JPH01115039A - X-ray tube device - Google Patents

Abstract

PURPOSE:To obtain an X-ray focus with a uniform distribution of electron intensity and to obtain sufficient X-ray intensity and to upgrade positioning precision of a filament and to prevent positioning shift and deformation from occurring at a high temperature, by composing a flat type cathode filament of the following parts: thermion discharge parts formed perpendicularly to an electron beam axis and U-shaped leg parts fixed in the range from the thermion discharge parts to filament support poles. CONSTITUTION:A cathode filament 301 is flatly shaped and it has both perpendicularly bent ends of its electron discharge part 301a and besides it has U-shaped or V-shaped leg parts 301b extended horizontally. These leg parts 301b are welded te be connected electrically with filament support poles 302. The leg parts 301b are selected in combinations of their lengths according to their temperature distribution so that they can completely absorb a difference of thermal expansion. Although the thermion discharge part 301a of the cathode filament 301 is heated at a high temperature, and so the temperature of the leg parts 301b becomes small because of heat conduction to the filament support poles 302 with large heat capacity. Hence an X-ray focus with a uniform distribution of electron intensity can be obtained to improve resolution of an X-ray image.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an X-ray tube device, and particularly to an improvement of its cathode structure.

(Prior Art) X-ray tube devices are generally used for medical purposes by being attached to, for example, an X-ray diagnostic device. equipment is used.

This X-ray tube device is of the so-called rotating anode type, with a vacuum envelope 3
1, a cathode structure 32 and an umbrella-shaped anode target 33 are arranged opposite to each other and eccentric from the tube axis.

The anode target 33 is rotated by a rotor 35 that is rotationally driven by a stator 34 by electromagnetic induction.

Now, the cathode structure 3 of the conventionally used X-ray tube device
2 is constructed as shown in FIG. 6, and a cathode filament 101 is disposed within a focusing groove 106 of a focusing electrode 102. The cathode filament], 01 is made of a tungsten coil for emitting thermoelectrons, and the thermoelectrons are focused by a focusing electrode 102. For this reason, the cathode filament 101 and the focusing electrode 102 are set to approximately the same potential.

In the figure, a broken line 103 represents an equipotential curve near the focusing electrode 102, a symbol 104 represents the trajectory of electrons emitted from approximately the center of the cathode filament 101, and a symbol 1
05 represents the trajectory of electrons emitted from a location close to the side surface of the cathode filament 101.

(Problems to be Solved by the Invention) In the conventional cathode assembly 32 described above, since the cathode filament 101 is used in a substantially temperature-limited region, the cathode filament 101 is A portion thereof protrudes into the focusing electrode 102. Therefore, the equipotential curve near the cathode filament 101 has a swollen shape at the center of the cathode filament 101, as shown by the broken line 103, and the electrons 105 emitted from the substantially side walls of the cathode filament 101 are directed laterally. Become. This electron 105 and the cathode filament 10
It is not possible to focus the electrons 104 emitted from the substantially central portion of the electron beam 1 toward the front in the same direction, and their trajectories intersect on the axis as shown. Therefore, at a position where approximately all the electrons are focused to some extent, a bimodal electron intensity distribution 107 is shown as shown.

However, as described above, since the electrons emitted from the cathode filament 101 cannot be focused sufficiently by the focusing electrode 102, it is necessary to use a small cathode to obtain a small focus at the position of the anode target 33. Therefore, unless the cathode temperature is raised, sufficient high density electrons cannot be obtained, which poses a problem in the reliability of the cathode filament 101.

Further, since the traveling directions of the electrons at the position of the anode target 33 are not aligned, a minute focus cannot be obtained, and furthermore, the electron distribution lacks sharpness, making it impossible to obtain the desired electron distribution. For this reason, it is not possible to simultaneously obtain a sufficiently high resolution and reduce the maximum temperature rise due to electron incidence on the anode target 33 to increase the amount of incident electrons. When a projection image is created using the X-rays generated from the anode target 33, these interfere with an increase in resolution and a reduction in photorenoise, making it impossible to obtain a sufficiently clear image.

One possible method for eliminating this drawback is to use a flat cathode filament, and an example of this is a proposal disclosed in Japanese Patent Laid-Open No. 55-68056.

The conventional example having this flat cathode filament is constructed as shown in FIGS. 7 and 8, and the reference numeral 201 in the figure is a cathode filament made of a belt-like flat plate and formed in the shape of a mouth. Filament support column 215.215
It is fixed to the surface and is directly heated by electricity, emitting thermoelectrons. In this case, the cathode filament 201 during operation of the X-ray tube device
Due to the thermal expansion, the central portion, that is, the electron emitting portion, is curved and shifted significantly upward, as shown by the broken line 201a. Both legs also deform outward. In particular, when the position of the electron emitting part changes as the filament temperature changes, the relative positional relationship with the focusing groove 206 of the focusing electrode 202 changes,
The shape of the focal point on the anode target 208 changes.

This also appears as a large change in not only the focal point shape but also the focal width W, which hinders the realization of a fine focal point.

In FIG. 7, a broken line 203 represents the equipotential curve near the focusing electrode 202, and a reference numeral 204 represents the equipotential curve near the focusing electrode 202.
1, reference numeral 205 represents the trajectory of electrons emitted from near the side of the cathode filament 201, and reference numeral 207 represents the electron intensity distribution.

This invention was made in view of the above circumstances, and by improving the shape of the cathode filament, an X-ray focus with a uniform electron intensity distribution and sufficient X-ray intensity can be obtained, and the positional accuracy of the filament can be improved. 1. The size of the X-ray focal point
It is an object of the present invention to provide an X-ray tube device with high positional accuracy and an improved space factor in the electron emission direction.

[Structure of the Invention] (Means for Solving the Problems) This invention provides a method in which a cathode structure and an anode target are disposed facing each other in a vacuum envelope, and the cathode structure is supported by at least a filament support column. In an X-ray tube device consisting of a flat cathode filament and a focusing electrode provided in front of the flat cathode filament, the flat cathode filament has a high-temperature thermionic emission section formed perpendicular to the electron beam axis, and a thermionic The X-ray tube device comprises a U-shaped or V-shaped leg that is bent perpendicularly from the emitting part, extends laterally, and is fixed to the filament support column.

(Function) According to this invention, since the thermionic emission surface is flat,
Thermionic emission directions coincide, electron focusing is good, and an X-ray focus having a uniform electron intensity distribution can be obtained. Furthermore, the thermionic emission surface is at a high temperature, for example 2300°C.
Even in the case where the legs are exposed, the thermal expansion of the legs is absorbed and the change in position is extremely small. Therefore, the range of focal spots previously accepted in the art can be narrowed, increasing the allowable input power and increasing the x-ray output for the same nominal focal spot size. Moreover, the thickness in the direction of thermionic emission can be made thinner, and the space factor can be improved.

In particular, when used in an X-ray apparatus for breast diagnosis, it is important to make the distance from the anode target surface to the rear surface of the cathode assembly as short as possible.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. Note that the same parts are represented by the same symbols.

This invention can be used, for example, for mammography with an anode voltage of 30 KV.
, maximum anode current 300mA, X-ray focus from 50μm to 0
．． An example of application to an X-ray tube device that can change the range of 5 mm will be shown.

That is, the main parts of the X-ray tube device according to the present invention are shown in FIGS.
The device is constructed as shown in the drawings and FIG. 4, and includes an anode target 33 and a cathode assembly 300 facing the anode target 33 in a vacuum envelope (not shown).

This cathode structure 300 includes a directly heated cathode filament 301
are attached to a pair of filament support posts 302.302. In this case, the cathode filament 301 is shaped like a flat plate, as shown in FIG.
m, and is made of a thin tungsten plate with a thickness of about 0.012 mm. An electron emitting part 301a is heated to a high temperature and emits thermoelectrons, and both ends of the electron emitting part 301a are bent approximately vertically, and U-shaped or V-shaped legs extend laterally. 301b, and this leg portion 301b is welded and electrically connected to the filament support column 302.302.

The combination of lengths of the U-shaped or 7-shaped leg portions 301b is selected depending on the temperature distribution so that the difference in thermal expansion can be completely absorbed.

In addition to pure tungsten, the material of the cathode filament 301 may also be a high melting point alloy material such as tungsten containing about 1 to 5% rhenium or lanthanum molybdenum.

A focusing electrode 303 is formed into a circular cup shape and focuses an electron beam so as to surround the cathode filament 301.
is arranged, and at least one of the filament support columns 302 and 302 is provided with an insulating support column (
(not shown). Furthermore, the focusing electrode 3
03, an electron beam limiting hole 304 is formed opposite to the thermionic emission section 301a of the cathode filament 301. The electron beam limiting hole 304 is made into a rectangle, for example, with an area smaller than the area of the thermionic emission section 301a.
It is located approximately 0', 7 mm (dimension dt) in front of the thermionic emission part 301a, and the opening surface on the thermionic emission part 301a side is substantially parallel to the thermionic emission part 301a. Continuing from and in front of the electron beam restriction hole 304, a focusing groove 305 is formed in the focusing electrode 303.

This focusing groove 305 has a diameter larger than that of the electron beam limiting hole 304, for example, a rectangular shape, is formed coaxially with the electron beam limiting hole 304 and the thermionic emission part 301a, and has a depth (d2).
is formed with sufficient depth. And the focusing groove 30
The bottom surface of 5 is tapered toward the electron beam restriction hole 304 . The dimension of this Taber surface along the direction of the central axis (C) is formed to be a small dimension that is less than a fraction of the depth (d2).

Incidentally, since the configuration other than the above is the same as that of the conventional X-ray tube device (FIG. 5), detailed explanation will be omitted.

During use of the X-ray tube device of the present invention having the cathode assembly 300 as described above, the thermionic emission portion 301a of the cathode filament 301 is heated to a high temperature of about 2800°C. The leg portion 301b of the cathode filament 301 has a low temperature with a large temperature gradient due to heat conduction to the filament support column 302 having a large heat capacity. especially,
The maximum temperature is about 600° C. where it is joined to the tip of the filament support column 302. In order to absorb the temperature difference between the upper part and the rear part of the filament support column 302, their lengths are optimally selected.

Furthermore, since the thermionic emission section 301a and the leg section 301b are perpendicular to each other, the length of the cathode assembly 300 can be extremely shortened. As a result, the size of the cathode side of the X-ray tube device can be extremely shortened. This has great significance when the X-ray tube device is used for breast diagnosis. That is, one end of the X-ray tube device does not hit the human body, causing great pain.

Now, in this invention, since the heat generating part of the cathode filament 301 exists locally near the thermionic emission part 301a, thermionic emission from other parts is suppressed, and unnecessary heating of other parts is eliminated. Furthermore, less electric power is required to heat the filament for heating the thermionic emission portion. In particular, since the filament current is kept low, even when the filament current is superimposed on the high voltage cable, voltage drops in the high voltage cable and heating of the high voltage cable can be prevented.

(Modified Example) In the above embodiment, the entire cathode filament 301 has the same width, but if the width is made wider in the middle, especially at the leg portions 301b, a convenient temperature distribution can be obtained. Furthermore, the thickness of the cathode filament 301 may be varied. especially,
If part or all of the thermionic emission section 301a is made thinner than the leg section 301b, even better temperature distribution can be obtained.

Further, the width and thickness of the leg portion 301b are the same as those of the thermionic emission portion 301.
It may be different than a.

Next, FIG. 2 shows a modification of the present invention, which provides the same effects as the above embodiment. That is, in the modification shown in FIG. 2, the thermionic emission section 301a and the leg section 301b are not continuously integrated as in the above embodiment, but are separate members joined together.

That is, the thermionic emission part 301a is made of a heat-resistant metal such as tungsten or its alloy, and the U-shaped or V-shaped leg part 30
The material of 1b may be the same as that of the thermionic emission part 301a,
Different) may be used. The thickness, width, and material are appropriately selected so as to completely absorb thermal expansion depending on the temperature distribution when the temperature rises.

In addition, in this modification, the mounting position of the thermionic emission part 301a can be adjusted in advance, and the expensive thermionic emission part 301a is
The materials used will be used more efficiently and will be cheaper.

[Effects of invention According to this invention, the following excellent effects can be obtained.

(2) An X-ray focus with a uniform electron intensity distribution is obtained, improving the resolution of X-ray images. ■The variation in the size of the X-ray focal point is reduced, allowing highly accurate X-ray intensity control.

(2) Since the thickness of the cathode structure can be reduced and the length of the X-ray tube device on the cathode side can be shortened, it is possible to provide an X-ray tube device particularly suitable for breast diagnostic devices.

(2) The heating power for the cathode filament is reduced, and in particular, the heating current is required to be small, and an X-ray imaging apparatus using a conventional X-ray tube device can be used without major modification.

(2) Deformation of the cathode filament due to thermal expansion can be prevented, and an X-ray tube device with sufficient reliability can be provided.

■The resonant frequency of the cathode filament is increased, so that the cathode filament does not shift its position even at high temperatures, and does not become out of focus or come into contact with the surroundings.

[Brief explanation of the drawing]

FIG. 1 shows the main parts (
2 is a perspective view showing a modified example of the present invention; FIGS. 3 and 4 are sectional views showing a cathode structure of an X-ray tube device according to an embodiment of the present invention; Fifth
The figure is a schematic configuration diagram showing the entire conventional XiI tube device.
7 and 7 are cross-sectional views showing two examples of cathode structures of conventional X-ray tube devices, and FIG. 8 is a cross-sectional view showing the main part (cathode filament) of FIG. 7. 31... Vacuum envelope, 33... Anode target, 3
00... Cathode assembly, 301... Cathode filament,
302... Filament support column, 301a... Thermionic emission part, 301b... Leg part. Applicant's agent Patent attorney Takehiko Suzue Figure 2

Claims (1)

[Claims] A cathode assembly and an anode target are disposed facing each other in a vacuum envelope, and the cathode assembly includes a flat cathode filament supported by a filament support column, and a focusing electrode provided in front of the cathode filament. In the X-ray tube device, the flat cathode filament has a thermionic emission part that is formed perpendicular to the electron beam axis and becomes high temperature, and is bent perpendicularly from the thermionic emission part and laterally bent. An X-ray tube device comprising: a U-shaped or V-shaped leg extending from above and fixed to the filament support column.