Weight fine-focus two-electrode pulsed x-ray tube

 

(57) Abstract:

The invention relates to x-ray techniques and can be used in pulsed x-ray apparatus for obtaining short x-ray flashes of high intensity for detection of fast processes in optically dense media, x-ray, radiography, medical diagnosis and so on, the Technical result is to increase the spatial uniformity, stability from shot to shot, the quality of x-ray radiation and a decrease in the rate of growth of the supply voltage. The result is due to the fact that explosive-emission cathode, made in the form of washers made of heat-resistant dielectric is applied to the comb formed by a metal washer having radial slots radiating from the center, with an internal diameter greater than the inner diameter of the dielectric spacers. The tips of the teeth of the comb are springy contacts with the end plane of the dielectric spacers, and the contact node dies with a dielectric washer facing the output window. The anode is made in the form of a rod or cone with a hemisphere, and stands for the cross-section plane perpendicular is the dius hemisphere. 2 Il.

The invention relates to x-ray techniques and can be used in pulsed x-ray apparatus for obtaining short x-ray flashes of high intensity for detection of fast processes in optically dense media, x-ray, radiography, medical diagnosis and so on

Known pulse three-electrode x-ray tube comprising an anode in the form of a rod, sharpened under the cone, a cathode in the form of a metal washer and a control electrode located in the vicinity of the cathode [1] . The device operates as follows. Between the anode and cathode is applied high DC voltage value in the hundreds of kilovolts. With the arrival of the pulse high voltage on the control electrode is an electrical breakdown between the cathode and control electrode. As a result of the breakdown plasma is formed, which serves as a source of electrons. The electrons are accelerated between the cathode and the anode and hampered by the material of the anode, resulting in the inhibition generated x-ray radiation. The duration of the radiation is determined by the time shorting diode plasma and is usually the amount mineeeeee application of high voltage control oscillator, what complicates the design of the x-ray apparatus. In addition, the use of high DC voltage requires a large insulating gap, on the order greater than the insulation distances for nanosecond pulses. This increases the dimensions and weight of the equipment, complicated maintenance.

These shortcomings deprived two-electrode pulsed x-ray tube comprising an anode in the form of a rod of small diameter with butt-end, tailored to the cone, hollow cylindrical cathode coaxially located with the anode and remote from him at some distance along the axis [2]. The end face of the cylindrical cathode to reduce the voltage of the occurrence of the emission of electrons confined so that the wall thickness is several micrometers. The distance to the anode and the diameter of the cylinder are determined from the parameters of high-voltage pulses. With the arrival of the pulse of high voltage to the anode on the sharpened end of the cathode cylinder occurs explosive emission of electrons. The resulting electrons bombard tapered portion of the anode. In the deceleration of electrons in the anode material generated x-ray radiation propagating along the axis through the cathode and in the and radiation - less than 15o, operating voltage is not less than 500 kV. The disadvantages of this device are the following: a) a significant excess of the profile of the x-ray focus on axial; b) small angular divergence of radiation; C) high level of operating voltage.

These deficiencies result in reduced sharpness of x-ray images from the center to the periphery, reduction of the sizes of x-ray images to reduce image contrast objects with low x-ray density.

The closest technical solution is of small weight fine-focus two-electrode pulsed x-ray tube [3]. The tube consists of a conical anode, a cathode in the form of a disk made of tantalum with a thickness of 20 μm with a Central hole, the edges of which serve as automatiom, the current lead connected to the anode of the output window and the insulating housing. The tube is similar to the previous operating voltage of the tube 120 to 200 kV, the angular divergence of radiation over 60o. For maximum x-ray output height extending beyond the plane of the conical cathode side of the anode should be 6 to 12 mm. At a height smaller than a certain size normal operation of the tube is broken, there is a big of drops to zero. Under optimum clearances stable generation of x-ray radiation begins when the rate of rise of voltage on the tube 1014In a/C. the Disadvantages of the described device are: a) amplitude and spatial instability of x-ray radiation, due to the high instability of the electron current explosive emission from a metal cathode and the formation of one Central issue, the position of which migrates from shot to shot; b) significant increase in the effective x-ray focus at distances from the axis of the tube, due to the great length of extension of the anode cone beyond the plane of the cathode; C) the necessity of securing the highest rate of rise of voltage on the tube for receiving the explosive emission of electrons from a metal cathode.

These drawbacks lead to the fact that: (a) satisfactory quality x-ray images can be obtained only at the front Desk and film exposure dozens or hundreds of pulses, i.e., to operate in the accumulation mode, when the fluctuations of the radiation from pulse to pulse are averaged; (b) it is impossible to use the tube in the fluoroscopic mode, for example, in roentgentelevision frame, i.e., during the 20 - 40 MS; C) the sharpness of the image decreases from the center to the periphery; g) the need to ensure high slew rate voltage leads to increased demands for high voltage generator to power the tube.

The aim of the present invention is to improve the spatial uniformity, stability from shot to shot, the quality of x-ray radiation and a decrease in the rate of growth of the supply voltage.

The objective is achieved due to the fact that weight fine-focus two-electrode pulsed x-ray tube comprising an anode, intended for inhibition of electron beam and x-ray generation, disc explosive-emission cathode for generating an electron beam, the current lead for supplying a high voltage, sealed insulating housing with a window for output radiation, which is located inside the vacuum separating the cathode and the anode, the cathode is made in the form of a washer made of heat-resistant insulator, which is in the comb formed by a metal washer having radial slots radiating from the center, with an internal diameter greater than the inner diameter of the dielectric washer, having pruines elektricheskoi washer facing the output window, and a cylindrical or conical part of the anode rod is terminated by a hemisphere and in favour of the cross-section plane perpendicular to the axis of the tube, passing through the contacts dielectric spacers and combs at a distance not exceeding the radius of the hemisphere chosen from the required dimensions of the x-ray focus.

In Fig. 1 a shows a variant of the device of Fig. 1B shown separately diode node. The tube consists of a cylindrical rod anode 1 of diameter d, is made from a material with high atomic number. The end face of the anode ends of the hemisphere. If you need to have a smaller size of the x-ray focus, the end face of the anode are in the form of a truncated cone with a hemispherical end. The cathode consists of a dielectric washer 2, which is a metal comb 3 in such a way that the tips of the teeth of the comb are springing contact with the end plane of the dielectric spacers. The end face of the anode is at a plane dielectric washer, which has the comb distance h r, where r is the radius of the hemisphere. Cathode Assembly fixed in a metal glass, vmontirovana grounded in the flange 4 of the tube. At the same flange fitted with a window 5 for outputting Apolonas the end of the body is set high flange 7, connected to the current lead 8. The current lead fortified anode 1, the tubulation 9 vacuum tube, hetaeras 10 to maintain a high vacuum.

The device operates as follows. With the arrival of the pulse of high voltage to the anode there is a high electric field strength in the area of high-current diode. In place of the metallic contact of teeth with a dielectric washer is a significant increase in the strength of the electric field, since the potential of the conductive metal combs is equal to zero, and the potential of a non-conductive dielectric washer is different from zero. Thus, due to the high electric field strength at the site of contact, there is a discharge in the micro gaps between metal and dielectric occurring with the formation of the plasma. Plasma is an electron emitter. The level and rate of rise of voltage at which discharge occurs, an order of magnitude lower than the desired level and rate of rise of voltage of the occurrence of explosive emission of electrons in the absence of the dielectric. Because such a sample is not locking the main electrodes, i.e., is partial to education requires negligible energy. Low voltage and energy needed is Rick. Thus, on the surface of the dielectric washer there are several sources of electrons, which are evenly spaced around the circumference. Under the influence of an electric field, the electrons are accelerated and bombard the anode. The emergence of multiple centers of emission, symmetrically located relative to the anode, can achieve spatial uniformity of the radiation, good its repetition from pulse to pulse. Because the distribution of electrons is limited by the surface of the dielectric spacers, the bombardment is subjected to only the spherical part of the anode, which ensures that minor changes in the current of the x-ray focus in the center and on the periphery of the image.

Comparative tests of industrial x-ray tube IMA-6, manufactured sealed x-ray tube with metal electrodes and claimed sealed x-ray tube. X-rays are converted into visible using ZnS fluorescent screen - CdSAg and were registered by the CCD connected to a personal computer. The processing programs are allowed to capture the intensity and distribution of the radiation for each received frame. X-ray tube IMA-6 is and tf= 0.5-1 1014In/sec. In trials at U = 140 kV and tf= 51012The tube was unstable. Instability was the variation of the radiation intensity from pulse to both the level and in space. However, more than 60% cases happened in the gaps in the generation of radiation. The test results of the inventive x-ray tube shown in Fig. 2. Dots represent the average relative intensity of x-ray tube for a series of 30 pulses after a certain number of thousands of pulses. The symbol indicated the intensity of x-ray sealed tube with a cathode in the form of a metal washer, and a symbol - intensity radiation tube of the proposed design. Axis abscess delayed a number of thousand pulses between a series of measurements. The presence of generation of radiation between measurements were recorded x-ray television system. Intervals denoted by the standard deviation of the intensity of radiation in each series. It is seen that the variation in the intensity level of the radiation of the proposed design significantly less than that of the tube with a cathode in the form of a metal washer. After 10 thousand pulses of the radiation intensity sealed asterousia equipment, and the tube of the proposed design at the moment withstood the test of more than 100 thousand and continues to work steadily.

Literature

1. G. Tomer. Physics of fast processes. M.: Mir, 1971, S. 340.

2. C. A. Zuckerman, M. A. Manakova. Sources of short x-ray flashes for the study of fast processes. // Technical physics letters, 1957, T. 27, No. 2, S. 43-57.

3. E., C. A., N. In. Belkin, N. A. Dron, D. N. Sleeve. Compact pulsed x-ray tube. // Pribory I Tekhnika eksperimenta, 1974, No. 5, S. 189-190.

Weight fine-focus two-electrode pulsed x-ray tube comprising an anode, intended for inhibition of electron beam and x-ray generation, disc explosive-emission cathode for generating an electron beam, the current lead for supplying a high voltage, sealed insulating housing with a window for output radiation, which is located inside the vacuum separating the cathode and the anode, wherein the cathode is made in the form of a washer made of heat-resistant insulator, which is in the comb formed by a metal washer having radial slots radiating from the center, with an inner diameter greater than the inner diameter of the dielectric the stroke node dies with a dielectric washer facing the output window, and a cylindrical or conical part of the anode rod is terminated by a hemisphere and in favour of the cross-section plane perpendicular to the axis of the tube passing through the contacts dielectric spacers and combs at a distance not exceeding the radius of the hemisphere.

 

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