Haruo Obara

Quasi-monochromatic radiography using a high-intensity quasi-x-ray laser generator

High-intensity quasi-monochromatic x-ray irradiation from the linear plasma target is described. The plasma x-ray 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 55 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 molybdenum 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 equal to the initial charging voltage of the main condenser, and the peak current was about 20 kA with a charging voltage of 55 kV. When the charging voltage was increased, the linear plasma x-ray source formed, and the characteristic x-ray intensities of K-series lines increased. The quasi- monochromatic radiography was performed by as new film-less computed radiography system.

Conventional metal plasma x-ray-flash techniques using vacuum discharges

The fundamental studies for producing plasma flash x rays using three types of generators are described. The flash x-ray generators used in this experiment are as follows: (a) solid-anode radiation tubes in conjunction with a large-capacity condenser of 199 nF, (b) liquid-anode radiation tubes utilizing a combined ceramic condenser of 10.7 nF, and (c) a flash vacuum ultraviolet (VUV) tube having a surface-discharge-glass substrate driven by a polarity- inversion-type transmission line with a condenser capacity of 14.3 nF. The radiation tubes were of the demountable types and were connected to vacuum pumps with pressures of about 1 X 10-3 Pa. Using type (a) and (b) generators, each condenser was charged from 40 to 60 kV by a power supply, and the electric charges in the condenser were discharged to the radiation tube after the triggering. In contrast, when a type (c) generator was employed, the condenser was charged from -20) to -30) kV, and the maximum output voltages of about -1) times the charged voltages were produced after closing a gap switch. Using these generators, the plasma flash x rays were easily generated, and high-intensity soft x rays of about 10 keV were obtained by using a solid-anode radiation tube. In particular, although the K(alpha) satellites were produced when a type (a) generator with a copper anode is employed, the intensities of the spectrum lines including satellites of copper K(alpha) were considered to be amplified by using a double anode (tungsten mounted copper anode).

Fundamental study on parallel-beam radiography using a polycapillary plate

Fundamental study on parallel beam radiography using a polycapillary plate is described. The x-ray generator used in this experiment is NST-1005 made by Sofron Inc. with maximum tube voltage and current of 100kV and 5.0 mA, respectively. In this experiment, the tube voltage was regulated from 20 to 30 kV, and the tube current had a constant value of 4.0 mA. The exposure time is regulated in order to control optimum film density. The polycapillary plate is J5022-21 made by Hamamatsu Photonics, and the outside and effective diameters are 87 and 77 mm, respectively. The thickness and the whole diameter of the polycapillary are 1.0 mm and 25 micrometers , respectively. The x- rays from the tube are formed to parallel beam by the polycapillary, and the radiogram is taken using an industrial x-ray film of Fuji IX 100 without using a screen. In the measurement of image resolution, we employed three brass spacers of 2, 30, and 60 mm in height. By the test chart, the resolution decreased according to increases in the spacer height without using the polycapillary. In contrast, the resolution seldom varied when the polycapillary was employed. In the polycapillary radiography of four tungsten wires, higher-contrast images of 50 micrometers wire were observed, and the line width seldom varied according to increases in the spacer height.

Polycapillary radiography using a quasi-x-ray-laser generator

The characteristics of a new quasi-x-ray laser generator and its application to polycapillary radiography are 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 new plasma 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 increase in the charging voltage. In the present work, the peak tube voltage was almost equal to 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 linear plasma x-ray source formed, and the characteristic x-ray intensities of K-series lines increased. In the radiogrpahy achieved with a computed radiography system, we employed a polycapilary plate with a hole diameter of 20 micrometers and a thickness of 1 mm. The image resolution was primarily determined by the resolution of the CR system and had a value of about 100micrometers .

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.

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.

Superposition of x-ray spectra using a brass-target plasma triode

In the plasma flash x-ray generator, a 200 nF condenser is charged up to 50 kV by a power supply, and flash x-rays are produced by the discharging. The x-ray tube is a demountable triode with a brass target containing 65% copper and 35% zinc by weight, and the turbomolecular pump evacuates air from the tube with a pressure of approximately 1 mPa. Target evaporation leads to the formation of weakly ionized linear plasma, consisting of metal ions and electrons, around the fine target, and intense characteristic x-rays are produced. 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 15 kA. When the charging voltage was increased, the linear plasma formed, and the K-series characteristic x-ray intensities of zinc Kα, copper Kα, and copper Kβ lines increased substantially. However hardly any zinc Kβ lines were detected. The x-ray pulse widths were approximately 700 ns, and the time-integrated x-ray intensity was approximately 1.2 mGy at 1.0 m from the x-ray source with a charging voltage of 50 kV.

Ignitron-driven soft flash x-ray generator

The fundamental study on a soft flash x-ray generator utilizing an ignitron is described. This generator consists of the following essential components: a high-voltage power supply, a high-voltage pulser having an ignitron, an oil diffusion pump, and a flash x-ray tube. The x-ray tube employs a molybdenum anode rod, a pipe-shaped carbon cathode, a polymethylmeth acrylate tube body, and a polyethylene terephthalate x-ray window. The space between the anode and the cathode electrodes (ac space) can be controlled by rotating the anode rod. The high-voltage condenser in the pulser is charged from 40 to 60 kV by the power supply, and the electric charges in the condenser are discharged to the tube by the ignitron through a 2.0 m coaxial cable. Because the maximum anode voltage of the ignitron is 50 kV, a free-air gap switch is employed in order to increase the high-voltage durability. In the present work, the anode electrode is connected to the ground, and the negative high-voltage output is applied to the cathode electrode. The flash x-rays are then produced. The peak cathode voltage and tube current had values of minus 56 kV and 11.5 kA, respectively, with a charging voltage of 60 kV and an ac space of 6.0 mm, and the pulse widths were less than 300 ns.

Enhanced K-edge angiography utilizing a super-fluorescent x-ray generator with a gadolinium-target tube

The gadolinium plasma flash x-ray generator is useful for performing high-speed enhanced K-edge angiography using cone beams because K-series characteristic x-rays from the gadolinium target are absorbed effectively by iodine-based contrast media. 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 cold-cathode 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 are approximately 160 kV and 40 kA, respectively. When the charging voltage was increased, the K-series characteristic x-ray intensities of gadolinium increased. Bremsstrahlung x-ray intensity rate decreased with increasing the charging voltage, and clean K lines were produced with a charging voltage of 80 kV. The x-ray pulse widths were approximately 100 ns, and the time-integrated x-ray intensity had a value of approximately 500 μGy at 1.0 m from the x-ray source with a charging voltage of 80 kV. Angiography was performed using a filmless computed radiography (CR) system and iodine-based contrast media. In the angiography of nonliving animals, we observed fine blood vessels of approximately 100 μm with high contrasts.

Novel monochromatic x-ray generators and their applications to high-speed radiography

Novel monochromatic x-ray generators and their applications to high-speed radiography are described. The five generators are as follows: a weakly ionized linear plasma x-ray generator, a monochromatic compact flash x-ray generator, a super-fluorescent plasma generator, a cerium x-ray generator using a 3.0-mm-thick aluminum filter, and a 100micron-focus x-ray generator utilizing the filter. Using the linear plasma generator with a copper target, we observed clean K lines and their harmonics, and soft flash radiography was performed with pulse widths of approximately 500 ns. The compact monochromatic flash x-ray generator produced clean molybdenum K lines easily, and high-speed radiography was performed with pulse widths of approximately 100 ns. Using a steady-state cerium x-ray generator, we performed real-time angiography utilizing an image intensifier and a high-sensitive camera (MLX) made by NAC Image Technology Inc. with a capture time of 1 ms. Finally, real-time magnification radiography was performed by twofold magnification imaging using a 100micron-focus x-ray generator and the high-sensitive camera.