Photomultiplier tube

Abstract

A photomultiplier tube capable of preventing discharge between dynodes while improving time characteristics is provided. [Solution] A photomultiplier tube 1 comprises a photocathode 3, N stages (N is an integer of 2 or more) of dynodes 10 that multiply electrons emitted from the photocathode 3, and an anode 7 that collects the electrons multiplied by the dynodes 10. The mth stage (m is an integer of 2 or more and N or less) dynode 10 is arranged to face the m-1th stage dynode 10. In the longitudinal direction of the dynodes 10, the width of an edge E of the mth stage dynode 10 facing the m-1th stage dynode 10 is smaller than the width of the m-1th stage dynode 10. In the longitudinal direction of the dynodes 10, the edge E of the mth stage dynode 10 is included inside the m-1th stage dynode 10.

Description

[Technical field]

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

[0002] There is known a photomultiplier tube that includes a photocathode, N stages (N is an integer of 2 or more) of dynodes 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 m-th stage (m is an integer of 2 or more and N or less) dynode is arranged to face the (m-1)th stage dynode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2002-42720 A Summary of the Invention [Problem to be solved by the invention]

[0004] Further improvement in time characteristics is required for the photomultiplier tube described above. One possible way to improve time characteristics is to bring opposing dynodes closer to each other to increase the electric field strength between stages (between dynodes). However, if the mth dynode and the (m-1)th dynode are brought closer to each other, there is a risk of discharge occurring between the mth dynode and the (m-1)th dynode, to which different potentials are applied.

[0005] The present disclosure has been made in consideration of the above-mentioned circumstances, and has an object to provide a photomultiplier tube capable of preventing discharge between dynodes while improving time characteristics. [Means for solving the problem]

[0006] The photomultiplier tube disclosed herein is [1] "a photomultiplier tube comprising a photocathode, N stages (N is an integer of 2 or more) of dynodes that multiply electrons emitted from the photocathode, and an anode that collects electrons multiplied by the dynodes, wherein the m-th stage (m is an integer of 2 or more and N or less) dynode is arranged to face the m-1st stage dynode, the width of the edge of the m-th stage dynode facing the m-1st stage dynode in the longitudinal direction of the dynodes is smaller than the width of the m-1st stage dynode, and in the longitudinal direction, the edge of the m-th stage dynode is included inside the m-1st stage dynode."

[0007] As a result of intensive research, the present inventors have found that discharge between dynodes is likely to occur from the end in the longitudinal direction of the dynode (hereinafter simply referred to as the "longitudinal direction"). Therefore, in the photomultiplier tube of the present disclosure, the longitudinal width of the edge of the m-th dynode on the m-1th dynode side is made smaller than the longitudinal width of the m-1th dynode. Furthermore, the edge of the m-th dynode is included inside the m-1th dynode in the longitudinal direction. This makes it possible to bring the opposing dynodes closer to each other to increase the electric field strength between the stages, while keeping the longitudinal end of the m-th dynode away from the longitudinal end of the m-1th dynode, thereby ensuring the distance between these ends and preventing discharge. In other words, it is possible to prevent discharge between dynodes while improving the time characteristics.

[0008] The photomultiplier tube of the present disclosure may be [2] "a photomultiplier tube according to [1], wherein the dynode has an arc-shaped cross section intersecting the longitudinal direction, and when viewed from the longitudinal direction, the edge of the m-th dynode extends into the m-1-th dynode." In this case, the m-th dynode and the m-1-th dynode can be brought close to each other while preventing discharge, thereby increasing the electric field strength between them.

[0009] The photomultiplier tube of the present disclosure may be [3] "a photomultiplier tube according to [1] or [2], wherein, in the longitudinal direction of the dynodes, the width of a first stage dynode is greater than the width of the second to Nth stages dynodes, and the second to Nth stages dynodes are included inside the first stage dynode in the longitudinal direction." In this case, the longitudinal ends of the second to Nth stages dynodes can be moved away from the longitudinal end of the first stage dynode to ensure a distance between these ends and prevent discharge.

[0010] The photomultiplier tube of the present disclosure may be [4] "a photomultiplier tube according to any of [1] to [3], wherein the kth stage (k is an integer other than m and equal to or greater than 2 and equal to or less than N) dynode is disposed opposite the k-1th stage dynode, and the width of the kth stage dynode in the longitudinal direction of the dynodes is equal to the width of the k-1th stage dynode." In this case, it is possible to increase the electron arrival efficiency (so-called interstage efficiency) between the kth stage dynode and the k-1th stage dynode. Effect of the Invention

[0011] According to the present disclosure, it is possible to provide a photomultiplier tube capable of preventing discharge between dynodes while improving the time characteristics. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view of a photomultiplier tube according to an embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing the electron multiplier section and the anode of FIG. [Diagram 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. [Diagram 5] FIG. 5 is a diagram showing the electron multiplier section and the anode in 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 in FIG. 1 when viewed from the Y direction. [Figure 8] Figure 8(a) is a simulation result showing the trajectory of an electron 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 an electron 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 an electron 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 an electron 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 an electron 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 an electron from the tenth dynode to the anode in an electron multiplier section according to an embodiment. [Figure 10] Fig. 10(a) is a graph showing the simulation results of the rise time of the comparative example and the embodiment, and Fig. 10(b) is a graph showing the simulation results of the fall time of the comparative example and the embodiment. [Figure 11] Fig. 11(a) is a graph showing measured values ​​of an output signal from an anode in a comparative example, and Fig. 11(b) is a graph showing measured values ​​of an output signal from an anode in an example. [Figure 12] Fig. 12(a) is a perspective view showing a part of an electron multiplier section according to a first modified example, and Fig. 12(b) is a perspective view showing 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 the fifth modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] 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.

[0014] 1, the photomultiplier tube 1 includes a tube 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 (N is an integer equal to or greater than 2) of so-called line focus type dynodes 10. In the following description, the side where light is incident on the photomultiplier tube 1 is referred to as the "front" and the opposite side as the "rear." In addition, the tube axis (central axis) of the tube body 2 is referred to as the "Z axis," the axis perpendicular to the plane (plane including the Z axis) on which the multiple stages of dynodes 10 are arranged is referred to as the "X axis," and the axis perpendicular to the Z axis and the X axis is referred to as the "Y axis."

[0015] The tubular body 2 accommodates a photocathode 3, a focusing electrode 5, an electron multiplier section 6, and an anode 7 in a vacuumed 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 whose central axis is the Z-axis and is located behind the oblate spherical portion 2a. The oblate spherical portion 2a and the cylindrical portion 2b are integrally formed as a single glass bulb.

[0016] 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 region of the oblate spheroid portion 2a. The photocathode 3 constitutes a transmissive photocathode and is made, for example, of a potassium cesium antimonide (bialkali) material or other well-known materials. 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.

[0017] 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.

[0018] The electron multiplier section 6 is disposed 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 formed of, for example, stainless steel or the like. The dynode 10 is an elongated member with the X direction as its longitudinal 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) protruding outward in the X direction to hold the dynode 10 within the tube 2.

[0019] 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 incidence of 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 dynode 10 has a cross section intersecting with its longitudinal direction that is arc-shaped. A different potential is applied to each dynode 10.

[0020] The anode 7 is disposed opposite the Nth dynode 10, which is the final stage. A predetermined voltage is applied to the anode 7. The anode 7 collects electrons multiplied by the Nth dynode 10. The anode 7 is configured to output the electrons emitted from the Nth dynode 10 as a signal current. In other words, the anode 7 is an electrode that has the function of collecting the electrons that can be used substantially as a signal current.

[0021] 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.

[0022] 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 the upstream side, to the rear side, or the 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.

[0023] The dynode 10 in the i-th stage (i is an integer greater than or equal to 2 and less than or equal to N) is arranged to face the dynode 10 in the i-1-th stage. In other words, the dynodes 10 in the Nth stage are 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 dynode 10 in the i-1-th stage than to the dynode 10 in the i-1-th stage. A negative potential, for example the same as that of the focusing electrode 5, is applied to the dynode 10a of the first stage. The dynodes 10 in the Nth stage are arranged so that their centre positions in the X direction are aligned.

[0024] 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; here, the electron collecting surface 73 extends following 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.

[0025] 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 part of it enters the 10th stage dynode 10j. As a result, the electron collecting surface 73 is close to the secondary electron emitting surface 11j. The anode 7 does not have an electron passing hole 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 hole is formed of a hole that passes electrons, and is included in, 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 set to, for example, 0V.

[0026] 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 to the anode 7 and electrons from the eighth-stage dynode 10h to 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 or the like.

[0027] A potential equal to or greater than the potential of the ninth stage dynode 10i is applied to the screen 20. For example, a potential equal to the potential of the tenth stage dynode 10j is applied to the screen 20. The screen 20 is configured as a separate body 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 screen 20 facing the tenth stage dynode 10j and the tenth stage dynode 10j, and are incident on the tenth stage dynode 10j (see the dashed arrow in the figure).

[0028] 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 be simply referred to as "width") is constant. The width of the edge E of the m-th 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 m-th dynode 10 facing the (m-1)th dynode 10 has a structure different from the width of the (m-1)th dynode 10 (hereinafter also referred to as a "nested structure"). In this embodiment, the m-th dynode 10 refers to a dynode 10 in a plurality of different odd-numbered stages (excluding the first stage).

[0029] 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 stages, the third, fifth, seventh and ninth dynodes 10c, 10e, 10g and 10i, are equal to each other. The widths of the different even-numbered stages, the second, fourth, sixth, eighth and tenth dynodes 10b, 10d, 10f, 10h and 10j, are equal to each other.

[0030] 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 stage dynode 10c is included inside the second stage dynode 10b, the fifth stage dynode 10e is included inside the fourth stage dynode 10d, the seventh stage dynode 10g is included inside the sixth stage dynode 10f, and the ninth stage dynode 10i is included inside the eighth stage dynode 10h.

[0031] In the X direction, the width of the first stage dynode 10a is greater than the width 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 stages 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 stages dynodes 10b to 10j are located more inside than the other end of the first stage dynode 10a.

[0032] 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 stage dynode 10e has a nested structure with a different width from the fourth stage dynode 10d, and in this nested structure, the edge E of the fifth stage dynode 10e penetrates into the internal space of the fourth stage dynode 10d (the space partitioned by the side wall 13W and bottom wall 13B). The edge E of the seventh stage dynode 10g has a nested structure with a different width from the sixth stage dynode 10f, and in this nested structure, the edge E of the seventh stage dynode 10g penetrates into the internal space of the sixth stage dynode 10f. The ninth-stage dynode 10i has a nested structure in which the edge E of the ninth-stage dynode 10i has a different width from the eighth-stage dynode 10h, and in this nested structure, the edge E of the ninth-stage dynode 10i enters the internal space of the eighth-stage dynode 10h. In other words, the fourth-stage dynode 10d side of the fifth-stage dynode 10e enters the internal space of the fourth-stage dynode 10d, the sixth-stage dynode 10f side of the seventh-stage dynode 10g enters the internal space of the sixth-stage dynode 10f, and the eighth-stage dynode 10h side of the ninth-stage dynode 10i enters the internal space of the eighth-stage dynode 10h.

[0033] Also, when viewed from the X direction, the edge E of the second stage dynode 10b enters 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 enters the internal space of the first stage dynode 10a. Also, the third stage dynode 10c does not enter the second stage dynode 10b, but is spaced apart from it. The fourth stage dynode 10d does not enter the third stage dynode 10c, but is spaced apart from it. The sixth stage dynode 10f does not enter the fifth stage dynode 10e, but is spaced apart from it. The eighth stage dynode 10h does not enter the seventh stage dynode 10g, but is spaced apart from it. The tenth stage dynode 10j does not overlap with the ninth stage dynode 10i, and is disposed apart from the ninth stage dynode 10b.

[0034] In the photomultiplier tube 1 configured as above, when measurement light is incident on the photocathode 3, electrons are emitted from the photocathode 3 and are 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 taken out as an output signal from the anode 7.

[0035] 8(a), 8(b) and 8(c) are simulation results showing a part of the trajectory of electrons in the electron multiplier section 906 according to the comparative example. FIG. 9(a), 9(b) and 9(c) are simulation results showing a part of the trajectory of electrons in the electron multiplier section 6 according to the embodiment. In each figure, a plurality of thin lines indicate the trajectory of electrons. As shown in FIG. 8(a), the electron multiplier section 906 according to the comparative example differs from the electron multiplier section 6 in that it includes a plurality of dynodes 910 instead of the plurality of dynodes 10 (see FIG. 3), includes an anode 907 instead of the anode 7 (see FIG. 3), and does not include a partition plate 20 (see FIG. 3).

[0036] The multiple dynodes 910 have the same width. The mth dynode 910 does not extend into the (m-1)th dynode 10 and is spaced apart from it. The 10th 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 10th 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 including a plurality of electron passing holes H0 that allow electrons to pass on the electron path from the 9th dynode 910i to the 10th dynode 910j.

[0037] In the electron multiplier section 906, some of the electrons emitted from the eighth stage dynode 910h skip the ninth stage dynode 910i and the tenth stage dynode 910j and are incident on the anode 907. As shown in FIG. 8(b), some of the electrons emitted from the ninth stage dynode 910i skip the tenth stage dynode 910j and are incident on the anode 907. Then, as shown in FIG. 8(c), some of the electrons emitted from the tenth stage 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 stage dynode 910j travel back and forth between the ninth stage dynode 910i and the tenth stage dynode 910j many times before colliding with the anode 907.

[0038] 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 entry.

[0039] As shown in Figure 9(b), some of the electrons emitted from the ninth stage dynode 10i attempt to skip the tenth stage dynode 10j and enter the anode 7, but are blocked by the partition plate 20 and prevented from entering. The electrons emitted from the ninth stage dynode 10i pass through the space K formed between the partition plate 20 and the tenth stage dynode 10j, and enter the tenth stage dynode 10j. Then, as shown in Figure 9(c), the electrons emitted from the tenth stage dynode 10j are collected by the electron collecting surface 73 of the anode 7.

[0040] 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 that faces the secondary electron emission surface 11j of the 10th stage dynode 10j, which is the final stage, extends along the secondary electron emission surface 11j. This makes it easier for electrons to be incident from the final stage dynode 10j to the anode 7. In addition, the anode 7 does not have an electron passing hole on the electron path from the 9th stage dynode 10i, which is one stage before the final stage, to the final stage dynode 10j, so that it is possible to prevent electrons from wandering due to the electron passing hole. As a result, it is possible to improve the time characteristics due to the anode 7. In particular, by preventing electrons from wandering, it is possible to improve the fall time characteristics of the signal waveform output from the anode 7.

[0041] 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.

[0042] The photomultiplier tube 1 includes 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.

[0043] 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 the incidence of electrons from the ninth dynode 10i to the anode 7.

[0044] In the photomultiplier tube 1, the partition plate 20 is disposed between the 9th stage dynode 10i and the 10th stage dynode 10j. Electrons emitted from the 9th stage dynode 10i pass through the space K between the partition plate 20 and the 10th stage dynode 10j and are incident on the 10th stage dynode 10j. In this case, it is possible to cause electrons from the 9th stage dynode 10i to be incident on the Nth stage dynode 10j by utilizing the space K between the partition plate 20 and the 10th stage dynode 10j.

[0045] As a result of extensive investigations, 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 stage dynodes 10c, 10e, 20g and 10i are made smaller than the X-direction widths of the second, fourth, sixth and eighth stage dynodes 10b, 10d, 10f and 10h. Furthermore, the edges E of the third, fifth, seventh and ninth stage dynodes 10c, 10e, 20g and 10i are included inside the second, fourth, sixth and eighth stage dynodes 10b, 10d, 10f and 10h in the X direction. As a result, opposing dynodes 10 are brought closer to each other to increase the electric field strength between the stages, while the X-direction ends of the third, fifth, seventh and ninth stage dynodes 10c, 10e, 20g and 10i are moved 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.

[0046] That is, in the photomultiplier tube 1, the mth dynode 10 is disposed to face the m-1th 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-1th dynode 10 is smaller than the width of the m-1th dynode 10, and in the X direction, the edge E of the mth dynode 10 is included inside the m-1th dynode 10. This makes it possible to prevent discharge between dynodes 10 while improving the temporal characteristics. In other words, the inter-electrode distance between dynodes 10 for preventing discharge can be reduced, the electric field strength can be increased, and the temporal characteristics can be improved.

[0047] In the photomultiplier tube 1, the dynode 10 has an arc-shaped cross section along the YZ plane. In the photomultiplier tube 1, the edge E of the 5th, 7th, and 9th stage dynodes 10e, 10g, and 10i is formed into a nested structure with a different width from the 4th, 6th, and 8th stage dynodes 10d, 10f, and 10h when viewed from the X direction, and the edge E of the 5th, 7th, and 9th stage dynodes 10e, 10g, and 10i enters into the 4th, 6th, and 8th stage dynodes 10d, 10f, and 10h, respectively. This makes it possible to bring the 4th and 5th stage dynodes 10d and 10e closer to each other while preventing discharge, thereby increasing the electric field strength between them. It makes it possible to bring the 6th and 7th stage dynodes 10f and 10g closer to each other while preventing discharge, thereby increasing the electric field strength between them. It makes it possible to bring the 8th and 9th stage dynodes 10h and 10i closer to each other while preventing discharge, thereby increasing the electric field strength between them.

[0048] 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 the dynode 10 opposite the secondary electron emission surface 11), and the group of electrons collected by the anode 7 will be a group of electrons with little difference in transit time, making it possible to easily improve the timing characteristics.

[0049] Furthermore, by forming adjacent dynodes 10, 10 at least on the upstream side of the N stages of dynodes 10 into a nested structure, it is possible to cut off electrons whose transit time is extremely long or short before they are multiplied. Furthermore, this also has the effect of preventing ions generated by the increase in electrons inside the dynode 10 from being fed back to the photocathode 3.

[0050] 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. In the X direction, the second to tenth dynodes 10b to 10j have a nested structure that is contained inside the first dynode 10a. In this case, the X-direction ends of the second to tenth dynodes 10b to 10j are moved away from the X-direction end of the first dynode 10a, ensuring the distance between these ends and preventing discharge.

[0051] FIG. 10(a) is a graph showing the results of a simulation of the rise time of the comparative example and the embodiment. FIG. 10(b) is a graph showing the results of a simulation of the fall time of the comparative example and the embodiment. The rise time is the time required for the output pulse peak value to reach 90% from 10%. The fall time is the time required for the output pulse peak value 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 embodiment corresponds to the electron multiplier unit 6 (see FIG. 9). The graph in the figure compares the values ​​at the 10th dynode 10j, 910j with the values ​​at the anode 7, 907. As shown in FIG. 10(a) and FIG. 10(b), in the comparative example, in the electron multiplication process from the 10th dynode 10j to the anode 7, both the rise time and the fall time are longer (worsened), whereas in the embodiment, it is confirmed that both the rise time and the fall time can be maintained.

[0052] 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. The time axes in Figures 11(a) and 11(b) correspond to each other. As shown in Figures 11(a) and 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.

[0053] In this embodiment, N, 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, 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 may be an even-numbered stage, or an integer equal to or greater than 2 and equal to or less than N.

[0054] In this embodiment, of the narrower dynodes 10c, 10e, 10g, 10i in the third, fifth, seventh, and ninth stages, the edges E of the 5th, seventh, and ninth stage dynodes 10e, 10g, 10i are recessed into the dynode 10 upstream thereof, but this is not limited to the above. All of the edges E of the 3rd, fifth, seventh, and ninth stage dynodes 10c, 10e, 10g, 10i may be recessed into the dynode 10 upstream thereof. Furthermore, the edges E of any of the 5th, seventh, and ninth stage dynodes 10e, 10g, 10i may be recessed into the dynode 10 upstream thereof. In other words, the edges E of at least any of the narrower dynodes 10 may be recessed into the dynode 10 upstream of that dynode 10. Furthermore, it is not necessary to recess the edges E of the 5th, seventh, and ninth stage dynodes 10e, 10g, 10i into the dynode 10 upstream thereof. In other words, the N stages of dynodes 10 may be arranged such that adjacent dynodes 10, 10 are spaced apart from each other when viewed in the X direction.

[0055] In this embodiment, it is sufficient that the width of the edge E of the m-th dynode 10 is 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.

[0056] In this embodiment, the side walls 13W of the fifth, seventh and ninth dynodes 10e, 10g and 10i which are inserted into the upstream dynode 10 may be provided with holding pieces (not shown) for holding them to an 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.

[0057] 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 electron stray and / or variations in the travel path, and so it is important to know how to suppress such deterioration. In this regard, the photomultiplier tube 1 of the present embodiment can be said to be particularly effective because it can effectively suppress deterioration of the time characteristics caused by electron stray and / or variations in the travel path, as described above.

[0058] The above-described aspect of the present disclosure is not limited to the above-described embodiment.

[0059] Fig. 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 Fig. 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 Fig. 3), an anode 107 instead of the anode 7 (see Fig. 3), and further includes a mesh electrode 130.

[0060] 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. Bent section 11R extends from the end of straight section 11L so as to bend towards the ninth stage dynode 10i. The rest of the configuration of dynode 110j is similar to that of dynode 10j.

[0061] 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. Here, 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.

[0062] Mesh electrode 130 is disposed on the electron path from the tenth stage dynode 110j to the anode 107. In other words, mesh electrode 130 is disposed between the anode 107 and the tenth stage dynode 110j. Mesh electrode 130 promotes the extraction of electrons from the tenth stage dynode 110j. Mesh electrode 130 is disposed close to secondary electron emission surface 111j of the tenth stage dynode 110j. Mesh electrode 130 includes a plurality of electron passing holes 130H that allow electrons to pass through.

[0063] A potential higher than that 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, and improves the output linearity (dynamic range). The mesh electrode 130 increases the electric field strength between the anode 107 and the tenth stage dynode 110j, and accelerates the electrons flying from the tenth stage dynode 110j toward the anode 107, thereby improving the time characteristics attributable to the anode 107.

[0064] This first modified example also has the above-mentioned effect of being able to improve the time characteristics attributable to the anode 107. It also has the above-mentioned effect of being able to prevent discharge between the dynodes 10 while improving the time characteristics. In the first modified example, the mesh electrode 130 promotes the extraction of electrons from the tenth dynode 110j, improving the output linearity (dynamic range).

[0065] 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, it is possible to utilize the mesh electrode 130 to promote the extraction of electrons from the tenth-stage dynode 110j.

[0066] In the first modification, the mesh electrode 130 is not electrically connected to the anode 107, but the mesh electrode 130 may be electrically connected to the anode 107. In this case, the mesh electrode 130 is not an electrode that collects electrons that can be used as a signal current, and does not substantially function as the anode 107. Incidentally, since the number of electrons that collide with the mesh electrode 130 is not zero, a signal caused by the electrons that enter the mesh electrode 130 may be superimposed on the output of the anode 107. However, since the probability that the electrons drawn from the tenth dynode 110j collide with the mesh electrode 130 is low (since the number of colliding electrons is very small), the effect on the time characteristics caused by the anode 107 is not large. In this way, the mesh electrode 130 is electrically connected to the anode 107, so that the number of parts can be reduced and the ease of assembly can be improved.

[0067] Fig. 12(b) is a perspective view showing a cross section of a portion of electron multiplier section 206 according to the second modified example. As shown in Fig. 12(b), electron multiplier section 206 differs from the above embodiment in that it does not include a 10th stage dynode 10j (see Fig. 3), includes a dynode 210i instead of a 9th stage dynode 10i (see Fig. 3), includes an anode 207 instead of anode 7 (see Fig. 3), and includes a partition plate 220 instead of partition plate 20 (see Fig. 3).

[0068] 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 bend towards the eighth stage dynode 10h. The rest of the configuration of dynode 210i is similar to that of dynode 10i.

[0069] The anode 207 is disposed between the eighth-stage dynode 10h and the ninth-stage dynode 210i. The 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 emitting surface 211i of the ninth-stage dynode 210i, and at least a portion of it extends along the secondary electron emitting surface 211i. In other respects, the anode 207 is configured in the same manner as the anode 7.

[0070] The partition plate 220 is disposed between the eighth-stage dynode 10h and the anode 207. The partition plate 220 prevents 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 integrally formed 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 is formed with an opening 220H penetrating through 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.

[0071] This second modified example also has the above-mentioned effect of making it possible to improve the time characteristics attributable to the anode 207. In addition, it also has the above-mentioned effect of making it possible 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.

[0072] Fig. 13 is a perspective view showing a part of an electron multiplier section 306 according to a third modified example. Fig. 14 is a view showing a part of an electron multiplier section 306 according to a third modified example when viewed from the Y direction. As shown in Figs. 13 and 14, the electron multiplier section 306 differs from the above embodiment in that it is provided with dynodes 310e, 310g, 310i instead of the 5th, 7th, 9th dynodes 10e, 10g, 10i (see Fig. 3).

[0073] The fifth stage dynode 310e has sidewalls 31W at both X-direction ends which extend at an angle relative to the YZ plane so that they widen outward as they move 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.

[0074] The seventh-stage dynode 310g has sidewalls 32W at both X-direction ends which extend at an angle relative to the YZ plane so that they widen outward as they move away from the sixth-stage dynode 10f. The width of the seventh-stage dynode 310g is smallest at edge E2 near the sixth-stage dynode 10f 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.

[0075] The ninth stage dynode 310i has sidewalls 33W at both X-direction ends which extend at an angle relative to the YZ plane so that they widen outward as they move 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.

[0076] The third modified example also has the above-mentioned effect of being able to improve the time characteristics of the anode 207. In addition, the third modified example also has the above-mentioned effect of being able to prevent discharge between the dynodes 10 while improving the time characteristics.

[0077] 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 a 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 a 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).

[0078] The seventh-stage dynode 410g has a constant width in the X direction, and 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 to say, 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 disposed opposite the k-1th dynode 10, and the width of the kth dynode 10 in the X direction is equal to the width of the k-1th dynode 10.

[0079] Edge E4 of the seventh dynode 410g does not extend into the sixth dynode 10f. When viewed in the X direction, the seventh dynode 410g is disposed away from the sixth dynode 10f. In other words, the above-mentioned nested structure is adopted only in at least any of the spaces (between dynodes 10) among the multiple spaces among the multiple dynodes 10 included in the electron multiplier section 406 (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.

[0080] Such a fourth modified example also has the above-mentioned effect of being able to improve the time characteristics attributable to the anode 207. In addition, it also has the above-mentioned effect of being able to prevent discharge between the dynodes 10 while improving the time characteristics.

[0081] Moreover, in the fourth modified example, 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 is adopted to improve time between stages where the time characteristics deteriorate, and the electron arrival efficiency can be increased between stages where they do not. It is possible to achieve both time characteristics and electron multiplication number.

[0082] Fig. 18 is a cross-sectional view showing an electron multiplier section 506 according to the fifth modified example. As shown in Fig. 18, electron multiplier section 506 differs from the above embodiment in that it includes a dynode 510j instead of the tenth stage dynode 10j (see Fig. 3), an anode 507 instead of the anode 7 (see Fig. 3), and does not include a partition plate 20 (see Fig. 3).

[0083] The width of the 10th stage dynode 510j in the X direction is constant. The width of the 10th stage dynode 510j is equal to the width of the 9th stage dynode 10i. The cross section of the 10th stage dynode 510j along the YZ plane has a U-shaped cross section that opens to the front. The secondary electron emission surface 511 of the 10th stage dynode 510j is provided on the front outer surface of the 10th stage dynode 510j (the surface facing the anode 507), and has a linear cross section along the YZ plane. The anode 507 has a mesh structure 530 including a plurality of electron passing holes H0 on the electron path from the 9th stage dynode 10i to the 10th stage dynode 510j.

[0084] This fifth modified example also achieves the above-mentioned effect of preventing discharge between the dynodes 10 (particularly between the fourth and fifth dynodes 10d, 10e, between the sixth and seventh dynodes 10f, 10e, and between the eighth and ninth dynodes 10h, 10i) while improving the time characteristics.

[0085] In the above embodiment and modified examples, the entire area of ​​the 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, but it is sufficient that at least a part 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.

[0086] In the above embodiment and modified example, the partition plate 20, 220 is provided, however, members of various shapes may be used in place of the partition plate 20, 220 as long as they form a wall portion that prevents electrons from being incident on the anode 7 from the N-1th dynode 10.

[0087] The respective configurations in the above embodiment and the above modification are not limited to the above-mentioned materials and shapes, and various materials and shapes can be applied. Furthermore, the respective configurations in the above embodiment and the above modification can be arbitrarily applied to the respective configurations in other embodiments or modifications. [Explanation of symbols]

[0088] 1...Photomultiplier tube, 3...Photocathode, 7,107,207,507...Anode, 10,10a~10j,110j,210i,310e, 310g,310i,410g,510j...da Inode, 11,11j,111j,211i,511...Secondary electron emission surface, 20,220...Screen plate (wall), 73,173,273...Electron collecting surface, 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; an m-th stage (m is an integer of 2 or more and N or less) dynode is disposed opposite to an m-1-th stage dynode; in a longitudinal direction of the dynodes, a width of an edge of the m-th stage dynode on the side of the (m-1)th stage dynode is smaller than a width of the (m-1)th stage dynode, a photomultiplier tube in which, in the longitudinal direction, the edge of the m-th dynode is included inside the (m-1)-th dynode.

2. The dynode has an arc-shaped cross section intersecting the longitudinal direction, 2. The photomultiplier tube according to claim 1, wherein, when viewed in the longitudinal direction, the edge of the mth dynode extends into the (m-1)th dynode.

3. In the longitudinal direction of the dynode, a width of the first stage dynode is larger than widths of the second to Nth stages of the dynode, 3. The photomultiplier tube according to claim 1, wherein the dynodes in the second to Nth stages are included inside the dynode in the first stage in the longitudinal direction.

4. the dynode in the kth stage (k is an integer not less than 2 and not more than N, and not more than m) is disposed opposite the dynode in the k-1th stage; 3. The photomultiplier tube according to claim 1, wherein a width of the kth dynode in the longitudinal direction of the dynode is equal to a width of the k-1th dynode.

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