RU209633U1 - Vacuum neutron tube - Google Patents

Abstract

The utility model relates to the field of applied physics and can be used in the development of neutron generators based on vacuum neutron tubes for the activation analysis of alloys and compounds. that in a vacuum neutron tube containing inside a vacuum-tight insulating housing a target electrode with a target saturated with a heavy hydrogen isotope, a controlled three-electrode ion source with anode, cathode and ignition electrodes, as well as means for maintaining the working pressure, the vacuum-tight housing of the neutron tube is made in the form of a cylinder made of insulating material, vacuum-hermetically attached on one side to the anode, and on the other to the target electrode, on the inside of the target electrode there is an electrically conductive cylinder with a screening grid of high transparency, mechanically and electrically connected with it, and on the outer side of the target electrode, an annular permanent magnet is coaxially located from two half-rings of different poles, which forms a magnetic field transverse with respect to the axis of the tube. 1 ill.

Description

The utility model relates to the field of applied physics and can be used in the development of neutron and x-ray generators, as well as neutron and x-ray tubes.

Known vacuum neutron tube containing a housing placed in it controlled three-electrode ion source, the cathode and anode which are saturated with hydrogen isotopes, and the target. The target and the ion source are located at opposite ends of the tube body towards each other. G. I. Kiryanov. Fast neutron generators. - M.: Energoatomizdat, 1990. - S. 122.

The disadvantage of the tube is a small resource of work.

A vacuum neutron tube is also known, containing a controlled 3-electrode spark source placed in a sealed sealed glass or ceramic case, which consists of an annular anode, a cathode and an igniting electrode, and a target. The target is made in the form of a molybdenum disk with a deposited titanium layer. The working gases are constantly occluded in the elements of the neutron tube: in the target - tritium or deuterium, on the anode and cathode of the ion source - deuterium. Collection of materials of the Intersectoral scientific and technical conference "Portable neutron generators and technologies based on them." – All-Russian Research Institute of Automation named after V.I. N.L. Dukhova, 2004. - S. 72.

The disadvantage of this tube is the rapid failure of the ion source of the tube and the short service life of the tube due to the lack of a system for suppressing secondary electron emission currents resulting from the bombardment of the tube target with deuterium ions.

The closest technical solution chosen for the prototype is a vacuum neutron tube containing a controlled 3-electrode spark source placed inside a vacuum-tight sealed glass case, which consists of an annular anode, a cathode and an igniting electrode and a target. The target is made in the form of a molybdenum disk with a deposited titanium layer. To form and accelerate ion beams and suppress secondary electron emission resulting from the bombardment of the tube target with deuterium ions, an ion-optical system of electrodes and an antidynatron grid connected to the grid electrode on the body of the neutron tube are used. RF patent No. 2316835, IPC G21G 4/02, H05H 3/06, H05H 5/03, 02/10/2008.

The body of the neutron tube is a vacuum-tight shell of two glass cylinders connected to each other by a glass-to-metal junction using a grid electrode. A target electrode is fixed at one end of the shell, and the anode electrode of a controlled 3-electrode spark source is fixed at the other end.

A potential difference is applied between the target and grid electrodes with the help of a bias resistance, which ensures suppression of the secondary electron emission.

The grid electrode is made in the form of a V-shaped ring made of kovar vacuum-hermetically soldered on both sides with glass cylinders. The implementation of four glass-to-metal junctions significantly complicates the design of the insulating housing of the neutron tube, leads to an increase in the length of the neutron tube, axial displacement of the two cylinders of the housing relative to each other. In places where glass is welded with a sharp edge of the kovar, there are "air bubbles", both individual inclusions and in the form of chains, due to which a large electric field strength appears. When the tube is triggered from places of greatest tension, corona discharges occur, especially from "air bubbles".

For stable operation of the tube in a neutron generator, it is necessary to introduce a bias resistance wound with a wire with a high electrical resistivity, a metal screen.

The technical result of the invention is to reduce the size of the neutron tube, simplify its manufacture, increase reliability, service life.

The technical result is achieved by the fact that in a vacuum neutron tube containing inside a vacuum-tight insulating housing a target electrode with a target saturated with a heavy isotope of hydrogen, a controlled three-electrode ion source with anode, cathode and ignition electrodes, as well as means for maintaining working pressure, vacuum-tight the body of the neutron tube is made in the form of a cylinder made of insulating material, vacuum-hermetically attached on one side to the anode electrode, and on the other to the target electrode, on the inside of the target electrode there is an electrically conductive cylinder with a screening grid of high transparency, mechanically and electrically connected to it, and on the outer side of the target electrode, an annular permanent magnet of two differently pole semirings is located coaxially, forming a magnetic field transverse with respect to the tube axis.

The essence of the invention is illustrated in the drawing, where:

1 - body;

2 - controlled 3-electrode spark ion source

3 - cathode;

4 - ignition electrode;

5 - anode;

6 - getters;

7 - target electrode;

8 - target;

9 - permanent magnet;

10 - electrically conductive cylinder;

11 - shielding mesh.

Vacuum neutron tube consists of a vacuum-tight housing 1, made in the form of a cylinder of insulating material. Housing 1 contains a three-electrode ion source 2 with cathode 3, ignition electrode 4, anode 5, means of maintaining the working pressure - getters 6, target electrode 7 with target 8. Housing 1 is vacuum-hermetically connected through kovar bushings by soldering to the anode electrode 5 of the ion source and target electrode 7. Vacuum-tight ceramics or glass can be used as the insulating material of housing 1. On the inner side of the target electrode, there is a hollow electrically conductive cylinder 10 with a screening grid 11 with high transparency, mechanically and electrically connected to it, as well as a target 8. On the outer side of the target electrode, an annular permanent magnet 9 is coaxially located from two differently pole semirings, forming a transverse relative to tube axis magnetic field.

To ensure the necessary vacuum in the volume of the tube body 1, getters 6 are used.

The neutron tube works as follows.

Anode 5 is supplied with a DC voltage that is insufficient to breakdown the vacuum gap, but a “pre-breakdown” electric field strength is created.

When a high-voltage pulse (5–15 kV) is applied to the ignition electrode 4, a “breakdown” occurs between the cathode 3 and the ignition electrode 4. The area between anode 5 and cathode 3 is ionized, as a result of which the electrical strength of the anode-cathode gap sharply decreases, which leads to the ignition of an arc discharge. As a result, the working gas (deuterium) is desorbed from anode 5 and cathode 3. The resulting plasma moves into the outlet of anode electrode 5 and exits into the accelerating gap "cathode - target electrode" of the tube, in which deuterium plasma ions are accelerated by a voltage pulse of 120–150 kV. When target 7, saturated with deuterium or tritium, is bombarded, as a result of a nuclear reaction, neutrons with an energy of 2.5 MeV or 14 MeV and secondary electrons are formed.

The current of secondary electrons is parasitic and can be a significant part of the total discharge current, reducing the service life of the neutron tube. In order to prevent the secondary electrons formed near the target 7 from reaching the electrodes of the ion source 2, a permanent magnet 9 is installed on the end of the target electrode 4. The permanent magnet 9 can be built into the target electrode 8. The secondary electrons knocked out of the target 7 enter the equipotential an electrically conductive cylinder 10 with a screening grid 11 and a target 7, and are returned to the target by a magnetic field, which prevents them from entering the acceleration gap.

Thanks to this technical solution, the design of the neutron tube is greatly simplified due to the absence of an antidynatron grid and a grid electrode on the body, its length, axial displacement of electrodes, and their number are reduced. In addition, the reliability of the proposed neutron tube should be higher than that of the prototype, since the number of vacuum-tight junctions of the kovar with the insulating material has decreased.

The effectiveness of the proposed technical solution was verified as a result of comparative tests on the same vacuum neutron tubes. An experiment was carried out with the measurement of the neutron yield during the suppression of secondary electrons with a permanent magnet and with the help of an antidynatron grid and a bias resistance. The results are the same within the measurement error.

Claims (1)

A vacuum neutron tube containing inside a vacuum-tight insulating housing a target electrode with a target saturated with a heavy hydrogen isotope, a controlled three-electrode ion source with anode, cathode and ignition electrodes, as well as means for maintaining the working pressure, characterized in that the vacuum-tight housing of the neutron tube made in the form of a cylinder of insulating material, vacuum-hermetically attached on one side to the anode, and on the other to the target electrode, on the inside of the target electrode there is an electrically conductive cylinder with a screening grid of high transparency, mechanically and electrically connected to it, and on the outside On the side of the target electrode, an annular permanent magnet of two half-rings of different poles is located coaxially, forming a magnetic field transverse with respect to the axis of the tube.

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