JP4627470B2 - Photomultiplier tube - Google Patents

Description

  The present invention relates to a photomultiplier tube.

  An example of a conventional photomultiplier tube is disclosed in Patent Document 1. This photomultiplier tube includes a light receiving face plate and a photocathode formed inside the light receiving face plate. In addition, this photomultiplier tube includes an electron multiplier section made up of flat dynodes stacked over a plurality of stages at a position facing the photocathode. Each dynode has a plurality of electron multiplying holes for multiplying electrons. An anode for collecting electrons from the electron multiplier is provided at the subsequent stage of the electron multiplier. A flat focusing electrode is disposed between the photocathode and the electron multiplier. The focusing electrode has a focusing portion composed of a plurality of slit-shaped channel openings, and a frame portion arranged around the focusing portion.

  Another example of the photomultiplier tube is described in Patent Document 2.

JP 9-320511 A JP-A-2000-3693

  For example, in a technical field such as optical CT, an extremely short pulsed light of about several picoseconds is irradiated on a living body, and weak light scattered in the living body and appearing on the living body surface again is detected. In order to detect such a slight change in light amount for an extremely short time, a photomultiplier tube capable of realizing a time resolution of about several picoseconds is preferably used. And in order to detect light more rapidly and with high precision, the improvement of the response speed and photoelectric conversion efficiency in a photomultiplier tube is calculated | required.

  In order to increase the response speed of the photomultiplier tube, it is effective to increase the voltage distribution of the first dynode. Further, in order to increase the photoelectric conversion efficiency of the photomultiplier tube, it is effective to increase the efficiency of collecting the electrons emitted from the photocathode. For example, the electrode line that becomes the boundary of the channel opening in the focusing electrode is provided. The efficiency of collecting electrons can be increased by making it thinner. However, in the conventional photomultiplier tube, if the voltage distribution of the first stage dynode is increased, the electric field (electron lens) in the vicinity of the converging portion may be distorted through the frame portion. This tendency becomes more prominent by making the electrode line of the focusing electrode thinner.

  An object of this invention is to provide the photomultiplier tube which can improve a response speed and photoelectric conversion efficiency.

  In order to solve the above-described problems, a photomultiplier tube according to the present invention has a photocathode that photoelectrically converts incident light and emits electrons, and a plurality of electron multiplier holes formed side by side in a predetermined direction. The plate-shaped dynodes are stacked in multiple stages, the first dynode is arranged facing the photocathode, an electron multiplier for multiplying the electrons emitted from the photocathode, and the multiplication Focusing is arranged between the anode for collecting the emitted electrons, the photocathode and the first stage dynode, and focuses the electrons emitted from the photocathode toward the electron multiplier hole of the first stage dynode. And a focusing electrode comprising a plurality of electrode lines arranged in a predetermined direction at intervals corresponding to a plurality of electron multiplier holes and focusing the electrons, and provided around the focusing unit. And a frame portion that supports the electrode wire, Pair of portions of the frame portion located on both sides of the focusing unit in, characterized in that it is arranged so as not to overlap with the first-stage dynode when viewed from the photocathode side.

  In the photomultiplier tube described above, the pair of portions of the frame portion located on both sides of the focusing portion in a predetermined direction are arranged so as not to overlap the first stage dynode as viewed from the photocathode side. Thereby, the distance between the frame portion and the first stage dynode can be sufficiently secured, and the distance between the frame portion and the focusing portion can be sufficiently secured, so that the electron lens of the focusing portion by the first stage dynode voltage can be secured. Can be reduced. Therefore, according to the above-mentioned photomultiplier tube, it is possible to increase the voltage distribution of the first stage dynode and make the electrode wire of the focusing electrode thinner than before, thereby improving the response speed and photoelectric conversion efficiency. it can.

  Further, the photomultiplier tube may be characterized in that the frame portion of the focusing electrode is formed to be thicker than the focusing portion, and the focusing portion is disposed near the end face on the photocathode side in the frame portion. In this way, the frame portion of the focusing electrode is formed thicker than the focusing portion, so that the mechanical strength of the focusing electrode is suitably maintained even if the electrode wire of the focusing portion is made thin in order to increase the electron collection efficiency. it can. In addition, if the electrode wire of the converging part is made thin, the focal length of the electron lens becomes long. However, according to this photomultiplier tube, the converging part is arranged near the end face on the photocathode side in the frame part, so the focal length It is possible to suppress the influence on the outer dimensions of the photomultiplier tube due to the increase in length.

  The photomultiplier tube may be characterized in that the distance between each of the pair of portions of the frame portion and the focusing portion is wider than the interval between the plurality of electrode lines. Thereby, it is possible to further reduce the influence of the focusing unit on the electron lens due to the first-stage dynode voltage.

  According to the photomultiplier tube of the present invention, response speed and photoelectric conversion efficiency can be improved.

  Embodiments of a photomultiplier tube according to the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a side sectional view showing a configuration of an embodiment of a photomultiplier tube according to the present invention. FIG. 2 is a plan view of the photomultiplier tube 1 when the light receiving face plate 11 is omitted in FIG. FIG. 1 shows an II cross section of the photomultiplier tube 1 shown in FIG. In each figure, an XYZ orthogonal coordinate system is shown for convenience of explanation.

  The photomultiplier tube 1 is configured by disposing an electron multiplier section 24 composed of a plurality of dynodes inside a vacuum vessel 10. The vacuum vessel 10 includes a circular light-receiving face plate 11 that receives incident light, a cylindrical metal side tube 12 that is disposed on the outer periphery of the light-receiving face plate 11, and a disk-shaped stem 13 that forms a base portion. It is configured.

  The light receiving face plate 11 is a window member for taking in the light incident on the photomultiplier tube 1. The light receiving surface plate 11 has a light incident surface 11 a that is located outside the vacuum vessel 10 and receives incident light, and an inner surface 11 b that is located inside the vacuum vessel 10. In FIG. 1, the light incident surface 11a and the inner surface 11b of the light receiving surface plate 11 are both provided in parallel with the XY plane. A photocathode 20 made of a semiconductor such as GaAs is formed on the inner surface 11b of the light-receiving face plate 11, and is held at a potential of 0V. In order to prevent thermal damage during the assembly of the photocathode 20, the light receiving face plate 11 and the metal side tube 12 are joined by a cold seal with an indium seal 14, and the outside thereof is held by a holding ring 14a.

  The electron multiplier 24 is a member for secondary electron multiplication of photoelectrons emitted from the photocathode 20. The electron multiplier 24 includes a metal channel type dynode 25 in which a plurality of electron multiplier holes 28 are formed in a rectangular flat metal member, and a secondary electron emission surface is formed on the inner wall of the electron multiplier hole 28. A plurality of layers are stacked in the Z-axis direction. The plurality of electron multiplying holes 28 each extend along the Y-axis direction, and are arranged in a slit shape along the X-axis direction (predetermined direction) (see FIG. 2). Of the plurality of dynodes 25, the first dynode 25 a located at the uppermost part (the endmost part in the positive Z-axis direction) is disposed to face the photocathode 20. Further, an anode electrode 26 and a final stage dynode 27 (both refer to FIG. 1) are sequentially arranged below the plurality of stages of dynodes 25 (in the negative Z-axis direction).

A focusing electrode 21 is disposed between the photocathode 20 and the first stage dynode 25a. Here, FIG. 3 is a perspective view showing a configuration of the focusing electrode 21 of the present embodiment. 4A is a side cross-sectional view showing the peripheral structure of the focusing electrode 21 in the II-II cross section of FIG. 3, and FIG. 4B is an enlarged view of a portion A in FIG. 4A. is there. Referring to FIGS. 3 and 4, the focusing electrode 21 includes a focusing portion 23 for focusing photoelectrons and a frame portion 22 provided around the focusing portion 23. The converging unit 23 includes a plurality of electrode lines 23a extending along the Y-axis direction. A plurality of electrode lines 23a are arranged in the X-axis direction at intervals d ₂ corresponding to the plurality of electron multiplying holes 28 of the first stage dynode 25a. A plurality of channel openings 23b arranged and formed in a slit shape are formed in the converging portion 23 by the plurality of electrode lines 23a. The plurality of channel openings 23b correspond to the plurality of electron multiplier holes 28 (see FIG. 4) of the first-stage dynode 25a, respectively.

  The frame part 22 is formed in a rectangular shape so as to surround the converging part 23, and supports both ends of each electrode line 23a by two sides extending in the X-axis direction. The frame portion 22 is formed to be thicker (the outer dimension in the Z-axis direction is larger) than each electrode line 23a of the converging portion 23. The focusing portion 23 (each electrode line 23 a) is disposed near the end surface (upper surface) 22 e on the photocathode 20 side in the frame of the frame portion 22.

The frame portion 22 has a pair of portions 22a and 22b located on both sides of the converging portion 23 in the X-axis direction. The pair of portions 22 a and 22 b constitute two sides extending in the Y-axis direction in the rectangular frame portion 22. The distance d ₁ between the side surfaces 22c, 22d of the pair of portions 22a, 22b and the electrode lines 23a located at both ends of the converging part 23 is the distance between the plurality of electrode lines 23a (that is, the opening width of the channel opening 23b) d. _It is wider than ₂ . Further, the pair of portions 22a and 22b do not overlap with the first stage dynode 25a when viewed from the photocathode 20 side (that is, a virtual plane B extending downward from the side surfaces 22c and 22d of the pair of portions 22a and 22b in the Z axis). Is arranged outside the outer surface of the first stage dynode 25a).

Examples of the focusing electrode 21 and the electron multiplying unit 24 of the present embodiment are as follows, for example.
Frame part 22 thickness: 0.3 [mm]
Line width of the electrode wire 23a: 0.03 [mm]
Interval d ₁ : 1.1 [mm]
Interval d ₂ : 1.0 [mm]
Voltage value of the first stage dynode 25a: 200.0 [V]

  Refer to FIGS. 1 and 2 again. The focusing electrode 21 is held at the same potential as the photocathode 20. Accordingly, the photoelectrons emitted from the photocathode 20 are focused on the trajectory by the electric field (electron lens) formed by the electrode line 23a of the converging portion 23, and enter the electron multiplier hole 28 of the first stage dynode 25a.

  Here, the effect obtained by the photomultiplier tube 1 of the present embodiment will be described. 5-7 is a figure which shows the creation process of the photomultiplier tube 1 in order to demonstrate the effect of the photomultiplier tube 1 of this embodiment. In these drawings, only parts that are considered necessary in the description are described in a simplified manner.

  Here, the effect obtained by the photomultiplier tube 1 of the present embodiment will be described. 5-7 is a figure which shows the creation process of the photomultiplier tube 1 in order to demonstrate the effect of the photomultiplier tube 1 of this embodiment. In these drawings, only parts that are considered necessary in the description are described in a simplified manner.

  FIG. 5A is a cross-sectional view showing a structure in the vicinity of a focusing electrode in a conventional photomultiplier tube. 5A shows the vacuum vessel 110, the photocathode 120, the first stage dynode 125a, and the focusing electrode 121 disposed between the photocathode 120 and the first stage dynode 125a. Yes. The focusing electrode 121 has a plurality of electrode lines 123 a and a frame portion 122. The inner side surface 122c of the frame portion 122 is disposed corresponding to the electron multiplying holes 128 at both ends of the first stage dynode 125a, and constitutes a part of the channel opening portion 123b together with the electrode line 123a.

In the photomultiplier tube having this configuration, when the width d ₃ of the electrode line 123a is relatively wide with respect to the distance (channel opening width) d ₄ between the electrode lines 123a, the aperture ratio (= d ₄ / ( d ₃ + d ₄ )) is kept low. Accordingly, the present inventors, as shown in FIG. 5 (b), was larger aperture ratio of the focusing electrode 121a by narrowing the width d ₃ of the electrode line 123a. Thereby, the aperture ratio of the focusing electrode 121a was greatly improved, and the collection efficiency of photoelectrons from the photocathode 120 to the first stage dynode 125a was improved. However, by making the electrode line 123a thinner, the curvature of the electric field (electron lens) of the focusing electrode 121a is reduced, and the focal length when the photoelectrons converge is extended. If the relationship between the focal length and the distance between the focusing portion and the first stage dynode 125a is not appropriate, it becomes a factor of reducing the collection efficiency of photoelectrons.

  Therefore, the present inventors moved each electrode line 123a of the focusing electrode 121b away from the first stage dynode 125a as shown in FIG. 6A according to the focal length when the photoelectrons converge. That is, each electrode line 123 a is disposed near the end surface 122 b on the photocathode 120 side in the frame portion 122. As a result, the collection efficiency of the photoelectrons is improved, and the electrode line 123a is moved away from the first stage dynode 125a without moving the focusing electrode 121b itself from the first stage dynode 125a. Succeeded in reducing the impact.

  However, by adjusting the focal length by moving the electrode line 123a away from the first stage dynode 125a, the following new problem emerged. Since the frame part 122 is formed thicker than the electrode lines 123a, the focal lengths of the electrode lines 123a and the frame part 122 located at both ends are different from the focal lengths of the electrode lines 123a. Then, by making each electrode line 123a thinner, such a difference in focal length becomes more remarkable.

  Therefore, as shown in FIG. 6B, the present inventors expand the inner diameter of the frame portion 122 and add an electrode wire 123a, thereby providing a dummy opening in the region along the frame portion 122 in the focusing electrode 121c. A portion 123c is provided. Thereby, the frame part 122 was moved away from the converging part composed of the electrode lines 123a, and an attempt was made to make the focal lengths between the electrode lines 123a uniform. However, as shown in FIG. 6B, if the opening width of the dummy opening 123c is smaller than the opening width of the channel opening 123b formed by the electrode lines 123a, the frame portion 122 is close to the electrode line 123a and the focal length is sufficient. It was found that it was not uniform. Further, when the distance between the frame portion 122 and the first stage dynode 125a is short, the dynode voltage of the first stage dynode 125a affects the focal length of the channel opening 123b via the frame portion 122.

  In order to solve this problem, the inventors of the present invention have a pair of portions 122a and 122b of the frame portion 122 positioned on both sides of the converging portion made of the electrode line 123a, like the converging electrode 121d shown in FIG. Arranged so as not to overlap the first stage dynode 125a when viewed from the photocathode 120 side. The shape of the focusing electrode 121d is the shape of the focusing electrode 21 shown in FIGS. With this configuration, the opening width of the dummy opening portion 123c can be made wider than the opening width of the channel opening portion 123b corresponding to the electron multiplying hole 28 by the electrode lines 123a. A sufficient distance between the frame portion 22) and the focusing portion (electrode line 123a, electrode line 23a shown in FIG. 3) can be secured, and the electric field (electron lens) between the electrode lines 123a (23a) by the frame portion 122 (22) can be secured. Can be sufficiently reduced. In addition, since the distance between the frame part 122 (22) and the first stage dynode 125a (25a) can be sufficiently secured, the influence of the dynode voltage of the first stage dynode 125a (25a) can be reduced, and the first stage dynode 125a ( The dynode voltage of 25a) can be increased.

  As described above, according to the photomultiplier tube 1 according to the present embodiment, the voltage distribution of the first stage dynode 25a can be increased and the electrode line 23a of the focusing electrode 21 can be made thinner than before. Response speed and photoelectric conversion efficiency can be improved.

  Further, as in the present embodiment, the frame portion 22 is preferably formed thicker than the converging portion 23. Thereby, the mechanical strength of the focusing electrode 21 can be favorably maintained even if the electrode line 23a of the focusing portion 23 is thinned in order to increase the collection efficiency of photoelectrons.

  The photomultiplier tube according to the present invention is not limited to the above-described embodiment, and various other modifications are possible. For example, in the above embodiment, the present invention is applied to a focusing electrode having a slit-like opening, but the present invention is also applicable to, for example, a focusing electrode having a matrix-like opening.

It is side surface sectional drawing which shows the structure of one Embodiment of the photomultiplier tube which concerns on this invention. It is a top view of a photomultiplier tube when a light receiving face plate is omitted from the photomultiplier tube shown in FIG. It is a perspective view which shows the structural example of a focusing electrode. (A) It is side surface sectional drawing which shows the periphery structure of the focusing electrode in the II-II cross section of FIG. (B) It is an enlarged view of A part in (a). (A), (b) It is a figure which shows the creation process of a photomultiplier tube. (A), (b) It is a figure which shows the creation process of a photomultiplier tube. It is a figure which shows the creation process of a photomultiplier tube.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Photomultiplier tube, 10 ... Vacuum container, 11 ... Light-receiving surface plate, 11a ... Light incident surface, 11b ... Inner surface, 12 ... Metal side tube, 13 ... Stem, 14 ... Indium seal, 14a ... Holding ring, 17 ... Pin 18 ... Hermetic glass, 20 ... Photocathode, 21 ... Focusing electrode, 22 ... Frame part, 23 ... Focusing part, 23a ... Electrode wire, 23b ... Channel opening, 24 ... Electron multiplication part, 25 ... Dynode, 25a ... First stage dynode, 26... Anode electrode, 27... Last stage dynode, 28.

Claims (3)

A photocathode that photoelectrically converts incident light and emits electrons;
A plate-shaped dynode having a plurality of electron multiplier holes formed side by side in a predetermined direction is laminated in a plurality of stages, and the first dynode is disposed to face the photocathode, An electron multiplier for multiplying the electrons emitted from the photocathode;
An anode for collecting the multiplied electrons;
A focusing electrode disposed between the photocathode and the first stage dynode, and focusing the electrons emitted from the photocathode toward the electron multiplier hole of the first stage dynode; Prepared,
The focusing electrode comprises:
A converging unit comprising a plurality of electrode lines arranged in the predetermined direction at intervals corresponding to the plurality of electron multiplier holes, and condensing the electrons;
A frame portion provided around the converging portion and supporting the electrode wire;
A pair of portions of the frame portion located on both sides of the converging portion in the predetermined direction are arranged so as not to overlap the first stage dynode when viewed from the photocathode side. , Photomultiplier tube. The frame portion of the focusing electrode is formed thicker than the focusing portion;
2. The photomultiplier tube according to claim 1, wherein the converging portion is disposed near an end face of the frame portion on the photocathode side.   3. The photomultiplier tube according to claim 1, wherein an interval between each of the pair of portions of the frame portion and the converging portion is wider than an interval between the plurality of electrode lines.

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