First stage dynode and photomultiplier tube

Abstract

The first-stage dynode is a first-stage dynode used in a photomultiplier tube, and has a bottom wall portion and a pair of side walls extending to one side from both ends of the bottom wall portion in a predetermined direction. An electron emission surface is formed by a bottom surface of one side of the bottom wall portion and a pair of side surfaces of one side of the pair of side walls, and the pair of side surfaces are curved surfaces that are concavely curved in a cross section parallel to the predetermined 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 used in the photomultiplier tube, dynodes presenting various shapes have been proposed. For example, in Patent Document 1, as a first-stage dynode for the purpose of improving the collection efficiency of photoelectrons, a dynode presenting a teacup shape with a flat bottom surface is recorded. In the first-stage dynode recorded in Patent Document 1, the electron emission surface is composed of the flat bottom surface in the shape of a teacup. In addition, Patent Document 2 records that as a first-stage dynode for the purpose of obtaining a signal current that is independent of the incident position of the photocathode, a dynode having a funnel-shaped receiving interface for the incidence of photoelectrons is shaped. In the first-stage dynode recorded in Patent Document 2, the electron emission surface is composed of three planes and one curved surface connected in a concave curved 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.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: U.S. Patent No. 4112325

[0006] Patent Document 2: Japanese Patent Publication No. 8-12772 Summary of the invention

[0007] Technical issues to be solved by the invention

[0008] However, in the first-stage dynode described in Patent Document 1, since the electron emission surface is constituted by a flat bottom surface in 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, and as a result, the transit time of the secondary electrons from the first-stage dynode to the second-stage dynode may differ. In addition, in the first-stage dynode described in Patent Document 2, a pair of side surfaces are provided on both sides of the electron emission surface in a manner orthogonal to the electron emission surface, so that the secondary electrons emitted from the central region 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 may repel and transit on the side surface of the same potential, and as a result, the transit time of the secondary electrons from the first-stage dynode to the second-stage dynode may differ. Therefore, in the first-stage dynodes described in Patent Documents 1 and 2, it is expected to be difficult to suppress the electron transit time difference (CTTD: Cathode Transit Time Difference) and the electron transit time spread (TTS: Transit Time Spread) in the photomultiplier tube.

[0009] 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 having such a first-stage dynode.

[0010] Technical solutions to solve problems

[0011] The first-stage dynode of one aspect of the present invention is a first-stage dynode used in a photomultiplier tube, comprising: a bottom wall portion; and a pair of side wall portions extending to one side from both ends of the bottom wall portion in a specified direction, wherein an electron emission surface is constituted 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, and the pair of side surfaces are curved surfaces that are concavely curved in a cross section parallel to the specified direction.

[0012] In the first-stage dynode, a pair of side surfaces are curved surfaces that are concavely curved in a cross section parallel to a specified direction. Therefore, the further each side surface moves away from the center of the electron emission surface in the specified 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 are also shortened by the amount that each side surface is close to an electron passage opening. Thus, according to the first-stage dynode, the electron transit time difference and the electron transit time dispersion can be suppressed in the photomultiplier tube.

[0013] In one aspect of the present invention, in the first-stage dynode, the curvature radius of each of the pair of side surfaces may be greater than 2 mm. According to this structure, the electron transit time difference and the electron transit time dispersion can be well suppressed in the photomultiplier tube.

[0014] In one aspect of the present invention, in the first-stage dynode, 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 holds. With this structure, the electron transit time difference and electron transit time dispersion can be well suppressed in the photomultiplier tube.

[0015] In one aspect of the present invention, the bottom surface of the first-stage dynode may be a curved surface that is concavely curved in a cross section perpendicular to a predetermined direction. According to this structure, it is easy to adjust the transit time of secondary electrons from the first-stage dynode to the second-stage dynode. As a result, the electron transit time difference and the electron transit time dispersion can be more reliably suppressed in the photomultiplier tube.

[0016] In one aspect of the present invention, in the first-stage dynode, the electron emission surface may be opposite to one electron passage opening. According to this structure, the photoelectrons incident on the electron emission surface and the secondary electrons emitted from the electron emission surface all pass through one (i.e., the same) electron passage opening, so the dependence of the electron transit time on the incident position of the photoelectron becomes smaller. As a result, the electron transit time difference and the electron transit time dispersion can be more reliably suppressed in the photomultiplier tube.

[0017] A photomultiplier tube according to one aspect of the present invention comprises a photocathode, a multi-stage dynode and an anode, the multi-stage dynode comprising a first-stage dynode and a second-stage dynode arranged on a prescribed plane, the first-stage dynode comprising: a bottom wall portion; and a pair of side wall portions extending from both ends of the bottom wall portion in a prescribed direction perpendicular to the prescribed plane toward the photocathode side and the second-stage dynode side, in the first-stage dynode, an electron emission surface is constituted 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 wall portions, and the pair of side surfaces are curved surfaces that are concavely curved in a cross section parallel to the prescribed direction.

[0018] According to this photomultiplier tube, for the reasons described above, it is possible to suppress the electron transit time difference and the electron transit time dispersion.

[0019] Effects of the Invention

[0020] According to the present invention, it is possible 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 having such a first-stage dynode. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a cross-sectional view of a photomultiplier tube according to one embodiment.

[0022] Figure 2 yes Figure 1 A cross-sectional view of the electron multiplier section and anode is shown.

[0023] Figure 3 This is a perspective view of a first-stage dynode according to one embodiment.

[0024] Figure 4 is along Figure 3 A cross-sectional view of the first-stage dynode along line IV-IV is shown.

[0025] Figure 5 is along Figure 3 The cross-sectional view of the first-stage dynode along line VV is shown.

[0026] Figure 6 It is a perspective view of the first-stage dynode of the comparative example.

[0027] Figure 7 It is a schematic diagram used to illustrate the transit orbit of an electron.

[0028] Figure 8 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 first embodiment.

[0029] Fig. 9 This 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 second embodiment.

[0030] 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.

[0031] 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.

[0032] Fig.12 It 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

[0033] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, the same or corresponding parts are denoted by the same reference numerals in each figure, and repeated description is omitted.

[0034] [Structure of photomultiplier tube]

[0035] 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 multiplying section 6 and an anode 7. The electron multiplying section 6 has a multi-stage (for example, 10-stage) dynode 10. In the following description, the side on which light is incident on the photomultiplier tube 1 is referred to as the "front", and the opposite side is referred to as the "rear". 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) on which 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".

[0036] 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 sphere having 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 integrally formed into a glass sphere. 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.

[0037] The photocathode 3 is disposed on the inner surface of the tube body 2. Specifically, the photocathode 3 is disposed on the inner surface of the front half of the oblate spherical portion 2a. The photocathode 3 constitutes a transmissive photoelectric surface, for example, formed of a 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 due to the photoelectric effect. As an example, the outer diameter of the photocathode 3 when viewed from the front side (i.e., 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 .

[0038] The accelerating electrode 4 is arranged at a position behind 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 at a position behind 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.

[0039] The electron multiplier section 6 is arranged at a position further back than the focusing electrode 5. The multi-stage dynodes 10 are arranged on a 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 multi-stage dynodes 10. The electron multiplier section 6, i.e., the multi-stage dynodes 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 in the form of a signal current.

[0040] 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 body 2. The support member is mounted on a tube seat (not shown) that seals the rear end of the cylindrical portion 2b. In addition, the tube seat is provided with wiring for voltage application and wiring for signal current output in the form of tube seat pins or cables.

[0041] [Structure of the Electron Multiplying Section]

[0042] like Figure 2 As shown, in the electron multiplying section 6, the multi-stage 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 collectively referred to as the 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 collectively referred to as the electron emission surface 10a.

[0043] The first-stage dynode 11 has an electron emission surface 11a and a photocathode 3 (see Figure 1 ) and the electron emission surface 12a of the second-stage dynode 12 are arranged opposite to each other. The second-stage dynode 12 is arranged such 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. Each dynode 10 after the third stage except the final-stage dynode 10 is similarly arranged such 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 arranged such 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.

[0044] 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 (details will be described later). The electron emission surface 11a of the first-stage dynode 11 is composed of a bottom surface on the photocathode 3 side and the second-stage dynode 12 side of the bottom wall 111 and a pair of side surfaces on the photocathode 3 side and the second-stage dynode 12 side of the pair of side walls 112.

[0045] 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 bottom wall portion 121 on the first-stage dynode 11 side and the third-stage dynode 13 side. 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.

[0046] 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 bottom wall portion 131 on the second-stage dynode 12 side and the fourth-stage dynode 10 side. 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.

[0047] A pair of electron lens forming electrodes 14 are provided in the region 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 in 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 in 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.

[0048] [Structure of the first-stage dynode]

[0049] like Figure 3 , Figure 4 and Figure 5 As shown, the first-stage dynode 11 has a bottom wall portion 111, a pair of side wall portions 112, a first holding portion 113, and a pair of second holding portions 114. The pair of side wall portions 112 extend from both ends of the bottom wall portion 111 in the X-axis direction (a predetermined direction perpendicular to a predetermined surface) toward 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 (photocathode 3 side (refer to Figure 1 and Figure 2 )) is directed outward (on the opposite side of the second-stage dynode (refer to 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.

[0050] The first holding portion 113 is formed into a flat plate (e.g., a rectangular plate) parallel to the XY plane. The pair of second holding portions 114 are respectively formed into flat plate shapes parallel to the YZ plane. The first-stage dynode 11 is mounted on a support member provided in the tube body 2 via the first holding portion 113 and the pair of second holding portions 114.

[0051] 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.

[0052] The bottom surface 111a constituting the electron emission surface 11a is a curved surface that is concavely curved 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, and composite surfaces thereof) with the X-axis direction as the length direction (the height direction of the cylinder). The pair of side surfaces 112a constituting the electron emission surface 11a are curved surfaces that are concavely curved in a cross section parallel to the X-axis direction (especially referring to Figure 5 ). In this embodiment, each side surface 112a is equivalent to a chamfered surface when 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.

[0053] 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 (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 larger than 2 mm. As an example, the width L of the electron emission surface 11a in the X-axis direction is larger than 20 mm and smaller than 50 mm.

[0054] The first-stage dynode 11 formed into the above shape is integrally formed from a metal plate (e.g., a stainless steel plate with a thickness of about 0.3 mm). That is, the bottom wall 111, a pair of side walls 112, a first holding portion 113, and a pair of second holding portions 114 are integrally formed from a metal plate. Here, integrally formed from a metal plate means that the metal plate is formed by subjecting it to plastic working such as press working.

[0055] [Function and Effect]

[0056] In the first-stage dynode 11, a pair of side surfaces 112a constituting the electron emission surface 11a are curved surfaces that are concavely curved in a cross section parallel to the X-axis direction. Therefore, the further each side surface 112a is away 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 by the amount that each side surface 112a is close to an electron passage opening 11b. Thus, 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.

[0057] 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 possible to form the electron emission surface only by the bottom surface 111a without providing a pair of side surfaces 112a, so that the width of the electron emission surface in the X-axis direction becomes larger. However, in the first-stage dynode having such an electron emission surface, since its size becomes larger, the outer diameter of the cylindrical portion 2b of the tube body 2 has to become larger, and it is difficult to ensure the water pressure resistance of the tube body 2. Furthermore, when the size of the first-stage dynode becomes larger, it is difficult to form the first-stage dynode by plastic processing such as pressing the metal plate. According to the first-stage dynode 11 described above, it is possible to suppress the size of the first-stage dynode 11 from increasing, and to suppress the electron transit time difference and the electron transit time dispersion in the photomultiplier tube 1 .

[0058] In addition, in the first-stage dynode 11 , the curvature radius R of each of the pair of side surfaces 112 a is larger than 2 mm. According to this structure, the electron transit time difference and the electron transit time dispersion can be suppressed well in the photomultiplier tube 1 .

[0059] 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 well suppressed in the photomultiplier tube 1.

[0060] In addition, in the first-stage dynode 11, the bottom surface 111a constituting the electron emission surface 11a is a curved surface that is concavely curved in a cross section perpendicular to the X-axis direction. According to this structure, it is easy to adjust the transit time of secondary electrons from the first-stage dynode 11 to the second-stage dynode 12. As a result, the electron transit time difference and the electron transit time dispersion can be suppressed more reliably in the photomultiplier tube 1.

[0061] In addition, in the first-stage dynode 11, the electron emission surface 11a is opposite to one electron passage opening 11b. According to this structure, 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, so the dependence of the electron transit time on the incident position of the photoelectron becomes smaller. As a result, the electron transit time difference and the electron transit time dispersion can be suppressed in the photomultiplier tube 1.

[0062] Here, the reason why the transit time of the secondary electrons to the second-stage dynode 12 in the first-stage dynode 11 is unlikely to vary will be described in more detail.

[0063] Figure 6 FIG. 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 a pair of side wall portions 112 are not provided, and a pair of second retaining portions 114 intersects with 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.

[0064] In the first stage dynode 15 of the comparative example, Figure 7 As shown in (a), secondary electrons emitted from the central region of the electron emission surface 15a due to the incident photoelectrons on the orbit A1 travel in a straight line along the orbit B1. On the contrary, secondary electrons emitted from the vicinity of the second holding portion 114 of the electron emission surface 15a due to the incident photoelectrons on the orbit A2 are repelled by the second holding portion 114 of the same potential and travel along the orbit B2. As a result, in the first-stage dynode 15 of the comparative example, the transit time of the secondary electrons to the second-stage dynode 12 is likely to differ.

[0065] On the other hand, in the first stage dynode 11, Figure 7 As shown in (b), secondary electrons emitted from the central region of the electron emission surface 11a due to the photoelectrons incident on the orbit A1 travel in a straight line along the orbit B1. In contrast, secondary electrons emitted from the vicinity of the second holding portion 114 of the electron emission surface 11a (i.e., the side 112a) due to the photoelectrons incident on the orbit A2 travel in a straight line along the orbit B1, are repelled by the second holding portion 114 of the same potential and travel along 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 both shortened by the amount that the side 112a approaches the electron passage opening 11b. As a result, the transit time of the secondary electrons from the first-stage dynode 11 to the second-stage dynode 12 is less likely to differ.

[0066] 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 preferably larger than 2 mm will be described based on simulation results.

[0067] First, as simulation models, 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 were prepared. Each first-stage dynode was equivalent to a structure formed by applying a press process to 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 was set to 30.6 mm.

[0068] Each first-stage dynode has the same structure as the first-stage dynode 11, and differs only in the following aspects: that is, the first-stage dynode of the first embodiment has a curvature radius R of 2 mm, the first-stage dynode of the second embodiment has a curvature radius R of 4 mm, the first-stage dynode of the third embodiment has a curvature radius R of 6 mm, and the first-stage dynode of the fourth embodiment has a curvature radius R of 8 mm.

[0069] In a simulation of 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 tubes are operated under the same conditions, the electron transit time difference and the electron transit time dispersion in the X-axis direction are measured.

[0070] 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 graph showing the dispersion of electron transit time at this time. Fig. 9 (a) is a diagram showing the electron transit time difference of the photomultiplier tube using the first-stage dynode of the second embodiment, Fig. 9 (b) is a graph showing the dispersion of electron transit time at this time. Fig.10 (a) is a diagram showing the electron transit time difference of the photomultiplier tube using the first-stage dynode of the third embodiment, Fig.10 (b) is a graph showing the dispersion of electron transit time at this time. Fig.11 (a) is a diagram showing the electron transit time difference of the photomultiplier tube using the first-stage dynode of the fourth embodiment, Fig.11 (b) is a graph showing the dispersion of electron transit time at this time.

[0071] like Figure 8 (a) Fig. 9 (a) Fig.10 (a) and Fig.11As 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.

[0072] According to the above simulation results, from the perspective of suppressing the electron transit time difference and electron transit time dispersion 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.

[0073] Next, the reason why R ≥ 0.1L is more preferably satisfied in the first-stage dynode 11 will be described based on simulation results.

[0074] According to the above simulation results, R≥0.1L does not hold in the first-stage dynode (L: 30.6mm, R: 2mm) of the first embodiment, but R≥0.1L holds in the first-stage dynode (L: 30.6mm, R: 4mm) of the second embodiment, the first-stage dynode (L: 30.6mm, R: 6mm) of the third embodiment, and the first-stage dynode (L: 30.6mm, R: 8mm) of the fourth embodiment. Therefore, it was confirmed through simulation that when the width L of the electron emission surface in the X-axis direction is not 30.6mm, it is more preferable that R≥0.1L holds in the first-stage dynode from the perspective of suppressing the electron transit time difference and the electron transit time dispersion in the photomultiplier tube.

[0075] First, as simulation models, the first-stage dynode of the first comparative example and the first-stage dynode of the fifth embodiment are prepared. Each first-stage dynode is equivalent to a structure formed by pressing 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 is 34 mm, and the curvature radius R of each of a pair of side surfaces is 0 mm (that is, the first-stage dynode of the first comparative example has the same curvature radius as that of the 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 radius of curvature 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).

[0076] In a simulation equivalent to the case where the first-stage dynode of the first comparative example and the first-stage dynode 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 the 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.

[0077] 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, from the perspective 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 in the first-stage dynode.

[0078] [Modifications]

[0079] The present invention is not limited to the above-mentioned embodiments. For example, the constituent materials and shapes are not limited to the above-mentioned materials and shapes, and various materials and shapes can be used. As an example, the first holding portion 113 is not limited to a rectangular plate shape, and can also be formed into other shapes such as a semicircular plate shape. In addition, the first-stage dynode 11 may not have the first holding portion 113.

[0080] In addition, the edge of each of the pair of second holding portions 114 may be formed so as to protrude from the edge of one of the bottom wall portion 111 and the pair of side wall portions 112, or may be formed so as to be recessed from the edge of one of the bottom wall portion 111 and the pair of side wall portions 112. In addition, the first-stage dynode 11 may not have the pair of second holding portions 114. In this case, for example, a metal film having the same shape as the second holding portion 114 is formed in advance by evaporation or the like on the surface of each of the pair of substrates sandwiching the first-stage dynode 11 in the X-axis direction, and the metal film is arranged in the portion where the second holding portion 114 is missing.

[0081] Alternatively, a plurality of electron passage openings may be formed facing the electron emission surface 11a so that photoelectrons incident on the electron emission surface 11a and secondary electrons emitted from the electron emission surface 11a pass through different electron passage openings. Alternatively, the bottom surface 111a constituting the electron emission surface 11a may include a flat region.

[0082] 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 may be formed in a block shape, and the electron emission surface 11a is formed by cutting or the like.

[0083] Description of Reference Numerals

[0084] 1...photomultiplier tube, 3...photocathode, 7...anode, 10...dynode, 11...first-stage dynode, 11a...electron emission surface, 11b...electron passage opening, 12...second-stage dynode, 111...bottom wall, 111a...bottom surface, 112...side wall, 112a...side surface.

Claims

1. A first-stage dynode for a photomultiplier tube, characterized in that: include: bottom wall part; and a pair of side wall portions extending to one side from both ends of the bottom wall portion, The electron emission surface 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 wall portions. The pair of side surfaces are respectively curved concavely in a cross section, and the cross section is a plane intersecting the bottom surface and the pair of side surfaces and extending in the opposite directions of the two end portions. When the width of the electron emission surface in the opposing direction is L and the radius of curvature of each of the pair of side surfaces is R, R≥0.1L holds.

2. The first-stage dynode according to claim 1, characterized in that: The curvature radius of each of the pair of side surfaces is greater than 2 mm.

3. The first-stage dynode according to claim 1, characterized in that: The bottom surface is a curved surface that is concavely curved in a cross section perpendicular to the opposing direction.

4. The first-stage dynode according to claim 2, characterized in that: The bottom surface is a curved surface that is concavely curved in a cross section perpendicular to the opposing direction.

5. The first-stage dynode according to any one of claims 1 to 4, characterized in that: The electron emission surface faces one electron passage opening.

6. A photomultiplier tube, characterized in that: It includes a photocathode, a multi-stage dynode and an 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: a bottom wall portion; and A pair of side wall portions extending from both ends of the bottom wall portion toward the photocathode side and the second-stage dynode side, In the first-stage dynode, the electron emission surface is formed by the bottom surface of the bottom wall portion 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. The pair of side surfaces are respectively curved concavely in a cross section, and the cross section is a plane intersecting the bottom surface and the pair of side surfaces and extending in a relative direction of the two end portions, the relative direction being perpendicular to the predetermined surface. When the width of the electron emission surface in the opposing direction is L and the radius of curvature of each of the pair of side surfaces is R, R≥0.1L holds.

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