Fundamental Studies for the High Intensity Flash X-ray generators for Biomedical Radiography

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Fundamental studies for the high intensity flash x-ray generators for biomedical radiography are described. The single flash x-ray generators are as follows: (a) a high intensity type (less than 100kV) for performing the soft radiography, (b) a low-impedance and high intensity type (less than 120kV) for obtaining radiographs of tissues deep inside of the human body, and (c) a portable type (less than 200kV). Each generators had the control functions for the x-ray intensity, the spectrum distribution, and the effective focal spot size, and mainly consisted of the following essential components: a high voltage generator, a pulse condenser, a gas gap system, a turbo molecular pump, and a flash x-ray tube using field emission.Two types of the triple-pulsed x-ray generators consisted of the following components: a high-voltage generating unit, a voltage divider unit, three high-voltage generating unit, three high-voltage pulsers used for a portable generator, a tiple parallel impulse switch … More ing system, a high-power gas diode having three terminals, a turbo molecular pump, and three remote x-ray tubes having cold cathode. For the single-tube generator, the pulsers were charged to the same or different voltages by using a voltage divider unit and were connected to the x-ray tube through a high-power gas diode using SF_6. For the triple-tube generator,since three pulsers were connected directly to the tubes without a diode, three x-ray outputs could be obtained simultaneously. The minimum time intervals for the single-tube and the triple-tube types were about 100 and 3us, respectively. The x-ray intensities increased in proportion to the third or fourth power of the charging voltage. The pulse width was less than 300ns, and the x-ray quality (average spectrum distribution) became hard according to increases in the charging voltage and increases in the thickness of metal filters inserted outside of the x-ray window. The effective focal spot size could be reduced by decreasing the anode angle, decreasing the cathode diameter, decreasing the anode-cathode space, and inserting the metal filters.The high-speed radiographic system consisted of the following components: two types of delay switches,i. e. (a) direct switching and (b) laser switching, a delayed pulse generator, a CR system,and an FX generator. When the radiographic object triggered the delay switch, a short electric pulse was produced and was transmitted to the delayed pulse generator. An accurate delayed x-ray pulse was produced when the delayed pulse was transmitted to the high-speed impulse switching system. Next, when the radiographic object was exposed to the controlled x-rays under the optimum radiographic conditions, the permeating x-rays produced the digital image. Since the time resolutions for two types of delay switches were less than 20ns, the total time resolution for the x-ray production was less than 1<micrn>s. Various kinds of high speed biomedical radiography, e. g., the stroboscopic radiographgs, the continuous delayed radiographs the energy subtraction radiographs, and the continuous three-dimensional analysis could be performed by controlling the radiographic conditions. Less