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Iron For Crystals Or Cheap Tomographs

June 07, 2002

Unlike the traditional X-ray photography, which imprints a black-and-white picture on the film, the X-ray tomograph reproduces coloured three-dimensional `movies` about the organs` behavior on the computer screen. The X-ray tomograph enables the scientists to find a thrombus in a blood vessel, to observe the dynamics of the abnormality of the cordial muscle and other organs. These advantages are due to the fact that photovoltaic power systems have been installed in the tomographs instead of the photographic film. The photovoltaic power systems consist of crystals (scintillators), which are sensitive to X-ray exposure. According to N.V. Klassen, about ten thousand scintillators are required for a single device. A lot of expense is involved in the growing up of each of these crystals: purification of raw materials from which the crystal will be grown, cutting of a prepared monocrystal into parts, and the most important, extremely expensive grinding and polishing of each crystal. The tomograph resolution and image sharpness primarily depend on the smoothness of the surface of the sensitive crystalline detectors. As a result, the price per crystal makes up about five dollars. The cost of a single photovoltaic power system makes several dozens of thousands dollars.
        
The physicists from Chernogolovka (http://www.issp.ac.ru/) have discovered the way to reduce the cost value of the system by dozens of times. They suggested that the surface of the crystals should be `ironed` with the help of the specially polished puncheon (mould), heated up to high temperature, the crystal surface being pressed so that all facets are processed. After that the crystal acquires the needed shape and its surface becomes atomically smooth. (With electromagnetic radiation, even the protuberances as small as of a dozen of atoms are capable to significantly distort the space signal quality). It was impossible to smooth out the crystals to such an extent before, applying the previous technology. The smoother the surface of the crystal is polished, the higher its sensitivity to the X-rays grows. And the higher the sensitivity is, the lower the intensity of the X-ray impulse becomes. Consequently, the radiation dose people are exposed to decreases. That is why presently the tomograph technology allows for much more frequent X-ray examinations, than under the traditional X-ray photography method, when the intervals between the sessions had to be no less than three months.
        
In the developed countries clinics are equipped with the computer X-ray tomographs, one device being available for 10 thousand people. However, in Russia the number of tomographs is very limited - a single device is available for only 10 million people, an extremely high cost being one of the reasons why the Russian clinics have got so few devices at their disposal. Applying a new method of polishing the crystal surface invented by the researchers of the Institute of Solid-State Physics will result in the substantial reduction of the device cost. Recently the scientists have initiated a new project. On the face of it, the idea seems to be rather absurd: the scientists do not grow the crystals, instead the same method of the `iron`- high-temperature vacuum squeezing- is applied. The original powder substance is pressed into solid crystals of the required shape. The project has been recognised one of the best Russian and American joint research projects and has won the grant of the American CRDF Foundation. The project is intended to develop the unique cost-efficient technology for the high-quality crystals (scintillators) production.

Informnauka (Informscience) Agency