JPS5840817B2 - Kaitenyoukiyoku X Senkan - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotating anode X-ray tube, particularly to shielding secondary electrons emitted from a rotating target as an anode.

In general, a rotating anode X-ray tube is equipped with an anode, a rotating target attached to the anode, a cathode, and a focusing electrode attached to the cathode, and a high voltage is applied between the anode and the cathode to move the cathode filament. The structure is such that thermoelectrons are emitted from the focusing electrode by heating and are made to continuously strike the inclined surface of a rotating target rotating at high speed to generate X-rays.

FIG. 1 is a cross-sectional view of essential parts of an example of a conventional rotating anode X-ray tube.
A focusing electrode 2 having a built-in filament (not shown) that emits thermoelectrons is attached thereto.

Further, an umbrella-shaped target 3 is disposed at a position facing the cathode 1 and the focusing electrode 2, and is fixed to a rotating body 5 with a nut 4 so as to be rotatable.

The umbrella-shaped target 3, nut 4, and rotating body 5 constitute an anode 6 that is electrically connected.

Further, a focal portion 7 is formed on the inclined surface of the target 3 at a portion where high-speed electrons are struck from the focusing electrode 2.

These components are hermetically sealed by an envelope 8 made of hard glass.

In the conventional rotating anode X-ray tube configured as described above, a high voltage is applied between the cathode 1 and the anode 6, and a filament (
(not shown), an electron stream is emitted from the focusing electrode 2 and hits the focal point 7 of the umbrella-shaped target 3 at high speed.
A line is emitted.

At this time, not only X-rays but also new secondary electrons are emitted from the focal point 7.

Some of these secondary electrons impinge on the vicinity of the focal point 7 of the umbrella-shaped target 3, while others impinge on the inner surface of the envelope 8 close to the umbrella-shaped target 3.

As a result, when the inner surface of the envelope 8 is struck, since the envelope 8 is made of an insulating material such as hard glass, the part where the secondary electrons strike is negatively charged. Alternatively, secondary electrons may be newly emitted and positive charges may be generated, forming partially positive and negative charge bands on the inner surface of the envelope 8.

The outer surface of the envelope 8 is charged with charges of opposite polarity in correspondence with the charges charged on the inner surface of the envelope 8.

As a result, charges of different polarities are discharged between the inner and outer surfaces of the envelope 8, thereby damaging the hard glass constituting the X-ray tube.

Furthermore, when the inner surface of the envelope 8 is charged with a large amount of positive charge, the electron flow emitted from the focusing electrode 2 is deflected toward the inner surface of the envelope 8 and is directed toward the inner surface of the envelope 8 facing the back surface of the umbrella-shaped target 3. It collides with the inner surface and causes an internal discharge.

Furthermore, if a large amount of negative charge is charged, it has various drawbacks, such as a tendency for discharge to occur between the inner surface of the envelope 8 and the umbrella-shaped target 3.

Therefore, in order to prevent the secondary electrons emitted from the focal point of the target from hitting the glass envelope, in conventional rotating anode X-ray tubes, a metal shield with the same potential as the anode is placed around the umbrella-shaped target. Although it absorbs secondary electrons well and has a good shielding effect, the temperature of the metal shield increases due to the secondary electrons absorbed by the metal shield, and it also receives heat radiation from the umbrella-shaped target. The shield body needs to be made of a heat-resistant metal material with a thick wall, and structural consideration must be taken to dissipate heat to the outside.

For this reason, the X-ray tube has the drawbacks of being large in size and having a complicated structure, so it has often been used for devices with relatively small load capacity.

In addition, high-voltage fixed anode X-ray tubes used for non-destructive testing of metals are equipped with a metal shielding tube in the anode area around the target, but there is also a metal shielding tube on the anode side. There is a structure in which the tip of the cylinder is covered with a shielding cylinder on the cathode side arranged concentrically.

In this case, the cathode side shield has the function of reliably focusing the electrons emitted from the cathode into the anode shield,
Shoot electrons at the target.

In addition, the scattered electrons generated by electrons hitting the target are absorbed by the shield cylinder on the anode side, so there is a problem similar to the structure in which the umbrella-shaped target is surrounded by a metal shield having the same potential as the anode. It has not been applied to X-ray tubes.

The purpose of the present invention is to provide a rotating anode X-ray system which has improved withstand voltage without the disadvantages of making the X-ray tube large and having a complicated structure like the aforementioned X-ray tube with a structure in which a jacket tube is attached to the anode. The purpose is to provide tubes.

In order to achieve such an object, the rotating anode X-ray tube according to the present invention uses a metal shielding member having the same potential as the cathode to surround the cathode, the focusing electrode, and the umbrella-shaped target serving as the anode. It is something.

The rotating anode X-ray tube according to the present invention will be explained in detail below with reference to the drawings.

FIG. 2 is a sectional view of a main part for explaining one embodiment of a rotating anode X-ray tube according to the present invention, and since the same symbols as in FIG. 1 represent the same elements, a description thereof will be omitted.

In the figure, one end of a cylindrical shielding member 9 is fixed with a support plate 9a so as to surround a focusing electrode 2 attached to a cathode 1, and the other end covers a part of the outer periphery and back side of an umbrella-shaped target 3. It is arranged to surround.

In this case, the other end of the shielding member 9 is disposed so as to protrude slightly toward the rotating body 5 from the back surface of the umbrella-shaped target 3.

As this shielding member 9, a mesh-like member is used, for example.

Further, the tip of the other end of the shielding member 9 is connected to an umbrella-shaped target 3.
It is bent toward the inner diameter side to form a curled portion 9b so that it can effectively cover the back side of the sheet and prevent electric discharge.

This shielding member 9 is provided with an X-ray emission port at a position close to the focal point 7 of the umbrella-shaped target 3.

In the rotating anode X-ray tube configured as described above, the shielding member 9 is electrically connected to the cathode 1 by the support plate 9a, so that an electric field having a negative potential that is the same as that of the cathode 1 is formed.

In this state, when an electron current is emitted from the focusing electrode 2 and hits the focal point 7 of the umbrella-shaped target 3 at high speed, X-rays and secondary electrons are newly emitted from the focal point 7.

The X-rays are then radiated to the outside from the X-ray emission port.

On the other hand, the newly emitted secondary electrons cannot fly toward the inner surface of the envelope 8 because the periphery thereof is surrounded by the shielding member 9 having a negative potential. Forms a path of electron movement that returns.

Therefore, the inner surface of the envelope 8 is no longer charged with electric charges, and no discharge phenomenon occurs within the X-ray tube, so that the withstand voltage of the X-ray tube can be improved.

In addition, since secondary electrons are also emitted along with X-rays, the X-ray emission port 10 provided in the shielding member 9 should be made of a material that is difficult for electrons to pass through and has good X-ray transparency in order to prevent the emission of secondary electrons. A more complete shielding effect can be obtained by covering the area with a board.

Further, the shielding member 9 bends its end portion toward the inner diameter side on the back side of the umbrella-shaped target 3 to form a curled portion 9b,
In addition, by arranging it close to the rotating body 5 side, it is possible to form an electric field with a negative potential and to shield the secondary electrons flying toward the back side of the umbrella-shaped target 3, resulting in a more complete shielding effect. can be raised.

FIG. 3 is a sectional view of a main part for explaining still another embodiment of the rotating anode X-ray tube according to the present invention, and since the same symbols as in FIGS. 1 and 2 are the same elements, their explanation is omitted. do.

In the figure, an end of a cylindrical shielding member 11 is fixed with a support plate 9a so as to surround a focusing electrode 2 attached to a cathode 1, and the other end is arranged so as to surround the outer periphery of an umbrella-shaped target 3. has been done.

Further, a comb-shaped shielding member 12 having a diameter larger than that of the rotating target 3 is fixed to the back surface of the umbrella-shaped target 3 with a nut 4 so that the bottom thereof is in contact with the back surface of the umbrella-shaped target 3.

The distal ends of these shielding members LL12 are bent outward to form curled portions 11a and 12a, respectively.

The shielding member 11 is located at a position close to the focal point 7 of the umbrella-shaped target 3. A CX-ray emission port 10 is provided.

In the rotating anode X-ray tube configured as described above, the shielding member 11 is electrically connected to the cathode 1 through the support plate 9a, so that an electric field of negative potential is formed.

On the other hand, since the shielding member 12 is inscribed in and fixed to the umbrella-shaped target 3, an electric field of a positive potential is formed.

In this state, when an electron stream is emitted from the focusing electrode 2 and hits the focal point 7 of the umbrella-shaped target 3 at high speed,
X-rays and new secondary electrons are emitted from the focal point 7.

The X-rays are then radiated to the outside from the X-ray emission port 10.

On the other hand, the secondary electrons emitted from the focal point 7 cannot fly toward the inner surface of the envelope 8 because the periphery is surrounded by the shielding member 11 having a negative potential. As shown in , an electron movement path is formed that returns to the slope of the umbrella-shaped target 3 and the comb-shaped shielding member 12.

Therefore, the secondary electrons cannot fly to the inner surface of the envelope 8 and be charged with positive or negative charges, and no discharge occurs inside the X-ray tube, so it is possible to improve the withstand voltage inside the X-ray tube. can.

In addition, a curled portion 11a is provided at the tip of the shielding member 11.12,
12a, an electric field with a negative potential is formed in the curled portion 11a, and an electric field with a positive potential is formed in the curled portion 12a,
Secondary electrons flying toward the inner surface of the envelope 8 from between the shielding members LL12 can be shielded, and a more reliable shielding effect can be achieved.

In addition, in order to prevent secondary electrons from passing through the X-ray emission port 10 provided in the shielding member 11, it is made even safer and more reliable by covering it with a beryllium plate or the like that is difficult for electrons to pass through and easy for X-rays to pass through. It can be used as a shield.

As explained above, in the rotating anode X-ray tube according to the present invention, the cathode, the focusing electrode, and the umbrella-shaped target as an anode are surrounded by a cylindrical metal shielding member, so that the rays emitted from the umbrella-shaped target are This is because it shields the electrons and prevents them from flying around the inner surface of the envelope.
Compared to conventional rotating anode X-ray tubes that do not have a secondary electron shielding member, the provision of a cylindrical shielding member makes it possible to completely shield secondary electrons flying into the inner surface of the envelope. This eliminates any negative influence on the flow of electrons emitted from the focusing electrode.

In addition, since the discharge phenomenon caused by the emission of secondary electrons is completely prevented, the X-ray tube has various excellent effects such as improved withstand voltage characteristics and longer service life.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part showing an example of a conventional rotating anode X-ray tube, and FIGS. 2 and 3 are sectional views of main parts showing an embodiment of a rotating anode X-ray tube according to the present invention. 1...Cathode, 2...Focusing electrode, 3...
...Umbrella-shaped target, 4...Natsuto, 5.
... Rotating body, 6 ... Anode, 7 ...
- Focal point, 8... Envelope, 9... Shielding member, 9a... Support plate, 9b... Curled part, 10...・・X-ray emission port, 11・・・・
・Shielding member, 11a... Curl part, 12...
...shielding member, 12a...curl portion.

Claims (1)

[Scope of Claims] 1. A cathode, a rotating target that is disposed opposite to the cathode and generates X-rays by electron bombardment, a rotating body that rotates the rotating target, and a rotating body that rotates the cathode and the anode. In a rotating anode X-ray tube equipped with a sealed envelope, the cathode and the rotating target are surrounded by a metal shielding member having the same potential as the cathode, and the secondary electrons emitted from the rotating target are Rotating anode
wire tube. 2. In the rotating anode X-ray tube according to claim 1, the cathode and the rotating target are surrounded by a metal shielding member, and a rotating target having a larger diameter than the rotating target is provided on the back side of the rotating target. A rotating anode X-ray tube characterized in that a metal shielding member that rotates integrally is provided to form a potential distribution that prevents secondary electrons emitted from the anode as the rotating target from flying to the inner surface of the envelope.