JPS63190235A - X-ray tube device - Google Patents

Abstract

PURPOSE:To obtain the X-ray focal point with uniform electron intensity distribution by constituting a flat plate-shaped cathode filament with a thermoelectron emitting section and a support section serving as a heating current passage and providing thin sections and thick sections longitudinally on the thermoelectron emitting section. CONSTITUTION:A filament 301 made of W thin plate is fitted to a pair of stanchions 302. The flat center section of the filament serves as an electron emitting section 301a, part of the rear face is etched and thin sections 301a-2 with a thickness of 5-15mum and thick sections 301a-1 are mixedly provided in the longitudinal direction. Both ends are folded at a right angle as leg sections and further folded 301b into a U shape and extended outward at a right angle and welded to the stanchions 302 near the height of the electron emitting section 301a. Accordingly to this constitution, the X-ray focal point with uniform electron intensity distribution can be obtained, the focal point size is reduced, and particularly the heating current is reduced.

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) Generally, an XS tube device is attached to an X* diagnostic device and used for medical purposes, but in cases such as stomach examination, an X-ray tube device as shown in FIG. is used.

This X-ray tube is of a so-called rotating anode type, and a cathode assembly and an umbrella-shaped anode target 33 are arranged opposite to each other in a vacuum envelope 31, eccentric from the tube axis.

The anode target 33 is then energized by the stator 34.
It is rotated by a rotor 35 that is rotationally driven by a-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. This cathode filament 101 is made of a tungsten coil in order to emit thermoelectrons, and focuses the thermoelectrons onto the electrode 1.
Focused by 02. For this reason, the cathode filament 1
01 and the focusing electrode 102 are set to approximately the same potential. In addition, in the figure, dot $! 2103 represents the equipotential curve near the focusing electrode 102, and 104 represents the cathode filament 101.
The reference numeral 105 represents the trajectory of electrons emitted from approximately the center of the cathode filament 101.

(Problems to be Solved by the Invention) In the above conventional cathode structure, the cathode filament 1
Since the cathode filament 101 is used in a substantially temperature-limited region, a part of the cathode filament 101 is made to protrude into the focusing lK 102 in order to strengthen the electric field near the cathode filament 101. 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 dotted line 103, and the anode filament 1
Electrons 105 emitted from substantially the sidewalls of 01 are directed to the side. This electron 105 and cathode filament 101
It is not possible to focus the electrons 104 emitted from approximately the center of the beam and the electrons 104 heading forward 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 impossible to achieve both a sufficiently high resolution and an increase in the amount of incident electrons by reducing the maximum temperature rise due to electron incidence on the anode target.

When creating a projection image using xli generated from the anode target 33, these interfere with increasing resolution and reducing 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 20i during operation of the xm tube device
Due to the thermal expansion, the central part, that is, the electron emitting part, is curved and shifted upward significantly as shown in -Fish $2201a. Both legs also deform outward. In particular, when the position of the electron emitting part changes with changes in filament temperature,
The relative positional relationship between the focusing electrode 202 and the focusing groove 206 changes, and 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.

Furthermore, in order to obtain a sufficiently large tube current, if the area of the electron emitting part of the flat cathode filament 201 is increased,
Not only does the filament current increase and a human field frost source is required, but there are also disadvantages such as a large voltage drop within the high voltage cable. Therefore, when using this cathode filament 201, it was necessary to significantly change the high voltage power supply.

In FIG. 7, a dotted line 203 represents an equipotential curve near the focusing electrode 202, and a reference numeral 204 represents an equipotential curve near the focusing electrode 202.
1, symbol @205 represents the trajectory of electrons emitted from near the side of the cathode filament 201, and symbol 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 intensity distribution and sufficient X-ray intensity can be obtained, and the filament characteristics are different from those of conventional coils. To provide an X-ray tube device which is similar to the case of a shaped cathode filament, can be installed without major modification of an existing X-ray tube device, and further increases the resonance frequency of the cathode filament and reduces the vibration of the anode target. The purpose is to

[Structure of the Invention] (Means for Solving the Problems) In the present invention, a cathode assembly and an anode target are disposed facing each other in a vacuum envelope, and the cathode assembly includes at least a flat cathode filament and its front part. In an X-ray tube device comprising an electron beam focusing electrode provided in The above-mentioned thermionic emission section is an X-ray tube device having a supporting section, and the thermionic emission section has a thin section extending in the longitudinal direction to increase electrical resistance and a thick section having appropriate mechanical strength.

(Function) According to this invention, since the thermionic emission surface is flat,
The emission directions of the thermoelectrons coincide, the electron focusing property is good, and an X-ray focus having a uniform intensity distribution can be obtained. Furthermore, it is possible to create a thermionic emission surface with a sufficient area to obtain a large tube current of 500 mA or more, and the filamentary flow for heating the thermionic emission surface is 10 A.
The current can be kept to a relatively low level. In addition, since the support part is maintained at a relatively low temperature and excess heat generation is prevented, the concentration of thermal stress on the filament support part is eliminated.
Reliability is improved and cathode heating power is reduced. In addition, the resonant frequency of the cathode filament increases, and vibrations caused by the rotation of the anode target during operation may cause damage due to contact with surrounding metal or instability of the tube current due to relative positional deviation with the electrode. do not have. Further, the thermionic emission surface has a partially thick portion, and this thick portion acts as a beam to maintain mechanical strength and prevent deformation due to thermal brain bulge even at high temperatures.

(Embodiment) Hereinafter, an embodiment 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 XIQ tube device that can change the range of 5 mm will be shown.

This is configured as shown in FIGS. 1 to 4, and an anode target 3 is placed in a vacuum envelope (not shown) of the X-ray tube V device.
3, and a cathode assembly 300 is provided opposite thereto. This cathode assembly 300 includes a directly heated cathode filament 30
1 is attached to a pair of filament support columns 302.302. In this case, the cathode filament 301 is
As is clear from the figure, it is shaped like a band and a flat plate, and for example, the width is uniform over the whole, about 3 mm, and the thickness is 0.0 mm.
It is made of a thin tungsten plate of about 3 mm. The central part is formed flat as an electron emitting part 301a, and a part of the back surface of this part is removed by etching or the like to form a thin part 301a-2 with a thickness of 5 μm to 15 μm. The thick part 301a-1 is formed to extend in the longitudinal direction so that the thick part 301a-1 coexists, and both sides thereof are bent at right angles to form legs. Further, it is bent into a U-shape to form a folded part 301b, each end of which is extended outward at right angles and welded to the filament support column 302, 302 at a height close to the electron emitting part 301a. electrically connected. The material of the cathode filament 301 is as follows:
In addition to pure tungsten, high melting point alloy materials such as tungsten and lanthanum molybdenum containing about 1 to 5% rhenium can also be used.

A circular cup-shaped electron beam focusing electric current tU303 is arranged so as to surround such a cathode filament 301,
The filament support columns 302 and 302 are fixed to this electron beam focusing electrode 303 via insulating support columns (not shown). Further, the electron beam focusing electrode 303 includes a thermionic emission portion 301a of the cathode filament 301.
An electron beam limiting hole 304 is formed opposite to the electron beam limiting hole 304 . This electron beam limiting hole 304 is located in the thermionic emission section 301.
It has a rectangular shape, for example, with an area smaller than the area of a, and is located about 0.7 mm (dimension d1) in front of the thermionic emission part 301a, and the opening surface on the thermionic emission part 301a side is substantially in line with the thermionic emission part 301a. are parallel to each other. A focusing groove 305 is formed in the electron beam focusing electrode 303 continuously and in front of the electron beam limiting hole 304. The electron beam limiting hole 304 is formed coaxially with the thermionic emission part 301a, and has a depth of d2.
) is formed with sufficient depth. And focusing groove 3
The bottom surface of 05 is formed in a tapered shape extending to the electron beam limiting hole 304. The dimension of this tapered surface along the direction of the central axis (C) is formed to be a small dimension, 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 cathode filament 301 whose legs are folded back into a U-shape is attached to the filament support column 302.
The part near the end welded to 302 has a relatively low temperature, but the thermionic emission part 301a and the part near it have a thin part 301a-2, so they generate more heat than other parts and become high temperature. However, thermionic emission becomes possible. At this time, the thick part 301a-1 works to reinforce the thermionic emission part 301a, but the cross-sectional area of this part is small, and the temperature difference is extremely small due to heat conduction from the surrounding area, and it is almost uniform. can emit a large number of thermoelectrons.

Now, in this invention, since the heat generating part of the cathode filament 301 exists locally near the thermionic emission part 301ap, thermionic emission from other parts is suppressed, unnecessary heating of other parts is eliminated, and 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.

Furthermore, since the thermionic emission section 301a has the thin wall portion 301a-2, it is light and has a high resonant frequency, so that the relative vibration of the thermionic emission section 301a due to vibrations caused by the rotation of the anode target 33 is small. Not only does it not cause any inconvenience such as contact with the surroundings, but also the Yoiko Beam Collection TEPCO FF1
Instability of the tube current due to relative positional deviation with 303 does not occur.

In addition, the electric resistance of the thermionic emission part 301a increases, and even when the filament width is 3 mm, the thermionic emission part 301a can be heated to more than 2500'' with a filament current of 10A or less, which is different from conventional X-rays. The present invention can be used without major modification of the tube device.Furthermore, the time required for heating the filament to a sufficiently high temperature from the application of the filament current is short, and the interruption of the tube current can be controlled by the interruption of the filament current. I can do it.

(Modification) In the above embodiment, the thermionic emission part 301a is the thick part 301.
Although a-1 is provided parallel to the longitudinal direction of the cathode filament 301, this portion may be formed into a mesh shape or may be formed into a curved line.

[Effect of the 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) 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 xIl 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 synergistic frequency of the cathode filament is increased, so that the cathode filament does not shift its position even in high humidity, 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 (
Figure 2 (a) is a perspective view showing the cathode filament).
A plan view viewed in the six directions of the arrows in the figure, (b) and (a)
Figure (C) is a cross-sectional view taken along line BB' and viewed in the direction of the arrow; 3 and 4 are cross-sectional views showing the cathode structure of an X-ray tube device according to an embodiment of the present invention, FIG. 5 is a schematic configuration diagram showing a conventional X-ray tube device, and FIGS. 6 and 7 are
The figure is a sectional view showing the cathode structure (two examples) of a conventional XIi tube device, and FIG. 8 is a sectional view showing the main part (cathode filament) of FIG. 7. 31... Vacuum envelope 33... Anode target 300... Cathode structure 301... Cathode filament 302... Filament support column 301 a... Thermionic emission part 301 a-1... Thickness Thin section 301a-2...Thin section Applicant's agent Patent attorney Takehiko Suzue Figure 7 Figure 8

Claims (4)

[Claims] (1) In an X-ray tube device in which a cathode assembly and an anode target are disposed facing each other in a vacuum envelope, the cathode assembly is composed of at least a flat cathode filament and an electron beam focusing electrode provided in front of the cathode filament. , the flat cathode filament has a thermionic emission part that becomes high temperature and a support part that mechanically supports the thermionic emission part and serves as a path for heating current, and the thermionic emission part has a longitudinal direction. An X-ray tube device characterized by having a thin wall portion and a thick wall portion extending in the direction. (2) The X-ray tube device according to claim 1, wherein the thin wall portion of the thermionic emission section extends in the longitudinal direction of the thermionic emission section, and the thermionic emission surface is a smooth surface. (3) The X-ray tube device according to claim 1 or 2, wherein the flat cathode filament is made of tungsten or an alloy thereof. (4) The X-ray tube device according to claim 1, 2, or 3, wherein the thickness of the thin portion is set in a range of 5 μm to 15 μm.