurate in identifying any material inside luggage, but mechanically complex and with limited speed.To improve this technology, he invented the patented "Inverse Fan-beam geometry", which avoids using mechanical movement of heavy X-ray components, thus allowing a simpler set-up and faster scanning.

In addition to the investigation and development of x-ray imaging principles he always had in mind the improvement of x-ray tube characteristics as major contributors to image quality and enabler of advanced technologies. In this context he invented x-ray tube set ups based on x-ray fluorescence having quite monochromatic x-ray output (REF_12), and investigated application scenarios (REF_13) including dose reduction options (REF_14). A lot of effort he spend in the investigation of a liquid metal based x-ray tube anode design aiming at high continous x-ray output for e.g. baggage inspection purposes. This concept was abbreviated with LIMAX and the main idea was to directly deposit the energy of the high energy electron beam - as needed for a bremsstrahlung X-ray source - into a turbulently flowing liquid metal. The liquids metal fulfills the purpose as high-Z material to produce the X-rays as well as as the cooling media (REF_15, REF_16).

Awards and honours
Geoffrey Harding received several awards for his work:


 * His article 'X ray diffraction computed tomography' was awarded the S Greenfield Award (best publication in Medical Physics) by the Association of American Physicists in Medicine in 1988.
 * The ComScan system, of which he is the inventor, was awarded the Innovation Prize of the Confederation of German Industry in 1991.
 * He received the Röntgen-Plakette in 1995, the centennial anniversary of the discovery of x rays.