RU2248643C1 - X-ray tube with field-radiating cathode - Google Patents

Abstract

FIELD: flaw inspections, customs examination equipment, medicine, and roentgen diagnosing spectroscopic installations.

SUBSTANCE: proposed X-ray tube has vacuum envelope accommodating anode, X-ray output aperture, cathode assembly incorporating field-radiating cathode in the form of bundle of carbon fibers placed in conducting or semiconducting shell, contact assembly of field-radiating cathode, and cap that functions as control electrode. In order to prevent stray surface electric conductance caused by sputtering of field-radiating cathode material on structural components of X-ray tube, dielectric washer is inserted in this tube wherein during X-ray tube assembly annular cavity is formed between inner hole of washer, field-radiating cathode shell, and upper end of field-radiating cathode contact assembly. Cavity provided in dielectric washer and also its slots prevent formation of solid conducting and semiconducting films which enhances stability of electrical and radiating characteristics of tube. For raising electric strength of tube and excluding breakdown of its envelope cap is installed on dielectric washer that functions as control electrode. Cap is installed so that axis of carbon fiber bundle is aligned with that of optoelectronic system of X-ray tube and symmetry axis of cap.

EFFECT: enhanced operating stability, electric strength, reliability, and service life of X-ray tubes with field-radiating cathode.

1 cl, 3 dwg

Description

The invention relates to x-ray tubes containing an autocathode made on the basis of carbon materials, and can be used as a source of x-ray radiation in flaw detection devices, inspection equipment, medical x-ray devices, diagnostic x-ray spectroscopy units.

Known x-ray tube containing an anode enclosed in a vacuum flask, a control electrode, a window for outputting x-ray radiation and a thermal cathode as an electron source [1]. Such an X-ray tube is powered by a high voltage power source and from a source for glowing the cathode. The expenditure of power on the cathode glow reduces the tube efficiency. In addition, the mandatory heating of the cathode leads to heat generation and undesirable heating of the x-ray tube.

An x-ray tube is also known, which contains an anode and an autocathode enclosed in a vacuum flask made of carbon filaments consisting of a large number of carbon fibers [2], and a window for outputting x-ray radiation. However, the known device does not provide for the protection of the dielectric part of the shell of the x-ray tube from its irradiation by electrons from the autocathode and from dusting by cathode sputtering products during operation of the x-ray tube. In addition, there is no possibility of changing or adjusting the current of the x-ray tube and the intensity of the x-ray radiation at a constant high voltage.

The closest in technical essence and the achieved result to the claimed invention is an X-ray tube [3], containing an autocathode and an anode with electrical leads enclosed in a vacuum flask, a control electrode in the form of a grid, a window for outputting X-ray radiation. A carbon nanostructured film fixed inside the x-ray tube is used as an autocathode, the film being selected from the group consisting of nanocrystalline graphite, carbon nanotubes, diamond, diamond-like carbon, or a combination of two or more elements selected from this group.

However, the known device does not provide for the protection of the dielectric part of the shell of the x-ray tube from its irradiation by electrons from the autocathode and from dusting by cathode sputtering products during operation of the x-ray tube.

These factors lead to a decrease in electric strength, reliability and durability of the X-ray tube due to the formation of conductive films and progressive conductivity between the electrodes of the X-ray tube and do not allow to obtain field emission and x-ray radiation with repeatable characteristics.

The aim of the present invention is to increase stability, electrical strength, reliability and increase the service life of x-ray tubes with autocathodes.

This goal is achieved by the fact that in the proposed x-ray tube containing an electron-optical system located in a vacuum flask, consisting of a self-cathode made of carbon material, an anode with electrical leads, and also a window for outputting x-ray radiation, the self-cathode is made in the form of a carbon fiber bundle enclosed in a shell and connected through the contact node of the cathode with an electrical outlet, and placed inside the hole of an additionally inserted dielectric washer in such a way that between a cathode is formed by the cathode’s shell, a hole in the washer and the end of the contact assembly, a cap is fixed to the dielectric washer with an electrical output in its end wall acting as a control electrode, and the axis of the carbon fiber bundle coincides with the axis of the electron-optical system of the x-ray tube and the axis of symmetry holes in the cap.

The proposed design is illustrated by drawings.

Figure 1 shows the design of the x-ray tube assembly.

Figure 2 presents the dielectric washer with longitudinal grooves made therein.

Figure 3 presents the dielectric washer with transverse grooves made therein.

X-ray tube (figure 1) contains placed in a vacuum flask 1 electron gun 2, the anode 3, made, in particular, chamber, a window for outputting x-ray radiation 4. As for the electron gun 2, it contains a cathode 5, cap 6 with electric pin 7, dielectric washer 8, contact node of the cathode 9

The bundle of carbon fibers 10 is enclosed in a sheath 11 to ensure the orientation of the carbon fibers, their mechanical fastening and vibration resistance. The shell 11 is made of a conductive or semiconducting material, for example, a conductor, semiconducting glass or metallized on the surface of a dielectric, i.e. material, excluding a random change in the potential of the shell relative to the carbon fiber bundle during operation of the x-ray tube. A bundle of carbon fibers 10 from the side of the emitter protrudes from the shell 11. For the passage of autoelectrons from the cathode to the anode in the end wall of the cap 6, which performs the function of a control electrode of the tube, a diaphragm is made in the form of a hole 12.

The contact node of the autocathode 9 is made of an electrically conductive material 13, for example, of an electrically conductive paste based on Ag, Al powder or other metals or conductive materials. The specified material 13 is deposited on the end of the carbon fiber bundle opposite from the emitter and part of the sheath, crimped by a metal shell 14, which can be made, for example, in the form of a cylinder or cylinder cut along a plane passing through its axis. The shell 14 has an electric (cathode) terminal 15 from the evacuated flask 1 and is rigidly connected to a dielectric washer 8, for example, glass cement, glue or hardened resin. The central axis of the shell 14, the carbon fiber bundle 10 enclosed in the shell 11, and the hole of the dielectric washer 8 are aligned with the axis of the electron-optical system of the x-ray tube.

The tube is assembled in such a way that a cavity 16 is formed between the inner walls of the hole in the washer 8, the shell 11, and the upper end of the contact assembly 9. This cavity is designed to prevent the formation of surface conductivity between the cathode 5 and the control electrode 6 due to the formation of conductive films and tracks on the surfaces of the cathode shell 11, the dielectric washer 8 and the control electrode 6. Conductive and semi-conductive films are formed during thermal vacuum processing of x-rays WCSS tube, and as a result the cathode sputtering material subjected to ion bombardment, and breakdown between the electrodes of the X-ray tube arising during training and during operation of the X-ray tube.

To prevent the formation of these films, in addition to the cavity 16 in the dielectric washer 8, longitudinal 17 (Fig. 2) and / or transverse 18 (Fig. 3) electric protective grooves can be made that increase the surface electric strength of the dielectric washer 8 and prevent the formation of surface conductivity between the autocathode 5 and a control electrode 6. Electro-protective grooves 17 and 18 increase the distance between the cathode 5 and the control electrode 6 and prevent the formation of spurious conductive films. The washer 8 with the electrical protection grooves 17 and 18 can be made inlaid, for example, from separate washers with holes and, in addition to the dielectric elements, can have metal elements holding the separate parts of the washer 8 together. The boundaries of the washers in figure 2 and 3 are shown in dotted lines.

The durability of the X-ray tube is proportional to the number of grooves and their depth, because the more grooves in the washer, the greater the area of the shadow, i.e. non-dusting areas of the washer and the higher its electric strength and, accordingly, the durability and reliability of the x-ray tube.

The number of grooves performed in a dielectric washer, their geometric shapes and sizes are determined by the dimensions of the field-electron gun in the x-ray tube and, as a result, by the dimensions of the dielectric washer, as well as the capabilities of the technological equipment.

и диаметром 20-50

Они являются центрами автоэлектронной эмиссии углеродных волокон. Автоэлектроны с катода 5 вылетают через отверстие 12, выполненное в торцевой стенке колпачка 6, и попадают в сильное ускоряющее электрическое поле между анодом 3 и колпачком 6. Диафрагмирующее отверстие 12 в колпачке 6 позволяет автоэлектронам лететь только на анод 3, предотвращая попадание автоэлектронов с катода на диэлектрическую часть оболочки 1 рентгеновской трубки. Размещение катодного узла, состоящего из автокатода 5, диэлектрической шабы 8 и контактного узла автокатода 9, в полости колпачка 6 исключает возможность попадания электронов с автокатода 5 на внутреннюю поверхность диэлектрической вакуумной колбы 1 рентгеновской трубки. В результате увеличивается электропрочность трубки, так как исключается вероятность зарядки и последующих пробоев диэлектрической оболочки вакуумной колбы.X-ray tube works as follows. When high positive potential is applied to the anode 3 relative to the cathode 5 and the voltage between the autocathode 5 and the control electrode 6 from the ends of the carbon fibers protruding from the sheath 11, field emission occurs. Numerous fibrils come to the surface of carbon fiber ends - tetragonal crystalline carbon formations elongated along the fiber axis 250-1000 long

and diameter 20-50

They are centers of field emission of carbon fibers. Autoelectrons from the cathode 5 fly out through the hole 12 made in the end wall of the cap 6 and fall into a strong accelerating electric field between the anode 3 and the cap 6. The diaphragm hole 12 in the cap 6 allows autoelectrons to fly only to the anode 3, preventing autoelectrons from the cathode to hit the dielectric part of the shell 1 of the x-ray tube. The placement of the cathode assembly, consisting of an autocathode 5, a dielectric plate 8 and a contact assembly of an autocathode 9, in the cavity of the cap 6 eliminates the possibility of electrons from the autocathode 5 on the inner surface of the dielectric vacuum bulb 1 of the x-ray tube. As a result, the electric strength of the tube increases, since the probability of charging and subsequent breakdowns of the dielectric shell of the vacuum flask is excluded.

As a result of the bombardment of the anode by high-energy electrons, x-ray radiation occurs, the rays of which exit the tube through window 4. When the potential changes on the cap 6, which acts as a control electrode, the electric field strength at the end surface of the emitting carbon fibers of the autocathode 5 changes, and thus X-ray tube current and X-ray intensity are adjusted.

During the operation of the X-ray tube between the electrodes, conductive and semiconducting films can form on the control electrode, on the shell, between the electrodes, and also on the surface of the dielectric bonding electrodes, between the electrodes, due to the ion bombardment and atomization of carbon from the fibers of the cathode and the sheath material. The appearance of the films leads to an increase in parasitic conductivity between the electrodes of the x-ray tube, its characteristics change, the electric strength deteriorates, the reliability decreases, and the durability decreases.

The elimination of these disadvantages is achieved in the proposed design using a dielectric washer 8 in the electron gun, in the upper part of which vertical 17 and / or horizontal grooves are made. In addition, the autocathode 5 is placed in the dielectric washer 8 so that a cavity 16 is formed between the central hole in the washer 8 and the sheath 11 in which the carbon fiber bundle 10 is enclosed. It may have, for example, an annular shape. In addition, the introduction of a dielectric washer provides alignment and alignment of the autocathode 5 in the optical system, which allows to increase the repeatability of the emission and radiative characteristics of the x-ray tube. The formation of the cavity 16 between the shell 11 and the dielectric washer 8, as well as the grooves 17 (figure 2) and 18 (figure 3) in the dielectric washer 8 prevents the formation of continuous conductive and semiconducting films between the cathode and the control electrode 6 on the surface of the dielectric washer 8 This is explained by the fact that during the operation of the x-ray tube in the cavity 16 and grooves 17 and 18, closed along the contour around the cathode, “shadow” areas for dusting onto which cathodic sputtering products cannot get during the tube operation are formed. Therefore, the conductive film on the surface of the dielectric washer 8 will have closed contours, not dusty areas (gaps) in the cavity 16 and grooves 17 and 18, preventing the occurrence of stray conductivity between the cathode 5 and the control electrode 6.

Tests of the inventive x-ray tube, related to the type of miniature, confirmed the effectiveness of its design solutions. The tube with a supply voltage of 50 kV and a current of 100 μA worked without failures for more than 10,000 hours, which indicates its high reliability and electric strength. Moreover, the instability of the characteristics of the x-ray tube was less than 1%.

Sources of information

1. EP patent No. 1037248, IPC H 01 J 9/32, H 01 J 35/02, 09/20/2000.

2. US patent No. 3883760, IPC H 01 J 35/06, 05/13/1975.

3. Patent application US No. 2003/0002627 A1, IPC H 01 J 35/06, published Jan 2. 2003 - a prototype.

Claims (1)

An x-ray tube containing an electron-optical system located in a vacuum shell, consisting of a self-cathode and an anode with electrical leads, a control electrode and a window for outputting x-ray radiation, characterized in that the self-cathode is made in the form of a bundle of carbon fibers enclosed in a shell and connected through a contact an autocathode assembly with an electrical outlet, and is placed inside the hole in an additionally inserted dielectric washer so that between the autocathode shell and the walls of the hole in the e and an end face of the contact assembly, a cavity is formed, the control electrode is made in the form of a cap with an electrical outlet and a hole in its end wall fixedly mounted on a dielectric washer, the axis of the carbon fiber bundle coinciding with the axis of the electron-optical system of the x-ray tube and the axis of symmetry of the hole in the cap .

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