Electron tube

Abstract

An electron tube (1) is provided with: a photoelectric surface (3) that converts incident light into photoelectrons; a plurality of dynodes (11) and anodes (6); an insulating substrate (12) that holds the dynode (11) and the dynode (11) and the anode (6) in an electrically insulated state; and a case (2) that houses the dynode (11), the anode (6), and the insulating substrate (12). The insulating substrate (12) has: a base layer (21) that is made of a polycrystalline material and has electrical insulation properties; an electrically insulating intermediate layer (22) comprising an amorphous material; and a surface layer (23) comprising a carbon-containing material and having a lower electrical resistance than the intermediate layer (22).

Description

Technical Field

[0001] The present invention relates to electron tubes. Background Art

[0002] A photomultiplier tube is a well-known example of an electron tube. A photomultiplier tube includes, for example, a photocathode having a photoelectric surface that converts incident light into photoelectrons; a multiplication section that multiplies the photoelectrons by emitting secondary electrons based on the incident photoelectrons; and an anode that collects the secondary electrons obtained by the multiplication.

[0003] The electron tube housing houses an electrically insulating substrate (insulating substrate) that holds the electrodes. 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 withstand voltage characteristics between the electrodes when the insulating substrate is charged. Prior art literature Patent Literature

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

[0005] In addition to the aforementioned charging problem, the insulating substrate placed within the electron tube housing can also cause luminescence due to electrons incident on the polycrystalline ceramic. This luminescence from the insulating substrate, incident on the photoelectric element, contributes to an increase in dark current. Therefore, in electron tubes equipped with a photoelectric element, a technology is needed that can simultaneously suppress both charging and luminescence in the insulating substrate.

[0006] The present invention has been made in order to solve the above-mentioned problem, and an object of the present invention is to provide an electron tube capable of simultaneously suppressing both charging of an insulating substrate and light emission. Methods used to solve problems

[0007] An electron tube according to one aspect of the present invention comprises: a photoelectric surface for converting incident light into photoelectrons; a plurality of electrodes; an insulating substrate for electrically insulating the electrodes from each other; and a housing for housing the electrodes and the insulating substrate, wherein the insulating substrate comprises: a base layer composed of a polycrystalline material and having electrical insulation; an intermediate layer composed of an amorphous material and having electrical insulation; and a surface layer composed of a carbon-containing material and having a lower electrical resistance than the intermediate layer.

[0008] In this electron tube, the electrically insulating base layer is made of a polycrystalline material, which can fully ensure the strength and electrical insulation of the insulating substrate as a whole. An intermediate layer made of an amorphous material and having electrical insulation is provided on the electrically insulating base layer. This intermediate layer can suppress the incidence of electrons on the base layer, which is a polycrystalline material, and can suppress the luminescence of the base layer caused by the incidence of these electrons. When the electrically insulating intermediate layer is located on the surface of the insulating substrate, it is easy for the surface to be charged. In this electron tube, by providing a surface layer made of a carbon-containing material and having a lower electrical resistance than the intermediate layer, the electrical resistance of the surface of the insulating substrate becomes smaller, and the charging of the surface can be suppressed. Therefore, in this electron tube, both the charging and the luminescence of the insulating substrate can be suppressed at the same time.

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

[0010] The thickness of the intermediate layer can be greater than that of the surface layer. By ensuring the thickness of the intermediate layer is sufficient, 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 based on a material containing at least one of a metal oxide, a metal nitride, and a metal fluoride, wherein carbon is contained in the base material. In this case, the resistance of the surface layer can be appropriately made lower than that of the intermediate layer.

[0012] The intermediate layer and the surface layer may be provided on at least the first surface on the electrode side of the base layer and the second surface on the opposite side of the electrode. In this case, by providing the intermediate layer and the surface layer on the surface of the insulating substrate where electrons are easily incident, both the charging and the luminescence of the insulating substrate can be more effectively suppressed.

[0013] The intermediate layer and the surface layer can be provided on the side surface connecting the first and second surfaces. In this case, the first and second surfaces can be electrically connected, thereby more reliably suppressing charging of the surface of the insulating substrate and suppressing luminescence caused by electrons incident on the side surfaces. This further enhances the effect of simultaneously suppressing both charging and luminescence of the insulating substrate.

[0014] The base layer may have an insertion hole into which a retaining sheet holding the electrode is inserted, and the intermediate layer and surface layer may be disposed within the insertion hole. Electrons are multiplied and pass through the electrode, making it easier for electrons to enter the vicinity of the insertion hole into which the retaining sheet is inserted. Therefore, by disposing the intermediate layer and surface layer within the insertion hole, the effect of simultaneously suppressing both charging and light emission in the insulating substrate can be further enhanced.

[0015] The intermediate layer and the surface layer may be provided on the entire surface of the base layer, thereby further enhancing the effects of simultaneously suppressing both static charge and light emission in all parts of the insulating substrate.

[0016] The intermediate layer and the surface layer may be made of the same material, and the alkali metal content of the intermediate layer is less than that of the surface layer. By making the intermediate layer and the surface layer the same material, the ease of manufacturing of these layers can be improved. In addition, by making the alkali metal content of the intermediate layer less than that of 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 is made electrically conductive. Therefore, both the charging and luminescence of the insulating substrate can be suppressed at the same time. Effects of the Invention

[0017] According to the present invention, both charging of the insulating substrate and light emission can be suppressed simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a cross-sectional view showing the internal structure of an electron tube according to one embodiment of the present invention. Figure 2 This is a perspective view of the multiplier unit and the insulating substrate. Figure 3 This is an enlarged cross-sectional view of a main portion of an insulating substrate. Figure 4 It is a graph showing the results of a test to confirm the light emission suppression effect of the present invention. DETAILED DESCRIPTION

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

[0020] Figure 1 This is a cross-sectional view showing the internal structure of an electron tube according to one embodiment of the present invention. In this embodiment, electron tube 1 is configured as a photomultiplier tube. Electron tube 1 includes a housing 2 made of, for example, Kovar metal or glass. Housing 2 houses a photoelectron (photocathode) 3 that converts incident light into photoelectrons, a focusing electrode 5 that guides photoelectrons emitted from photoelectron 3 to a multiplication unit 4, a multiplication unit 4 that multiplies the photoelectrons as secondary electrons, and an anode 6 that collects the secondary electrons multiplied by multiplication unit 4.

[0021] The shell 2 is formed into a roughly cylindrical shape with both ends open. An incident window 7 made of, for example, glass is provided at the opening at one end of the shell 2. A tube stem 8 made of, for example, metal and glass is provided at the opening at the other end of the shell 2. The interior of the shell 2 is hermetically sealed by the incident window 7 and the tube stem 8. The shell 2, the incident window 7, and the tube stem 8 form a vacuum container, and the interior of the shell 2 is maintained in a high vacuum state. A photoelectric surface 3 is formed on the surface of the vacuum side of the incident window 7. The incident window 7 and the photoelectric surface 3 constitute a photocathode. A plurality of tube stem pins 10 pass through the tube stem 8. Each tube stem pin 10 is electrically connected to the photoelectric surface 3, the focusing electrode 5, the multiplier 4, and the anode 6, respectively.

[0022] The photoelectric surface 3 includes a photoelectric conversion layer that converts incident light into photoelectrons. More preferably, the photoelectric surface 3 is provided with an electron emission layer on the inner space side of the photoelectric conversion layer that facilitates 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 alkali metals such as cesium, potassium, and sodium. In this embodiment, the photoelectric surface 3 is a photoelectric surface containing an alkali metal originating from at least one of the photoelectric conversion layer and the electron emission layer.

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

[0024] The multiplication section 4 disposed between the focusing electrode 5 and the anode 6 is composed of a multi-stage dynode (electrode) 11 of a so-called line-focusing type. Each dynode 11 has a secondary electron surface 11a for performing secondary electron multiplication on photoelectrons. The secondary electron surface 11a is formed, for example, in a circular arc shape in cross section. The secondary electron surfaces 11a, 11a between adjacent dynodes 11, 11 are disposed so as to face each other. A negative potential, for example, the same voltage as that of the focusing electrode 5, is applied to the first-stage dynode 11. A negative potential having 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 0V.

[0025] At both ends of the longitudinal direction of each dynode 11, a retaining piece 11b is provided for retaining the dynode 11 in the housing 2. The retention of the dynode 11 in the housing 2 is as follows: Figure 2As shown, a pair of insulating substrates 12, 12 is used. The insulating substrates 12 are provided with a plurality of insertion holes 13 into which the retaining tabs 11b of each dynode 11 are inserted. By inserting the retaining tabs 11b of each dynode 11 into these insertion holes 13, the dynodes 11 are sandwiched between the pair of insulating substrates 12, 12, and each dynode 11 is held within the housing 2 in an electrically insulated state. In this embodiment, the anode 6 is also held within the housing 2 in an electrically insulated state from each dynode 11 using a similar structure.

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

[0027] The base layer 21 is a layer serving as the base of the insulating substrate 12. The base layer 21 is made of a polycrystalline material and has electrical insulating properties. Examples of polycrystalline materials having electrical insulating properties include ceramic materials. In the case where the electron tube 1 is a photomultiplier tube as in the present embodiment, for example, ceramics such as white alumina (alumina) composed of aluminum oxide (Al2O3) can be used. In the present embodiment, the base layer 21 is formed into a rectangular plate (substrate) with the long side being the direction of extension of the shell 2 (the direction connecting the incident window 7 and the tube seat 8) and the short side being the direction perpendicular thereto.

[0028] The base layer 21 has a first surface 21a on the electrode (each dynode 11 and anode 6) side, a second surface 21b on the opposite side to the electrode (shell 2) side, and four side surfaces 21c connecting the first surface 21a and the second surface 21b (see FIG. Figure 2 The plurality of insertion holes 13 are provided so as to penetrate the base layer 21 across the first surface 21 a and the second surface 21 b .

[0029] The intermediate layer 22 is a layer that suppresses the incidence of electrons on the base layer 21 of the polycrystalline material. The intermediate layer 22 is composed of an amorphous material and has electrical insulation properties. That is, the intermediate layer 22 is composed of an electrically insulating amorphous layer. As an amorphous material, for example, aluminum oxide as aluminum oxide (Al2O3) can be listed. As other amorphous materials, for example, glass, metal oxides, metal nitrides, metal fluorides, etc. can be listed. In this embodiment, the amorphous material itself has electrical insulation properties, but the intermediate layer 22 can also 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 surface resistance of the insulating substrate 12. The surface layer 23 has a lower resistance than the intermediate layer 22 and is a conductive layer. The surface layer 23 is composed of a material containing carbon (C). The carbon in the surface layer 23 may be unevenly distributed near the surface of the surface layer 23 or uniformly or randomly dispersed throughout the surface layer 23.

[0031] Examples of materials serving as the base material of the carbon-containing material include magnesium oxide (MgO) and alucone, an organic-inorganic hybrid material. Other base materials include metal oxides (Be, Mg, Ba, Sc, Y, lanthanoids (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), and metal fluorides (Li, Na, Mg, Ca, Sr, Ba, Sc, Y, lanthanoids (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), Zr, Hf, Zn, Al, Ga, In), and the like.

[0032] Thus, the carbon-containing material is preferably a material containing at least one of a metal oxide, a metal nitride, and a metal fluoride as a base material, wherein the base material contains carbon. In this embodiment, the surface layer 23 is also composed of an amorphous material. That is, the surface layer 23 is composed 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 portion of the material forming the photoelectric element 3. In this embodiment, during the step of forming the photoelectric element 3, a portion of the alkali metal constituting the photoelectric element 3 is introduced into the surface layer 23, thereby forming the alkali metal-containing surface layer 23. In this case, by making the surface layer 23 contain carbon, the alkali metal can be more efficiently introduced into the surface layer 23.

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

[0035] Examples of regions where the intermediate layer 22 and the surface layer 23 are formed include, for example, regions between electrodes where a voltage of 100 V or greater is applied, for creeping discharge. Furthermore, for gap discharge, examples include regions corresponding to the anode 6 where a strong electric field (e.g., 200 V / cm or greater) is applied. In this embodiment, the regions where the intermediate layer 22 and the surface layer 23 are most preferentially formed include the regions corresponding to the anode 6 and the final dynode 11 on the first and second surfaces 21a, 21b (the regions overlapping the anode 6 and the final dynode 11 when viewed from the relative direction of the pair of insulating substrates 12, 12). The intermediate layer 22 and the surface layer 23 are preferably formed, for example, in at least half of the region on the anode 6 side of the region that divides the first and second surfaces 21a, 21b of the insulating substrate 12 into two at the center of the longitudinal 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, approximately 1 to 200,000. As an example, the thickness T1 of the intermediate layer 22 is approximately 10 nm to several hundred μm, and the thickness T2 of the surface layer 23 is approximately 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). ALD is a method of depositing atomic layers one by one to obtain a thin film by repeating a step of adsorption of compound molecules, a film formation step by reaction, and a purge step 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, when aluminum oxide (Al2O3) is used as the constituent material of the intermediate layer 22, during the film formation cycle of the intermediate layer 22, for example, an H2O adsorption process, an H2O removal process, a trimethylaluminum adsorption process, and a trimethylaluminum removal process are sequentially performed. Furthermore, for example, when MgO (carbon-containing MgO) is used as the constituent material of the surface layer 23, during the film formation cycle of the surface layer 23, for example, an H2O adsorption process, an H2O removal process, an organic metal containing magnesium adsorption process, and a organic metal containing magnesium removal process are sequentially performed.

[0039] When using atomic layer deposition to form a 30nm thick intermediate layer 22 of aluminum oxide (Al2O3) and a 5nm thick surface layer 23 of MgO (carbon-containing MgO) on the surface of a base layer 21, 300 cycles of aluminum oxide (Al2O3) film formation are performed, followed by 40 cycles of MgO (carbon-containing MgO) film formation. This results in a total of 35nm thick intermediate layer 22 and surface layer 23 formed on the surface of the base layer 21.

[0040] In addition, other methods besides atomic layer deposition can be used to form the intermediate layer 22. Examples of other methods include electron beam deposition, sputtering deposition, and coating.

[0041] As described above, in the electron tube 1, since the electrically insulating base layer 21 is composed of a polycrystalline material, the overall strength and electrical insulation of the insulating substrate 12 are fully ensured. The electrically insulating base layer 21 is provided with an electrically insulating intermediate layer 22 composed of an amorphous material. This intermediate layer 22 suppresses the incidence of electrons on the polycrystalline base layer 21, thereby suppressing the emission of light from the base layer 21 caused by this electron incidence. When the electrically insulating intermediate layer 22 is located on the surface of the insulating substrate 12, charging of the surface is likely to occur. However, in the electron tube 1, by providing a surface layer 23 composed of a carbon-containing material with a lower electrical resistance than the intermediate layer, the surface resistance of the insulating substrate 12 is reduced, thereby suppressing charging of the surface. Therefore, in the electron tube 1, both charging of the insulating substrate 12 and emission of light can be suppressed simultaneously.

[0042] In this embodiment, the surface layer 23 contains an alkali metal. In particular, the surface layer 23 is more likely to contain an alkali metal by containing carbon. As described above, the alkali metal, which is a constituent material of the photoelectric element 3, is preferably incorporated into the surface layer 23 during the formation process of the photoelectric element 3. However, the surface layer 23 may also contain an alkali metal by other means. By including an alkali metal in the surface layer 23, the surface resistance of the insulating substrate 12 can be reduced to a more appropriate level. Therefore, the surface charge 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, the incidence of electrons into the base layer 21 can be effectively suppressed. Therefore, the light emission of the insulating substrate 12 can be more reliably suppressed.

[0044] In this embodiment, the carbon-containing material constituting the surface layer 23 is based on a material containing at least one of a metal oxide, a metal nitride, and a metal fluoride, and the base material contains carbon. Thus, the resistance of the surface layer 23 can be appropriately lower than that of the intermediate layer 22. In this embodiment, appropriate adjustments are made, namely, by using a material that exhibits an electrically insulating tendency (high resistance) as the base material, making the base material contain carbon and an alkali metal, and further making the thickness T2 of the surface layer 23 smaller than the thickness T1 of the intermediate layer 22 (i.e., by appropriately controlling the thickness of the surface layer 23), thereby making the resistance of the surface layer 23 lower than that of the intermediate layer 22.

[0045] In this embodiment, 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. In this way, by providing the intermediate layer 22 and the surface layer 23 on the surface where electrons are easily incident on the insulating substrate 12, it is possible to effectively suppress both the charging and the luminescence of the insulating substrate 12 at the same time. 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, covering the entire surface of the base layer 21. Therefore, the effect of suppressing both the charging and the luminescence at the same time in all parts of the insulating substrate 12 can be further improved.

[0046] Providing the intermediate layer 22 and the surface layer 23 on the side surface 21c allows the first surface 21a and the second surface 21b to be electrically connected, thereby more reliably suppressing the surface charging of the insulating substrate 12 and suppressing the emission of light caused by electrons incident on the side surface 21c. Furthermore, since the focusing electrode 5, the dynode 11, and the anode 6 constituting the multiplying section 4 multiply and pass electrons, electrons are more likely to be incident on the vicinity of the insertion hole 13 inserted into the retaining sheet 11b. However, providing the intermediate layer 22 and the surface layer 23 on the inner surface of the insertion hole 13 further enhances the effect of simultaneously suppressing both the charging of the insulating substrate 12 and the emission of light.

[0047] The intermediate layer 22 and the surface layer 23 are composed of the same material, and the alkali metal content in the intermediate layer 22 can be lower than that in the surface layer 23. For example, by making the intermediate layer 22 and the surface layer 23 respectively of MgO (MgO containing carbon), the intermediate layer 22 can be a thin layer of alkali metals and carbon, and the surface layer 23 can be a rich layer of alkali metals and carbon, thereby making the intermediate layer 22 electrically insulating and the surface layer 23 electrically conductive. This structure can improve the ease of manufacturing of the intermediate layer 22 and the surface layer 23 by making them of the same material, while simultaneously suppressing both charging and light emission of the insulating substrate 12.

[0048] Figure 4This graph shows the results of a test to verify the luminescence suppression effect of the present invention. The test shown in this figure calculated the luminescence intensity in the ultraviolet region based on measured values ​​when electrons were incident on an insulating substrate with modified intermediate and surface layers formed on the base layer. The luminescence intensity was calculated using an electron (electron beam) acceleration voltage of 1 kV.

[0049] In Comparative Example 1, neither an intermediate layer nor a surface layer was provided, and an insulating substrate was formed with only a base layer made of white alumina. In Comparative Example 2, no intermediate layer was provided, and a 5nm thick surface layer of carbon-containing MgO was formed on the surface of a base layer made of white alumina to form an insulating substrate. In contrast, in Example 1, a 100μm thick intermediate layer of glass and a 5nm thick surface layer of carbon-containing MgO were formed on the surface of a base layer made of white alumina to form an insulating substrate. In Example 2, a 30nm thick intermediate layer of aluminum oxide (Al2O3) and a 5nm thick surface layer of carbon-containing MgO were formed on the surface of a base layer made of white alumina to form an insulating substrate.

[0050] like Figure 4 As shown, when the luminous intensity of the insulating substrate in Comparative Example 1 is 100, the luminous intensity of the insulating substrate in Comparative Example 2 is 44.3. According to this result, even in the case where only a surface layer of carbon-containing MgO is provided in the base layer, a certain degree of luminous intensity suppression effect can be obtained. The luminous intensity in Examples 1 and 2 is calculated based on the attenuation rate of the luminous intensity of the 5nm thick carbon-containing MgO in Comparative Example 2. That is, when the film thickness of the intermediate layer and the surface layer becomes n times thicker than the 5nm thick carbon-containing MgO, the luminous intensity is calculated as the nth power of 0.443. As a result, the luminous intensity of the insulating substrate in Example 1 is 7.5, and the luminous intensity of the insulating substrate in Example 2 is 0.5.

[0051] The resistance of the surface layer using carbon-containing MgO is lower than that of the intermediate layer. In Examples 1 and 2, when an intermediate layer of tens of nanometers is provided on the surface of the base layer, charging of the insulating substrate can occur solely in this intermediate layer. In contrast, by further providing a surface layer using 5 nm of carbon-containing MgO, the problem of charging the insulating substrate when the electrically insulating intermediate layer is located on the surface of the insulating substrate can be eliminated. These results demonstrate that the structure of the present invention, in which both the intermediate layer and the surface layer are provided on the surface of the base layer, helps to simultaneously suppress charging and luminescence of the insulating substrate. Description of Reference Signs

[0052] 1...electromagnetic tube, 2...housing, 3...photoelectric surface, 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 the intermediate layer, T2...thickness of the surface layer.

Claims

1. An electron tube, characterized in that: include: A photoelectric surface that converts incident light into photoelectrons; Multiple electrodes; an insulating substrate for holding the electrodes in an electrically insulated state; and a housing for housing the electrodes and the insulating substrate, The insulating substrate comprises: A base layer composed of a polycrystalline material and having electrical insulation properties; an intermediate layer composed of an amorphous material and having electrical insulating properties; and The surface layer is made of a carbon-containing material and has a lower electrical resistance than the intermediate layer.

2. The electron tube according to claim 1, wherein: The surface layer also contains an alkali metal.

3. The electron tube according to claim 1 or 2, characterized in that: The thickness of the intermediate layer is greater than that of the surface layer.

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

5. The electron tube according to any one of claims 1 to 4, characterized in that: The intermediate layer and the surface layer are provided on at least a first surface of the base layer on the electrode side and a second surface on the opposite side to the electrode.

6. The electron tube according to claim 5, wherein: The intermediate layer and the surface layer are provided on the side surface connecting the first surface and the second surface.

7. The electron tube according to claim 5 or 6, characterized in that: The base layer has an insertion hole into which a holding sheet for holding the electrode is inserted, and the intermediate layer and the surface layer are provided on an inner surface of the insertion hole.

8. The electron tube according to any one of claims 5 to 7, characterized in that: The intermediate layer and the surface layer are provided on the entire surface of the base layer.

9. The electron tube according to any one of claims 1 to 8, characterized in that: The intermediate layer and the surface layer are made of the same material, 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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