Hidenori Ojima

High-speed soft x-ray techniques

The construction and the characteristics of recent high- speed soft x-ray generators designed by the authors are described. The flash x-ray generators having cold-cathode radiation tubes are three types as follows: (1) soft generator utilizing an ignitron, (2) plasma generator for producing high-intensity characteristic x rays, and (3) water-window generator having a high-durability fermite capillary. In general, when we employed the flash x-ray generators with diodes, the pulse widths had values of less than 200 ns. Next, the x-ray duration was almost equivalent to the durations of the tube voltage and current during their damped oscillations when the water-window generator was employed. The maximum tube voltage was increased up to 100 kV, and the tube currents achieved with high-intensity generators were more than 10 kA. In order to obtain kilohertz-range repetition rates, we have developed two types of stroboscopic x-ray generators having hot-cathode tubes as follows: (4) low-photon-energy generator utilizing and triode and (5) high-photon-energy generator with a diode. As the duration was controlled in a microsecond range by using the low-photon-energy generator, sufficient x-ray intensifier for the normal radiography were obtained. The maximum photon energy could be increased up to about 200 keV by the high-photon-energy generator having a double transformer. Using these generation, we performed high-speed soft radiography.

Dual-energy flash x-ray generator

The fundamental studies on a dual-energy flash x-ray generator for performing the energy-selective two-direction radiography are described. This generator consisted of the following components: a negative high- voltage power supply, a polarity-inversion-type high-voltage pulser having a 5 nF combined ceramic condenser, a turbo molecular pump, and two flash x-ray tubes. The condenser in the pulser was charged from -60 to -80 kV, and the electric charges in the condenser were discharged to two x-ray tubes. The maximum output voltage from the pulser was about -1.5 times the charged voltage because the cable transmission line was employed. Using a tube, the maximum tube voltage was about 110 kV. The maximum tube current and the x-ray intensity were less than 3 kA and 5 (mu) C/kg at 0.5 m per pulse, respectively. In contrast, the tube current and the intensity has approximately half the above values when two tubes were employed. The pulse widths were less than 200 ns, and two shots of flash x rays were obtained simultaneously. Each photon energy of flash x rays can be changed by controlling the space between the anode and cathode electrodes.

High-speed soft x-ray generators in biomedicine

The constructions and the fundamental studies of high-speed soft x-ray generators which can be used for performing biomedical radiography with maximum photon energies of less than 150 keV are described. The flash x- ray generators having cold-cathode radiation tubes are classified to four types: (1) high-intensity single flash x-ray generators, (2) dual- energy flash x-ray generators, (3) single plasma flash x-ray generators, and (4) repetitive compact flash x-ray generators. In general, when we employed flash x-ray generators with diodes, the pulse widths had values of less than 200 ns. In the case where we employed a long-duration flash x-ray generator having a triode, the width could be increased up to about 40 microsecond(s) . The maximum tube currents achieved with high-intensity generators were more than 10 kA, and the maximum repetition rate of a compact generator has a value of about 0.4 kHz. In order to obtain higher repetition rates of more than 1 kHz, we developed three types of pulsed x-ray generators having hot-cathode tubes as follows: (5) a 30 kHz high-dose-rate generator, (6) a 30 kHz variable-duration microsecond generator, and (7) two 10 kHz high-photon-energy generators. When a high-dose-rate generator was employed, the maximum tube current can be increased up to about 2 A by applying the positive grid voltage. In contrast, as the duration was controlled in a microsecond range by using a microsecond generator, the sufficient x-ray intensities for the normal radiography were obtained. The maximum photon energy could be increased more than 100 keV using a high-voltage transformer in conjunction with a diode. Using these generators, we performed various kinds of high- speed soft radiographies.

Tentative study on x-ray enhancement by fluorescent emission of radiation by plasma x-ray source

Tentative study on characteristic x-ray enhancement by fluorescent emission of radiation by plasma x-ray source is described. The enhancement was performed by the plasma flash x-ray generator having a cold-cathode triode. And the generator employs a high-voltage power supply, a low-impedance coaxial transmission line with a gap switch, a high-voltage condenser with a capacity of 200 nF, a turbo-molecular pump, a thyristor pulser as a trigger device, and a flash x-ray tube. The high-voltage main condenser is charged up to 60 kV by the power supply, and the electric charges in the condenser are discharged to the tube after triggering the cathode electrode. The flash x-rays are then produced. The x-ray tube is of a demountable triode that is connected to the turbo molecular pump with a pressure of approximately 1 mPa. As the electron flows from the cathode electrode are roughly converged to the target by the electric field in the tube, the plasma x-ray source, which consists of metal ions and electrons, forms by the target evaporating. Both the tube voltage and current displayed damped oscillations, and their peak values increased according to increases in the charging voltage. In the present work, the peak tube voltage was almost equivalent to the initial charging voltage of the main condenser, and the peak current was less than 30 kA. The characteristic x-ray intensity substantially increased according to the growth in the plasma x-ray source. When the linear plasma x-ray source formed, the bremsstrahlung x-rays were absorbed without using a monochromatic filter, and high- intensity characteristic x-rays were produced.

Tentative study on high-photon-energy quasi-x-ray laser generator by forming plasma x-ray source

Tentative study on high-photon-energy quasi-x-ray-laser generator by forming plasma x-ray source is described. The generator employs a high-voltage power supply, a low-impedance coaxial transmission line, a high-voltage condenser with a capacity of about 200 nF, a turbo-molecular pump, a thyristor pulse generator as a trigger device, and a flash x-ray tube. The high-voltage main condenser is charged up to 60 kV by the power supply, and the electric charges in the condenser are discharged to the tube after triggering the cathode electrode. The flash x-rays are then produced. The x-ray tube is of a demountable triode that is connected to the turbo molecular pump with a pressure of approximately 1 mPa. As the electron flows from the cathode electrode are roughly converged to the copper target by the electric field in the tube, the plasma x- ray source, which consists of metal ions and electrons, forms by the target evaporating. Both the tube voltage and current displayed damped oscillations, and their peak values increased according to increases in the charging voltage. In the present work, the peak tube voltage was much higher than the initial charging voltage of the main condenser, and the peak current was about 25 kA with a charging voltage of 60 kV. When the charging voltage was increased, the plasma x-ray source formed, and the characteristic x-ray intensities of K-series lines increased. When the plate target was employed, we observed high-intensity characteristic x-rays from the axial direction of the linear plasma x-ray source. In the case where the rod target was employed, we detected higher-intensity characteristic x-rays.

Characteristics of the plasma flash x-ray generator and applications

Various characteristics of a plasma flash x-ray generator having a cold-cathode radiation tube and its application to high-speed soft radiography are described. The x-ray generator employs a high-voltage power supply, a low-impedance coaxial transmission line with a gap switch, a high-voltage condenser with a capacity of about 200 nF, a turbo-molecular pump, a thyristor pulser as a trigger device, and a flash x-ray tube. The high-voltage main condenser is charged up to 60 kV by the power supply, and the electric charges in the condenser are discharged to the tube after triggering the cathode electrode. The flash x-rays are then produced. The x-ray tube is of a demountable triode which is connected to the turbo molecular pump with a pressure of approximately 1 mPa. As the electron flows from the cathode electrode are roughly converged to the target by the electric field in the tube, the plasma x-ray source which consists of metal ions and electrons is produced by the target evaporating. Both the tube voltage and current displayed damped oscillations, and their peak values increased according to increases in the charging voltage. In the present work, the peak tube voltage was almost equivalent to the initial charging voltage of the main condenser, and the peak current was less than 30 kA. In this experiment, we employed four types of plasma targets as follows: (1) single target, (2) coaxial double target, (3) alloy target, and (4) plate target. When the single target in conjunction with the monochromatic filter was employed, high-intensity quasi- monochromatic x-rays were obtained. Next, the characteristic x-ray intensities from the outer target increased in the case where the double target was used. By using the alloy (copper tungsten) target, the x-ray intensities of the copper K-series lines increased. Finally, when the linear plasma x-ray source was formed by using the plate target, the bremsstrahlung x- rays were absorbed and were converted into florescent rays, and high-intensity characteristic x-rays were produced.

Plasma flash x-ray generator (PFXG-02)

In the plasma flash x-ray generator, high-voltage main condenser of about 200 nF is charged up to 50 kV by a power supply, and electric charges in the condenser are discharged to an x-ray tube after triggering the cathode electrode. The flash x-rays are then produced. The x-ray tube is of a demountable triode that is connected to a turbo molecular pump with a pressure of approximately 1 mPa. As electron flows from the cathode electrode are roughly converged to a rod iron target of 3.0 mm in diameter by electric field in the x-ray tube, the weakly ionized linear plasma, which consists of iron ions and electrons, forms by target evaporating. At a charging voltage of 50 kV, the maximum tube voltage was almost equal to the charging voltage of the main condenser, and the peak current was about 20 kA. When the charging voltage was increased, the linear plasma formed, and the K-series characteristic x-ray intensities increased. The x-ray pulse widths were about 800 ns, and the time-integrated x-ray intensity had a value of about 10 μC/kg at 1.0 m from x-ray source with a charging voltage of 50 kV. The plasma x-rays were diffused after passing through two lead slits.

Unsteady drag force measurements over bodies with various configurations in a vertical shock tube

Paper reports the result of unsteady drag force measurements and their comparison with numerical simulation. Experiments were conducted in a vertical shock tube consisting of a 300 mm i.d. and 2.5 m long high-pressure chamber and a 300 mm × 300 mm square low-pressure channel of 5 m in length. Models with various configurations installed with accelerometers in them were suspended along the low-pressure test section and then planar shock waves at shock Mach number of 1.22 in air were loaded on these models. Model shapes were cones with smooth and coarse surface finish, a double cone a sphere, a 2:3 ellipsoid and a cylinder. The time variation of drag forces exerted on the models was compared to that obtained by solving numerically the Euler equations. A good agreement was obtained between the experiments and numerical results. Unsteady drag force over these models shows peak value and gradually decreases to its steady value.

Quasi-monochromatic cerium flash angiography

The cerium target plasma flash x-ray generator is useful in order to perform high-speed enhanced K-edge angiography using cone beams because K-series characteristic x rays from the cerium target are absorbed effectively by iodine-based contrast mediums. In the flash x-ray generator, a 150 nF condenser is charged up to 80 kV by a power supply, and flash x rays are produced by the discharging. The x-ray tube is a demountable diode, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Since the electric circuit of the high-voltage pulse generator employs a cable transmission line, the high-voltage pulse generator produces twice the potential of the condenser charging voltage. At a charging voltage of 80 kV, the estimated maximum tube voltage and current were approximately 160 kV and 40 kA, respectively. When the charging voltage was increased, the K-series characteristic x-ray intensities of cerium increased. The K lines were clean and intense, and hardly any bremsstrahlung rays were detected at all. The x-ray pulse widths were approximately 100 ns, and the time-integrated x-ray intensity had a value of approximately 10 μC/kg at 1.0 m from the x-ray source with a charging voltage of 80 kV. In the angiography, we employed a film-less computed radiography (CR) system and iodine-based microspheres.

Application of harder stroboscopic x-ray generator to high-speed radiography

The radiographic characteristics and the applications of an improved high-photon-energy stroboscopic x-ray generator are described. This generator is primarily designed in order to increase the maximum photon energy of the pulse x-rays and is composed of the following essential components: a thyratron pulse generator, a high-voltage transformer having a ferrite core with a maximum output voltage of 300 kV, a sequence controller, a DC power supply for the cathode (filament), and an x-ray tube. The main condenser of about 50 nF in the thyratron pulse generator is charged up to 15 kV, and the electric charges in the condenser are discharged repetitively to the primary coil of the transformer. Because the high- voltage pulses from the secondary coil are then applied to the x-ray tube, repetitive harder x-rays are produced. The x-ray tube is of a triode having a hot-cathode that is primarily driven at the temperature-limited current region. In this triode, because the grid is connected to the cathode, this tube is driven as a diode. The tube voltage roughly increased in proportion to the charging voltage, and the maximum value was about 300 kV. Thus, the maximum photon energy had a value of about 300 keV. The tube current was primarily regulated by the filament temperature and had values of less than 2 A. The x-ray output displayed almost single pulses, and the width of the first pulse was about 300 ns. The maximum repetition rate was about 1 kHz, and the dimension of the x-ray source had values of about 3.5 X 3.5 mm. The high-speed radiography was primarily performed by both the delayed and the multiple- shot radiographies using a new computed radiography (CR) system.