Photoelectron multiplier

Abstract

To provide a photoelectron multiplier capable of improving time characteristics due to an anode.SOLUTION: A photoelectron multiplier 1 includes: a photocathode 3; ten dynodes 10 that multiply electrons emitted from the photocathode 3; and an anode 7 that collects electrons multiplied by the dynode 10. The anode 7 has an electron collection surface 73 that faces a secondary electron emission surface 11j of a tenth dynode 10j and extends along the secondary electron emission surface 11j. The anode 7 has no electron passage hole on the electron path from the ninth dynode 10i to the tenth dynode 10j.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] A photomultiplier tube is known that includes a photocathode, N stages of dynodes (N is an integer of 2 or more) that multiply electrons emitted from the photocathode, and an anode that collects the electrons multiplied by the dynodes (see, for example, Patent Document 1). In such a photomultiplier tube, the anode includes a mesh structure, and the mesh structure has a plurality of electron passing holes on an electron path from the (N-1)th stage dynode to the Nth stage dynode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 7-245078 Summary of the Invention [Problem to be solved by the invention]

[0004] In the photomultiplier tubes described above, electrons are less likely to collide with the anode, and they may wander before striking the anode. In this case, the time characteristics of the signal waveform output from the anode, such as the fall time (the time it takes for the output pulse crest value to return from 90% to 10% of its peak value), may deteriorate.

[0005] The present disclosure has been made in view of the above circumstances, and has an object to provide a photomultiplier tube that can improve the time characteristics attributable to the anode. [Means for solving the problem]

[0006] The photomultiplier tube disclosed herein is [1] "a photomultiplier tube comprising a photocathode, N stages of dynodes (N is an integer of 2 or more) that multiply electrons emitted from the photocathode, and an anode that collects electrons multiplied by the dynodes, wherein the anode faces the secondary electron emission surface of the Nth stage dynode and has an electron collection surface at least a portion of which extends along the secondary electron emission surface, and which does not have an electron passing hole on the electron path from the N-1th stage dynode to the Nth stage dynode."

[0007] In this photomultiplier tube, at least a portion of the anode facing the secondary electron emission surface of the Nth dynode extends along the secondary electron emission surface. This anode does not have an electron passing hole on the electron path from the (N-1)th dynode to the Nth dynode. This prevents electrons from straying due to the electron passing hole in the anode and makes it easier for electrons to be incident on the anode from the Nth dynode. As a result, it is possible to improve the time characteristics attributable to the anode.

[0008] The photomultiplier tube of the present disclosure may be [2] "the photomultiplier tube according to [1], wherein the anode is disposed between the (N-1)th dynode and the Nth dynode." In this case, it becomes easier to dispose the anode close to the Nth dynode, and the photomultiplier tube can be configured to increase the electric field strength between the anode and the Nth dynode.

[0009] The photomultiplier tube of the present disclosure may be [3] "the photomultiplier tube according to [1] or [2], which is provided with a wall portion disposed between the N-1th dynode and the anode, for blocking electrons from being incident on the anode from the N-1th dynode." In this case, it is possible to prevent electrons from skipping the Nth dynode and moving from the N-1th dynode to the anode.

[0010] The photomultiplier tube of the present disclosure may be [4] "the photomultiplier tube according to [3], wherein a potential equal to or greater than the potential of the N-1th dynode is applied to the wall portion." In this case, the wall portion can effectively block electrons from being incident on the anode from the N-1th dynode.

[0011] The photomultiplier tube of the present disclosure may be [5] "the photomultiplier tube according to [3] or [4], wherein the wall portion is integrally formed with the Nth stage dynode." In this case, the wall portion can be easily provided by utilizing the Nth stage dynode.

[0012] The photomultiplier tube of the present disclosure may be [6] "a photomultiplier tube according to any one of [3] to [5], wherein the wall portion is disposed between the N-1th dynode and the Nth dynode, and electrons emitted from the N-1th dynode pass through the space between the wall portion and the Nth dynode and are incident on the Nth dynode." In this case, it is possible to cause electrons from the N-1th dynode to be incident on the Nth dynode by utilizing the space between the wall portion and the Nth dynode.

[0013] The photomultiplier tube of the present disclosure may be [7] "the photomultiplier tube according to any one of [1] to [6], which is provided with an extraction electrode disposed between the anode and the Nth dynode, for facilitating extraction of electrons from the Nth dynode." In this case, extraction of electrons from the Nth dynode can be promoted, improving output linearity (dynamic range).

[0014] The photomultiplier tube of the present disclosure may be [8] "the photomultiplier tube according to [7], wherein a potential higher than the potential of the Nth dynode is applied to the extraction electrode." In this case, the extraction electrode can efficiently extract electrons.

[0015] The photomultiplier tube of the present disclosure may be [9] "the photomultiplier tube according to [7] or [8], in which the extraction electrode is a mesh electrode." In this case, the mesh electrode can be used to promote extraction of electrons from the Nth dynode. [Effects of the Invention]

[0016] According to the present disclosure, it is possible to provide a photomultiplier tube capable of improving the time characteristics attributable to the anode. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a cross-sectional view of a photomultiplier tube according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing the electron multiplier section and the anode of FIG. [Figure 3] FIG. 3 is an enlarged perspective view of a part of FIG. [Figure 4] FIG. 4 is a perspective view showing the electron multiplier section and the anode of FIG. [Figure 5] FIG. 5 is a diagram showing the electron multiplier section and the anode of FIG. 1 when viewed from the Y direction. [Figure 6] FIG. 6 is a perspective view showing a part of the electron multiplier unit of FIG. [Figure 7] FIG. 7 is a diagram showing a part of the electron multiplier unit of FIG. 1 when viewed from the Y direction. [Figure 8] Figure 8(a) is a simulation result showing the trajectory of electrons from the eighth dynode to the ninth dynode in an electron multiplier section according to a comparative example. Figure 8(b) is a simulation result showing the trajectory of electrons from the ninth dynode to the tenth dynode in an electron multiplier section according to a comparative example. Figure 8(c) is a simulation result showing the trajectory of electrons from the tenth dynode to the anode in an electron multiplier section according to a comparative example. [Figure 9]Fig. 9(a) is a simulation result showing the trajectory of electrons from the eighth dynode to the ninth dynode in an electron multiplier section according to an embodiment. Fig. 9(b) is a simulation result showing the trajectory of electrons from the ninth dynode to the tenth dynode in an electron multiplier section according to an embodiment. Fig. 9(c) is a simulation result showing the trajectory of electrons from the tenth dynode to the anode in an electron multiplier section according to an embodiment. [Figure 10] 10(a) is a graph showing the simulation results of the rise time of the comparative example and the example, and FIG. 10(b) is a graph showing the simulation results of the fall time of the comparative example and the example. [Figure 11] Fig. 11(a) is a graph showing the measured values ​​of the output signal from the anode in the comparative example, and Fig. 11(b) is a graph showing the measured values ​​of the output signal from the anode in the example. [Figure 12] Fig. 12(a) is a perspective view showing a cross section of a part of an electron multiplier section according to a first modified example, and Fig. 12(b) is a perspective view showing a cross section of a part of an electron multiplier section according to a second modified example. [Figure 13] FIG. 13 is a perspective view showing a part of an electron multiplier section according to a third modified example. [Figure 14] FIG. 14 is a diagram showing a part of the electron multiplier section according to the third modified example when viewed from the Y direction. [Figure 15] FIG. 15 is a perspective view showing a part of an electron multiplier section according to a fourth modified example. [Figure 16] FIG. 16 is a diagram showing a part of the electron multiplier section according to the fourth modified example when viewed from the Y direction. [Figure 17] FIG. 17 is a diagram showing a part of the electron multiplier section according to the fourth modified example when viewed from the X direction. [Figure 18] FIG. 18 is a cross-sectional view showing an electron multiplier section according to a fifth modified example. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, the embodiments will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and duplicated explanations will be omitted.

[0019] As shown in FIG. 1 , the photomultiplier tube 1 comprises a tubular body 2, a photocathode 3, a focusing electrode 5, an electron multiplier section 6, an anode 7, and a partition plate (wall section) 20. The electron multiplier section 6 has N stages of so-called line-focus dynodes 10 (N is an integer equal to or greater than 2). In the following description, the side of the photomultiplier tube 1 from which light is incident will be referred to as the "front," and the opposite side will be referred to as the "rear." Furthermore, the tube axis (central axis) of the tubular body 2 will be referred to as the "Z-axis," an axis perpendicular to the plane (plane including the Z-axis) on which the multiple stages of dynodes 10 are arranged will be referred to as the "X-axis," and an axis perpendicular to the Z-axis and X-axis will be referred to as the "Y-axis."

[0020] The tubular body 2 accommodates a photocathode 3, a focusing electrode 5, an electron multiplier section 6, and an anode 7 in an evacuated space. The tubular body 2 is a light-transmitting glass bulb. The tubular body 2 has an oblate spherical portion 2a whose central axis is the Z axis, and a cylindrical portion 2b located behind the oblate spherical portion 2a and whose central axis is the Z axis. The oblate spherical portion 2a and the cylindrical portion 2b are integrally formed as a single glass bulb.

[0021] The photocathode 3 is provided on the inner surface of the tube body 2. Specifically, the photocathode 3 is provided on the inner surface of the front half of the oblate spheroid portion 2a. The photocathode 3 constitutes a transmission-type photocathode and is made of, for example, a potassium antimonide-cesium (bialkali) material or other well-known material. When light is incident on the photocathode 3 from the front side, electrons (photoelectrons) are emitted from the photocathode 3 to the rear side due to the photoelectric effect.

[0022] The focusing electrode 5 is disposed behind the photocathode 3. A predetermined voltage is applied to the focusing electrode 5. The focusing electrode 5 is configured to focus the electrons emitted from the photocathode 3 toward the electron multiplier section 6.

[0023] The electron multiplier section 6 is located rearward of the focusing electrode 5. The electron multiplier section 6, i.e., the Nth stage dynode 10, multiplies the electrons emitted from the photocathode 3 (secondary electron multiplication). The dynode 10 is made of, for example, stainless steel or the like. The dynode 10 is an elongated member with its longitudinal direction in the X direction. The dynode 10 includes a bottom wall 13B (see FIG. 6) having an arc-shaped cross section along the YZ plane (a plane including the Y and Z axes), and side walls 13W (see FIG. 6) provided at both ends of the bottom wall 13B in the X direction. The side walls 13W of the dynode 10 are provided with holding pieces (not shown) that protrude outward in the X direction to hold the dynode 10 within the tubular body 2.

[0024] Each of the N stages of dynodes 10 has a secondary electron emission surface 11 that multiplies electrons. The secondary electron emission surface 11 emits secondary electrons in response to incident electrons. The secondary electron emission surface 11 is provided on the inner surface of the bottom wall 13B of the dynode 10, and has an arc-shaped cross section along the YZ plane. In other words, the cross section of the dynode 10 that intersects with its longitudinal direction has an arc-shaped shape. A different potential is applied to each dynode 10.

[0025] Anode 7 is disposed opposite the Nth dynode 10, which is the final stage. A predetermined voltage is applied to anode 7. Anode 7 collects electrons multiplied by the Nth dynode 10. Anode 7 is configured to output the electrons emitted from the Nth dynode 10 as a signal current. In other words, anode 7 is an electrode that has the function of collecting the electrons that can be used substantially as a signal current.

[0026] The focusing electrode 5, each dynode 10 of the electron multiplier section 6, and the anode 7 are supported by a support member (not shown) such as an insulating support substrate within the tubular body 2. The support member is attached to a stem (not shown) that seals the rear end of the cylindrical portion 2b. The stem is provided with wiring for applying voltage and wiring for outputting signal current as stem pins or cables.

[0027] 1 and 2, the electron multiplier section 6 of this embodiment has ten stages of dynodes 10 (that is, N=10). The ten stages of dynodes 10 include, from the front side, or upstream side, to the rear side, or downstream side, a first stage dynode 10a, a second stage dynode 10b, a third stage dynode 10c, a fourth stage dynode 10d, a fifth stage dynode 10e, a sixth stage dynode 10f, a seventh stage dynode 10g, an eighth stage dynode 10h, a ninth stage dynode 10i, and a tenth stage dynode 10j.

[0028] The i-th dynode 10 (i is an integer greater than or equal to 2 and less than or equal to N) is arranged to face the i-1-th dynode 10. In other words, the N-th dynode 10 is arranged so that the secondary electron emission surfaces 11, 11 between adjacent dynodes 10, 10 face each other. A higher potential is applied to the i-th dynode 10 than to the i-1-th dynode 10. A negative potential, for example the same as that of the focusing electrode 5, is applied to the first-stage dynode 10a. The N-th dynodes 10 are arranged so that their centres in the X direction are aligned.

[0029] 2 and 3, the anode 7 includes a bottom wall 71 having an arc-shaped cross section along the YZ plane, and side walls 72 provided at both ends of the bottom wall 71 in the X direction. The outer surface of the bottom wall 71 has an electron collecting surface 73. The electron collecting surface 73 faces the secondary electron emission surface 11j of the tenth dynode 10j, and at least a portion of the electron collecting surface 73 extends along the secondary electron emission surface 11j. In the example shown, the electron collecting surface 73 has an arc-shaped cross section along the YZ plane.

[0030] The anode 7 is disposed between the 9th-stage dynode 10i and the 10th-stage dynode 10j. The anode 7 is disposed so that a portion of it extends into the 10th-stage dynode 10j. This brings the electron collecting surface 73 into close proximity with the secondary electron emitting surface 11j. The anode 7 does not have electron passing holes on the electron path from the 9th-stage dynode 10i to the 10th-stage dynode 10j. The anode 7 is a solid, plate-shaped metal member. The electron passing holes are formed by holes that allow electrons to pass through, and include, for example, a mesh structure, a honeycomb structure, and a multi-hole structure. In other words, the anode 7 does not have at least one of a mesh structure, a honeycomb structure, and a multi-hole structure on the electron path from the 9th-stage dynode 10i to the 10th-stage dynode 10j. A potential equal to or higher than the potential of the 10th-stage dynode 10 is applied to the anode 7. The potential of the anode 7 is, for example, 0 V.

[0031] The partition plate 20 is disposed between the ninth-stage dynode 10i and the anode 7. The partition plate 20 blocks electrons from the ninth-stage dynode 10i from entering the anode 7 and electrons from the eighth-stage dynode 10h from entering the anode 7. The partition plate 20 is disposed between the ninth-stage dynode 10i and the tenth-stage dynode 10j. The partition plate 20 is a flat member extending in the X direction. The width of the partition plate 20 in the X direction is greater than the width of the dynode 10 in the X direction and is also greater than the width of the anode 7 in the X direction (see FIG. 5). The partition plate 20 is formed from, for example, stainless steel.

[0032] A potential equal to or greater than the potential of the ninth-stage dynode 10i is applied to the partition plate 20. For example, a potential equal to the potential of the tenth-stage dynode 10j is applied to the partition plate 20. The partition plate 20 is configured separately from the tenth-stage dynode 10j. For example, as shown in Figure 3, electrons emitted from the ninth-stage dynode 10i pass through the space K between the end of the partition plate 20 on the tenth-stage dynode 10j side and the tenth-stage dynode 10j, and are incident on the tenth-stage dynode 10j (see the dashed arrow in the figure).

[0033] 2, 4, 5, 6 and 7, the sidewall 13W of the dynode 10 extends along the YZ plane, and the width of the dynode 10 in the X direction (hereinafter, the width in the X direction will also be referred to simply as "width") is constant. The width of the edge E of the mth dynode 10 (m is an integer of 2 or more and N or less) facing the (m-1)th dynode 10 is smaller than the width of the (m-1)th dynode 10. In other words, the width of the edge E of the mth dynode 10 facing the (m-1)th dynode 10 has a different structure (hereinafter, also referred to as a "nested structure") than the width of the (m-1)th dynode 10. In this embodiment, the mth dynode 10 refers to a plurality of different odd-numbered dynodes 10 (excluding the first dynode).

[0034] Specifically, the width of the third-stage dynode 10c is smaller than the width of the second-stage dynode 10b. The width of the fifth-stage dynode 10e is smaller than the width of the fourth-stage dynode 10d. The width of the seventh-stage dynode 10g is smaller than the width of the sixth-stage dynode 10f. The width of the ninth-stage dynode 10i is smaller than the width of the eighth-stage dynode 10h. The widths of the different odd-numbered dynodes 3, 5, 7, and 9, 10c, 10e, 10g, and 10i, are all equal. The widths of the different even-numbered dynodes 2, 4, 6, 8, and 10, 10b, 10d, 10f, 10h, and 10j, are all equal.

[0035] In the X direction, the edge E of the mth dynode 10 is included inside the (m-1)th dynode 10. That is, in the X direction, one side wall 13W of the mth dynode 10 is located more inside than one side wall 13W of the (m-1)th dynode 10, and the other side wall 13W of the mth dynode 10 is located more inside than the other side wall 13W of the (m-1)th dynode 10. In this embodiment, in the X direction, the third dynode 10c is included inside the second dynode 10b, the fifth dynode 10e is included inside the fourth dynode 10d, the seventh dynode 10g is included inside the sixth dynode 10f, and the ninth dynode 10i is included inside the eighth dynode 10h.

[0036] In the X direction, the width of the first-stage dynode 10a is greater than the widths of the second- to tenth-stage dynodes 10b to 10j. In the X direction, the second- to tenth-stage dynodes 10b to 10j are included inside the first-stage dynode 10a. In other words, in the X direction, one ends of the second- to tenth-stage dynodes 10b to 10j are located more inside than one end of the first-stage dynode 10a, and the other ends of the second- to tenth-stage dynodes 10b to 10j are located more inside than the other end of the first-stage dynode 10a.

[0037] When viewed from the X direction, the edge E of the mth dynode 10 penetrates into the (m-1)th dynode 10. Specifically, when viewed from the X direction, the edges E of dynodes 10 in different odd-numbered stages (excluding the first and third stages) penetrate into the dynode 10 adjacent to the dynode 10 on the upstream side of the dynode in question. More specifically, the edge E of the fifth dynode 10e has a nested structure with a different width than the fourth dynode 10d, and in this nested structure, the edge E of the fifth dynode 10e penetrates into the internal space of the fourth dynode 10d (the space partitioned by the side wall 13W and bottom wall 13B). The edge E of the seventh dynode 10g has a nested structure with a different width than the sixth dynode 10f, and in this nested structure, the edge E of the seventh dynode 10g penetrates into the internal space of the sixth dynode 10f. The ninth-stage dynode 10i has a nested structure in which the edge E is different in width from the eighth-stage dynode 10h, and in this nested structure, the edge E of the ninth-stage dynode 10i extends into the internal space of the eighth-stage dynode 10h. In other words, the fourth-stage dynode 10d side of the fifth-stage dynode 10e extends into the internal space of the fourth-stage dynode 10d, the sixth-stage dynode 10f side of the seventh-stage dynode 10g extends into the internal space of the sixth-stage dynode 10f, and the eighth-stage dynode 10h side of the ninth-stage dynode 10i extends into the internal space of the eighth-stage dynode 10h.

[0038] Furthermore, when viewed from the X direction, the edge E of the second-stage dynode 10b extends into the first-stage dynode 10a. Specifically, the edge E of the second-stage dynode 10b has a nested structure with a width different from that of the first-stage dynode 10a, and in this nested structure, the edge E of the second-stage dynode 10b extends into the internal space of the first-stage dynode 10a. Furthermore, the third-stage dynode 10c does not extend into the second-stage dynode 10b, but is spaced apart from it. The fourth-stage dynode 10d does not extend into the third-stage dynode 10c, but is spaced apart from it. The sixth-stage dynode 10f does not extend into the fifth-stage dynode 10e, but is spaced apart from it. The eighth-stage dynode 10h does not extend into the seventh-stage dynode 10g, but is spaced apart from it. The tenth stage dynode 10j does not intersect with the ninth stage dynode 10i and is arranged apart from the ninth stage dynode 10b.

[0039] In the photomultiplier tube 1 configured as described above, when measurement light is incident on the photocathode 3, electrons are emitted from the photocathode 3, focused by the focusing electrode 5, and sent to the electron multiplier section 6. In the electron multiplier section 6, the electrons are sequentially incident on and emitted from the secondary electron emitting surfaces 11a-11j of the first to tenth dynodes 10a-10j, where they are multiplied. The multiplied electrons are then collected by the electron collecting surface 73 of the anode 7 and extracted from the anode 7 as an output signal.

[0040] 8(a), 8(b), and 8(c) are simulation results showing a portion of the trajectories of electrons in an electron multiplier unit 906 according to a comparative example. 9(a), 9(b), and 9(c) are simulation results showing a portion of the trajectories of electrons in an electron multiplier unit 6 according to an example. In each figure, multiple thin lines indicate the trajectories of electrons. As shown in FIG. 8(a), the electron multiplier unit 906 according to the comparative example differs from the electron multiplier unit 6 in that it includes multiple dynodes 910 instead of the multiple dynodes 10 (see FIG. 3), an anode 907 instead of the anode 7 (see FIG. 3), and does not include a partition plate 20 (see FIG. 3).

[0041] The multiple dynodes 910 are all equal in width. The mth dynode 910 does not extend into the (m-1)th dynode 10 and is spaced apart from it. The tenth dynode 910j has a U-shaped cross section along the YZ plane that opens to the front. The secondary electron emission surface 911 of the tenth dynode 910j is provided on the outer surface of the rear side of the dynode 910, and has a linear cross section along the YZ plane. The anode 907 has a mesh structure 930 on the electron path from the ninth dynode 910i to the tenth dynode 910j that includes a plurality of electron passing holes H0 that allow electrons to pass through.

[0042] In the electron multiplier section 906, some of the electrons emitted from the eighth dynode 910h skip over the ninth and tenth dynodes 910i and 910j and are incident on the anode 907. As shown in Figure 8(b), some of the electrons emitted from the ninth dynode 910i skip over the tenth dynode 910j and are incident on the anode 907. Then, as shown in Figure 8(c), some of the electrons emitted from the tenth dynode 910j wander around in the vicinity of the mesh structure 930 until they are collected by the anode 907. Specifically, some of the electrons emitted from the tenth dynode 910j travel back and forth between the ninth and tenth dynodes 910i and 910j many times before colliding with the anode 907.

[0043] In contrast, as shown in Figure 9(a), in the electron multiplier section 6 of the embodiment, some of the electrons emitted from the eighth dynode 10h attempt to skip the ninth dynode 10i and the tenth dynode 10j and enter the anode 7, but are blocked by the partition plate 20, preventing this entrance.

[0044] As shown in Figure 9(b), some of the electrons emitted from the ninth dynode 10i attempt to skip the tenth dynode 10j and enter the anode 7, but are blocked by the partition plate 20, preventing this incidence. The electrons emitted from the ninth dynode 10i pass through the space K formed between the partition plate 20 and the tenth dynode 10j, and enter the tenth dynode 10j. Then, as shown in Figure 9(c), the electrons emitted from the tenth dynode 10j are collected by the electron collecting surface 73 of the anode 7.

[0045] As described above, the photomultiplier tube 1 includes a photocathode 3, N stages (here, N=10) of dynodes 10 that multiply electrons emitted from the photocathode 3, and an anode 7 that collects the electrons multiplied by the dynodes 10. In the photomultiplier tube 1, the anode 7, which faces the secondary electron emission surface 11j of the tenth dynode 10j (the final stage), extends along the secondary electron emission surface 11j. This facilitates electron injection from the final dynode 10j to the anode 7. Furthermore, the anode 7 does not have an electron passing hole on the electron path from the ninth dynode 10i (the dynode immediately before the final stage) to the final dynode 10j, preventing electrons from straying due to the electron passing hole. As a result, the time characteristics of the anode 7 can be improved. In particular, preventing electrons from straying can improve the fall time characteristics of the signal waveform output from the anode 7.

[0046] In the photomultiplier tube 1, the anode 7 is disposed between the ninth dynode 10i and the tenth dynode 10j. In this case, it becomes easier to dispose the anode 7 close to the tenth dynode 10j, and the electric field strength between the anode 7 and the tenth dynode 10j can be increased.

[0047] The photomultiplier tube 1 is provided with a partition 20 that is disposed between the ninth-stage dynode 10i and the anode 7 and blocks electrons from being incident on the anode 7 from the ninth-stage dynode 10i. In this case, it is possible to prevent electrons from being incident on the anode 7 from the ninth-stage dynode 10i, skipping the tenth-stage dynode 10j. As a result, it is possible to improve the time characteristics (particularly the rise time characteristics) attributable to the anode 7.

[0048] In the photomultiplier tube 1, a potential equal to or greater than the potential of the ninth dynode 10i is applied to the partition plate 20. In this case, the partition plate 20 can effectively block electrons from the ninth dynode 10i from entering the anode 7.

[0049] In the photomultiplier tube 1, the partition plate 20 is disposed between the ninth-stage dynode 10i and the tenth-stage dynode 10j. Electrons emitted from the ninth-stage dynode 10i pass through the space K between the partition plate 20 and the tenth-stage dynode 10j and are incident on the tenth-stage dynode 10j. In this case, the space K between the partition plate 20 and the tenth-stage dynode 10j can be used to cause electrons from the ninth-stage dynode 10i to be incident on the Nth-stage dynode 10j.

[0050] As a result of extensive research, the inventors have found that discharge between dynodes 10 is likely to occur from the ends in the X direction, which is the longitudinal direction of the dynodes 10. Therefore, in the photomultiplier tube 1, the X direction widths of the edges E of the third, fifth, seventh, and ninth dynodes 10c, 10e, 20g, and 10i are made smaller than the X direction widths of the second, fourth, sixth, and eighth dynodes 10b, 10d, 10f, and 10h. Furthermore, the edges E of the third, fifth, seventh, and ninth dynodes 10c, 10e, 20g, and 10i are included inside the second, fourth, sixth, and eighth dynodes 10b, 10d, 10f, and 10h in the X direction. This brings opposing dynodes 10 closer to each other, increasing the electric field strength between the stages, while also moving the X-direction ends of the third, fifth, seventh, and ninth stage dynodes 10c, 10e, 20g, and 10i away from the X-direction ends of the second, fourth, sixth, and eighth stage dynodes 10b, 10d, 10f, and 10h, ensuring a sufficient distance between these ends and preventing discharge.

[0051] That is, in the photomultiplier tube 1, the mth dynode 10 is arranged to face the (m-1)th dynode 10, and in the X direction, which is the longitudinal direction of the dynodes 10, the width of the edge E of the mth dynode 10 facing the (m-1)th dynode 10 is smaller than the width of the (m-1)th dynode 10, and in the X direction, the edge E of the mth dynode 10 is included inside the (m-1)th dynode 10. This makes it possible to prevent discharge between dynodes 10 while improving the timing characteristics. In other words, the inter-electrode distance between dynodes 10 required to prevent discharge can be reduced, the electric field strength can be increased, and the timing characteristics can be improved.

[0052] In the photomultiplier tube 1, the dynode 10 has an arc-shaped cross section along the YZ plane. Furthermore, in the photomultiplier tube 1, the fifth, seventh, and ninth-stage dynodes 10e, 10g, and 10i have nested structures in which the edge E of each dynode is different from the width of the fourth, sixth, and eighth-stage dynodes 10d, 10f, and 10h, respectively, as viewed in the X direction. The edge E of each dynode is recessed into the fourth, sixth, and eighth-stage dynodes 10d, 10f, and 10h, respectively. This allows the fourth and fifth-stage dynodes 10d and 10e to approach each other while preventing discharge, thereby increasing the electric field strength between them. The sixth and seventh-stage dynodes 10f and 10g to approach each other while preventing discharge, thereby increasing the electric field strength between them. The eighth and ninth-stage dynodes 10h and 10i to approach each other while preventing discharge, thereby increasing the electric field strength between them.

[0053] Furthermore, by nesting adjacent dynodes 10, 10 in this manner, electrons with extremely long or short transit times can be cut out (electrons with extremely long or short transit times can be configured to strike the surface of dynode 10 opposite the secondary electron emission surface 11), and the group of electrons collected by anode 7 will be a group of electrons with little difference in transit time, making it possible to easily improve timing characteristics.

[0054] Furthermore, by nesting adjacent dynodes 10, 10 at least on the upstream side of the N stages of dynodes 10, it is possible to cut off electrons with extremely long or short transit times before they multiply. Furthermore, this also has the effect of preventing ions generated by the increase in electrons inside the dynodes 10 from being fed back to the photocathode 3.

[0055] In the photomultiplier tube 1, the width of the first dynode 10a in the X direction is greater than the width of the second to tenth dynodes 10b to 10j. In the X direction, the second to tenth dynodes 10b to 10j have a nested structure in which they are contained inside the first dynode 10a. In this case, the X-direction ends of the second to tenth dynodes 10b to 10j are spaced away from the X-direction end of the first dynode 10a, ensuring a sufficient distance between these ends and preventing discharge.

[0056] FIG. 10(a) is a graph showing the results of a simulation of the rise time for the comparative example and the working example. FIG. 10(b) is a graph showing the results of a simulation of the fall time for the comparative example and the working example. The rise time is the time it takes for the peak value of the output pulse to reach 90% from 10%. The fall time is the time it takes for the peak value of the output pulse to return from 90% to 10%. For both the rise time and the fall time, the shorter the time, the better the time characteristics. The comparative example corresponds to the electron multiplier unit 906 (see FIG. 8), and the working example corresponds to the electron multiplier unit 6 (see FIG. 9). The graph in the figure compares the values ​​at the tenth dynodes 10j and 910j with the values ​​at the anodes 7 and 907. As shown in FIGS. 10(a) and 10(b), in the comparative example, both the rise time and the fall time are longer (deteriorated) during the electron multiplication process from the tenth dynode 10j to the anode 7, whereas in the working example, both the rise time and the fall time are maintained.

[0057] Fig. 11(a) is a graph showing the measured values ​​of the output signal from the anode 907 in the comparative example, and Fig. 11(b) is a graph showing the measured values ​​of the output signal from the anode 7 in the example. 11(a) and 11(b), the time axes correspond to each other. As shown in FIG. 11(a) and FIG. 11(b), it is confirmed that the rise time and fall time of the anode 7 can be significantly improved in the example compared to the comparative example.

[0058] In this embodiment, N, which is the total number of stages of dynodes 10, is set to 10, but N is not particularly limited as long as it is an integer equal to or greater than 2. In this embodiment, m, which is the stage of dynodes 10 with smaller widths, is set to 3, 5, 7, or 9 (odd-numbered stages), but m is not particularly limited as long as it can be an even-numbered stage or an integer equal to or greater than 2 and equal to or less than N.

[0059] In this embodiment, of the narrower third, fifth, seventh, and ninth dynodes 10c, 10e, 10g, and 10i, the edges E of the fifth, seventh, and ninth dynodes 10e, 10g, and 10i are recessed into the dynode 10 located upstream, but this is not limited to this. The edges E of all of the third, fifth, seventh, and ninth dynodes 10c, 10e, 10g, and 10i may be recessed into the dynode 10 located upstream. Furthermore, the edges E of any one of the fifth, seventh, and ninth dynodes 10e, 10g, and 10i may be recessed into the dynode 10 located upstream. In other words, the edges E of at least any one of the narrower dynodes 10 may be recessed into the dynode 10 located upstream of that dynode 10. Furthermore, the edges E of the fifth, seventh, and ninth dynodes 10e, 10g, and 10i do not have to be recessed into the dynode 10 located upstream. That is, the dynodes 10 of the Nth stage may be arranged such that adjacent dynodes 10, 10 are spaced apart from each other when viewed in the X direction.

[0060] In this embodiment, the width of the edge E of the m-th dynode 10 may be made smaller than the width of the (m-1)th dynode 10. Therefore, for example, the width of the m-th dynode 10 other than the edge E may be larger than the width of the (m-1)th dynode 10.

[0061] In this embodiment, the side walls 13W of the fifth, seventh and ninth dynodes 10e, 10g and 10i inserted into the upstream dynode 10 may be provided with holding pieces (not shown) for holding them to the insulating support substrate on the side away from the upstream dynode 10. In this case, it is possible to further prevent discharge between the dynodes 10 while improving the time characteristics.

[0062] In the field of photomultiplier tubes, improving the time characteristics caused by the anode is synonymous with suppressing deterioration of the time characteristics caused by stray electrons and / or variations in the travel paths, and therefore, how to suppress such deterioration is important. In this regard, the photomultiplier tube 1 of this embodiment can be said to be particularly effective because, as described above, it can effectively suppress deterioration of the time characteristics caused by stray electrons and / or variations in the travel paths.

[0063] As described above, one aspect of the present disclosure is not limited to the above embodiment.

[0064] Figure 12(a) is a perspective view showing a cross section of a portion of an electron multiplier section 106 according to a first modified example. As shown in Figure 12(a), the electron multiplier section 106 differs from the above embodiment in that it includes a dynode 110j instead of the tenth dynode 10j (see Figure 3), an anode 107 instead of the anode 7 (see Figure 3), and further includes a mesh electrode 130.

[0065] The tenth-stage dynode 110j includes a straight section 11L whose cross section along the YZ plane is linear, and a curved section 11R whose cross section along the YZ plane is curved. Curved section 11R extends from the end of straight section 11L so as to curve toward the ninth-stage dynode 10i. The rest of the configuration of dynode 110j is similar to that of dynode 10j.

[0066] The anode 107 has an L-shaped cross section along the YZ plane. The outer surface of the anode 107 facing the tenth dynode 110j has an electron collecting surface 173. The electron collecting surface 173 faces the secondary electron emission surface 111j of the tenth dynode 110j, and at least a portion of the electron collecting surface 173 extends along the secondary electron emission surface 111j. In this case, the electron collecting surface 173 extends in a plane following the secondary electron emission surface 111j of the straight portion 11L. In other respects, the anode 107 is configured similarly to the anode 7.

[0067] Mesh electrode 130 is disposed on the electron path from tenth-stage dynode 110j to anode 107. In other words, mesh electrode 130 is disposed between anode 107 and tenth-stage dynode 110j. Mesh electrode 130 facilitates extraction of electrons from tenth-stage dynode 110j. Mesh electrode 130 is disposed close to secondary electron emission surface 111j of tenth-stage dynode 110j. Mesh electrode 130 includes a plurality of electron passing holes 130H that allow electrons to pass through.

[0068] A potential higher than the potential of the tenth-stage dynode 110j is applied to the mesh electrode 130. It is preferable that the mesh electrode 130 is not electrically connected to the anode 107. The mesh electrode 130 constitutes an extraction electrode that extracts electrons from the tenth-stage dynode 110j, improving the output linearity (dynamic range). The mesh electrode 130 increases the electric field strength between the anode 107 and the tenth-stage dynode 110j, accelerating electrons flying from the tenth-stage dynode 110j toward the anode 107, thereby improving the time characteristics attributable to the anode 107.

[0069] This first modification also achieves the aforementioned effect of improving the time characteristics attributable to the anode 107. It also achieves the aforementioned effect of preventing discharge between the dynodes 10 while improving the time characteristics. In the first modification, the mesh electrode 130 promotes extraction of electrons from the tenth dynode 110j, thereby improving the output linearity (dynamic range).

[0070] Furthermore, in the first modified example, a potential higher than the potential of the tenth-stage dynode 110j is applied to the mesh electrode 130. In this case, the mesh electrode 130 can efficiently extract electrons. In the first modified example, the mesh electrode 130 is used as an extraction electrode. In this case, the mesh electrode 130 can be used to promote the extraction of electrons from the tenth-stage dynode 110j.

[0071] In the first modification, mesh electrode 130 is electrically disconnected from anode 107. However, mesh electrode 130 may be electrically connected to anode 107. In this case, mesh electrode 130 does not actually collect electrons that can be used as a signal current, and does not actually function as anode 107. Incidentally, since the number of electrons that collide with mesh electrode 130 is not zero, a signal caused by electrons incident on mesh electrode 130 may be superimposed on the output of anode 107. However, since the probability that electrons extracted from the tenth dynode 110j will collide with mesh electrode 130 is low (since the number of colliding electrons is very small), the impact on the time characteristics caused by anode 107 is not significant. In this way, electrically connecting mesh electrode 130 to anode 107 reduces the number of parts and improves ease of assembly.

[0072] Figure 12(b) is a perspective view showing a cross section of a portion of an electron multiplier section 206 according to a second modified example. As shown in Figure 12(b), the electron multiplier section 206 differs from the above embodiment in that it does not include the tenth-stage dynode 10j (see Figure 3), includes a dynode 210i instead of the ninth-stage dynode 10i (see Figure 3), includes an anode 207 instead of the anode 7 (see Figure 3), and includes a partition plate 220 instead of the partition plate 20 (see Figure 3).

[0073] In the electron multiplier section 206, N=9, and nine stages of dynodes 10 are provided. The ninth stage dynode 210i includes a straight section 21L whose cross section along the YZ plane is linear, and a curved section 21R whose cross section along the YZ plane is curved. Curved section 21R extends from the end of straight section 21L so as to curve towards the eighth stage dynode 10h. The rest of the configuration of dynode 210i is similar to that of dynode 10i.

[0074] The anode 207 is disposed between the eighth-stage dynode 10h and the ninth-stage dynode 210i. A cross section of the anode 207 along the YZ plane is formed along the ninth-stage dynode 210i. The outer surface of the anode 207 facing the ninth-stage dynode 210i has an electron collecting surface 273. The electron collecting surface 273 faces the secondary electron emission surface 211i of the ninth-stage dynode 210i, and at least a portion of the electron collecting surface 273 extends along the secondary electron emission surface 211i. In other respects, the anode 207 is configured similarly to the anode 7.

[0075] The partition plate 220 is disposed between the eighth-stage dynode 10h and the anode 207. The partition plate 220 blocks electrons from entering the anode 207 from the eighth-stage dynode 10h. The partition plate 220 is disposed between the eighth-stage dynode 10h and the ninth-stage dynode 210i. The partition plate 220 is a flat member extending in the X direction. The partition plate 220 is formed integrally with the ninth-stage dynode 210i. The partition plate 220 is provided so as to be continuous with the end of the curved portion 21R of the ninth-stage dynode 210i. The partition plate 220 has an opening 220H that penetrates through it in the thickness direction. The opening 220H forms a space K. Electrons emitted from the eighth-stage dynode 10h pass through the space K in the partition plate 220 and enter the ninth-stage dynode 210i. A potential equal to or higher than the potential of the eighth dynode 10h is applied to the partition plate 220. In other respects, the partition plate 220 is configured in the same manner as the partition plate 20.

[0076] This second modified example also achieves the above-mentioned effect of being able to improve the time characteristics attributable to the anode 207. It also achieves the above-mentioned effect of being able to prevent discharge between the dynodes 10 while improving the time characteristics. Furthermore, in the second modified example, the partition plate 220 is configured integrally with the final-stage dynode 210i, so that the partition plate 220 can be easily provided by utilizing the final-stage dynode 210i.

[0077] Figure 13 is a perspective view showing a part of an electron multiplier section 306 according to a third modified example. Figure 14 is a view showing a part of an electron multiplier section 306 according to the third modified example when viewed from the Y direction. As shown in Figures 13 and 14, the electron multiplier section 306 differs from the above embodiment in that it is equipped with dynodes 310e, 310g, and 310i instead of the fifth, seventh, and ninth dynodes 10e, 10g, and 10i (see Figure 3).

[0078] The fifth-stage dynode 310e has sidewalls 31W at both X-direction ends that extend at an angle to the YZ plane, widening outward as it moves away from the fourth-stage dynode 10d. The width of the fifth-stage dynode 310e is smallest at edge E1 closest to the fourth-stage dynode 10d and increases as it moves away from the fourth-stage dynode 10d, until edge Z1 opposite edge E1 corresponds to the width of the fourth-stage dynode 10d. The rest of the configuration of dynode 310e is similar to that of dynode 10e.

[0079] The seventh-stage dynode 310g has sidewalls 32W at both X-direction ends that extend at an angle to the YZ plane, widening outward as it moves away from the sixth-stage dynode 10f. The width of the seventh-stage dynode 310g is smallest at edge E2 on the sixth-stage dynode 10f side and increases as it moves away from the sixth-stage dynode 10f, until it reaches the width of the sixth-stage dynode 10f at edge Z2 opposite edge E2. The rest of the configuration of dynode 310g is similar to that of dynode 10g.

[0080] The ninth-stage dynode 310i has sidewalls 33W at both X-direction ends that extend at an angle to the YZ plane, widening outward as it moves away from the eighth-stage dynode 10h. The width of the ninth-stage dynode 310i is smallest at edge E3 closest to the eighth-stage dynode 10h and increases as it moves away from the eighth-stage dynode 10h, until edge Z3 opposite edge E3 corresponds to the width of the eighth-stage dynode 10h. The rest of the configuration of dynode 310i is similar to that of dynode 10i.

[0081] This third modification also has the above-mentioned effect of being able to improve the time characteristics of the anode 207. It also has the above-mentioned effect of being able to prevent discharge between the dynodes 10 while improving the time characteristics.

[0082] Fig. 15 is a perspective view showing a part of an electron multiplier section 406 according to a fourth modified example. Fig. 16 is a view showing a part of an electron multiplier section 406 according to the fourth modified example when viewed from the Y direction. Fig. 17 is a view showing a part of an electron multiplier section 406 according to the fourth modified example when viewed from the X direction. As shown in Figs. 15, 16 and 17, the electron multiplier section 406 differs from the above embodiment in that it includes a dynode 410g instead of the seventh-stage dynode 10g (see Fig. 3).

[0083] The width of the seventh-stage dynode 410g in the X direction is constant, and the sidewall 13W extends along the YZ plane. The width of the seventh-stage dynode 410g is equal to the width of the sixth-stage dynode 10f. That is, in the fourth modified example, the kth (k is an integer greater than or equal to 2 and less than N and other than m; here, k=7) dynode 10 is arranged to face the (k-1)th dynode 10, and the width of the kth dynode 10 in the X direction is equal to the width of the (k-1)th dynode 10.

[0084] Edge E4 of the seventh-stage dynode 410g does not extend into the sixth-stage dynode 10f. When viewed in the X direction, the seventh-stage dynode 410g is positioned away from the sixth-stage dynode 10f. In other words, the nested structure described above is adopted only in at least any of the spaces between the multiple dynodes 10 included in the electron multiplier section 406 (between dynodes 10) (here, between the fourth and fifth dynodes 10d, 10e and between the eighth and ninth dynodes 10h, 10i). The rest of the configuration of dynode 410g is similar to that of dynode 10g.

[0085] This fourth modification also has the above-mentioned effect of being able to improve the time characteristics attributable to the anode 207. It also has the above-mentioned effect of being able to prevent discharge between the dynodes 10 while improving the time characteristics.

[0086] Furthermore, in the fourth modification, the kth dynode 410g is arranged to face the k-1th dynode 410f. In the X direction, the width of the kth dynode 410g is equal to the width of the k-1th dynode 410f. In this case, it is possible to improve the electron arrival efficiency (so-called inter-stage efficiency) between the kth dynode 410f and the k-1th dynode 410f. A nested structure can be adopted between stages where time characteristics deteriorate to improve time, and between stages where they do not, the electron arrival efficiency can be increased. It is possible to achieve both time characteristics and electron multiplication number.

[0087] Figure 18 is a cross-sectional view showing an electron multiplier section 606 according to the fifth modified example. As shown in Figure 18, the electron multiplier section 606 differs from the above-described embodiment in that it includes dynodes 610c, 610e, 610g, and 610i instead of the third, fifth, seventh, and ninth dynodes 10c, 10e, 10g, and 10i (see Figure 3).

[0088] The widths of the second to tenth stage dynodes 10b, 610c, 10d, 610e, 10f, 610g, 10h, 610i, and 10j are equal to one another. The third, fifth, seventh, and ninth stage dynodes 610c, 610e, 610g, and 610i do not extend into the second, fourth, sixth, and eighth stage dynodes 10b, 610d, 10f, and 10h, respectively, and are spaced apart from the second, fourth, sixth, and eighth stage dynodes 10b, 610d, 10f, and 10h, respectively. The other configurations of the third, fifth, seventh, and ninth stage dynodes 610c, 610e, 610g, and 610i are similar to those of dynodes 10c, 10e, 10g, and 10i.

[0089] In the fifth modified example, the above-mentioned effect that the time characteristics attributable to the anode 7 can be improved can also be achieved.

[0090] In the above embodiment and modified examples, the entire electron collecting surface 73, 173, 273 of the anode 7, 107, 207 does not have to extend along the secondary electron emission surface 11 of the Nth dynode 10, as long as at least a portion of the electron collecting surface 73, 173, 273 of the anode 7, 107, 207 extends along the secondary electron emission surface 11 of the Nth dynode 10. In the above embodiment and modified examples, a nested structure may be applied alternately from the upstream side to the downstream side between multiple stages in the Nth dynode 10.

[0091] In the above embodiment and modified example, partition plates 20, 220 are provided, but members of various shapes may be used instead of partition plates 20, 220 as long as they form a wall that blocks electrons from entering the anode 7 from the N-1th dynode 10.

[0092] The components in the above-described embodiment and modified examples are not limited to the materials and shapes described above, and various materials and shapes can be applied. Furthermore, the components in the above-described embodiment and modified examples can be arbitrarily applied to the components in other embodiments or modified examples. [Explanation of symbols]

[0093] 1...Photomultiplier tube, 3...Photocathode, 7,107,207...Anode, 10,10a~10j,110j,210i,310e,310g,310i,410g,610c,610e,610g,610i...Die Node, 11,11j,111j,211i...secondary electron emission surface, 20,220...screen plate (wall), 73,173,273...electron collection surface, 130...mesh electrode (extraction electrode), E, ​​E1~E4...edge, K...space.

Claims

1. A photocathode; N stages (N is an integer of 2 or more) of dynodes that multiply electrons emitted from the photocathode; an anode that collects the electrons multiplied by the dynode; The anode is an electron collecting surface facing the secondary electron emitting surface of the Nth dynode and at least a portion of which extends along the secondary electron emitting surface; A photomultiplier tube having no electron passing holes on an electron path from the (N-1)th stage dynode to the Nth stage dynode.

2. 2. The photomultiplier tube according to claim 1, wherein the anode is disposed between the N-1th stage dynode and the Nth stage dynode.

3. 3. The photomultiplier tube according to claim 1, further comprising a wall portion disposed between the N-1th stage dynode and the anode, the wall portion preventing electrons from being incident on the anode from the N-1th stage dynode.

4. 4. The photomultiplier tube according to claim 3, wherein a potential applied to the wall portion is equal to or greater than a potential of the N-1th dynode.

5. 5. The photomultiplier tube according to claim 3, wherein the wall portion is integral with the Nth dynode.

6. the wall portion is disposed between the (N-1)th stage dynode and the Nth stage dynode, 5. The photomultiplier tube according to claim 3, wherein electrons emitted from the (N-1)th dynode pass through a space between the wall portion and the Nth dynode and are incident on the Nth dynode.

7. 3. The photomultiplier tube according to claim 1, further comprising an extraction electrode disposed between the anode and the Nth stage dynode, for facilitating extraction of electrons from the Nth stage dynode.

8. 8. The photomultiplier tube according to claim 7, wherein a potential applied to the extraction electrode is higher than a potential of the Nth dynode.

9. The photomultiplier tube according to claim 7 , wherein the extraction electrode is a mesh electrode.

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