JPH11233052A - X-ray image tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray image tube in which electric leakage on a wall surface inside a vacuum enclosure is reduced. SOLUTION: This X-ray image tube is equipped with an input part 13 to input an X-ray image, an output part 18 to output an output image corresponding to the X-ray image inputted in the input part 13, a vacuum enclosure 11 with the input part 13 and the output part 18 placed inside, and an ion pump 20 placed in the vacuum enclosure 11 to maintain a degree of vacuum in the vacuum enclosure 11, and a heating body 22 is provided on the input part 13 side of the ion pump 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an X-ray image tube for converting radiation such as X-rays and γ-rays into a visible light image.

[0002]

2. Description of the Related Art Conventionally, an X-ray image tube has been used to convert radiation such as X-rays and γ-rays into a visible light image.

Here, a conventional X-ray image tube will be described with reference to FIG. Reference numeral 40 denotes an external container having an electromagnetic shielding action, and a portion of a vacuum envelope 41 constituting an X-ray image tube is housed inside the external container 40.
An input window 42 is provided on the front surface of the vacuum envelope 41. An input section 43 is provided on the inner surface of the input window 42 on the vacuum side. The input unit 43 includes an input fluorescent screen 44 for converting an X-ray image into a visible light image, and a photoelectric screen 45 for emitting photoelectrons according to the intensity of light of the visible light image converted by the input fluorescent screen 44.
It is composed of

When an X-ray image is input to an X-ray image tube,
Photoelectrons corresponding to the line image are emitted from the input unit 43. The photoelectrons are accelerated and focused by the first to third focusing electrodes 46, 47, 48 and the anode 49 using the photocathode 45 as a cathode, and incident on the output unit 50 provided at the other end in the vacuum envelope 41. I do. The photoelectrons incident on the output unit 50 are amplified by the output phosphor screen and converted into a visible light image that faithfully reproduces the shadow of the X-ray image input to the input unit 43. Further, an ion pump 51 is disposed on the side of the output section 50 of the vacuum envelope 41 in order to maintain the degree of vacuum in the vacuum envelope 41 (see Japanese Patent Application Laid-Open No. H7-142019).

The photocathode 45 of the input section 43 is manufactured by, for example, a method in which alkali metal molecules are introduced into a vacuum envelope and filled, and a thin alkali metal molecule film is formed on the input phosphor screen. I have.

[0006]

The photocathode of an X-ray image tube is manufactured by a method in which an alkali metal molecule is introduced into a tube and filled therein to form an alkali metal molecule film on an input phosphor screen. At this time, the alkali metal molecular film also adheres to the electrodes arranged in the vacuum envelope tube and the inner wall surfaces thereof. For example, an introduction tube for introducing alkali metal molecules into the tube is usually provided on the output side of the vacuum envelope. Therefore, the alkali metal molecular film may be formed thick on the inner wall surface of the tube on the output unit side. The alkali metal molecular film has a property of increasing the radiation efficiency of electrons in a vacuum. On the other hand, there is a problem that a discharge is easily generated between electrodes to which a high voltage is applied.

By the way, 50 is provided between the electrodes of the ion pump.
A voltage of 0 V to several kV is applied. For this reason, if an alkali metal molecular film adheres near the ion pump, discharge occurs and the operation becomes unstable. In addition, the vacuum characteristics of the image tube cannot be maintained. Further, light emission generated by discharge may be detected at the input portion of the image tube, and a discharge image may be generated at the output portion of the image tube even when X-rays do not enter. It should be noted that the discharge causing the unstable operation may also occur between the electrode of the ion pump and the third focusing electrode near the electrode.

In order to prevent such discharge, there is a method of using a power supply circuit capable of applying a voltage lower than the voltage of the third focusing electrode and higher than the ground voltage (0 V) as the cathode voltage of the ion pump. See Japanese Patent Application Laid-Open No. 7-142019). However, this method requires a Zener diode that can be cut off to a high voltage, and increases the cost.

In order to reduce the cost, there is a method of externally heating the vicinity of the ion pump after forming the photocathode to remove alkali metal molecules attached to the inside of the tube. In this method, heat is applied to the alkali metal molecules by transmitting external heat to the inner surface by utilizing heat conduction of a vacuum envelope portion made of glass. For this reason, the vacuum envelope may generate cracks or distortion due to the heat, which may affect the strength of the glass constituting the vacuum envelope. Therefore, there is a problem that sufficient heating cannot be performed.

An object of the present invention is to solve the above-mentioned drawbacks and to provide an X-ray image tube in which electric leakage on the inner surface of a vacuum envelope is reduced.

[0011]

According to the present invention, there is provided an input section for inputting an X-ray image, an output section for outputting an output image corresponding to the X-ray image input to the input section, the input section and the input section. An X-ray image tube comprising: a vacuum envelope in which an output unit is disposed; and an ion pump disposed in the vacuum envelope to maintain a degree of vacuum in the vacuum envelope. A heating element for generating heat is provided on the input surface side of the ion pump.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to a schematic sectional view of FIG. Reference numeral 11 denotes a vacuum envelope constituting the X-ray image tube, which is formed of, for example, glass. An input window 12 is provided on the front surface of the vacuum envelope 11, and an input unit 13 is provided on the vacuum-side inner surface of the input window 12. The input unit 13 includes an input fluorescent screen 14 that converts an X-ray image into a visible light image, a photoelectric screen 15 that emits photoelectrons according to the intensity of light of the visible light image converted by the input fluorescent screen 14, and the like. ing.

The latter half of the vacuum envelope 11 has, for example, a structure in which a large-diameter portion 11a and a small-diameter portion 11b are continuous. The third focusing electrode 16 is arranged in the inner space of the large diameter portion 11a of the vacuum envelope 11. The third focusing electrode 16 is formed in a ring shape as a whole, and has a portion 1 protruding toward the input side.
6a, an intermediate portion 16b, and a portion 16c protruding on the side opposite to the input side.

Below the third focusing electrode 16, the vacuum envelope 1
The anode 17 is arranged in the inner space of the small diameter portion 11b. Below the anode 17, at the end of the vacuum envelope 11, there is arranged an output part 18 made of a phosphor. Then, from the large diameter portion 11a of the vacuum envelope 11 to the small diameter portion 11a.
At the transition to b, a concave portion protruding outward, that is, a storage portion 19 is provided, and an ion pump 20 for maintaining a vacuum inside the vacuum envelope 11 is disposed in the storage portion 19.

The ion pump 20 has two electrode parts, an anode part 20b and a cathode part 20a made of a getter material such as titanium, and the anode voltage is set higher than the cathode voltage. A voltage of about 500 V to about several tens kV is applied between the anode section 20b and the cathode section 20a through the anode terminal 21b and the cathode terminal 21a embedded in the vacuum envelope 11. The two electrode terminals 21 a and 21 b are insulated by the glass material of the vacuum envelope 11.

A heating element 22 is disposed in front of the ion pump 20 disposed in the storage section 19, that is, on the input section 13 side. The heating element 22 is provided in the housing 1 of the vacuum envelope.
9, and between the housing 19 and the third focusing electrode, the inner surface of the vacuum envelope is made of a metal that can be heated to 150 ° C. or higher. For example, an electric resistance that generates heat by an electric current, a metal that generates heat at a high frequency, or the like is used. However, the electric resistance is more suitable in that the heating state can be easily controlled.

Here, the structure of the above-mentioned X-ray image tube near the ion pump as viewed from the output section will be described with reference to FIG. In FIG. 2, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and redundant description is partially omitted.

Reference numeral 19 denotes a cylindrical storage portion.
The ion pump 20 is disposed inside the device. And
The heating element 22 has, for example, a size such that its annular outer edge portion extends outside the storage portion 19.

According to the above-described structure, when forming the photoelectric surface, alkali metal molecules adhere to the inner surface of the vacuum envelope, such as the storage part storing the ion pump or between the storage part and the third focusing electrode. Also, the alkali metal molecules can be removed by the heat generated by the heating element. For this reason, it is possible to prevent a decrease in insulation between the two terminals of the ion pump or between the ion pump and the third focusing electrode,
Electric leakage can be reduced.

For example, infrared rays radiated from the heating element are absorbed most by the inner surface of the vacuum envelope. Therefore, the temperature of the inner surface is increased, and the alkali metal molecules can be efficiently heated and removed. The infrared rays generated by the heating element are absorbed by the wall of the vacuum envelope. Therefore, the temperature of the outer surface of the vacuum envelope is kept low, and the stress applied to the glass of the vacuum envelope 11 is reduced.

The heating element is formed, for example, in a ring or spiral shape whose outer edge is larger than the opening of the storage section. For this reason, the area | region which remains without removing an alkali metal can be reduced. In addition, the heating element has a ring shape, which facilitates manufacture. If the heating element has a spiral shape, the heating element is arranged so as to cover the accommodating portion of the ion pump, and the removal of the alkali metal is ensured. Further, if a material having a getter effect for absorbing gas in the tube is used as the heating element, an X-ray image tube having excellent productivity can be formed. Examples of the material having the getter effect include Ti and Zr.
A sintered material obtained by sintering the powder of the above can be used.

In order to heat the alkali metal satisfactorily, it is desirable that the distance between the heating element and the electrode of the ion pump in the storage part be at most 30 mm.

Next, another embodiment of the present invention will be described.
This will be described with reference to the cross-sectional view of FIG. 3, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and duplicate description is partially omitted.

In this embodiment, a storage portion 19 which is provided so as to protrude outward at a transition portion from the large-diameter portion 11a to the small-diameter portion 11b of the vacuum envelope 11 is made of metal. It is hermetically sealed as a part of the enclosure 11. Then, the metal housing 19 is connected to the cathode of the ion pump 20, and set to the same potential as the cathode to operate. In this case, the metal housing 19 can also be used as a cathode. Therefore, the number of components is reduced, and space is saved.

[0025]

According to the present invention, it is possible to realize an X-ray image tube with reduced electric leak on the inner surface of the vacuum envelope.

[Brief description of the drawings]

FIG. 1 is a schematic partial cross-sectional view for explaining an embodiment of the present invention.

FIG. 2 is a schematic structural diagram for describing an embodiment of the present invention, and is a diagram viewed from an output surface side.

FIG. 3 is a schematic partial cross-sectional view for explaining another embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view for explaining a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Vacuum envelope 12 ... Input window 13 ... Input part 14 ... Input fluorescent screen 15 ... Photocathode 16 ... Third focusing electrode 17 ... Anode 18 ... Output part 19 ... Storage part 20a ... Anode part 20b ... Cathode part 21a ... Anode terminal 21b ... Cathode terminal 22 ... Heating element

Claims (5)

[Claims] 1. An input unit for inputting an X-ray image, an output unit for outputting an output image corresponding to the X-ray image input to the input unit, and a vacuum in which the input unit and the output unit are arranged. In an X-ray image tube including an envelope and an ion pump arranged in the vacuum envelope to maintain a degree of vacuum in the vacuum envelope, an X-ray image tube is provided on the input unit side of the ion pump. An X-ray image tube comprising a heating element for generating heat. 2. The X-ray image tube according to claim 1, wherein the heating element is formed of an electric resistor whose temperature rises to 150 ° C. or more by passing electricity. 3. A part of the vacuum envelope is provided with an outwardly projecting recess for accommodating the ion pump, and the outer edge of the heating element is located outside the recess. The X-ray image tube according to claim 1. 4. The X-ray image tube according to claim 1, wherein the heating element is formed of a getter material that absorbs gas in the vacuum envelope when heat is generated. 5. A part of a vacuum envelope is provided with an outwardly projecting recess for accommodating an ion pump, and a heating element is arranged within 30 mm from an opening of the recess. An X-ray image tube as described.