Photomultiplier tube

Abstract

This photomultiplier tube comprises: a photoelectric surface; N stages of dynodes (where N is an integer of 2 or more) that multiply electrons emitted from the photoelectric surface; and an anode that collects the electrons multiplied by the dynodes. The mth stage dynode (where m is an integer that is not less than 2 and not more than N) is disposed opposite from the m-1th stage dynode. In the longitudinal direction of the dynodes, the width of the edge of mth stage dynode on the m-1th stage dynode side thereof is less than the width of the m-1th stage dynode. In the longitudinal direction, said edge of the mth stage dynode is contained inside the m-1th stage dynode.

Description

photomultiplier tube

[0001] The present disclosure relates to photomultiplier tubes.

[0002] There is known a photomultiplier tube 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 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.

[0003] Japanese Patent Application Laid-Open No. 2002-42720

[0004] Further improvements in the time characteristics are required for the photomultiplier tubes described above. One possible way to improve the time characteristics is to bring opposing dynodes closer to each other to increase the electric field strength between stages (between the dynodes). However, bringing the mth dynode and the (m-1)th dynode closer to each other risks the occurrence of discharge between the mth and (m-1)th dynodes, to which different potentials are applied.

[0005] The present disclosure has been made in view of the above circumstances, and has an object to provide a photomultiplier tube that can prevent discharge between dynodes while improving time characteristics.

[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 mth stage (m is an integer of 2 or more and N or less) of the dynode is arranged to face the m-1th stage of the dynode, the width of the edge of the mth stage dynode facing the m-1th stage dynode in the longitudinal direction of the dynodes is smaller than the width of the m-1th stage dynode, and the edge of the mth stage dynode is included inside the m-1th stage dynode in the longitudinal direction."

[0007] As a result of extensive research, the inventors have found that discharge between dynodes is likely to occur from the ends of the dynodes in their longitudinal direction (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 mth dynode facing the (m-1)th dynode is made smaller than the longitudinal width of the (m-1)th dynode. Furthermore, this edge of the mth dynode is included inside the (m-1)th dynode in the longitudinal direction. This brings the opposing dynodes closer to each other to increase the electric field strength between the stages, while also positioning the longitudinal end of the mth dynode away from the longitudinal end of the (m-1)th dynode, ensuring a sufficient distance between these ends and preventing discharge. In other words, it is possible to prevent discharge between dynodes while improving the temporal characteristics.

[0008] The photomultiplier tube of the present disclosure may be [2] "a photomultiplier tube according to [1], wherein the dynodes have an arc-shaped cross section intersecting the longitudinal direction, and the edge of the m-th dynode extends into the (m-1)th dynode as viewed from the longitudinal direction." 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] "the photomultiplier tube according to [1] or [2], wherein, in the longitudinal direction of the dynodes, the width of the first-stage dynode is greater than the width of the second- to N-stage dynodes, and the second- to N-stage dynodes are included inside the first-stage dynode in the longitudinal direction." In this case, the longitudinal ends of the second- to N-stage dynodes can be moved away from the longitudinal end of the first-stage dynode, ensuring a distance between these ends and preventing discharge.

[0010] The photomultiplier tube of the present disclosure may be [4] "the photomultiplier tube according to any one of [1] to [3], wherein the kth stage (k is an integer greater than or equal to 2 and less than N, and other than m) 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 inter-stage efficiency) between the kth stage dynode and the k-1th stage dynode.

[0011] According to the present disclosure, it is possible to provide a photomultiplier tube that can prevent discharge between dynodes while improving the time characteristics.

[0012] FIG. 1 is a cross-sectional view of a photomultiplier tube according to an embodiment. FIG. 2 is a cross-sectional view showing the electron multiplier section and anode of FIG. 1 . FIG. 3 is an enlarged perspective view of a portion of FIG. 2 . FIG. 4 is a perspective view showing the electron multiplier section and anode of FIG. 1 . FIG. 5 is a view showing the electron multiplier section and anode of FIG. 1 as viewed from the Y direction. FIG. 6 is a perspective view showing a portion of the electron multiplier section of FIG. 1 . FIG. 7 is a view showing a portion of the electron multiplier section of FIG. 1 as viewed from the Y direction. FIG. 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. FIG. 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. FIG. 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. 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 example. 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 example. 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 example. FIG. 10( a) is a graph showing the simulation results of rise time for a comparative example and an example. FIG. 10( b) is a graph showing the simulation results of fall time for a comparative example and an example. FIG. 11( a) is a graph showing the actual measured values ​​of the output signal from the anode in a comparative example. FIG. 11( b) is a graph showing the actual measured values ​​of the output signal from the anode in an example. FIG. 12( a) is a perspective view showing a cross section of a portion of an electron multiplier section according to a first modified example. FIG. 12( b) is a perspective view showing a cross section of a portion of an electron multiplier section according to a second modified example. Fig. 13 is a perspective view showing a part of an electron multiplier section according to a third modified example. Fig. 14 is a view showing a part of an electron multiplier section according to the third modified example when viewed from the Y direction. Fig. 15 is a perspective view showing a part of an electron multiplier section according to a fourth modified example. Fig. 16 is a view showing a part of an electron multiplier section according to the fourth modified example when viewed from the Y direction.Fig. 17 is a diagram showing a part of an electron multiplier section according to a fourth modified example when viewed from the X direction. Fig. 18 is a cross-sectional view showing an electron multiplier section according to a fifth modified example.

[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 comprises 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 of so-called line-focus dynodes 10 (N is an integer of 2 or greater). 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 tube 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."

[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 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.

[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 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.

[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 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 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 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.

[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, cables, or the like.

[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 (upstream) to the rear side (downstream), a first dynode 10a, a second dynode 10b, a third dynode 10c, a fourth dynode 10d, a fifth dynode 10e, a sixth dynode 10f, a seventh dynode 10g, an eighth dynode 10h, a ninth dynode 10i, and a tenth dynode 10j.

[0023] The i-th dynode 10 (i is an integer of 2 or more and N or less) is arranged so as to face the i-1th dynode 10. In other words, the Nth 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-1th 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 Nth dynodes 10 are arranged so that their centres 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; in this case, the electron collecting surface 73 extends in tandem with 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 ninth-stage dynode 10i and the tenth-stage dynode 10j. The anode 7 is disposed so that a portion of it extends into the tenth-stage dynode 10j. This brings the electron collecting surface 73 close to the secondary electron emitting surface 11j. The anode 7 does not have electron passing holes on the electron path from the ninth-stage dynode 10i to the tenth-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 are 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 ninth-stage dynode 10i to the tenth-stage dynode 10j. A potential equal to or higher than the potential of the tenth-stage dynode 10 is applied to the anode 7. The potential of the anode 7 is, for example, 0 V.

[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 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 Figure 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 dynode 10i is applied to the screen 20. For example, a potential equal to the potential of the tenth dynode 10j is applied to the screen 20. The screen 20 is constructed separately from the tenth dynode 10j. For example, as shown in Figure 3, electrons emitted from the ninth dynode 10i pass through the space K between the end of the screen 20 on the tenth dynode 10j side and the tenth dynode 10j, and are incident on the tenth 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 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 is different from the width of the (m-1)th dynode 10 (hereinafter this will be referred to as a "nested structure"). In this embodiment, the mth dynode 10 refers to a plurality of different odd-numbered dynodes 10 (excluding the first dynode).

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

[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 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.

[0031] In the X direction, the width of the first dynode 10a 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 are included inside the first dynode 10a. In other words, in the X direction, one end of the second to tenth dynodes 10b to 10j is located more inside than one end of the first dynode 10a, and the other ends of the second to tenth dynodes 10b to 10j are located more inside than the other end of the first 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 a plurality of different odd-numbered dynodes 10 (excluding the first and third dynodes) 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 width different from that of 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 width different from that of 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 dynode 10i has a nested structure in which the edge E is different in width from the eighth dynode 10h, and in this nested structure, the edge E of the ninth dynode 10i extends into the internal space of the eighth dynode 10h. In other words, the fourth dynode 10d side of the fifth dynode 10e extends into the internal space of the fourth dynode 10d, the sixth dynode 10f side of the seventh dynode 10g extends into the internal space of the sixth dynode 10f, and the eighth dynode 10h side of the ninth dynode 10i extends into the internal space of the eighth dynode 10h.

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

[0034] 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 emission surfaces 11a to 11j of the first to tenth dynodes 10a to 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.

[0035] 8( a), 8(b), and 8(c) are simulation results showing part of the trajectories of electrons in the electron multiplier unit 906 according to the comparative example. 9(a), 9(b), and 9(c) are simulation results showing part of the trajectories of electrons in the electron multiplier unit 6 according to the 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 the partition plate 20 (see FIG. 3).

[0036] 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 that includes a plurality of electron passing holes H0 that allow electrons to pass through, on the electron path from the ninth dynode 910i to the tenth dynode 910j.

[0037] In the electron multiplier section 906, some of the electrons emitted from the eighth dynode 910h skip 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 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.

[0038] In contrast, as shown in Figure 9(a), in the electron multiplier section 6 according to 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.

[0039] 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 and prevented from entering. 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.

[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 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 incidence 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 stage 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 due to the anode 7 can be improved. In particular, preventing electron straying can 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 is provided with a partition 20 that is disposed between the ninth dynode 10i and the anode 7 and blocks electrons from being incident on the anode 7 from the ninth dynode 10i. In this case, it is possible to prevent electrons from being incident on the anode 7 from the ninth dynode 10i, skipping the tenth 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 electrons from being incident on the anode 7 from the ninth dynode 10i.

[0044] 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.

[0045] 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 positioning 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.

[0046] 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.

[0047] In the photomultiplier tube 1, the dynodes 10 have an arc-shaped cross section along the YZ plane. Furthermore, in the photomultiplier tube 1, the fifth, seventh, and ninth dynodes 10e, 10g, and 10i have a nested structure in which the edge E of each dynode is different from the width of the fourth, sixth, and eighth dynodes 10d, 10f, and 10h when viewed from the X direction, and the edge E of each dynode is recessed into the fourth, sixth, and eighth dynodes 10d, 10f, and 10h, respectively. This allows the fourth and fifth dynodes 10d and 10e to be brought closer together while preventing discharge, thereby increasing the electric field strength between them. The sixth and seventh dynodes 10f and 10g to be brought closer together while preventing discharge, thereby increasing the electric field strength between them. The eighth and ninth dynodes 10h and 10i to be brought closer together while preventing discharge, thereby increasing the electric field strength between them.

[0048] Furthermore, by nesting adjacent dynodes 10, 10 in this manner, it is possible to cut out electrons with extremely long or short transit times (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 temporal characteristics.

[0049] 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.

[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, 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 positioned away from the X-direction end of the first dynode 10a, ensuring a sufficient distance between these ends and preventing discharge.

[0051] FIG. 10( a) is a graph showing the results of a simulation of the rise time for the comparative example and the example. FIG. 10( b) is a graph showing the results of a simulation of the fall time for the comparative example and the 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 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 example, it is confirmed that both the rise time and the fall time can be maintained.

[0052] 11(a) is a graph showing actual measured values ​​of the output signal from the anode 907 in the comparative example. FIG. 11(b) is a graph showing actual measured values ​​of the output signal from the anode 7 in the example. The time axes in FIGS. 11(a) and 11(b) correspond to each other. As shown in FIGS. 11(a) and 11(b), it is confirmed that the example can achieve significant improvements in the rise time and fall time of the anode 7 compared to the comparative example.

[0053] In this embodiment, N, which is the total number of stages of the 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 the 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 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 upstream thereof, 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 upstream thereof. Furthermore, the edges E of any of the fifth, seventh and ninth dynodes 10e, 10g and 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, the edges E of the fifth, seventh and ninth dynodes 10e, 10g and 10i do not have to be recessed into the dynode 10 upstream thereof. That is, the dynodes 10 of the N stages 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, the width of the edge E of the mth dynode 10 may be made smaller than the width of the (m-1)th dynode 10. Therefore, for example, the width of the mth dynode 10 other than the edge E may be greater 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 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.

[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 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.

[0058] As described above, one aspect of the present disclosure is not limited to the above embodiment.

[0059] Figure 12(a) is a perspective view showing a cross section of a portion of the electron multiplier unit 106 according to the first modified example. As shown in Figure 12(a), the electron multiplier unit 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.

[0060] The tenth 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 towards the ninth 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; 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.

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

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

[0064] This first modified example also achieves the above-mentioned effect of being able to improve the time characteristics attributable to the anode 107. It also achieves 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, thereby improving the output linearity (dynamic range).

[0065] Furthermore, in the first modified example, a potential higher than the potential of the tenth 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 use the mesh electrode 130 to promote the extraction of electrons from the tenth dynode 110j.

[0066] Although the mesh electrode 130 is electrically disconnected from the anode 107 in the first modification, 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 actually 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 incident on the mesh electrode 130 may be superimposed on the output of the anode 107. However, since the probability that electrons extracted from the tenth dynode 110j will collide with the mesh electrode 130 is low (since the number of colliding electrons is very small), the impact on the time characteristics caused by the anode 107 is not significant. In this way, electrically connecting the mesh electrode 130 to the anode 107 reduces the number of parts and improves ease of assembly.

[0067] 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 dynode 10j (see Figure 3), includes a dynode 210i instead of the ninth 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).

[0068] In the electron multiplier section 206, N=9, and nine dynodes 10 are provided. The ninth dynode 210i includes a straight portion 21L whose cross section along the YZ plane is linear, and a curved portion 21R whose cross section along the YZ plane is curved. Curved portion 21R extends from the end of straight portion 21L so as to curve towards the eighth 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 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 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 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.

[0071] 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.

[0072] Fig. 13 is a perspective view showing a part of an electron multiplier section 306 according to the third modified example. Fig. 14 is a view showing a part of the electron multiplier section 306 according to the 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-described embodiment in that it is provided with dynodes 310e, 310g, and 310i instead of the fifth, seventh, and ninth dynodes 10e, 10g, and 10i (see Fig. 3).

[0073] The fifth dynode 310e has side walls 31W at both X-direction ends that extend at an angle to the YZ plane, widening outward as it moves away from the fourth dynode 10d. The width of the fifth dynode 310e is smallest at the edge E1 closest to the fourth dynode 10d and increases as it moves away from the fourth dynode 10d, until the edge Z1 opposite edge E1 corresponds to the width of the fourth dynode 10d. The rest of the configuration of the dynode 310e is similar to that of dynode 10e.

[0074] The seventh-stage dynode 310g has side walls 32W at both X-direction ends that extend at an angle to the YZ plane so that they widen outward with increasing distance from the sixth-stage dynode 10f. The width of the seventh-stage dynode 310g is smallest at edge E2 facing the sixth-stage dynode 10f and increases with increasing distance from the sixth-stage dynode 10f, until edge Z2 opposite edge E2 corresponds to the width of the sixth-stage dynode 10f. The rest of the configuration of dynode 310g is similar to that of dynode 10g.

[0075] The ninth dynode 310i has side walls 33W at both X-direction ends that extend at an angle to the YZ plane so as to widen outward with increasing distance from the eighth dynode 10h. The width of the ninth dynode 310i is smallest at edge E3 closest to the eighth dynode 10h and increases with increasing distance from the eighth dynode 10h, until edge Z3 opposite edge E3 corresponds to the width of the eighth dynode 10h. The rest of the configuration of the dynode 310i is similar to that of the dynode 10i.

[0076] 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.

[0077] Fig. 15 is a perspective view showing a part of an electron multiplier section 406 according to the 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).

[0078] The seventh-stage dynode 410g has a constant width in the X direction, and its 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 positioned 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 positioned away from the sixth 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.

[0080] The fourth modification 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] Furthermore, 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 can be adopted between stages where time characteristics deteriorate to improve time, and between stages where this is not the case to increase the electron arrival efficiency. 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 tenth-stage dynode 10j (see Fig. 3), an anode 507 instead of anode 7 (see Fig. 3), and does not include partition plate 20 (see Fig. 3).

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

[0084] This fifth modified example also achieves the above-mentioned effect of being able to prevent discharge between the dynodes 10 (in particular, 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 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 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 plates 20, 220 are provided, but members of various shapes may be used in place of the partition plates 20, 220 as long as they are members that form a wall that blocks electrons from being incident on the anode 7 from the N-1th dynode 10.

[0087] 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.

[0088] 1...photoelectron multiplier tube, 3...photoelectric surface, 7, 107, 207, 507...anaode, 10, 10a to 10j, 110j, 210i, 310e, 310g, 310i, 410g, 510j...dianode, 11, 11j, 111j, 211i, 511...secondary electron emission surface, 20, 220...front plate (wall), 73, 173, 273...electron collecting surface, E, E1 to E4...end edge, K...space.

Claims

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 mth stage (m is an integer of 2 or more and N or less) dynode is positioned opposite the m-1th stage dynode, the width of the edge of the mth stage dynode facing the m-1th stage dynode in the longitudinal direction of the dynodes is smaller than the width of the m-1th stage dynode, and the edge of the mth stage dynode is included inside the m-1th stage dynode in the longitudinal direction.

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

3. A photomultiplier tube according to claim 1 or 2, wherein the width of the first stage dynode in the longitudinal direction of the dynodes is greater than the widths of the second to Nth stage dynodes, and the second to Nth stage dynodes are included inside the first stage dynode in the longitudinal direction.

4. A photomultiplier tube according to claim 1 or 2, wherein the kth dynode (k is an integer between 2 and N, and is other than m) is arranged to face the k-1th dynode, and the width of the kth dynode in the longitudinal direction of the dynodes is equal to the width of the k-1th dynode.

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