Photomultiplier tube

Abstract

A photomultiplier is provided with: a container having a window section formed from a light-transmitting material, and a tubular section connected to the window section and defining a vacuum space together with the window section; a photoelectric surface which is formed from a photoelectron-emitting material comprising sodium, potassium, and antimony, is provided on a first surface on the vacuum space side of the window, and emits photoelectrons in accordance with incident light; and an electron multiplication unit that emits secondary electrons in response to incidence of the photoelectrons emitted from the photoelectric surface, and multiplies the secondary electrons. An aluminum oxide layer is formed between the photoelectric surface and the window part and on the surface of the tubular part.

Description

Technical Field

[0001] One aspect of the present disclosure relates to a photomultiplier tube. Background Art

[0002] Japanese Patent Publication No. 2021-044118 describes a photomultiplier tube, which is composed of a photoelectric surface, a multiplication unit, and an anode arranged in a vacuum container. In the photomultiplier tube, photoelectrons are emitted from the photoelectric surface according to the incidence of light. The photoelectrons emitted from the photoelectric surface are multiplied as secondary electrons in the multiplication unit and captured in the anode. In the photomultiplier tube described in Patent Document 1, the photoelectric surface is formed of a photoelectron emitting material containing an alkali metal and is disposed on the inner surface of the container. Summary of the invention

[0003] The technical problem that the invention is intended to solve

[0004] The inventors of the present invention have found that when the above-mentioned photomultiplier tube is used in a high temperature environment (e.g., 175°C to 200°C), a unique problem may occur. That is, when the photomultiplier tube is operated in a high temperature environment, the alkali metal contained in the photoelectric surface moves in the container, and the sensitivity of the photoelectric surface may be deteriorated. In addition, in a high temperature environment, hydrogen or helium can easily penetrate the container and invade the container. Therefore, the after pulse caused by hydrogen or helium may increase.

[0005] One aspect of the present disclosure aims to provide a photomultiplier tube capable of suppressing sensitivity degradation of a photoelectric element and increase in after pulses even when used in a high-temperature environment.

[0006] Means for solving technical problems

[0007] One aspect of the present disclosure provides a photomultiplier tube, which is [1] "a photomultiplier tube comprising: a container having a window portion formed of a light-transmitting material, and a tubular portion connected to the window portion and defining a vacuum space together with the window portion; a photoelectric surface formed of a photoelectron emitting material composed of sodium, potassium and antimony, disposed on a surface of the window portion on the vacuum space side, and emitting photoelectrons in response to incident light; and an electron multiplying portion, which emits secondary electrons in response to the incidence of the photoelectrons emitted from the photoelectric surface and multiplies the secondary electrons, wherein a protective layer containing a trivalent metal oxide of Group III or Group XIII is formed between the photoelectric surface and the window portion and on the surface of the tubular portion."

[0008] In this photomultiplier tube, a protective layer containing a trivalent metal oxide of the third group or the thirteenth group is formed between the photoelectric surface and the window portion. Thus, when the photomultiplier tube is operated in a high-temperature environment, the alkali metals (sodium and potassium) contained in the photoelectric surface can be suppressed from moving in the window portion, and the sensitivity degradation of the photoelectric surface caused by the change in the composition ratio of the alkali metals constituting the photoelectric surface can be suppressed. In addition, the protective layer is also formed on the surface of the tubular portion. Thus, it is possible to suppress hydrogen or helium from penetrating the tubular portion into the container in a high-temperature environment, and to suppress the increase of after-pulses caused by hydrogen or helium. Therefore, according to this photomultiplier tube, when used in a high-temperature environment, it is possible to suppress the sensitivity degradation of the photoelectric surface and the increase of after-pulses.

[0009] The photomultiplier tube according to one aspect of the present disclosure may also be [2] "the photomultiplier tube according to [1], wherein the protective layer is formed on the surface of the tubular portion on the vacuum space side". In this case, in addition to suppressing hydrogen or helium from penetrating the tubular portion from the outside into the container, it is also possible to suppress hydrogen or helium present inside the tubular portion from leaking into the container, thereby further suppressing the increase of after pulses.

[0010] The photomultiplier tube according to one aspect of the present disclosure may be [3] "the photomultiplier tube according to [1] or [2], wherein the protective layer is formed on a surface of the tubular portion on the opposite side to the vacuum space". In this case, an increase in afterpulses can be more effectively suppressed.

[0011] The photomultiplier tube according to one aspect of the present disclosure may be [4] "a photomultiplier tube according to any one of [1] to [3], wherein the protective layer is also formed on a surface of the window portion opposite to the vacuum space". In this case, it is possible to suppress hydrogen or helium from penetrating through the window portion into the container.

[0012] The photomultiplier tube according to one aspect of the present disclosure may be [5] "the photomultiplier tube according to any one of [1] to [4], wherein the protective layer is an ALD layer". In this case, the protective layer can be densely formed, and the sensitivity degradation of the photoelectric element and the increase of the after pulse can be effectively suppressed.

[0013] The photomultiplier tube according to one aspect of the present disclosure may also be [6] "a photomultiplier tube according to any one of [1] to [5], wherein the thickness of the protective layer is not less than 10 nm and not more than 100 nm". In this case, it is possible to suppress the transmission of light in the window portion from being blocked by the protective layer, and effectively suppress the sensitivity degradation of the photoelectric surface and the increase of after-pulses.

[0014] The photomultiplier tube according to one aspect of the present disclosure may be [7] "the photomultiplier tube according to any one of [1] to [6], wherein the protective layer is an aluminum oxide layer." In this case, the sensitivity degradation of the photoelectric element and the increase of the after pulse can be effectively suppressed.

[0015] The photomultiplier tube of one aspect of the present disclosure may also be, [8] "the photomultiplier tube according to [7], wherein the thickness of the protective layer is not less than 10 nm and not more than 30 nm". In this case, it is possible to suppress the transmission of light in the window portion from being blocked by the protective layer, and effectively suppress the sensitivity degradation of the photoelectric surface and the increase of after pulses.

[0016] The photomultiplier tube according to one aspect of the present disclosure may be [9] "the photomultiplier tube according to any one of [1] to [6], wherein the protective layer is an yttrium oxide layer." In this case, the sensitivity degradation of the photoelectric element and the increase of the after pulse can be effectively suppressed.

[0017] The photomultiplier tube according to one aspect of the present disclosure may also be

[10] "the photomultiplier tube according to [9], wherein the thickness of the protective layer is not less than 10 nm and not more than 100 nm". In this case, it is possible to suppress the transmission of light in the window portion from being blocked by the protective layer, and more effectively suppress the sensitivity degradation of the photoelectric surface and the increase of after pulses.

[0018] According to one aspect of the present disclosure, it is possible to provide a photomultiplier tube capable of suppressing sensitivity degradation of a photoelectric element and increase in after pulses even when used in a high-temperature environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a cross-sectional view of a photomultiplier tube according to an embodiment.

[0020] Figure 2 This is a graph showing the comparison results of life characteristics.

[0021] Figure 3 This is a table showing the comparison results of the post pulse.

[0022] Figure 4 (a) to (c) are graphs showing the measurement results of after pulses.

[0023] Figure 5 is a cross-sectional view of a photomultiplier tube according to a first modification.

[0024] Figure 6 is a cross-sectional view of a photomultiplier tube according to a second modification.

[0025] Figure 7 (a) and (b) are diagrams for explaining the first experiment and the second experiment.

[0026] Figure 8 This is a table showing the experimental results of the first experiment and the second experiment.

[0027] Fig. 9 (a) to (d) are photographs of samples 1 to 3 in the first experiment.

[0028] Fig.10 (a) to (c) are photographs of sample 4 and sample 5 in the first experiment.

[0029] Fig.11 (a) to (d) are photographs of samples 6 to 9 in the first experiment.

[0030] Fig.12 (a) to (c) are photographs of samples 10 to 12 in the first experiment.

[0031] Fig.13 (a) to (d) are photographs of samples 1 to 3 in the second experiment.

[0032] Fig.14 (a) to (c) are photographs of Sample 4 and Sample 5 in the second experiment.

[0033] Fig.15 (a) to (d) are photographs of samples 6 to 9 in the second experiment.

[0034] Fig.16 (a) to (c) are photographs of samples 10 to 12 in the second experiment.

[0035] Fig.17 This is a table showing comparison results of after pulses of the third embodiment and the third comparative example.

[0036] Fig.18 (a) and (b) are graphs showing the measurement results of the after pulses of the third embodiment and the third comparative example. DETAILED DESCRIPTION

[0037] Hereinafter, one embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. In the following description, the same reference numerals are used for the same or corresponding elements, and repeated descriptions are omitted.

[0038] like Figure 1 As shown, a photomultiplier tube 1 (PMT) includes a container 10, a photoelectric element 20, a focusing electrode 30, an electron multiplier section 40, and an anode 50. The photoelectric element 20, the focusing electrode 30, the electron multiplier section 40, and the anode 50 are arranged in the container 10. The container 10 has a base section 11 and an electron tube section 12, and the electron tube section 12 is composed of a window section 13 and a tubular section 14.

[0039] In the photomultiplier tube 1, light L (incident light) passing through the window 13 is incident on the photoelectric surface 20, and photoelectrons are emitted from the photoelectric surface 20 according to the incidence of the light L. The photoelectrons emitted from the photoelectric surface 20 are focused by the focusing electrode 30, multiplied as secondary electrons in the electron multiplier section 40, and captured in the anode 50. Thus, the photomultiplier tube 1 functions as a photodetector. The photomultiplier tube 1 of this example is a high-temperature PMT that can be used in a high-temperature environment (e.g., 175°C to 200°C), and can be used, for example, in oil exploration. The structure of each part is described below.

[0040] The container 10 is formed of a light-transmitting material such as glass. The container 10 is hermetically sealed and defines a vacuum space S inside. The stem portion 11 is formed in a substantially disk shape, for example. A substantially cylindrical protrusion 11a is formed in the center of the stem portion 11 and protrudes toward the opposite side of the vacuum space S. A plurality of stem pins 15 are fixed to the stem portion 11 and penetrate the stem portion 11 along a direction A (a direction parallel to the center line of the tubular portion 14).

[0041] As described above, the electron tube portion 12 has the window portion 13 and the tubular portion 14. The window portion 13 is a panel (substrate) portion of the electron tube portion 12, and is formed in a substantially circular plate shape, for example. The window portion 13 has a first surface 13a (inner surface) on the vacuum space S side and a second surface 13b (outer surface) on the opposite side to the first surface 13a (vacuum space S). In this example, the first surface 13a is a curved surface that is curved into a substantially spherical shape in a manner that is concave toward the opposite side to the vacuum space S, and the second surface 13b is a flat surface that is perpendicular to the direction A.

[0042] The tubular portion 14 is a side tube portion of the electron tube portion 12, and is formed, for example, in a cylindrical shape having a center line parallel to the direction A. One end of the tubular portion 14 is connected to the outer edge of the window portion 13, and the other end of the tubular portion 14 is connected to the outer edge of the base portion 11. The vacuum space S is defined by the base portion 11, the window portion 13, and the tubular portion 14.

[0043] The photoelectric element 20 is provided in a thin film shape on the first surface 13a of the window portion 13. The photoelectric element 20 is formed on the substantially entire first surface 13a and extends in a curved manner along the first surface 13a. In this embodiment, as described later, an aluminum oxide layer 60 (protective layer) is formed between the first surface 13a and the photoelectric element 20, and the photoelectric element 20 is provided on the first surface 13a via the aluminum oxide layer 60.

[0044] The photoelectric surface 20 is formed by a photoelectron emitting material that emits photoelectrons according to the incidence of light. In this example, the photoelectron emitting material constituting the photoelectric surface 20 includes antimony (Sb), and sodium (Na) and potassium (K) as alkali metals. In this case, the photoelectric surface 20 is obtained by reacting sodium and potassium with antimony to activate. The photoelectric surface 20 is, for example, a Na2K photoelectric surface containing Na2K with a molar ratio of 2:1 to K. The Na2K photoelectric surface exhibits low noise. The meaning of exhibiting low noise is that in the operation of the photomultiplier tube 1, the current (dark current) flowing in the state where the light L is not incident on the photoelectric surface 20 is small. The photoelectric surface 20 acts as a photocathode that emits photoelectrons according to the incidence of light L.

[0045] The focusing electrode 30 focuses the photoelectrons emitted from the photoelectric element 20. The focusing electrode 30 is disposed to face the window portion 13. An opening 30a is formed at the center of the focusing electrode 30. The opening 30a functions as an entrance for the photoelectrons emitted from the photoelectric element 20 to enter the electron multiplying portion 40.

[0046] The electron multiplier section 40 is disposed between the focusing electrode 30 and the anode 50. The electron multiplier section 40 emits secondary electrons in response to the incidence of photoelectrons sent from the focusing electrode 30, and multiplies the secondary electrons. The electron multiplier section 40 is, for example, composed of a plurality of (10 in this example) dynodes 41. The plurality of dynodes 41 are arranged in multiple stages between the focusing electrode 30 and the anode 50. Each dynode 41 is formed in a curved shape or a flat plate shape, and emits secondary electrons toward the dynode 41 of the next stage through the collision of secondary electrons emitted from the dynode 41 of the previous stage. Thus, the secondary electrons are multiplied in sequence. The multiplied secondary electrons are captured by the anode 50. In addition, the electron multiplier section 40 can have any structure as long as it can emit secondary electrons for multiplication in response to the incidence of photoelectrons.

[0047] The photomultiplier tube 1 further includes an aluminum oxide layer 60. The aluminum oxide layer 60 includes a first portion 61, a second portion 62, a third portion 63, and a fourth portion 64. The first portion 61 is formed on the entire surface of the first surface 13a on the vacuum space S side of the window portion 13. The first portion 61 is interposed between the first surface 13a of the window portion 13 and the photoelectric element 20. In other words, the photoelectric element 20 is provided on the first surface 13a via the first portion 61.

[0048] The second portion 62 is formed on the entire surface of the second surface 13b of the window portion 13 on the side opposite to the vacuum space S. The third portion 63 is formed on the entire surface of the surface 14a (inner surface) of the tubular portion 14 on the side opposite to the vacuum space S. The fourth portion 64 is formed on the entire surface of the surface 14b (outer surface) of the tubular portion 14 on the side opposite to the vacuum space S. The first portion 61 and the third portion 63 are connected and formed integrally with each other. The second portion 62 and the fourth portion 64 are connected and formed integrally with each other. The aluminum oxide layer 60 is not formed on the base portion 11.

[0049] The aluminum oxide layer 60 is, for example, an ALD layer. The ALD layer refers to a layer formed by atomic layer deposition (ALD: Atomic Layer Deposition). The atomic layer deposition method is a method of depositing atomic layers layer by layer to obtain a thin film by repeatedly performing an adsorption process of compound molecules, a film formation process based on a reaction, and a purification process to remove excess molecules. The aluminum oxide layer 60 is formed to a uniform thickness by the ALD method.

[0050] As an example, when manufacturing the photomultiplier tube 1, the aluminum oxide layer 60 is formed on the entire surface of the window portion 13 and the tubular portion 14 (i.e., the entire surface of the first surface 13a and the second surface 13b, and the entire surface of the surface 14a and the surface 14b) by the ALD method. Then, the tube holder portion 11 is welded to the end of the tubular portion 14 to seal the container 10. The thickness of the aluminum oxide layer 60 is, for example, not less than 10 nm and not more than 100 nm. above ≤ 10 nm, preferably ≤ 30 nm above The aluminum oxide layer 60 is made of, for example, aluminum oxide (Al2O3, aluminum oxide).

[0051] [Function and Effect]

[0052] In the photomultiplier tube 1, a first portion 61 of an aluminum oxide layer 60 (protective layer) is formed between the photoelectric element 20 and the window 13. Thus, even when the photomultiplier tube 1 is operated in a high-temperature environment, the alkali metal (alkali block) contained in the photoelectric element 20 can be suppressed from moving in the window 13, and the sensitivity degradation of the photoelectric element 20 caused by the change in the composition ratio of the alkali metal constituting the photoelectric element 20 can be suppressed. In addition, a third portion 63 and a fourth portion 64 of the aluminum oxide layer 60 are formed on the surface of the tubular portion 14. Thus, it is possible to suppress hydrogen or helium from penetrating the tubular portion 14 into the container 10 in a high-temperature environment (the gas barrier property can be improved), and the increase of after pulses caused by hydrogen or helium can be suppressed. Thus, according to the photomultiplier tube 1, even when it is used in a high-temperature environment, the sensitivity degradation of the photoelectric element 20 can be suppressed, and the increase of after pulses can be suppressed.

[0053] The third portion 63 of the aluminum oxide layer 60 is formed on the surface 14a on the vacuum space S side of the tubular portion 14. Thus, in addition to suppressing the intrusion of hydrogen or helium from the outside into the container 10 through the tubular portion 14, it is also possible to suppress the leakage of hydrogen or helium existing inside the tubular portion 14 into the container 10, and further suppress the increase of after pulses.

[0054] The fourth portion 64 of the aluminum oxide layer 60 is formed on the surface 14 b of the tubular portion 14 on the opposite side to the vacuum space S. Thus, an increase in after pulses can be more effectively suppressed.

[0055] The second portion 62 of the aluminum oxide layer 60 is formed on the second surface 13 b of the window 13 on the opposite side to the vacuum space S. This can prevent hydrogen or helium from penetrating through the window 13 into the container 10 .

[0056] The aluminum oxide layer 60 is an ALD layer. Thus, the aluminum oxide layer 60 can be densely formed, and the sensitivity degradation of the photoelectric element 20 and the increase of the after pulse can be effectively suppressed.

[0057] The thickness of the aluminum oxide layer 60 is not less than 10 nm and not more than 30 nm. Thus, it is possible to suppress the transmission of light in the window portion 13 from being blocked by the aluminum oxide layer 60, and effectively suppress the sensitivity degradation of the photoelectric element 20 and the increase of the after pulse. That is, when the thickness of the aluminum oxide layer 60 is not less than 10 nm, the sensitivity degradation of the photoelectric element 20 and the increase of the after pulse can be effectively suppressed. In addition, when the thickness of the aluminum oxide layer 60 is not more than 30 nm, it is possible to suppress the transmission of the light L in the window portion 13 from being blocked by the first portion 61 and the fourth portion 64 of the aluminum oxide layer 60.

[0058] The aluminum oxide layer 60 is not formed on the tube seat portion 11. Thus, the time and materials required for the process of forming the aluminum oxide layer 60 on the tube seat portion 11 can be omitted, and the manufacturing can be facilitated. In addition, the aluminum oxide layer 60 can also be formed on the tube seat portion 11. In this case, the gas barrier property can be further improved. In this case, the aluminum oxide layer 60 can also be formed on the entire inner surface and the outer surface of the container 10, for example.

[0059] In addition, when the third portion 63 of the aluminum oxide layer 60 is formed on the surface 14a on the vacuum space S side of the tubular portion 14, a slight dark current may be generated, but the increase of the after pulse can be suppressed. Specifically, when the aluminum oxide layer 60 does not have the third portion 63, the alkali metal introduced excessively into the vacuum space S when the photoelectric element 20 is formed is absorbed by the tubular portion 14, so the generation of the dark current caused by the excessively introduced alkali metal can be suppressed. On the other hand, when the third portion 63 of the aluminum oxide layer 60 is formed on the surface 14a on the vacuum space S side of the tubular portion 14, the alkali metal introduced excessively into the vacuum space S is difficult to be absorbed by the tubular portion 14, and a part of the alkali metal may remain in the vacuum space S, and there is a possibility that the dark current caused by the residual alkali metal will be generated. However, since it is important to suppress the increase of the after pulse when used in a high temperature environment, the aluminum oxide layer 60 is formed on the surface 14a on the vacuum space S side of the tubular portion 14 in the photomultiplier tube 1 to suppress the increase of the after pulse.

[0060] Below, refer to Figure 2 to Figure 4 The results of the confirmation experiment are described. Figure 2 : is a graph showing the comparison results of life characteristics. In this experiment, the life characteristics of the photomultiplier tubes of Examples 1 to 4 and Comparative Examples 1 to 3 were evaluated. Examples 1 to 4 correspond to the case where the thickness of the aluminum oxide layer 60 in the photomultiplier tube 1 of the embodiment is 20 nm, and Comparative Examples 1 to 3 correspond to the case where the aluminum oxide layer 60 is not provided in the photomultiplier tube 1 of the embodiment. Each photomultiplier tube was operated at an ambient temperature of 200°C, and its output value was measured. Figure 2 The vertical axis of the graph represents the output value (%) when the output value after 1 hour from the start of the measurement is set to 100%, and the horizontal axis represents the elapsed time from the start of the measurement. In this experiment, the measurement is continued until the output value of any photomultiplier tube (here, Comparative Example 1) reaches 50%.

[0061] according to Figure 2 It can be seen that when the output values ​​of Examples 1 to 4 at the end of the measurement (about 100 hours later) are compared with the output values ​​of Comparative Examples 1 to 3, the output values ​​of Examples 1 to 4 are higher than those of Comparative Examples 1 to 3, and the life characteristics of Examples 1 to 4 are better than those of Comparative Examples 1 to 4.

[0062] Figure 3: is a table showing the comparison results of the after-pulse. In this experiment, the increase rate of the after-pulse was measured for the photomultiplier tubes of the first embodiment, the second embodiment and the comparative example. The first embodiment and the second embodiment correspond to the case where the thickness of the aluminum oxide layer 60 in the photomultiplier tube 1 of the embodiment is 10nm and 20nm respectively, and the comparative example corresponds to the case where the aluminum oxide layer 60 is not provided in the photomultiplier tube 1 of the embodiment. The photomultiplier tubes were stored for 20 hours at an ambient temperature of 200°C without being operated, and the increase rate of the after-pulse when they were operated after 20 hours from the start of storage was measured. The number of samples (N) of the first embodiment, the second embodiment and the comparative example was set to 5, and the average value of the five samples was set to the increase rate of the after-pulse.

[0063] Regarding the comparative example, the increase rates of the after-pulses of the five samples are 165%, 200%, 194%, 239%, and 213%, respectively, with an average value of 202%. Regarding the first embodiment, the increase rates of the after-pulses of the five samples are 184%, 202%, 161%, 177%, and 167%, respectively, with an average value of 178%. Regarding the second embodiment, the increase rates of the after-pulses of the five samples are 165%, 156%, 143%, 145%, and 171%, respectively, with an average value of 156%.

[0064] according to Figure 3 It can be seen that the increase rate of the after-pulse in the first and second embodiments is smaller than that in the comparative example. It can be seen that the increase of the after-pulse can be suppressed by forming the aluminum oxide layer 60. In addition, the increase rate of the after-pulse in the second embodiment is smaller than that in the first embodiment. It can be seen that the thicker the aluminum oxide layer 60 is, the more effectively the increase of the after-pulse can be suppressed.

[0065] In addition, the after-pulse refers to a virtual pulse observed after the output pulse corresponding to the incidence of the light of the detection object, and is generated when hydrogen or helium exists in the container 10. The more the amount of gas present in the container 10, the larger the after-pulse is observed as a peak. In addition, the longer the photomultiplier tube is kept in an inoperative state, the more the after-pulse increases. The after-pulse can affect the detection accuracy of the photomultiplier tube, so it is required to suppress it.

[0066] Figure 4 The first embodiment, the second embodiment and the comparative example in this experiment, as well as the operating conditions and Figure 3 The vertical axis represents the output value, and the horizontal axis represents the elapsed time.

[0067] like Figure 4As shown in (a), in the case of the comparative example, after pulses caused by hydrogen (H2) and methane (CH4) were detected after 20 hours. In addition, after pulses caused by these after pulses were also detected. Figure 4 (b) and Figure 4 As shown in (c), in the case of the first and second embodiments, after-pulses caused by hydrogen were detected after 20 hours, but the after-pulses were smaller than those in the comparative example. This shows that the increase of after-pulses can be suppressed by forming the aluminum oxide layer 60.

[0068] In addition, if the first embodiment and the second embodiment are compared, the after pulse of the second embodiment is smaller than the after pulse of the first embodiment. Therefore, it can be seen that the thicker the aluminum oxide layer 60 is, the more effectively the increase of the after pulse can be suppressed. Figure 4 The suppressive effect of the afterpulse caused by hydrogen is shown in FIG. 1 , but it is also considered that the afterpulse caused by helium is also suppressed in the same manner.

[0069] [Modifications]

[0070] exist Figure 5 In the first modification shown, the aluminum oxide layer 60 does not have the second portion 62 and the fourth portion 64, but only has the first portion 61 and the third portion 63. Figure 6 In the second modification shown, the aluminum oxide layer 60 does not have the second portion 62, but only has the first portion 61, the third portion 63, and the fourth portion 64. By these first and second modifications, as in the above-mentioned embodiment, even when used in a high temperature environment, it is possible to suppress the sensitivity degradation of the photoelectric element and the increase of the after pulse.

[0071] In addition, in the first and second modified examples, the aluminum oxide layer 60 does not have the second portion 62. That is, the aluminum oxide layer 60 is not formed on the second surface 13b of the window portion 13 on the opposite side to the vacuum space S. In this case, it is possible to suppress the transmission of light in the window portion 13 from being blocked by the aluminum oxide layer 60. On the other hand, from a manufacturing point of view, it is preferable that the aluminum oxide layer 60 has the second portion 62 as in the above-mentioned embodiment. That is, in the case of forming the aluminum oxide layer 60 by the ALD method, it is easier to form the aluminum oxide layer 60 on the entire surface of the electron tube portion 12 than to form it except for the second portion 62, and therefore, from a manufacturing point of view, it is preferable that the aluminum oxide layer 60 has the second portion 62.

[0072] The present disclosure is not limited to the above-mentioned embodiments and modifications. For example, the materials and shapes of each structure are not limited to the above-mentioned materials and shapes, and various materials and shapes can be used. The aluminum oxide layer 60 may not be an ALD layer. For example, the aluminum oxide layer 60 may also be formed by electron beam evaporation, sputtering evaporation, coating, etc. A base layer may also be provided between the aluminum oxide layer 60 and the photoelectric surface 20. The base layer is, for example, a beryllium oxide (BeO) layer.

[0073] A protective layer formed of a material other than aluminum oxide may also be provided to replace the aluminum oxide layer 60. As the material of the protective layer, oxides and nitrogen oxides of trivalent metal elements of the third group or the thirteenth group, such as aluminum oxynitride (AlON), yttrium oxide (Y2O3), and lanthanum oxide (La2O3) may be cited. Nitride oxide is a type of oxide. In addition, the protective layer is not limited to a layer composed of a single material, and may also be a layer composed of multiple materials, such as an alternating laminated film of aluminum oxide and silicon oxide (SiO2). On the other hand, as materials that are not suitable for the protective layer, titanium oxide (TiO2), silicon oxide (SiO2), magnesium fluoride (MgF2), magnesium oxide (MgO), tantalum oxynitride (TaON), hafnium oxide (HfO2), etc. may be cited.

[0074] Below, refer to Figure 7 to Figure 16 The results of the effect confirmation experiment are described below. In this experiment, the alkali metal barrier effect (lifetime characteristics) of the protective layer was confirmed. Figure 7 As shown, sample 100 is a sample obtained by coating a protective film 102 on a quartz glass 101. After exposing sample 100 to sodium vapor at 400 to 500 degrees, the degree of penetration of alkali (sodium) into sample 100 is confirmed. The quartz glass 101 and the protective film 102 turn black due to the penetration of alkali, and therefore, by confirming the degree, the alkali metal barrier effect of the protective film 102 can be evaluated. That is, there is a correlation between the appearance of sample 100 and the alkali metal barrier effect. Experiments were conducted on 11 samples 1 to 11 (No. 1 to No. 11) with different materials for the protective film 102 and sample 12 (No. 12) without forming the protective film 102. Reference Figure 8 , the structure of each sample is described later.

[0075] Two experiments, the first experiment and the second experiment, were conducted. In the first experiment, Figure 7As shown in (a), the sample 100 after being exposed to sodium vapor is placed on a white paper 103, and the sample 100 is observed from a direction D1 (opposite to the paper 103). Thus, the appearance of the sample 100 caused by the reflected light L2 when the light L1 is incident on the sample 100 is confirmed. The light L1 is the light from the fluorescent lamp. When the sample 100 looks transparent, it is judged that the alkali has not penetrated, and the alkali metal barrier effect of the protective film 102 is good. When the sample 100 is black and looks opaque, it is judged that the alkali has penetrated, and the alkali metal barrier effect of the protective film 102 is not good.

[0076] In the second experiment, Figure 7 As shown in (b), the sample 100 after being exposed to sodium vapor is arranged in front of the fluorescent lamp 105, and the sample 100 is observed from the direction D2 (opposite to the fluorescent lamp 105). Thus, the appearance of the sample 100 caused by the transmitted light of the light L3 from the fluorescent lamp 105 is confirmed. In the case where the sample 100 looks bright, it is judged that the alkali has not penetrated and the alkali metal barrier effect is good. In the case where the sample 100 looks dim, it is judged that the alkali has penetrated and the alkali metal barrier effect of the protective film 102 is not good.

[0077] Figure 8 TABLE 1 is a table showing the experimental results of the first experiment and the second experiment. In the column of "Alkali metal barrier effect", materials with "0" show good alkali metal barrier effect, and materials with "×" show poor alkali metal barrier effect.

[0078] like Figure 8 As shown, the protective films 102 of samples 1, 3, 5 to 11 are respectively composed of aluminum oxide, yttrium oxide, lanthanum oxide, magnesium oxide, silicon oxide, titanium oxide, hafnium oxide, tantalum oxynitride, and magnesium fluoride. The protective film 102 of sample 2 is composed of aluminum oxide nitride, which is a mixture of aluminum oxide and aluminum nitride. The protective film 102 of sample 4 has a structure in which three pairs of aluminum oxide and silicon oxide are stacked. The protective films 102 of samples 1, 2, 4, 6 to 8, 10, and 11 are ALD films, and the protective films 102 of samples 3, 5, and 9 are electron beam evaporated films.

[0079] The materials of the protective film 102 of samples 1 to 5 (aluminum oxide, aluminum oxynitride, yttrium oxide, silicon oxide, lanthanum oxide) are trivalent metal oxides. The materials of samples 3 and 5 (yttrium oxide, lanthanum oxide) are also rare earth metal oxides. The material of the protective film 102 of sample 6 (magnesium oxide) is a divalent metal oxide. The material of the protective film 102 of sample 7 (silicon oxide) is a tetravalent non-metallic oxide. The materials of samples 8 and 9 (titanium oxide, hafnium oxide) are tetravalent metal oxides. The material of the protective film 102 of sample 10 (tantalum oxynitride) is a pentavalent metal oxide. The material of the protective film 102 of sample 11 (magnesium fluoride) is not an oxide.

[0080] like Figure 8 As shown, the alkali metal barrier effect is good for samples 1 to 5, but poor for samples 6 to 12. It can be seen that the materials of the protective film 102 of samples 1 to 5 with good alkali metal barrier effect are all trivalent metal oxides (trivalent metal oxides of the third group or the thirteenth group) (including nitrogen oxides).

[0081] Figures 9 to 16 These are photos of the experimental results in the first experiment and the second experiment. Figures 9 to 12 This is a photo of the experimental results in the first experiment. Figure 13 to Figure 16 is a photo of the experimental results in the second experiment. Figures 9 to 16 As shown, the appearance of samples 1 to 5 in the first experiment and the second experiment was good. On the other hand, the appearance of samples 6 to 12 in the first experiment and the second experiment was not good. Fig.15 and Fig.16 The photograph was black and white, but in fact, samples 6 to 12 in the second experiment appear to contain red. In addition, as an experiment different from the first and second experiments, a protective film was formed on the inner wall of the vacuum tube to perform gas analysis, and it was confirmed that the two samples corresponding to the above-mentioned samples 1 and 4 (a sample in which the protective film is composed of aluminum oxide and a sample in which the protective film has a structure in which three pairs of aluminum oxide and silicon oxide are stacked) have good gas barrier properties.

[0082] In the above embodiment, the entire aluminum oxide layer 60 is formed to have a uniform thickness, but it may be partially formed to have different thicknesses. For example, the thickness of the third portion 63 and the fourth portion 64 formed on the tubular portion 14 may be thicker than the thickness of the first portion 61 and the second portion 62 of the aluminum oxide layer 60 formed on the window portion 13. In this case, it is possible to suppress the transmission of light in the window portion 13 from being blocked by the first portion 61 and the second portion 62, and at the same time, the third portion 63 and the fourth portion 64 suppress the penetration of hydrogen or helium through the tubular portion 14 into the container 10.

[0083] The thickness of the first portion 61 of the aluminum oxide layer 60 may also be 5 nm. In this case, the effect of suppressing the sensitivity degradation of the photoelectric element 20 (alkali metal barrier effect) can be obtained. The thickness of the first portion 61 can also be 300nm or less. In this case, the refractive index of the aluminum oxide layer 60 is a value between the refractive index of the window portion 13 and the refractive index of the photoelectric element 20, so that the light L incident from the window portion 13 can be suppressed from being reflected by the first portion 61.

[0084] Reference Fig.17 and Fig.18 , the results of the gas barrier property confirmation experiment are described. Fig.17: is a table showing the comparison results of the after-pulse of the third embodiment and the third comparative example. In this experiment, the increase rate of the after-pulse was measured for the photomultiplier tubes of the third embodiment and the third comparative example. The third embodiment corresponds to the case where a protective layer (yttrium oxide layer) formed of yttrium oxide is provided in the photomultiplier tube 1 of the embodiment instead of the aluminum oxide layer 60. In the third embodiment, the yttrium oxide layer is formed by electron beam evaporation. The thickness of the yttrium oxide layer is set to 100 nm. The third comparative example corresponds to a case where the aluminum oxide layer 60 (protective layer) is not provided in the photomultiplier tube 1 of the embodiment. Figure 3 Similarly, the photomultiplier tubes were stored at an ambient temperature of 200°C for 20 hours without being operated, and the increase rate of the after-pulse when the photomultiplier tubes were operated after 20 hours from the start of storage was measured. The number of samples (N) of the third embodiment and the third comparative example was set to 5, and the average value of the five samples was taken as the increase rate of the after-pulse.

[0085] Regarding the third comparative example, the post-pulse increase rates of the five samples are 276%, 219%, 236%, 299%, and 319%, respectively, with an average value of 270%. Regarding the third embodiment, the post-pulse increase rates of the five samples are 274%, 202%, 247%, 228%, and 255%, respectively, with an average value of 241%.

[0086] according to Fig.17 It can be seen that the increase rate of the after-pulse in the third embodiment is smaller than the increase rate of the after-pulse in the third comparative example. This shows that the increase of the after-pulse can be suppressed by providing the yttrium oxide layer.

[0087] Fig.18 1 is a graph showing the measurement results of the after pulse of the third embodiment and the third comparative example. Fig.17 The vertical axis represents the output value, and the horizontal axis represents the elapsed time.

[0088] like Fig.18 As shown in (a), in the case of the third comparative example, an after pulse caused by hydrogen (H2) was detected after 20 hours. Fig.18 As shown in (b), in the case of the third embodiment, afterpulses caused by hydrogen were detected after 20 hours, but the afterpulses were smaller than those in the case of the third comparative example. It can be seen that the increase of afterpulses can be suppressed by providing an yttrium oxide layer.

[0089] according to Fig.17 and Fig.18It can be seen that even when an yttrium oxide layer is provided in the photomultiplier tube 1 of the embodiment instead of the aluminum oxide layer 60, the increase of the after pulse can be suppressed (the gas barrier property can be improved). In addition, in the above-mentioned Example 3, the thickness of the yttrium oxide layer is 100 nm, but the thickness of the yttrium oxide layer can also be greater than 10 nm and less than 100 nm. In this case, the gas barrier property can be improved as in the case of Example 3.

Claims

1. A photomultiplier tube, wherein: have: A container having a window portion formed of a light-transmitting material and a tubular portion connected to the window portion and defining a vacuum space together with the window portion; a photoelectric surface formed of a photoelectron emitting material composed of sodium, potassium and antimony, provided on a surface of the window portion on the vacuum space side, and emitting photoelectrons in response to incident light; and an electron multiplying section that emits secondary electrons in response to the incidence of the photoelectrons emitted from the photoelectric surface and multiplies the secondary electrons, A protective layer containing a trivalent metal oxide of Group III or Group XIII is formed between the photoelectric element and the window portion and on the surface of the tubular portion.

2. The photomultiplier tube according to claim 1, wherein: The protective layer is formed on a surface of the tubular portion on the vacuum space side.

3. The photomultiplier tube according to claim 1 or 2, wherein: The protective layer is formed on a surface of the tubular portion on an opposite side to the vacuum space.

4. The photomultiplier tube according to any one of claims 1 to 3, wherein The protective layer is also formed on a surface of the window portion on an opposite side to the vacuum space.

5. The photomultiplier tube according to any one of claims 1 to 4, wherein The protective layer is an ALD layer.

6. The photomultiplier tube according to any one of claims 1 to 5, wherein The thickness of the protective layer is greater than or equal to 10 nm and less than or equal to 100 nm.

7. The photomultiplier tube according to any one of claims 1 to 6, wherein The protective layer is an aluminum oxide layer.

8. The photomultiplier tube according to claim 7, wherein: The thickness of the protective layer is greater than or equal to 10 nm and less than or equal to 30 nm.

9. The photomultiplier tube according to any one of claims 1 to 6, wherein The protective layer is an yttrium oxide layer.

10. The photomultiplier tube according to claim 9, wherein: The thickness of the protective layer is greater than or equal to 10 nm and less than or equal to 100 nm.

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