JPS61198536A - Focal length adjustable x-ray tube - Google Patents

Abstract

PURPOSE:To reduce a focal length into an allowable range, by sealing a battery and an X-ray tube in an X-ray tube container so that a bias negative as to a filament is applied to a convergence electrode. CONSTITUTION:In an X-ray tube 2, a glow by-pass diode 7 is connected between a filament 5 and a cathode 4. The X-ray tube 2 and a compensatory bias battery 6 are sealed in a tube container 1. The filament 5 is electrically insulated from the convergence electrode portion 4a of the cathode 4 by an electric insulator 8. A positive bias is applied to the filament 5 by the battery 6. Thermoelectrons emitted from the filament are condensed by the electronic lens action of the convergence electrode portion 4a so that the thermoelectrons proceed to an X-ray focus. Since the bias is applied to the filament, the direction of emission of thermoelectrons from the side portions of the filament is restricted to promote the condensation to reduce the focal length of the X-ray tube 2.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention is used in the field of X-ray tubes and X-ray tube cathode structure.

The present invention relates to an X-ray tube in which hot electrons from a cathode filament are focused by an electron lens of a focusing electrode to form a focal point at an anode.

(b) Conventional technology Conventionally, the focal point of an X-ray tube is formed as follows.

Thermionic electrons generated from the filament of the cathode are accelerated by a high voltage applied between the anode and the cathode, and are focused by the electron lens formed by the focusing electrode of the cathode. Form a focal point of dimensions.

(c) Problems to be solved by the invention Parameters that affect the dimensions of the focal point formed in this way include the groove of the focusing electrode, the filament depth, and the distance between the cathode and anode. . In the prior art, it is difficult to increase the precision of these dimensions, resulting in variations in focal spot dimensions. Since the focal spot size is a factor that determines the rating of the X-ray tube, variations in the focal spot dimension lead to variations in the performance of the X-ray tube itself, and there is a problem in that it reduces the yield of shipped products. .

The present invention attempts to solve these problems, such as the groove of the focusing electrode that has limited dimensional accuracy, the filament), the large gap between the 721 can and the positive ↑ box, etc. It is an object of the present invention to provide an X-ray tube with a two-circle focal point size, which can adjust fGi5 to a smaller value than the allowable range caused by.

(d) Means for determining the interval yHI:A 1'+'4 The interval Wfi'5 is a positive (
This is solved by enclosing a battery in the X-ray tube container together with the X-ray tube for applying a negative buff to the focusing electrode in the can with respect to the filament.

If the X-ray tube generates a glow discharge at that time, a glow bypass electrode should be inserted between the focusing electrode and the filament to protect the )/r lament.

(E > 11) It is unavoidable that there is a limit to the dimensional accuracy of the 1V flux current (small groove, filament depth, distance between the cathode and anode of 4'J). By biasing the page, a focus that is larger than the tolerance can be reduced to within the tolerance.

(f) Example A preferred practical example of the invention will be explained on the basis of the drawings.

Fig. 1 is a basic configuration circuit diagram showing one embodiment, Fig. 2 is an explanatory diagram of focal point formation according to the present invention, Fig. 3 is an explanatory diagram of the operation of the present invention, and Fig. 4 is a circuit diagram of another embodiment. . Here, 1
is the X-ray tube container, 2 is the X-ray tube, 3 is the positive tα, 4 is the cathode, which consists of a focusing electrode 4a and a filament 5, 6, 6a, and 6.
b is a battery, ■ is a diode, 8a and 8b are insulators, 9a
and 9b are correction electrodes in the focal length direction, and 10a and 10b are correction electrodes in the width direction.

In the illustrated example of FIG. 2, the filament 5 is insulated by the focusing electrode 4a of the cathode 4 and the insulator 8a, and is positively biased by the battery 6. The thermoelectrons emitted from the filament 5 are focused type 4ii4a as shown in the figure.
The electron lens forms a focusing (X-ray focal point), but as a bias voltage is applied, the trajectory of the thermoelectrons emitted from the side of the filament 5 is suppressed, and the focal point size is changed to increase focusing performance. becomes smaller.

Generally, the focal spot size has a distribution as shown in Figure 3,
In the case of distribution a, items outside the allowable range (diagonally hatched portions) occur and are treated as defective.

This tendency is greater as the X-ray tube has a finer focus. Therefore, according to the present invention, the distribution in FIG. 3 is designed and manufactured so that there is no abnormality below the lower limit of the allowable range, and for those with a focus larger than the upper limit of the allowable φ6 range (horizontal line hatching), the page By using the biased focusing electrode 4a, the size is reduced within the upper limit range, thereby suppressing the occurrence of defective products.

Such a correction bias battery 6 is used together with the X-ray tube 2.
It is sealed in a wire tube container 1. An example of its basic circuit is shown in FIG.

Note that if the filament 5 is insulated from the cathode 4, the filament 4 may be damaged if glow discharge occurs in the X-ray tube, so a glow bypass diode 7 is inserted between the filament 5 and the cathode 4, and the battery 6, it is sealed in the tube container 1. Note that A and B indicate the center of focus.

In the illustrated embodiment, it is not possible to individually reduce the width and length of the focus. An embodiment in which this is possible is shown in FIG. As shown in this illustrated example, by separately providing correction electrodes 9a, 9b in the length direction and correction electrodes 10a, 10b in the width direction, the length and width can be individually reduced according to the focal spot size. I can do it. In this case, the filament 5 does not need to be insulated from the focusing electrode 4a.

(G) Effects of the Invention The present invention makes it possible to bring the center of dispersion close to the upper limit within the allowable focus dimensions, so the emission of thermionic electrons is reduced to 1 bar on average, and the filament assembly precision is micron. This is extremely expensive in terms of order, and since it can be adjusted electrically after assembly, it is easy to adjust and has the effect of providing an X-ray tube with stable performance.

[Brief explanation of drawings]

FIG. 1 is a basic configuration circuit diagram showing one embodiment of the present invention, and FIG.
3 is an explanatory diagram of focal point formation according to the present invention, FIG. 3 is an explanatory diagram of the operation of the present invention, and FIG. 4 is a circuit diagram of another embodiment. 1 is a tube container, 2 is an X-ray tube, 3 is an anode, 4 is a cathode, 4a is a focusing electrode, 5 is a filament, 6 is a battery, 7 is a diode, 8 is an insulator, and 9 and 10 are correction electrodes.

Claims (3)

[Claims] (1) In the cathode consisting of a focusing electrode and a filament,
A battery for applying a negative bias to the focusing electrode on the filament is enclosed in the X-ray tube container along with the X-ray tube, and the upper limit of the allowable range of the focal point is corrected to reduce its size. Features: Adjustable focus size X-ray tube. (2) The focal size adjustable X-ray tube according to claim 1, characterized in that the filament is insulated from the focusing electrode and a glow bypass diode is inserted between the two. (3) A focal point according to claim 1, characterized in that a lengthwise correction electrode and a widthwise correction electrode are additionally inserted into the focal point, and the dimensions of both are individually adjusted to be small. Adjustable size X-ray tube.