Electron tube

Abstract

The electron tube 1 includes a photocathode 3 which converts incident light into photoelectrons, a plurality of dynodes 11 and an anode 6, an insulating substrate 12 which holds the dynodes 11, 11 in an electrically insulated state from one another and from the dynode 11 to the anode 6, and a housing 2 which accommodates the dynodes 11, the anode 6, and the insulating substrate 12. The insulating substrate 12 has a base layer 21 made of a polycrystalline material and having electrical insulation properties, an intermediate layer 22 made of an amorphous material and having electrical insulation properties, and a surface layer 23 made of a material containing carbon and having lower electrical resistance than the intermediate layer 22.

Description

[Technical field]

[0001] The present disclosure relates to electron tubes. [Background technology]

[0002] A photomultiplier tube is known as an example of an electron tube, and is configured to include, for example, a photocathode including a photocathode that converts incident light into photoelectrons, a multiplier section that multiplies the photoelectrons by secondary electron emission based on the incident photoelectrons, and an anode that collects the secondary electrons obtained by the multiplication.

[0003] An electrically insulating substrate (insulating substrate) that holds the electrodes is housed inside the housing of the electron tube. For example, in the photomultiplier tube described in Patent Document 1, a chromium oxide film is formed on the surface of a ceramic substrate that constitutes the insulating substrate, thereby improving the voltage resistance characteristics between the electrodes when the insulating substrate becomes charged. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 4,604,545 Summary of the Invention [Problem to be solved by the invention]

[0005] In addition to the above-mentioned charging problem, the insulating substrate disposed inside the housing of the electron tube may also have the problem of light emission caused by electrons being incident on the polycrystalline ceramic. The light emission from the insulating substrate is one of the causes of an increase in dark current when the light is incident on the photocathode. Therefore, in electron tubes equipped with a photocathode, a technology is required that can suppress both the charging and the light emission of the insulating substrate.

[0006] The present disclosure has been made to solve the above-mentioned problems, and has an object to provide an electron tube that can suppress both charging of an insulating substrate and light emission. [Means for solving the problem]

[0007] An electron tube according to one aspect of the present disclosure includes a photocathode that converts incident light into photoelectrons, a plurality of electrodes, an insulating substrate that holds the electrodes in an electrically insulated state, and a housing that houses the electrodes and the insulating substrate, and the insulating substrate has a base layer made of a polycrystalline material and having electrical insulation properties, an intermediate layer made of an amorphous material and having electrical insulation properties, and a surface layer made of a material containing carbon and having lower electrical resistance than the intermediate layer.

[0008] In this electron tube, since the electrically insulating base layer is made of a polycrystalline material, the strength and electrical insulation of the insulating substrate as a whole can be sufficiently ensured. The electrically insulating base layer is provided with an intermediate layer made of an amorphous material and having electrical insulation. This intermediate layer can suppress the incidence of electrons into the polycrystalline base layer, and can suppress the light emission in the base layer caused by the incidence of the electrons. If the electrically insulating intermediate layer is located on the surface of the insulating substrate, charging is likely to occur on the surface. However, in this electron tube, by providing a surface layer made of a material containing carbon and having a lower electrical resistance than the intermediate layer, the electrical resistance of the surface of the insulating substrate is reduced, and charging on the surface can be suppressed. Therefore, in this electron tube, both charging and light emission of the insulating substrate can be suppressed.

[0009] The surface layer may further contain an alkali metal. When the surface layer further contains an alkali metal, the electrical resistance of the surface of the insulating substrate can be reduced to a more appropriate level. Therefore, charging of the surface of the insulating substrate can be more reliably suppressed.

[0010] The thickness of the intermediate layer may be greater than the thickness of the surface layer. By ensuring a sufficient thickness of the intermediate layer, the incidence of electrons into the base layer can be effectively suppressed. Therefore, the light emission of the insulating substrate can be more reliably suppressed.

[0011] The carbon-containing material may be a material containing at least one of a metal oxide, a metal nitride, and a metal fluoride as a base material, and may contain carbon in the base material. In this case, the electrical resistance of the surface layer can be appropriately made smaller than that of the intermediate layer.

[0012] The intermediate layer and the surface layer may be provided at least on a first surface of the base layer facing the electrode and a second surface of the base layer facing the electrode. In this case, by providing the intermediate layer and the surface layer on the surface of the insulating substrate on which electrons are likely to be incident, both charging and light emission of the insulating substrate can be more effectively suppressed.

[0013] The intermediate layer and the surface layer may be provided on the side surface connecting the first surface and the second surface. In this case, the first surface and the second surface are electrically connected to each other, so that the charging of the surface of the insulating substrate can be more reliably suppressed, and light emission due to electron incidence on the side surface can be suppressed. This further improves the effect of suppressing both the charging and the light emission of the insulating substrate.

[0014] The base layer may have an insertion hole into which a holding piece that holds an electrode is inserted, and the intermediate layer and the surface layer may be provided on the inner surface of the insertion hole. Since electrons are multiplied or pass through the electrode, electrons are likely to be incident on the vicinity of the insertion hole into which the holding piece is inserted. Therefore, by providing the intermediate layer and the surface layer on the inner surface of the insertion hole, the effect of suppressing both charging and light emission of the insulating substrate can be further improved.

[0015] The intermediate layer and the surface layer may be provided on the entire surface of the base layer, thereby making it possible to further improve the effect of suppressing both charging and light emission at all parts of the insulating substrate.

[0016] The intermediate layer and the surface layer may be made of the same material, and the content of the alkali metal in the intermediate layer may be smaller than the content of the alkali metal in the surface layer. By making the intermediate layer and the surface layer of the same material, the ease of manufacturing these layers can be improved. In addition, by making the content of the alkali metal in the intermediate layer smaller than the content of the alkali metal in the surface layer, even if the intermediate layer and the surface layer are made of the same material, the intermediate layer can be made electrically insulating, while the surface layer can be made conductive. Therefore, both charging and light emission of the insulating substrate can be suppressed. Effect of the Invention

[0017] According to the present disclosure, both charging and light emission of the insulating substrate can be suppressed. [Brief description of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view showing an internal configuration of an electron tube according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a perspective view of a multiplication section and an insulating substrate. [Diagram 3] FIG. 2 is an enlarged cross-sectional view of a main portion of an insulating substrate. [Figure 4] FIG. 13 is a diagram showing the results of a confirmation test of the luminescence suppression effect in the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, preferred embodiments of an electron tube according to one aspect of the present disclosure will be described in detail with reference to the drawings.

[0020] 1 is a cross-sectional view showing the internal configuration of an electron tube according to an embodiment of the present disclosure. In this embodiment, the electron tube 1 is configured as a photomultiplier tube. The electron tube 1 includes a housing 2 made of, for example, Kovar metal or glass. Inside the housing 2, there are accommodated a photocathode (photocathode) 3 that converts incident light into photoelectrons, a focusing electrode 5 that guides the photoelectrons emitted from the photocathode 3 to a multiplier section 4, the multiplier section 4 that multiplies the photoelectrons into secondary electrons, and an anode 6 that collects the secondary electrons multiplied by the multiplier section 4.

[0021] The housing 2 has a generally cylindrical shape with both ends open. An entrance window 7 made of, for example, glass is provided at the opening at one end of the housing 2. A stem 8 made of, for example, metal or glass is provided at the opening at the other end of the housing 2. The inside of the housing 2 is hermetically sealed by the entrance window 7 and the stem 8. The housing 2, the entrance window 7, and the stem 8 form a vacuum container, and the inside of the housing 2 is kept in a high vacuum state. A photocathode 3 is formed on the surface of the entrance window 7 on the vacuum side. The entrance window 7 and the photocathode 3 form a photocathode. A plurality of stem pins 10 penetrate the stem 8. Each stem pin 10 is electrically connected to the photocathode 3, the focusing electrode 5, the multiplication section 4, and the anode 6, respectively.

[0022] The photocathode 3 includes a photoelectric conversion layer that converts incident light into photoelectrons. More preferably, the photocathode 3 includes an electron emission layer on the inner space side of the photoelectric conversion layer, which facilitates the emission of photoelectrons generated in the photoelectric conversion layer into the inner space of the housing 2. Of the photoelectric conversion layer and the electron emission layer, at least the electron emission layer contains an alkali metal such as cesium. The photoelectric conversion layer may also contain an alkali metal such as cesium, potassium, or sodium. In this embodiment, the photocathode 3 is a photocathode that contains an alkali metal resulting from at least one of the photoelectric conversion layer and the electron emission layer.

[0023] The focusing electrode 5 is, for example, cup-shaped. An opening 5a having, for example, a circular cross section is provided in the center of the focusing electrode 5. The focusing electrode 5 is disposed so that the opening 5a faces the photocathode 3. The anode 6 is, for example, linear or flat. The anode 6 is disposed downstream of the multiplication section 4. A mesh electrode may be attached to the opening 5a of the focusing electrode 5 or between the anode 6 and the multiplication section 4.

[0024] The multiplication section 4, which is disposed between the focusing electrode 5 and the anode 6, is composed of a plurality of stages of dynodes (electrodes) 11 of a so-called line focus type. The dynodes 11 of each stage have a secondary electron surface 11a which multiplies photoelectrons into secondary electrons. Each of the secondary electron surfaces 11a has, for example, an arc-shaped cross section. The secondary electron surfaces 11a, 11a between adjacent dynodes 11, 11 are disposed so as to face each other. A negative potential of the same voltage as that of the focusing electrode 5, for example, is applied to the first stage dynode 11. A negative potential of a smaller absolute value than that of the (n-1)th stage dynode 11 is applied to the nth stage dynode 11. The potential of the anode 6 is set to 0V.

[0025] Each dynode 11 is provided at both longitudinal ends with a retaining piece 11b for retaining the dynode 11 within the housing 2. To retain the dynode 11 within the housing 2, a pair of insulating substrates 12, 12 are used, as shown in Fig. 2. The insulating substrate 12 is provided with a plurality of insertion holes 13 into which the retaining piece 11b of each dynode 11 is inserted. The retaining pieces 11b of each dynode 11 are inserted into these insertion holes 13, and each dynode 11 is sandwiched between the pair of insulating substrates 12, 12, so that each dynode 11 is retained within the housing 2 in an electrically insulated state. In this embodiment, the anode 6 is also retained within the housing 2 in a similar structure, electrically insulated from each dynode 11.

[0026] Next, the above-mentioned insulating substrate 12 will be described in more detail. Fig. 3 is an enlarged cross-sectional view of a main part of the insulating substrate. As shown in Fig. 3, the insulating substrate 12 has a base layer 21, an intermediate layer 22, and a surface layer 23.

[0027] The base layer 21 is a layer that serves as the base of the insulating substrate 12. The base layer 21 is made of a polycrystalline material and has electrical insulation properties. An example of an electrically insulating polycrystalline material is a ceramic material. When the electron tube 1 is a photomultiplier tube as in this embodiment, for example, aluminum oxide (Al 2 O 3) is used. In this embodiment, the base layer 21 has a rectangular plate shape (substrate) with a long side in the extension direction of the housing 2 (the direction connecting the entrance window 7 and the stem 8) and a short side perpendicular to the long side.

[0028] The base layer 21 has a first surface 21a on the electrode (dynodes 11 and anode 6) side, a second surface 21b on the opposite side (housing 2) from the electrodes, and four side surfaces 21c connecting the first surface 21a and the second surface 21b (see FIG. 2). The above-mentioned multiple insertion holes 13 are all provided so as to penetrate the base layer 21 across the first surface 21a and the second surface 21b.

[0029] The intermediate layer 22 is a layer that suppresses the incidence of electrons into the base layer 21, which is a polycrystalline material. The intermediate layer 22 is made of an amorphous material and has electrical insulation properties. In other words, the intermediate layer 22 is composed of an electrically insulating amorphous layer. Examples of the amorphous material include aluminum oxide (Al 2 O 3 ) is alumina. Other amorphous materials include, for example, glass, metal oxides, metal nitrides, and metal fluorides. In this embodiment, the amorphous material itself has electrical insulation properties, but the intermediate layer 22 may be made electrically insulating by adding an electrically insulating material to the amorphous material.

[0030] The surface layer 23 is a layer that suppresses charging on the surface of the insulating substrate 12 by reducing the electrical resistance of the surface. The electrical resistance of the surface layer 23 is smaller than the electrical resistance of the intermediate layer 22, and the surface layer 23 is a layer that exhibits electrical conductivity. The surface layer 23 is made of a material that contains carbon (C). The carbon in the surface layer 23 may be unevenly distributed near the surface of the surface layer 23, or may be uniformly or randomly dispersed throughout the surface layer 23.

[0031] Examples of materials that can be used as the substrate of the carbon-containing material include magnesium oxide (MgO) and alcone, which is an organic-inorganic hybrid material. Other substrate materials include metal oxides (Be, Mg, Ba, Sc, Y, lanthanides (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), Ti, Zr, Hf, Zn, B, Al, Ga, In, Si), metal nitrides (Be, Y, B, Al, Ga, Si, Ge), metal fluorides (Li, Na, Mg, Ca, Sr, Ba, Sc, Y, lanthanides (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), Zr, Hf, Zn, Al, Ga, In), etc.

[0032] In this way, the carbon-containing material is preferably a material that uses a material containing at least one of a metal oxide, a metal nitride, and a metal fluoride as a base material and contains carbon in the base material. In this embodiment, the surface layer 23 is also made of an amorphous material. That is, the surface layer 23 is made of a conductive amorphous layer.

[0033] In this embodiment, the surface layer 23 contains an alkali metal. Examples of the alkali metal include Li, Na, K, Rb, and Cs. In this embodiment, the alkali metal contained in the surface layer 23 is, for example, at least a part of the material forming the photocathode 3. In this embodiment, in the process of forming the photocathode 3, a part of the alkali metal constituting the photocathode 3 is taken into the surface layer 23, thereby forming the surface layer 23 containing an alkali metal. In this case, when the surface layer 23 contains carbon, the alkali metal can be taken into the surface layer 23 more efficiently.

[0034] The intermediate layer 22 and the surface layer 23 are provided at least on the first surface 21a and the second surface 21b of the base layer 21. The intermediate layer 22 and the surface layer 23 may be provided on the side surface 21c or on the inner surface of the insertion hole 13. In this embodiment, they are provided on the entire surface of the base layer 21. That is, in this embodiment, the intermediate layer 22 and the surface layer 23 are provided on the entire surface of the first surface 21a, the entire surface of the second surface 21b, the entire surfaces of the four side surfaces 21c, and the entire inner surfaces of each insertion hole 13.

[0035] The intermediate layer 22 and the surface layer 23 may be formed in a region corresponding to the space between the electrodes to which a voltage of 100 V or more is applied for creeping discharge. In addition, the intermediate layer 22 and the surface layer 23 may be formed in a region corresponding to the anode 6 to which a strong electric field (e.g., 200 V / cm or more) is applied for gap discharge. In this embodiment, the intermediate layer 22 and the surface layer 23 are formed with the highest priority in a region corresponding to the anode 6 and the final dynode 11 on the first surface 21a and the second surface 21b (a region overlapping with the anode 6 and the final dynode 11 when viewed from the opposing direction of the pair of insulating substrates 12, 12). The intermediate layer 22 and the surface layer 23 are preferably formed in at least a half region on the anode 6 side of the region obtained by dividing the first surface 21a and the second surface 21b of the insulating substrate 12 into two at the center in the long side direction of the base layer 21.

[0036] In this embodiment, the thickness T1 of the intermediate layer 22 is greater than the thickness T2 of the surface layer 23. The ratio (T2 / T1) of the thickness T2 of the surface layer 23 to the thickness T1 of the intermediate layer 22 is, for example, about 1 to 200,000. As one example, the thickness T1 of the intermediate layer 22 is about 10 nm to several hundred μm, and the thickness T2 of the surface layer 23 is about 3 nm to 10 nm.

[0037] The intermediate layer 22 and the surface layer 23 can be formed, for example, by atomic layer deposition (ALD). The atomic layer deposition is a technique for depositing atomic layers one by one to obtain a thin film by repeatedly performing a step of adsorbing compound molecules, a step of forming a film by reaction, and a step of purging to remove excess molecules.

[0038] The film formation cycle using the atomic layer deposition method includes a film formation cycle for the intermediate layer 22 and a film formation cycle for the surface layer 23. For example, the intermediate layer 22 is made of alumina (Al 2 O 3 ), in the deposition cycle of the intermediate layer 22, for example, H 2 O adsorption process, H 2 The O purging step, the trimethylaluminum adsorption step, and the trimethylaluminum purging step are performed in this order. In addition, when the material of the surface layer 23 is MgO (MgO containing carbon), for example, in the film formation cycle of the surface layer 23, 2 O adsorption process, H 2 The O purging step, the magnesium-containing organometallic adsorption step, and the magnesium-containing organometallic purge step are carried out in this order.

[0039] A 30 nm thick alumina (Al 2 O 3 When the intermediate layer 22 made of alumina (Al) and the surface layer 23 made of MgO (MgO containing carbon) having a thickness of 5 nm are formed on the surface of the base layer 21, 2 O 3 ) is performed 300 times, and then, MgO (MgO containing carbon) is performed 40 times. As a result, the intermediate layer 22 and the surface layer 23 having a total thickness of 35 nm can be formed on the surface of the base layer 21.

[0040] It should be noted that methods other than atomic layer deposition can also be used to form the intermediate layer 22. Examples of other methods include electron beam deposition, sputter deposition, and coating.

[0041] As described above, in the electron tube 1, since the electrically insulating base layer 21 is made of a polycrystalline material, the strength and electrical insulation of the insulating substrate 12 as a whole can be sufficiently ensured. The electrically insulating base layer 21 is provided with the electrically insulating intermediate layer 22 made of an amorphous material. This intermediate layer 22 can suppress the incidence of electrons into the polycrystalline base layer 21, and can suppress the light emission in the base layer 21 caused by the incidence of the electrons. If the electrically insulating intermediate layer 22 is located on the surface of the insulating substrate 12, charging is likely to occur on the surface. However, in the electron tube 1, by providing the surface layer 23 made of a material containing carbon and having a lower electrical resistance than the intermediate layer, the electrical resistance of the surface of the insulating substrate 12 is reduced, and charging on the surface can be suppressed. Therefore, in the electron tube 1, both charging and light emission of the insulating substrate 12 can be suppressed.

[0042] In this embodiment, the surface layer 23 contains an alkali metal. In particular, the surface layer 23 contains carbon, which makes it more likely to contain an alkali metal. As described above, it is preferable to incorporate an alkali metal, which is a constituent material of the photocathode 3, into the surface layer 23 in the process of forming the photocathode 3, but the surface layer 23 may also contain an alkali metal separately. When the surface layer 23 contains an alkali metal, the electrical resistance of the surface of the insulating substrate 12 can be reduced to a more appropriate level. Therefore, charging of the surface of the insulating substrate 12 can be more reliably suppressed.

[0043] In this embodiment, the thickness T1 of the intermediate layer 22 is greater than the thickness T2 of the surface layer 23. By ensuring a sufficient thickness T1 of the intermediate layer 22, it is possible to effectively suppress the incidence of electrons into the base layer 21. Therefore, it is possible to more reliably suppress the light emission of the insulating substrate 12.

[0044] In this embodiment, the carbon-containing material constituting the surface layer 23 has a base material containing at least one of a metal oxide, a metal nitride, and a metal fluoride, and contains carbon in the base material. This allows the electrical resistance of the surface layer 23 to be appropriately smaller than that of the intermediate layer 22. In this embodiment, a material that tends to be electrically insulating (has high electrical resistance) is used as the base material, carbon and an alkali metal are contained in the base material, and further, the thickness T2 of the surface layer 23 is made smaller than the thickness T1 of the intermediate layer 22 (i.e., the thickness of the surface layer 23 is appropriately controlled), thereby appropriately adjusting the electrical resistance of the surface layer 23 to be smaller than that of the intermediate layer 22.

[0045] In this embodiment, they are provided at least on the first surface 21a and the second surface 21b of the base layer 21. In this manner, by providing the intermediate layer 22 and the surface layer 23 on the surface of the insulating substrate 12 onto which electrons are likely to be incident, it is possible to effectively suppress both charging and light emission of the insulating substrate 12. Furthermore, in this embodiment, the intermediate layer 22 and the surface layer 23 are provided on the first surface 21a, the second surface 21b, the side surface 21c, and the inner surface of the insertion hole 13 of the base layer 21, respectively, and cover the entire surface of the base layer 21. Therefore, the effect of suppressing both charging and light emission can be further improved in all parts of the insulating substrate 12.

[0046] When the intermediate layer 22 and the surface layer 23 are provided on the side surface 21c, the first surface 21a and the second surface 21b are electrically connected, so that charging of the surface of the insulating substrate 12 can be more reliably suppressed, and light emission due to electrons being incident on the side surface 21c can be suppressed. Furthermore, in the focusing electrode 5, the dynode 11 constituting the multiplier section 4, and the anode 6, electrons are multiplied and pass through, so that electrons are likely to be incident near the insertion hole 13 into which the holding piece 11b is inserted. However, by providing the intermediate layer 22 and the surface layer 23 on the inner surface of the insertion hole 13, the effect of suppressing both charging and light emission of the insulating substrate 12 can be further improved.

[0047] The intermediate layer 22 and the surface layer 23 may be made of the same material, and the content of alkali metal in the intermediate layer 22 may be smaller than the content of alkali metal in the surface layer 23. For example, the intermediate layer 22 and the surface layer 23 may each be made of MgO (MgO containing carbon), the intermediate layer 22 may be a poor layer of alkali metal and carbon, and the surface layer 23 may be a rich layer of alkali metal and carbon, so that the intermediate layer 22 has electrical insulation properties and the surface layer 23 has conductivity. With this configuration, the intermediate layer 22 and the surface layer 23 are made of the same material, which improves the ease of manufacturing these layers and suppresses both charging and emission of electricity in the insulating substrate 12.

[0048] 4 is a diagram showing the results of a test to confirm the light emission suppression effect of the present disclosure. The test shown in the figure was conducted by calculating the light emission intensity in the ultraviolet region from actual measurements when electrons were incident on insulating substrates in which the intermediate layer and surface layer formed on the surface of the base layer were changed. In calculating the light emission intensity, the accelerating voltage of the electrons (electron beam) was set to 1 kV.

[0049] In Comparative Example 1, neither an intermediate layer nor a surface layer was provided, and the insulating substrate was constructed only from a base layer made of white alumina. In Comparative Example 2, no intermediate layer was provided, and an insulating substrate was constructed by forming a 5 nm thick surface layer made of MgO containing carbon on the surface of a base layer made of white alumina. In contrast, in Example 1, an insulating substrate was constructed by forming a 100 μm thick intermediate layer made of glass and a 5 nm thick surface layer made of MgO containing carbon on the surface of a base layer made of white alumina. In Example 2, an insulating substrate was constructed by forming a 30 nm thick alumina (Al 2 O 3 An intermediate layer of MgO containing carbon and a surface layer of MgO containing carbon with a thickness of 5 nm were formed on the surface of a base layer of white alumina to form an insulating substrate.

[0050] As shown in FIG. 4, when the emission intensity of the insulating substrate in Comparative Example 1 is set to 100, the emission intensity of the insulating substrate in Comparative Example 2 is 44.3. From this result, it was found that even when only a surface layer made of MgO containing carbon is provided on the base layer, a certain degree of emission intensity suppression effect is achieved. The emission intensities in Examples 1 and 2 were calculated based on the attenuation rate of the emission intensity of MgO containing carbon with a thickness of 5 nm in Comparative Example 2. That is, when the film thickness of the intermediate layer and the surface layer is n times that of MgO containing carbon with a thickness of 5 nm, the emission intensity was calculated by taking the attenuation rate as the nth power of 0.443. As a result, the emission intensity of the insulating substrate in Example 1 was 7.5, and the emission intensity of the insulating substrate in Example 2 was 0.5.

[0051] The electrical resistance of the surface layer made of MgO containing carbon is smaller than that of the intermediate layer. In the case where an intermediate layer of several tens of nm is provided on the surface of the base layer in Examples 1 and 2, the intermediate layer alone may cause charging of the insulating substrate. In contrast, by further providing a surface layer made of MgO containing 5 nm of carbon, the problem of charging of the insulating substrate when an electrically insulating intermediate layer is located on the surface of the insulating substrate is solved. From these results, it can be seen that the configuration in which the intermediate layer and surface layer according to the present disclosure are provided on the surface of the base layer contributes to suppressing both charging and light emission of the insulating substrate. [Explanation of symbols]

[0052] 1...electron tube, 2...housing, 3...photocathode, 6...anode (electrode), 11...dynode (electrode), 12...insulating substrate, 13...insertion hole, 21...base layer, 21a...first surface, 21b...second surface, 21c...side surface, 22...intermediate layer, 23...surface layer, T1...thickness of intermediate layer, T2...thickness of surface layer.

Claims

1. a photocathode that converts incident light into photoelectrons; A plurality of electrodes; an insulating substrate that holds the electrodes in an electrically insulated state; a housing that houses the electrode and the insulating substrate; The insulating substrate is a base layer made of a polycrystalline material and having electrical insulation properties; an intermediate layer made of an amorphous material and having electrical insulation properties; a surface layer made of a material containing carbon and having a lower electrical resistance than the intermediate layer.

2. 2. The electron tube of claim 1, wherein the surface layer further comprises an alkali metal.

3. 2. The electron tube according to claim 1, wherein the thickness of said intermediate layer is greater than the thickness of said surface layer.

4. An electron tube as described in claim 2, wherein the thickness of the intermediate layer is greater than the thickness of the surface layer.

5. 4. The electron tube according to claim 3, wherein said carbon-containing material has a base material made of a material containing at least one of a metal oxide, a metal nitride, and a metal fluoride, and said base material contains carbon.

6. An electron tube as described in claim 4, wherein the carbon-containing material has a base material containing at least one of a metal oxide, a metal nitride, and a metal fluoride, and contains carbon in the base material.

7. 2. The electron tube according to claim 1, wherein said intermediate layer and said surface layer are provided at least on a first surface of said base layer that faces said electrode and a second surface that faces opposite said electrode.

8. 8. The electron tube according to claim 7, wherein the intermediate layer and the surface layer are provided on a side surface connecting the first surface and the second surface.

9. the base layer has an insertion hole into which a holding piece for holding the electrode is inserted, 8. The electron tube according to claim 7, wherein the intermediate layer and the surface layer are provided on an inner surface of the insertion hole.

10. 8. The electron tube according to claim 7, wherein said intermediate layer and said surface layer are provided over the entire surface of said base layer.

11. the intermediate layer and the surface layer are made of the same material; 11. The electron tube according to claim 1, wherein the content of the alkali metal in the intermediate layer is smaller than the content of the alkali metal in the surface layer.

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