JPS6251132A - Manufacture of electron tube having photoelectric surface - Google Patents

Abstract

PURPOSE:To easily obtain a photoelectric surface of high sensitivity, by providing resistance measuring terminals near a photoelectric surface making portion to detect a resistance change resulting from the reaction of the material for the photoelectric surface and an alkali metal, and by controlling the production of the photoelectric surface depending on the detected resistance change. CONSTITUTION:A resistance measuring section 13, in which a pair of resistance measuring terminals 12 are provided at a prescribed distance from each other on an electrically insulating base, is disposed near the photoelectric surface making portion of the input surface 2 of an X-ray image tube or the like. Electricity is then applied to a heater 10 to evaporate a material such as antimony for a photoelectric surface 8 to coat the photoelectric surface making portion with the material. The thickness of the coating film of the material is controlled by measuring the resistance through the resistance measuring section 13. An alkali metal generator 11 is then heated to evaporate an alkali metal such as cesium to deposit the alkali metal on the thin film of the material. The progress of the reaction of the alkali metal and the material is precisely detected by measuring the resistance through the resistance measuring section 13, to control the deposition of the alkali metal. This results in easily providing the photoelectric surface of high sensitivity and stability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing an electron tube having a photocathode.

[Technical background of the invention and its problems]

The photocathode of an electron tube with a photocathode, such as an image orthicon, an image tube, or an X-ray image tube, is formed by depositing a photocathode base material such as antimony, bismuth, or silver on the photocathode forming part, and then forming a thin film of it. , formed by vapor deposition of alkali metals such as cesium, sodium, and potassium. In order for the formed photocathode to exhibit high sensitivity, it is necessary to ensure that the photocathode matrix and the subsequently deposited alkali metal form the required metal compound. It is necessary to appropriately control the film thickness of the surface base material and the amount of alkali metal subsequently deposited.

Conventionally, the film thickness of the photocathode base material has been determined by providing a set of resistance measuring terminals near the photocathode forming part, and simultaneously depositing the photocathode base material on the photocathode forming part. The resistance of the photocathode base material deposited between the resistance measurement terminals can be measured, or the emitter and receiver can be placed outside the envelope near the photocathode forming part through the envelope to measure the resistance of the photocathode. The film thickness of the photocathode base material deposited on the photocathode forming part is determined by a method such as measuring the light transmittance of the photocathode base material deposited on the inner surface of the envelope at the same time as the photocathode base material is deposited on the photocathode forming part. was under control. Regarding alkali metals, the amount of vapor deposition is controlled by projecting light onto the photocathode forming portion from outside the envelope and detecting the photoelectric sensitivity.

However, controlling the film thickness of the photocathode base material by measuring the resistance or light transmittance described above is a method of indirectly determining the film thickness of the photocathode base material in the photocathode forming part. The film thickness required for the formation area is extremely thin, measuring tens to hundreds of layers, making it practically unreliable.Also, controlling the amount of alkali metal vapor deposited by detecting the photoelectric sensitivity described above is difficult if the conditions of the emitted light match the actual conditions. Since this is not the same as when the electron tube is operated, it is difficult to judge from the obtained photoelectric sensitivity detection value whether the most desirable high-sensitivity photocathode has been formed.

Regarding the control of the amount of alkali metal vapor deposited, in addition to the photoelectric sensitivity detection described above, it is also possible to control the energization heating of the alkali metal generator, but since the alkali metal generator generates alkali metal vapor through a chemical reaction, However, it is difficult to accurately control the amount of vapor deposition using such a method. Furthermore, Japanese Patent Laid-Open No. 48-43523 discloses a method for detecting the amount of ionized alkali metal deposited on the photocathode forming portion by detecting the amount of ionized alkali metal deposited when the alkali metal is deposited. However, even if such a deposition amount is detected, no reaction with the photocathode base material is detected, and therefore it is not possible to detect whether the most desirable photocathode has been formed.

[Purpose of the invention]

The present invention aims to enable easy manufacture of an electron tube having a desired photocathode by detecting the reaction between a photocathode base material and an alkali metal necessary for forming a highly sensitive photocathode.

[Summary of the invention]

A terminal for resistance measurement is provided at or near the photocathode formation part of the electron tube, and a photocathode base material is deposited on the photocathode formation part and the installation part of the resistance measurement terminal. By detecting the resistance change caused by the reaction between the photocathode base material and the alkali metal through the measurement terminal and controlling the photocathode formation based on this detection result, a highly sensitive photocathode is formed and the desired This makes it possible to easily manufacture an electron tube having a photocathode.

[Embodiments of the invention]

Hereinafter, the present invention will be described based on embodiments with reference to the drawings.

FIG. 1 shows an embodiment of an X-ray image tube. This X-ray image tube has an input surface (2) inside one end of the envelope (1).
, an output surface (3) is provided inside the other end of the envelope (1) opposite to this input surface (2), and an external surface is provided between the input surface (2) and the output surface (3). A seven-node electrode (6) is provided along the inner surface of the enclosure (1) to surround the plurality of grid electrodes (4), (5) and the output surface (3). The input surface (2) consists of an X-ray emitting phosphor layer (7) provided on a spherical substrate and a photocathode (8) that converts the light emitted from the phosphor layer (7) into photoelectrons.

In this X-ray image tube, the X-ray emitting phosphor layer (7) on the input surface (2) absorbs the X-rays that have passed through the subject and emits light, and this light emission generates photoelectrons on the photocathode (8). A plurality of grid electrodes (4), (5) and an anode electrode (6
) to focus and accelerate the image of the subject on the output surface (3). Note that in order to make the field size of the subject image obtained on the output surface (3) variable, some types have different electrode configurations.

This X-ray image tube has an input surface (3), an output surface (3), grid electrodes (4), (5) and After arranging and assembling the anode electrodes (6) in a predetermined relationship and evacuating the air, a photocathode base material and an alkali metal are deposited on the input surface to form a photocathode (8). In order to form this photocathode (8), during the assembly, a photocathode base material heater (10) is installed at the other end of the envelope to evaporate a photocathode base material such as antimony (SB) by heating it with electricity. An alkali metal generadar (11) is installed that generates alkali metal, such as cesium (Cs) vapor, by indirect heating.

Furthermore, in manufacturing this X-ray image tube, a set of resistance measurement terminals (12) is provided on the insulating base near the input surface.
Resistance measuring sections (13) are provided at a distance of -100 mm from each other. The terminals (12) of this resistance measuring section (13) are connected to an external power source (not shown), and are continuously measured by detecting the current flowing between both terminals (12) or the voltage drop between both terminals (12). It is now possible to measure the resistance between both terminals (12).

The formation of the photocathode (8) begins with a photocathode base material heater (lO).
The photocathode base material attached to the heater (10), that is, antimony in this example, is vapor-deposited on the photocathode forming portion of the input surface by heating with electricity. At this time, the antimony is
3) is also deposited on the insulating substrate.

The thickness of the antimony film deposited on the photocathode forming section can be determined by measuring the resistance of the antimony thin film deposited on the insulating substrate of the resistance measuring section (13) via a set of resistance measuring terminals (12), or A light emitter (14) and a light receiver (15) are installed on the outside of the envelope (1) near the input surface through the envelope (1), and the light from the antimony thin film deposited on the inner surface of the envelope (1) is emitted. By measuring the transmittance, the film thickness is controlled to a predetermined value. Next, the alkali metal generator (1
1) is heated to vapor deposit an alkali metal, that is, cesium in this example, on the antimony thin film formed on the photocathode forming portion. This cesium is deposited on the resistance measuring section (13) at the same time as the photocathode forming section, and reacts with the previously formed antimony thin film. The progress of this reaction is detected by measuring the resistance between the - pair of terminals (12) of the resistance measuring section (13).

In other words, the antimony-cesium photocathode formed is
Cs and Sb compounds are stable and highly sensitive, and as shown by curve (17) in Figure 2, the reaction between antimony and cesium progresses, and the ratio of cesium to antimony increases over time, changing its composition. As the temperature increases, the resistance value changes greatly.

Therefore, the cesium deposition is controlled by detecting this change in resistance via the set of terminals (12) and recording and reading it, for example, on a recording device.

In an X-ray image tube, it is desired to reduce the X-ray exposure of the subject as much as possible, so the photocathode (8) is made of X-ray emitting phosphor that emits light by absorbing the small amount of X-rays that have passed through the subject. The layer (7) must convert weak light into photoelectrons, and is required to have high light absorption and high photoelectric conversion ability.

This kind of photocathode can be used to control the film thickness of the photocathode base material, which has been done in the past, to measure photoelectric sensitivity, which is performed under conditions different from those during actual operation of an X-ray image tube, and to control the amount of alkali metal evaporated. You can't expect much from detection. However, if the deposition of alkali metal is controlled by detecting the change in resistance caused by the reaction between the photocathode base material and the alkali metal as described above, it is easy to create a stable photocathode with good light absorption and high sensitivity. can be formed into In addition, it is usually difficult to form the required photocathode by a single evaporation of the photocathode base material and alkali metal, so it is formed by alternately repeating the evaporation of the photocathode base material and the alkali metal. The method of controlling the vapor deposition based on this resistance change allows the composition change of the photocathode base material to be sensitively detected each time it is repeated through each process, and an optimal photocathode can be obtained.

Next, other embodiments will be described.

In the above embodiment, a resistance measuring section having a set of resistance measuring terminals provided on an insulating substrate is arranged near the input surface, and the vapor deposition of alkali metal is detected by detecting the resistance change of this resistance measuring section. As described above, this resistance measuring section can also detect resistance changes by attaching a resistance measuring terminal to a part of the input surface, such as an X-ray emitting phosphor layer. good.

Furthermore, in the above embodiment, the resistance change caused by the reaction between the photocathode base material and the alkali metal was detected, and the vapor deposition of the alkali metal was controlled based on the detection result. It is optional to use a method of measuring photoelectric sensitivity in combination.

Further, in the above embodiment, a case was described in which a photocathode was formed using antimony and cesium, but the present invention provides a photocathode formed of a two-phase system, a three-phase system, a four-phase system, etc. of a photocathode base material and an alkali metal. It can also be applied to the formation of For example, Ma,
The alkaline photocathode is made of Na, K(Cs)Sb, and a substitution reaction between the alkali metals occurs during the process of forming the photocathode. Accurately detect,
It can be a highly sensitive photocathode.

Although the above embodiment described an X-ray image tube,
The present invention can also be applied to other electron tubes having a photocathode, such as image orthicons and image tubes.

[Brief explanation of drawings]

Figure 1 is a diagram for explaining the method of manufacturing an X-ray image tube, which is an embodiment of the present invention, and Figure 2 shows the resistance value that changes as the reaction between the photocathode base material and the alkali metal progresses. It is a curve diagram. (2)...Input surface (7)...X
Line-emitting phosphor layer (8)...photocathode
(10)...Photocathode base material heater (11)...Alkali metal generator (12)...Resistance measurement terminal (1
3)...Resistance measuring section (14)...Emitter (15)...Receiver

Claims (1)

[Claims] A terminal for resistance measurement is provided at or near the photocathode formation part of the electron tube, and after a photocathode base material is vapor-deposited on the photocathode formation part and the installation part of the resistance measurement terminal, the alkali metal is vapor-deposited while the resistance measurement terminal is evaporated. A method for manufacturing an electron tube having a photocathode, characterized in that a change in resistance caused by a reaction between the photocathode base material and the alkali metal is detected through a terminal, and formation of the photocathode is controlled based on the detection result.