Teiji Oizumi

Repetitive flash x‐ray generator having a high‐durability diode driven by a two‐cable‐type line pulser

The fundamental studies of a repetitive soft flash x‐ray generator having a high‐durability diode for high‐speed radiography in biomedical and technological fields are described. This generator consisted of the following essential components: a constant negative high‐voltage power supply, a line‐type high‐voltage pulser with two 10 m coaxial‐cable condensers, each with a capacity of 1.0 nF, a thyratron pulser as a trigger device, an oil‐diffusion pump, and a flash x‐ray tube. The x‐ray tube was of a diode type which was evacuated by an oil‐diffusion pump with a pressure of approximately 6.7×10−3 Pa and was composed of a planar tungsten anode, a planar ferrite cathode, and a polymethylmethacrylate tube body. The space between the anode and cathode electrodes (AC space) could be regulated from the outside of the tube. The two cable condensers were charged from −40 to −60 kV by a power supply, and the output voltage was about −1.5 times the charged voltage. Both the first peak voltage and current increased a...

Fundamental Study on a Long-Duration Flash X-Ray Generator with a Surface-Discharge Triode

Fundamental studies on a long-duration flash X-ray generator are described. This generator consisted of the following components: a high-voltage power supply with a maximum voltage of 100 kV, an energy-storage condenser of 500 nF, a main discharge condenser of 10 nF, a turbo molecular pump, a thyratron pulser as a trigger device, and a surface-discharge triode. The effective pulse width was less than 30 µs, and the X-ray intensity approximately had a value of 0.6 µC/kg at 1.0 m per pulse with a charged voltage of 60 kV. The maximum tube voltage was equivalent to the initial charged voltage of the condenser, and the peak tube current was less than 40 A. With this generator, we could obtain stable X-ray intensity maximized by preventing damped oscillations of the tube voltage and current.

Sub-kilohertz flash X-ray generator utilising a glass-enclosed cold-cathode triode.

The construction and fundamental studies are described for a subkilohertz X-ray generator for producing low-dose rate flash X-rays. The X-ray tube was a glass-enclosed cold-cathode triode, composed of a tungsten plate target, a rod-shaped graphite cathode, a mesh-type trigger electrode made of tungsten wires, and a glass tube body. The coaxial condenser was charged up to 60 kV by a power supply, and the electric charges in the condenser were discharged to the X-ray tube repetitively when a negative high-voltage pulse was applied to the trigger electrode. The maximum tube voltage before the discharging was equivalent to the initial charged voltage of the condenser, and the maximum tube current was about 0.3 kA with a charged voltage of 60 kV. The X-ray durations were about 1 μs, and the X-ray intensity was about 0.47 μC kg−1 at 0.5 m per pulse with a charged voltage of 60 kV. The maximum repetition rate of the X-rays was about 0.4 kHz, and high-speed radiography was performed.

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.

10 kHz microsecond pulsed X-ray generator utilising a hot-cathode triode with variable durations for biomedical radiography

A 10 kHz pulsed X-ray generator utilising a hot-cathode triode in conjunction with a new type of grid control device for controlling X-ray duration is described. The energy-storage condenser was charged up to 70 kV by a power supply, and the electric charges in the condenser were discharged to the X-ray tube repetitively by the grid control device. The maximum values of the grid voltage (negative value), the tube voltage, and the tube current were −1.5 kV, 70 kV, and 0.4 A, respectively. The duration of the flash X-ray pulse was primarily determined by the time constant of the grid control device and the cut-off voltage of thermoelectrons. The X-ray duration was controlled within a region of less than 1 ms; the X-ray intensity with a pulse width of 0.27 ms, a charged voltage of 70 kV, and a peak tube current of 0.4 A was 0.92 μC kg−1 at 0.5 m per pulse. The maximum repetition rate was about 10 kHz, and the size of the focal spot was about 3.5×3.5 mm.

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).

Repetitive compact flash x-ray generators for soft radiography

The construction and the fundamental studies for the repetitive flash x-ray generators designed by Japan Impulse Laboratory in Iwate Medical University are described. These generators are classified to the following two major types: (1) generators having diodes, and (2) generators having triodes. In order to generate high-voltage impulses, we employed the following transmission lines (pulsers): (a) high-voltage-inversion type with a maximum output voltage Vom of about 80 kV, (b) high-voltage- inversion type having a coaxial cable (Vom equals 130 kV), (c) two-stage Marx pulser (Vom equals 150 kV), (d) two-cable-type Blumlein (Vom equals 120 kV), (e) modified Blumlein (Vom equals 120 kV), (f) fundamental transmission line for triode (Vom equals 100 kV), and (g) transmission line for an enclosed triode (Vom equals 100 kV). Using these generators we succeeded in performing high-speed radiography as follows: (a) delayed radiography; (b) multiple-shot radiography; and (c) cineradiography.

Disk-cathode flash X-ray tube driven by a repetitive two-stage Marx pulser

Fundamental studies of a repetitive flash X-ray generator using a diskcathode radiation tube are described. The high-voltage pulser employed a modified two-stage surge-Marx circuit. The two condensers in the pulser were charged from 40 to 60 kV, and the electric charges were discharged to the X-ray tube repetitively to generate flash X-rays. The total capacity during the main discharge was 425 pF, and the maximum output voltage from the pulser was about 1·9 times the charged voltage. The flash X-ray tube of the demountable-diode type and was composed of a rodshaped anode tip made of tungsten, a disk cathode made of graphite and a tube body made of polymethylmethacrylate. The peak tube voltage was primarily determined by the anode-cathode (A-C) space, and the peak tube current was less than 0·5 kA. Thus the maximum photon energy could be easily controlled by varying the A-C space, and the tube current roughly increased according to increases in the charged voltage. The pulse width ranged from 40 to 100 ns, and the X-ray intensity was less than 1·1 μC kg−1 at 0·5 m per pulse. The repetition rate was less than 50 Hz, and the effective focal spot size was equivalent to the anode diameter.