First stage dynode and photomultiplier tube

Abstract

The first-stage dynode is a first-stage dynode for a photomultiplier tube, comprising a bottom wall portion, a pair of side wall portions extending toward one side from both ends of the bottom wall portion in a specified direction, a first retaining portion extending toward the outside from the end of the bottom wall portion, and a pair of second retaining portions extending toward one side from both ends of the pair of side wall portions in a specified direction. An electron emission surface opposite to an electron passage opening is formed by a bottom surface on one side of the bottom wall portion and a pair of side surfaces on one side of the pair of side wall portions. The bottom surface is a curved surface bent into a concave shape in a cross section perpendicular to the specified direction, and each of a pair of side surfaces is a curved surface bent into a concave shape in a cross section parallel to the specified direction.

Description

Technical Field

[0001] The invention relates to a first-stage dynode and a photomultiplier tube. Background Art

[0002] As the first-stage dynode for a photomultiplier tube, dynodes presenting various shapes have been proposed. For example, in the specification of U.S. Patent No. 4112325, a dynode presenting a teacup-shaped shape with a flat bottom surface is described as a first-stage dynode for the purpose of improving the collection efficiency of photoelectrons. In the first-stage dynode described in the specification of U.S. Patent No. 4112325, the electron emission surface is formed by the flat bottom surface of the teacup shape. In addition, in the gazette of Japanese Patent Publication No. 8-12772, as a first-stage dynode for the purpose of obtaining a signal current that is not dependent on the incident position of the photocathode, a dynode presenting a funnel-shaped receiving port for the incidence of photoelectrons is described. In the first-stage dynode described in the gazette of Japanese Patent Publication No. 8-12772, the electron emission surface is formed by three planes and one curved surface connected in a concave manner, and a pair of side surfaces are provided on both sides of the electron emission surface in a manner orthogonal to the electron emission surface. Summary of the invention

[0003] However, in the first-stage dynode described in the specification of U.S. Patent No. 4112325, since the electron emission surface is formed by a flat bottom surface of a teacup shape, it becomes difficult to adjust the transit time of the secondary electrons from the first-stage dynode to the second-stage dynode, resulting in a difference in the transit time of the secondary electrons from the first-stage dynode to the second-stage dynode. In addition, in the first-stage dynode described in Japanese Patent Publication No. 8-12772, since a pair of side surfaces are provided on both sides of the electron emission surface in a manner orthogonal to the electron emission surface, the secondary electrons emitted from the central area of ​​the electron emission surface transit in a straight line, while the secondary electrons emitted from the vicinity of the side surface of the electron emission surface repel and transit on the side surface of the same potential, resulting in a difference in the transit time of the secondary electrons from the first-stage dynode to the second-stage dynode. Therefore, in the first-stage dynode described in US Pat. No. 4,112,325 and Japanese Patent Publication No. 8-12772, it is expected to be difficult to suppress the cathode transit time difference (CTTD) and the transit time spread (TTS) in the photomultiplier tube.

[0004] Therefore, an object of the present invention is to provide a first-stage dynode capable of suppressing electron transit time differences and electron transit time dispersion in a photomultiplier tube, and a photomultiplier tube including the first-stage dynode.

[0005] The first-stage dynode of the present invention is a first-stage dynode for a photomultiplier tube, wherein the first-stage dynode comprises a bottom wall portion, a pair of side wall portions extending to one side from both ends of the bottom wall portion in a specified direction, a first retaining portion extending outward from the end of the bottom wall portion, and a pair of second retaining portions extending to one side from both ends of the pair of side wall portions in a specified direction. An electron emission surface opposite to an electron passage opening is formed by a bottom surface on one side of the bottom wall portion and a pair of side surfaces on one side of the pair of side wall portions. The bottom surface is a curved surface bent into a concave shape in a cross section perpendicular to the specified direction, and each of the pair of side surfaces is a curved surface bent into a concave shape in a cross section parallel to the specified direction.

[0006] In the first-stage dynode, each of a pair of side surfaces constituting the electron emission surface is a curved surface that is curved into a concave shape on a cross section parallel to a prescribed direction. Therefore, the farther each side surface is from the center of the electron emission surface in the prescribed direction, the closer it is to an electron passage opening. As a result, the transit distance of the photoelectrons incident on each side surface and the transit distance of the secondary electrons emitted from each side surface become shorter as each side surface approaches an electron passage opening. In addition, the bottom surface constituting the electron emission surface is a curved surface that is curved into a concave shape on a cross section perpendicular to the prescribed direction. Therefore, it is easy to adjust the transit time of the secondary electrons from the first-stage dynode to the second-stage dynode. In addition, the photoelectrons incident on the electron emission surface and the secondary electrons emitted from the electron emission surface both pass through one (i.e., the same) electron passage opening, and the dependence of the electron transit time on the incident position of the photoelectron is reduced. Therefore, according to the first-stage dynode, the electron transit time difference and the electron transit time dispersion can be suppressed in the photomultiplier tube.

[0007] In the first-stage dynode of the present invention, the first holding portion may be in the form of a flat plate. According to this structure, the first-stage dynode can be easily and stably mounted by using the first holding portion on a support member provided in the tube body of the photomultiplier tube.

[0008] In the first-stage dynode of the present invention, each of the pair of second holding portions may be in a flat plate shape. According to this structure, the first-stage dynode can be easily and stably mounted on a support member provided in the tube body of the photomultiplier tube using the pair of second holding portions.

[0009] In the first-stage dynode of the present invention, the bottom wall, the pair of side walls, the first holding portion, and the pair of second holding portions may be integrally formed of a metal plate. This structure can facilitate the manufacture of the first-stage dynode and simplify the structure.

[0010] In the first-stage dynode of the present invention, the curvature radius of each of the pair of side surfaces may be larger than 2 mm. According to this structure, the electron transit time difference and the electron transit time dispersion can be appropriately suppressed in the photomultiplier tube.

[0011] In the first-stage dynode of the present invention, when the width of the electron emission surface in a predetermined direction is L and the curvature radius of each of a pair of side surfaces is R, R≧0.1L may also hold. With this configuration, the electron transit time difference and electron transit time dispersion can be appropriately suppressed in the photomultiplier tube.

[0012] The photomultiplier tube of the present invention comprises a photocathode, a multistage dynode, and an anode. The multistage dynode comprises a first-stage dynode and a second-stage dynode arranged on a prescribed surface. The first-stage dynode comprises a bottom wall portion, a pair of side walls extending from both ends of the bottom wall portion in a prescribed direction perpendicular to the prescribed surface to the photocathode side and the second-stage dynode side, a first retaining portion extending from the end of the bottom wall portion on the photocathode side to the opposite side of the second-stage dynode, and a pair of second retaining portions extending from both ends of the pair of side walls in the prescribed direction to the photocathode side and the second-stage dynode side. In the first-stage dynode, an electron emission surface opposite to an electron passage opening is formed by a bottom surface on the photocathode side and the second-stage dynode side of the bottom wall portion and a pair of side surfaces on the photocathode side and the second-stage dynode side of the pair of side walls. The bottom surface is a curved surface curved into a concave shape in a cross section perpendicular to the prescribed direction, and each of the pair of side surfaces is a curved surface curved into a concave shape in a cross section parallel to the prescribed direction.

[0013] According to this photomultiplier tube, due to the above-mentioned reasons, it is possible to suppress the electron transit time difference and the electron transit time dispersion. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a cross-sectional view of a photomultiplier tube according to one embodiment.

[0015] Figure 2 yes Figure 1 A cross-sectional view of the electron multiplier and anode shown.

[0016] Figure 3 This is a perspective view of a first-stage dynode according to one embodiment.

[0017] Figure 4 It is along Figure 3 A cross-sectional view of the first-stage dynode along line IV-IV is shown.

[0018] Figure 5 It is along Figure 3 A cross-sectional view of the first-stage dynode along the V-V line is shown.

[0019] Figure 6 It is a perspective view of the first-stage dynode of the comparative example.

[0020] Figure 7 It is a schematic diagram used to illustrate the transit orbit of an electron.

[0021] Figure 8This is a diagram showing the electron transit time difference and electron transit time dispersion of the photomultiplier tube using the first-stage dynode of the first embodiment.

[0022] Fig. 9 It is a diagram showing the electron transit time difference and the electron transit time dispersion of the photomultiplier tube using the first-stage dynode of the second embodiment.

[0023] Fig.10 It is a diagram showing the electron transit time difference and the electron transit time dispersion of the photomultiplier tube using the first-stage dynode of the third embodiment.

[0024] Fig.11 It is a diagram showing the electron transit time difference and the electron transit time dispersion of the photomultiplier tube using the first-stage dynode of the fourth embodiment.

[0025] Fig.12 This is a diagram showing the difference in electron transit time between the photomultiplier tube using the first-stage dynode of the first comparative example and the photomultiplier tube using the first-stage dynode of the fifth embodiment. DETAILED DESCRIPTION

[0026] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in each figure, the same or corresponding parts are given the same reference numerals, and repeated descriptions are omitted.

[0027] [Structure of photomultiplier tube]

[0028] like Figure 1 As shown, the photomultiplier tube 1 includes a tube body 2, a photocathode 3, an accelerating electrode 4, a focusing electrode 5, an electron multiplier section 6, and an anode 7. The electron multiplier section 6 has a multi-stage (for example, 10-stage) dynode 10. In the following description, the light incident side is referred to as the "front" and the opposite side is referred to as the "rear" with respect to the photomultiplier tube 1. In addition, the tube axis (central axis) of the tube body 2 is referred to as the "Z axis", the axis orthogonal to the surface (surface including the Z axis) where the multi-stage dynode 10 is arranged is referred to as the "X axis", and the axis orthogonal to the Z axis and the X axis is referred to as the "Y axis".

[0029] The tube body 2 accommodates the photocathode 3, the accelerating electrode 4, the focusing electrode 5, the electron multiplying section 6 and the anode 7 in a vacuumed space. The tube body 2 is a glass vacuum tube with light transmittance. The tube body 2 has an oblate spherical portion 2a with the Z axis as the central axis and a cylindrical portion 2b with the Z axis as the central axis on the rear side of the oblate spherical portion 2a. The oblate spherical portion 2a and the cylindrical portion 2b are formed integrally as a glass vacuum tube. As an example, the outer diameter of the oblate spherical portion 2a when viewed from the front side is about 200 mm, and the outer diameter of the cylindrical portion 2b is about 85 mm.

[0030] The photocathode 3 is set on the inner surface of the tube body 2. Specifically, the photocathode 3 is set on the inner surface of the front half of the oblate spherical part 2a. The photocathode 3 constitutes a transmissive photoelectric surface, for example, formed of potassium antimonide·cesium type (double alkali) material, or other well-known materials. When light is incident on the photocathode 3 from the front side, photoelectrons are emitted from the photocathode 3 to the rear side through the photoelectric effect. As an example, the outer diameter of the photocathode 3 when observed from the front side (that is, the effective diameter of the photomultiplier tube 1) is about 200 mm. In addition, Figure 1 The dashed line shown indicates the orbit (representative orbit) of the photoelectrons emitted from the photocathode 3 .

[0031] The accelerating electrode 4 is arranged on the rear side of the photocathode 3. A predetermined voltage is applied to the accelerating electrode 4. The accelerating electrode 4 is configured to accelerate the photoelectrons emitted from the photocathode 3 toward the electron multiplying section 6. The focusing electrode 5 is arranged on the rear side of the accelerating electrode 4. A predetermined voltage is applied to the focusing electrode 5. The focusing electrode 5 is configured to focus the photoelectrons emitted from the photocathode 3 toward the electron multiplying section 6.

[0032] The electron multiplier section 6 is arranged on the rear side of the focusing electrode 5. The multistage dynodes 10 are arranged on the YZ plane (a plane including the Y axis and the Z axis). Each dynode 10 is formed of, for example, stainless steel. A predetermined voltage is applied to each of the multistage dynodes 10. The electron multiplier section 6, i.e., the multistage dynode 10, is configured to multiply the photoelectrons emitted from the photocathode 3. The anode 7 is arranged on the YZ plane in a state opposite to the final-stage dynode 10. A predetermined voltage is applied to the anode 7. The anode 7 is configured to output the secondary electrons emitted from the final-stage dynode 10 as a signal current.

[0033] The accelerating electrode 4, the focusing electrode 5, the dynodes 10 of the electron multiplier 6, and the anode 7 are supported by a support member (not shown) in the tube 2. The support member is attached to a stem (not shown) at the rear end of the sealed cylindrical portion 2b. In addition, wiring for voltage application and wiring for signal current output are provided on the stem as a stem pin or a cable.

[0034] [Structure of the Electron Multiplying Section]

[0035] like Figure 2As shown, in the electron multiplying section 6, the multistage dynode 10 includes a first-stage dynode 11, a second-stage dynode 12, and a third-stage dynode 13. In the following description, each dynode including the first-stage dynode 11, the second-stage dynode 12, and the third-stage dynode 13 is referred to as a dynode 10. In addition, the electron emission surface (surface where electrons are incident and secondary electrons are emitted) of each dynode including the electron emission surface 11a of the first-stage dynode 11, the electron emission surface 12a of the second-stage dynode 12, and the electron emission surface 13a of the third-stage dynode 13 is referred to as an electron emission surface 10a.

[0036] The first-stage dynode 11 is arranged so that the electron emission surface 11a and the photocathode 3 (see Figure 1 ) and the electron emission surface 12a of the second-stage dynode 12. The second-stage dynode 12 is configured so that the electron emission surface 12a is opposite to the electron emission surface 11a of the first-stage dynode 11 and the electron emission surface 13a of the third-stage dynode 13. The dynodes 10 after the third stage except the final stage dynode 10 are similarly configured so that the electron emission surface 10a thereof is opposite to the electron emission surface 10a of the previous stage dynode 10 and the electron emission surface 10a of the subsequent stage dynode 10. The final stage dynode 10 is configured so that the electron emission surface 10a thereof is opposite to the electron emission surface 10a of the previous stage dynode 10 and the anode 7.

[0037] The first-stage dynode 11 has a bottom wall 111, a pair of side walls 112, a first holding portion 113, and a pair of second holding portions 114 (described in detail later). The electron emission surface 11a of the first-stage dynode 11 is composed of a bottom surface of the bottom wall 111 on the photocathode 3 side and the second-stage dynode 12 side and a pair of side surfaces of the pair of side walls 112 on the photocathode 3 side and the second-stage dynode 12 side.

[0038] The second-stage dynode 12 has a bottom wall portion 121 and a pair of holding portions 122. The electron emission surface 12a of the second-stage dynode 12 is constituted by the bottom surface of the first-stage dynode 11 side and the third-stage dynode 13 side of the bottom wall portion 121. The pair of holding portions 122 extend from both ends of the bottom wall portion 121 in the X-axis direction (direction parallel to the X-axis) to the first-stage dynode 11 side and the third-stage dynode 13 side.

[0039] The third-stage dynode 13 has a bottom wall portion 131 and a pair of holding portions 132. The electron emission surface 13a of the third-stage dynode 13 is constituted by the bottom surface of the second-stage dynode 12 side and the fourth-stage dynode 10 side of the bottom wall portion 131. The pair of holding portions 132 extend from both ends of the bottom wall portion 131 in the X-axis direction to the second-stage dynode 12 side and the fourth-stage dynode 10 side.

[0040] A pair of electron lens forming electrodes 14 are provided in the regions between the first-stage dynode 11, the second-stage dynode 12, and the third-stage dynode 13. Specifically, one electron lens forming electrode 14 is formed integrally with one holding portion 132 in a manner extending to a region between one second holding portion 114 and one holding portion 122. Another electron lens forming electrode 14 is formed integrally with another holding portion 132 in a manner extending to a region between another second holding portion 114 and another holding portion 122. A predetermined voltage applied to the third-stage dynode 13 is applied to the pair of electron lens forming electrodes 14. Thus, in the region between the first-stage dynode 11 and the second-stage dynode 12, the potential distribution in the X-axis direction is flattened.

[0041] [Structure of the first-stage dynode]

[0042] like Figure 3 , Figure 4 and Figure 5 As shown, the first-stage dynode 11 has a bottom wall 111, a pair of side walls 112, a first holding portion 113, and a pair of second holding portions 114. The pair of side walls 112 extend from both ends of the bottom wall 111 in the X-axis direction (a predetermined direction perpendicular to a predetermined surface) to one side (the photocathode 3 side and the second-stage dynode 12 side (refer to Figure 1 and Figure 2 The first holding portion 113 extends from the front side of the bottom wall portion 111 (the photocathode 3 side (refer to Figure 1 and Figure 2 ))'s end is toward the outside (the opposite side of the second-stage dynode ( Figure 1 and Figure 2 The pair of second holding portions 114 extends toward one side from both ends of the pair of side wall portions 112 in the X-axis direction.

[0043] The first holding portion 113 is in the shape of a flat plate (e.g., a rectangular plate) parallel to the XY plane. Each of the pair of second holding portions 114 is in the shape of a flat plate parallel to the YZ plane. The first-stage dynode 11 is mounted on a supporting member provided in the tube body 2 via the first holding portion 113 and the pair of second holding portions 114.

[0044] The electron emission surface 11a of the first-stage dynode 11 is composed of the bottom surface 111a on one side of the bottom wall portion 111 and the pair of side surfaces 112a on one side of the pair of side walls 112. The electron emission surface 11a is opposite to one electron passage opening 11b. In the first-stage dynode 11, one electron passage opening 11b is defined by the bottom wall portion 111, the pair of side walls 112, and the edge of one side of the pair of second holding portions 114. That is, the photoelectrons incident on the electron emission surface 11a and the secondary electrons emitted from the electron emission surface 11a all pass through one (i.e., the same) electron passage opening 11b.

[0045] The bottom surface 111a constituting the electron emission surface 11a is a curved surface that is curved into a concave shape in a cross section perpendicular to the X-axis direction (see in particular Figure 4 In this embodiment, the bottom surface 111a is a cylindrical surface (elliptical cylinder, hyperbolic cylinder, parabolic cylinder, composite surface of these, etc.) with the X-axis direction set as the length direction (height direction of the cylinder). Each of the pair of side surfaces 112a constituting the electron emission surface 11a is a curved surface that is curved into a concave shape in a cross section parallel to the X-axis direction (especially refer to Figure 5 ). In this embodiment, each side surface 112a is equivalent to a chamfered surface in the case where a rounded inner chamfer is applied to the corner (corner portion) formed by the bottom surface 111a and the inner surface of each second holding portion 114. In addition, the bottom surface 111a and each side surface 112a are connected to each other in a continuous curvature. In addition, each side surface 112a and the inner surface of each second holding portion 114 are also connected to each other in a continuous curvature.

[0046] The width of the electron emission surface 11a in the X-axis direction is L, and the curvature radius of each of the pair of side surfaces 112a is R (see Figure 5 ), R≧0.1L holds true in the first-stage dynode 11. In addition, the curvature radius R of each of the pair of side surfaces 112a is greater than 2 mm. As an example, the width L of the electron emission surface 11a in the X-axis direction is greater than 20 mm and less than 50 mm.

[0047] The first-stage dynode 11 having the above-mentioned shape is integrally formed of a metal plate (e.g., a stainless steel plate with a thickness of about 0.3 mm). That is, the bottom wall 111, the pair of side walls 112, the first retaining portion 113, and the pair of second retaining portions 114 are integrally formed of a metal plate. Here, integrally formed of a metal plate means that the metal plate is formed by performing plastic processing such as stamping processing on the metal plate.

[0048] [Function and Effect]

[0049] In the first-stage dynode 11, each of a pair of side surfaces 112a constituting the electron emission surface 11a is a curved surface that is curved into a concave shape in a cross section parallel to the X-axis direction. Therefore, the farther each side surface 112a is from the center of the electron emission surface 11a in the X-axis direction, the closer it is to an electron passage opening 11b. As a result, the transit distance of the photoelectrons incident on each side surface 112a and the transit distance of the secondary electrons emitted from each side surface 112a are shortened accordingly as each side surface 112a approaches an electron passage opening 11b. In addition, the bottom surface 111a constituting the electron emission surface 11a is a curved surface that is curved into a concave shape in a cross section perpendicular to the X-axis direction. Therefore, it is easy to adjust the transit time of the secondary electrons from the first-stage dynode 11 to the second-stage dynode 12. In addition, the photoelectrons incident on the electron emission surface 11a and the secondary electrons emitted from the electron emission surface 11a all pass through the same (i.e., the same) electron passage opening 11b, thereby reducing the dependence of the electron transit time on the incident position of the photoelectron. Therefore, according to the first-stage dynode 11, the electron transit time difference and the electron transit time dispersion can be suppressed in the photomultiplier tube 1.

[0050] In addition, even if the entire electron emission surface is formed into a spherical shape, for example, in the first-stage dynode having such an electron emission surface, it is difficult to adjust the transit time of the secondary electrons from the first-stage dynode to the second-stage dynode, and the electron transit time difference and the electron transit time dispersion cannot be effectively suppressed in the photomultiplier tube. In addition, in order to suppress the electron transit time difference and the electron transit time dispersion, it is also considered that the electron emission surface is constituted by only the bottom surface 111a without a pair of side surfaces 112a, and the width of the electron emission surface in the X-axis direction is increased. However, in the first-stage dynode having such an electron emission surface, since its size increases, the outer diameter of the cylindrical portion 2b of the tube body 2 has to be increased, so that it is difficult to ensure the water pressure resistance of the tube body 2. In addition, when the size of the first-stage dynode increases, it becomes difficult to form the first-stage dynode by plastic processing such as stamping on the metal plate. According to the first-stage dynode 11 described above, it is possible to suppress an increase in size thereof, and to suppress a difference in electron transit time and dispersion of electron transit time in the photomultiplier tube 1 .

[0051] In addition, the first holding portion 113 of the first-stage dynode 11 is in a flat plate shape. With this configuration, the first-stage dynode 11 can be easily and stably mounted on a support member provided in the tube body 2 of the photomultiplier tube 1 using the first holding portion 113 .

[0052] In addition, each of the pair of second holding portions 114 is in a flat plate shape in the first-stage dynode 11. With this structure, the first-stage dynode 11 can be easily and stably mounted on a support member provided in the tube body 2 of the photomultiplier tube 1 using the pair of second holding portions 114.

[0053] In the first-stage dynode 11, the bottom wall 111, the pair of side walls 112, the first holding portion 113 and the pair of second holding portions 114 are integrally formed of a metal plate. This structure can facilitate the manufacture and simplify the structure of the first-stage dynode 11.

[0054] In addition, in the first-stage dynode 11, the curvature radius R of each of the pair of side surfaces 112a is larger than 2 mm. According to this structure, in the photomultiplier tube 1, the electron transit time difference and the electron transit time dispersion can be appropriately suppressed.

[0055] In the first-stage dynode 11, when the width of the electron emission surface 11a in the X-axis direction is L and the curvature radius of each of the pair of side surfaces 112a is R, R≧0.1L holds. With this structure, the electron transit time difference and electron transit time dispersion can be appropriately suppressed in the photomultiplier tube 1.

[0056] Here, the reason why the transit time of the secondary electrons to the second-stage dynode 12 is unlikely to vary in the first-stage dynode 11 described above will be described in more detail.

[0057] Figure 6 1 is a three-dimensional diagram of the first-stage dynode 15 of the comparative example. Figure 6 As shown, the first-stage dynode 15 of the comparative example is different from the first-stage dynode 11 described above mainly in that the pair of side wall portions 112 are not provided and the pair of second retaining portions 114 intersect the bottom wall portion 111. In the first-stage dynode 15 of the comparative example, the bottom surface 111a constitutes an electron emission surface 15a opposite to an electron passage opening 15b.

[0058] In the first-stage dynode 15 of the comparative example, Figure 7 As shown in (a), the photoelectrons are incident on the central area of ​​the electron emission surface 15a through the orbit A1, and the secondary electrons emitted from the central area transit in a straight line through the orbit B1. In contrast, the photoelectrons are incident on the vicinity of the second holding portion 114 of the electron emission surface 15a through the orbit A2, and the secondary electrons emitted from the vicinity are repelled by the second holding portion 114 of the same potential and transit through the orbit B2. As a result, in the first-stage dynode 15 of the comparative example, a difference is likely to occur in the transit time of the secondary electrons to the second-stage dynode 12.

[0059] On the other hand, in the first-stage dynode 11, as Figure 7As shown in (b), the photoelectrons are incident on the central area of ​​the electron emission surface 11a through the orbit A1, and the secondary electrons emitted from the central area transit linearly on the orbit B1. In contrast, the photoelectrons are incident on the vicinity of the second holding portion 114 of the electron emission surface 11a (i.e., the side 112a) through the orbit A2, and the secondary electrons emitted from the vicinity are repelled by the second holding portion 114 of the same potential and transit on the orbit B2, but the transit distance of the photoelectrons incident on the vicinity and the transit distance of the secondary electrons emitted from the vicinity are shortened by the distance of the side 112a approaching the electron passage opening 11b. As a result, in the first-stage dynode 11 described above, it is difficult to produce a difference in the transit time of the secondary electrons to the second-stage dynode 12.

[0060] Next, the reason why the curvature radius R of each of the pair of side surfaces 112 a constituting the electron emission surface 11 a in the first-stage dynode 11 is more preferably larger than 2 mm will be described together with simulation results.

[0061] First, as simulation models, the first-stage dynodes of the first embodiment, the first-stage dynodes of the second embodiment, the first-stage dynodes of the third embodiment, and the first-stage dynodes of the fourth embodiment are prepared. Each first-stage dynode is equivalent to being formed by stamping a stainless steel plate with a thickness of 0.3 mm. In each first-stage dynode, the width L of the electron emission surface in the X-axis direction is set to 30.6 mm.

[0062] Each first-stage dynode has the same structure as the first-stage dynode 11 described above, and differs from each other only in the following points. That is, the radius of curvature R in the first-stage dynode of the first embodiment is set to 2 mm, the radius of curvature R in the first-stage dynode of the second embodiment is set to 4 mm, the radius of curvature R in the first-stage dynode of the third embodiment is set to 6 mm, and the radius of curvature R in the first-stage dynode of the fourth embodiment is set to 8 mm.

[0063] In a simulation equivalent to a situation in which the first-stage dynode of the first embodiment, the first-stage dynode of the second embodiment, the first-stage dynode of the third embodiment, and the first-stage dynode of the fourth embodiment are respectively installed in the same photomultiplier tube and the photomultiplier tube is operated under the same conditions, the electron transit time difference and the electron transit time dispersion in the X-axis direction are measured.

[0064] Figure 8 (a) is a diagram showing the electron transit time difference of the photomultiplier tube using the first-stage dynode of the first embodiment, Figure 8 (b) is a diagram showing the dispersion of electron transit time in this case. Fig. 9 (a) is a diagram showing the electron transit time difference of a photomultiplier tube using the first-stage dynode of the second embodiment, Fig. 9 (b) is a diagram showing the dispersion of electron transit time in this case. Fig.10 (a) is a diagram showing the electron transit time difference of a photomultiplier tube using the first-stage dynode of the third embodiment, Fig.10 (b) is a diagram showing the dispersion of electron transit time in this case. Fig.11 (a) is a diagram showing the electron transit time difference of a photomultiplier tube using the first-stage dynode of the fourth embodiment, Fig.11 (b) is a diagram showing the dispersion of electron transit time in this case.

[0065] like Figure 8 (a) Fig. 9 (a) Fig.10 (a) and Fig.11 As shown in (a), in the photomultiplier tubes using the first-stage dynode of the second embodiment, the first-stage dynode of the third embodiment, and the first-stage dynode of the fourth embodiment, the electron transit time difference in the X-axis direction is further uniformed at both ends in the X-axis direction compared to the photomultiplier tube using the first-stage dynode of the first embodiment. Figure 8 (b) Fig. 9 (b) Fig.10 (b) and Fig.11 As shown in (b), in the photomultiplier tubes using the first-stage dynode of the second embodiment, the first-stage dynode of the third embodiment, and the first-stage dynode of the fourth embodiment, the electron transit time dispersion in the X-axis direction is further reduced compared with the photomultiplier tube using the first-stage dynode of the first embodiment.

[0066] Based on the above simulation results, it can be said that in order to suppress the difference in electron transit time and the dispersion of electron transit time in the photomultiplier tube, it is more preferable that the curvature radius R of each of the pair of side surfaces constituting the electron emission surface is larger than 2 mm.

[0067] Next, the reason why it is more preferable that R≧0.1L holds true in the first-stage dynode 11 will be described together with simulation results.

[0068] According to the above simulation results, in the first-stage dynode (L: 30.6 mm, R: 2 mm) of the first embodiment, R≧0.1L does not hold, but in the first-stage dynode (L: 30.6 mm, R: 4 mm) of the second embodiment, the first-stage dynode (L: 30.6 mm, R: 6 mm) of the third embodiment, and the first-stage dynode (L: 30.6 mm, R: 8 mm) of the fourth embodiment, R≧0.1L holds. Therefore, even if the width L of the electron emission surface in the X-axis direction is not 30.6 mm, it can be said that in terms of suppressing the electron transit time difference and the electron transit time dispersion in the photomultiplier tube, it is more preferable that R≧0.1L holds in the first-stage dynode, which is confirmed by simulation.

[0069] First, as simulation models, the first-stage dynode of the first comparative example and the first-stage dynode of the fifth embodiment were prepared. Each first-stage dynode was formed by stamping a stainless steel plate with a thickness of 0.3 mm. In the first-stage dynode of the first comparative example, the width L of the electron emission surface in the X-axis direction was set to 34 mm, and the curvature radius R of each of a pair of side surfaces was set to 0 mm (i.e., the first-stage dynode of the first comparative example had the same curvature radius R as the first-stage dynode of the fifth embodiment). Figure 6 In the first-stage dynode of the fifth embodiment, the width L of the electron emission surface in the X-axis direction is set to 34 mm, and the curvature radius R of each of a pair of side surfaces is set to 5 mm (that is, the first-stage dynode of the fifth embodiment has the same structure as the first-stage dynode 11 described above).

[0070] In a simulation corresponding to the case where the first-stage dynodes of the first comparative example and the first-stage dynodes of the fifth embodiment are respectively mounted on the same photomultiplier tube and the photomultiplier tube is operated under the same conditions, the electron transit time difference in the X-axis direction is measured. Fig.12 (a) is a diagram showing the electron transit time difference of a photomultiplier tube using the first-stage dynode of the first comparative example, Fig.12 (b) is a diagram showing the electron transit time difference of the photomultiplier tube using the first-stage dynode of the fifth embodiment.

[0071] like Fig.12 As shown in (a) and (b), in the photomultiplier tube using the first-stage dynode of the fifth embodiment, the electron transit time difference in the X-axis direction is uniformed at both ends in the X-axis direction compared to the photomultiplier tube using the first-stage dynode of the first comparative example. According to the simulation results, it can be said that in terms of suppressing the electron transit time difference and the electron transit time dispersion in the photomultiplier tube, it is more preferable that R≧0.1L is established in the first-stage dynode.

[0072] [Modifications]

[0073] The present invention is not limited to the above-mentioned embodiments. 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. As an example, the first retaining portion 113 is not limited to a rectangular plate shape, and can also be in other shapes such as a semicircular plate shape.

[0074] In addition, the edge of each of the pair of second retaining portions 114 may be formed to protrude from the edge of the bottom wall portion 111 and the pair of side walls 112 , or may be formed to be recessed from the edge of the bottom wall portion 111 and the pair of side walls 112 .

[0075] In addition, the bottom wall 111, the pair of side walls 112, the first holding portion 113, and the pair of second holding portions 114 may not be formed in a plate shape. As an example, the bottom wall 111, the pair of side walls 112, the first holding portion 113, and the pair of second holding portions 114 are formed in a block shape, and the electron emission surface 11a may also be formed by cutting or the like.

[0076] According to the present invention, a first-stage dynode capable of suppressing electron transit time differences and electron transit time dispersion in a photomultiplier tube and a photomultiplier tube including the first-stage dynode can be provided.

Claims

1. A first-stage dynode for a photomultiplier tube, wherein: have: bottom wall part; A pair of side wall portions extending toward one side from both ends of the bottom wall portion in a predetermined direction; A first retaining portion extending outward from an end portion of the bottom wall portion; and a pair of second holding portions extending from both ends of the pair of side wall portions in the prescribed direction toward the one side, The electron emission surface facing one electron passage opening is formed by the bottom surface of the one side of the bottom wall portion and the pair of side surfaces of the one side of the pair of side walls. The bottom surface is a curved surface that is curved into a concave shape in a cross section perpendicular to the specified direction. Each of the pair of side surfaces is a curved surface that is curved in a concave shape in a cross section parallel to the predetermined direction.

2. The first-stage dynode according to claim 1, wherein: The first holding portion is in a flat plate shape.

3. The first-stage dynode according to claim 1, wherein: Each of the pair of second holding portions has a flat plate shape.

4. The first-stage dynode according to claim 2, wherein: Each of the pair of second holding portions has a flat plate shape.

5. The first-stage dynode according to any one of claims 1 to 4, wherein: The bottom wall portion, the pair of side wall portions, the first holding portion, and the pair of second holding portions are integrally formed of a metal plate.

6. The first-stage dynode according to any one of claims 1 to 4, wherein: The respective curvature radii of the pair of side surfaces are greater than 2 mm.

7. The first-stage dynode according to claim 5, wherein: The respective curvature radii of the pair of side surfaces are greater than 2 mm.

8. The first-stage dynode according to any one of claims 1 to 4, wherein: When the width of the electron emission surface in the predetermined direction is L and the radius of curvature of each of the pair of side surfaces is R, R≧0.1L holds.

9. The first-stage dynode according to claim 5, wherein: When the width of the electron emission surface in the predetermined direction is L and the radius of curvature of each of the pair of side surfaces is R, R≧0.1L holds.

10. The first-stage dynode according to claim 6, wherein: When the width of the electron emission surface in the predetermined direction is L and the radius of curvature of each of the pair of side surfaces is R, R≧0.1L holds.

11. The first-stage dynode according to claim 7, wherein: When the width of the electron emission surface in the predetermined direction is L and the radius of curvature of each of the pair of side surfaces is R, R≧0.1L holds.

12. A photomultiplier tube, wherein: have: Photocathode; Multi-stage multiplier; as well as anode, The multi-stage dynodes include a first-stage dynode and a second-stage dynode arranged on a predetermined surface. The first-stage dynode has: bottom wall part; A pair of side wall portions extending from both ends of the bottom wall portion in a predetermined direction perpendicular to the predetermined surface toward the photocathode side and the second-stage dynode side; a first holding portion extending from an end portion of the bottom wall portion on the photocathode side toward a side opposite to the second-stage dynode; as well as A pair of second holding portions extending from both ends of the pair of side wall portions in the predetermined direction toward the photocathode side and the second-stage dynode side; In the first-stage dynode, the bottom surface of the bottom wall on the photocathode side and the second-stage dynode side and the pair of side surfaces of the pair of side walls on the photocathode side and the second-stage dynode side constitute an electron emission surface opposite to an electron passage opening. The bottom surface is a curved surface that is curved into a concave shape in a cross section perpendicular to the specified direction. Each of the pair of side surfaces is a curved surface that is curved in a concave shape in a cross section parallel to the predetermined direction.

Images