RU2393581C1 - Gas discharge device - source of x-ray radiation - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: radiation source comprises quartz or ceramic tube and high-voltage metal electrode with taper thread. Inner diametre D of dielectric tube is related to diametre d of central high-voltage electrode as (2/1; 2/1.5; 2/1.8). Dielectric tube wall has orifice, where through and with the help metal branch pipe, X-ray source is pumped out by vacuum pump and working gas (helium, argon, nitrogen, air etc) is fed into X-ray source. One end of said tube has outlet window for X-ray radiation. Said window is made from aluminium, beryllium or polyethylene. Dielectric tube outer surface has second earthed metal cylindrical electrode. Second end of the tube accommodates vacuum-tight high-voltage isolated terminal whereto high variable voltage is fed from power supply. X-ray radiation is readily absorbed in thin layers of polymer insulation, this is why it is suitable for control over metal and gas defects in polymer cable insulation.

EFFECT: simple design, relatively long-wave range of X-ray radiation (20-200 nm).

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Description

The present invention relates to measuring technique and can be used, for example, to control metal and gas defective inclusions in polymer cable insulation using x-ray radiation from an electric gas barrier discharge (EGBR).

The use of x-ray radiation from traditional vacuum x-ray tubes to control defects in polymer cable insulation does not allow to provide the necessary image contrast of metal and gas inclusions. This is due to the fact that the radiation of vacuum X-ray tubes is quite short-wavelength (10-100A) and is poorly absorbed in thin layers of low-density materials (polymer cable dielectrics with a thickness of not more than 4-8 mm and thin aluminum, copper and air inclusions with a thickness of several microns). The short-wavelength X-ray radiation of vacuum X-ray tubes practically does not notice such defects in polymer insulation.

Known gas discharge radiation source / Patent of the Russian Federation No. 2310947, H01J 61/16, 2007 / containing a power source, a flask with a working medium formed by two coaxially mounted tubes of a dielectric material transparent to radiation, as well as two electrodes located on the inside the surface of the inner tube and on the outer surface of the outer tube. A metal heat exchanger is installed in the inner tube of the flask, which is also a high-voltage electrode. The heat exchanger is cooled by forcedly pumping cooling gas through the inner cavity of the inner tube

Known ion sources of x-ray radiation with an anticathode / Guinier A. Crystal X-ray. Publishing House of Physics and Math. literature, M., 1961, p.66 /, using low-pressure gas (below 0.01 atm.), very sensitive to the pressure of the residual gas. The main disadvantage of these sources is the need for a special pressure control system. Ion tubes are sources of inhibitory and characteristic x-rays with a wavelength of less than 10 nm, which is poorly absorbed by polymers. The main disadvantage of the x-ray radiation of these tubes is its high penetrating ability, when it is impossible to detect metal and gas defects in thin polymer cable insulation, as well as the high cost of the x-ray tubes and x-ray equipment themselves.

Known radiation source / US Patent No. 5198717, H01J 65/04; H01J 007/24, 1993 /. Structurally, it is a power source, a sealed flask and a cooling system. The flask is made of two quartz tubes coaxially mounted and welded along the ends. The space between the tubes, which is a flask, is filled with a working medium - gas. The electrodes are located on the outer surface of the outer tube and on the inner surface of the inner tube. In this case, the external electrode is grounded, and a high voltage is applied to the electrode inside the inner tube. A double cooling circuit is used to cool the inner tube. The first of these forms a stream of deionized water, which is cooled in an external heat exchanger. The second circuit forms an external flow of coolant cooling the heat exchanger.

The closest analogue is a radiation source / RF Patent No. 2258975, H01J 61/30, 2005 /, containing a gas-filled glass-shaped flask made of a dielectric with an output window transparent at the working wavelength, a power source with electrodes, the flask is placed in a metal screen housing, on the outer surface of the exit window there is a grounded perforated electrode, and the high-voltage electrode is located on the inner surface of the bottom of the flask and is connected to the power source located in the same housing over the shortest distance, while Additionally, a cooling air injection device is installed in the housing.

A disadvantage of the known devices is that they do not allow to provide the necessary image contrast of metal and gas inclusions to control defects in polymer cable insulation.

The objective of the invention is to provide a device that allows for a relatively long wavelength range of x-ray radiation (20-200 nm). X-ray radiation of this wave range is well absorbed in thin layers of polymer cable insulation and for this reason it is advantageous to use it to control metal and gas defects in polymer cable insulation.

The problem is achieved in that in a known radiation source containing a dielectric tube with an exit window transparent at the working wavelength filled with working gas, two electrodes - an external and an internal high-voltage electrode, an internal high-voltage electrode made cylindrical, is located along the central axis, and the ratio the inner diameter D of the dielectric tube to the diameter d of the central high-voltage electrode is 2/1; 2 / 1.5; 2 / 1.8.

A general view of the device is shown in FIG.

The radiation source contains a quartz or ceramic pipe 1, a high-voltage metal electrode with a tapered thread 2, a tube for pumping and supplying gas 3, an aluminum or beryllium window for the output of x-ray radiation 4, a grounded metal electrode 5.

Along the central axis of the dielectric tube is the first metal (copper) high-voltage electrode 2 with a thread. The ratio of the inner diameter D of the dielectric tube to the diameter d of the central high-voltage electrode is 2: 1; 2: 1.5; 2: 1.8. Pitch and thread height depend on the diameter of the internal high-voltage electrode. The wall thickness of the dielectric tube is from 1 to 10 mm, depending on the diameter of the internal high-voltage electrode. The length of the dielectric tube is 10d. There is a through hole in the wall of the dielectric tube through which the X-ray source is pumped out using a metal pipe 3 and the gas is pumped into the X-ray source (helium, argon, nitrogen, air, etc.). At one end of the pipe there is an exit window for x-ray radiation 4. The window is made of aluminum, beryllium or polyethylene. On the outer surface of the dielectric tube is a second - a grounded metal electrode 5 of a cylindrical shape. At the second end of the pipe there is a vacuum-tight high-voltage insulated contact, to which a high alternating voltage from the power source is connected.

The device operates as follows:

At a distance of 10 mm from the exit window of the gas-discharge device - an X-ray source - there is a specially selected sample of polyvinyl chloride insulation of the AVVG power cable containing a metal inclusion in the form of aluminum shavings. On the opposite side, at a distance of 1 mm from the surface of the cable insulation, there is a camera for recording an x-ray image of the cable insulation. An alternating high-voltage voltage (40 kV, exposure time 10, 15 and 20 min) is supplied to the high-voltage electrode. After exposure, an x-ray film appears.

Figure 2 presents an x-ray photo of the polymer cable insulation of the AVVG power cable containing aluminum chips (four triangular pieces, 15 μm thick), obtained using x-ray radiation, U = 40 kV, P = 0.3 atm, 1 - exposure time - 10 minutes, 2 - exposure time - 15 minutes, 3 - exposure time - 20 minutes.

It can be seen that the pieces of aluminum shavings located in the thickness of the PVC cable insulation clearly differ in the x-ray photograph as a bright image.

The technical effect of our gas-discharge device — an X-ray source — for controlling metal and gas inclusions in polymer cable insulation is simplicity of execution, the absence of an anticathode, and the relatively long-wavelength range of X-ray radiation — 20-200 nm. X-ray radiation of this wave range is well absorbed in thin layers of polymer cable insulation and for this reason it is advantageous to use it to control metal and gas defects in polymer cable insulation.

Claims (1)

A gas-discharge device is an X-ray source containing a dielectric tube with an exit window that is transparent at the working wavelength and filled with working gas, two electrodes - an external and an internal high-voltage electrode, characterized in that the internal electrode having a cylindrical shape is located along the central axis, and the ratio the inner diameter D of the dielectric tube to the diameter d of the central high-voltage electrode is 2: 1; 2: 1.5; 2: 1.8.

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