JPH05159740A - Photomultiplier - Google Patents

Abstract

PURPOSE:To improve quantum efficiency by providing the first photoelectron generating means and the second photoelectron generating means for generating a photoelectron by using at least light of not contributing to generation of the photoelectron by this first means. CONSTITUTION:By radiating light passing through a light incident window 4 to the first photocathode film 7 formed in a transmitting glass plate 5, a photoelectron is generated. This photoelectron is attracted to a side of an electrode 11 by an electric field formed by the first mesh-shaped electrode 9 and the focusing electrode 11 or the like, and the photoelectron passing through a mesh of the electrode 11 is attracted to a side of the first step dynode 12 and accelerated. Light radiated through the film 7 without generating the photoelectron is incident upon the second cathode film 8, and the photoelectron is generated by probability of about several 10% the incident light. This photoelectron is attracted to sides of the second mesh-shaped electrode 10 and the electrode 11, and the photoelectron passing through the mesh of this electrode 11 is attracted to the side of the dynode 12 and accelerated. In this way, quantum efficiency can be improved.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a photomultiplier tube used for photon detection.

[0002]

2. Description of the Related Art In recent years, photomultiplier tubes have been widely used for highly sensitive detection of photons in fields such as science and engineering, medicine, environment and space. By the way, the photocathode of the photomultiplier tube has a role of converting the light incident thereon into photoelectrons. The quantum efficiency (the efficiency of converting light into photoelectrons) is an important factor that determines the sensitivity of detecting photons.

In the past, great efforts have been made to develop various compound semiconductors having a small work function as materials for photocathodes in order to increase the quantum efficiency. As a result, a photomultiplier tube with a quantum efficiency of nearly 30% has been produced, depending on the wavelength of light. Thus, the quantum efficiency at the photocathode of the photomultiplier tube is so important that it governs its ability to detect photons. For example, even if the quantum efficiency is 33%, the photon can be detected only after three photons are incident, and therefore it is desired that the quantum efficiency can be significantly improved.

[0004]

Although the above-mentioned efforts have been made to increase the quantum efficiency, there is a strong demand to further increase the efficiency.
However, it has not been possible to achieve a significant improvement in the conventional example.

The present invention has been made in view of the above points, and an object thereof is to provide a photomultiplier tube having a large quantum efficiency without significantly deteriorating the time resolution of the photomultiplier tube.

[0006]

The photomultiplier tube of the present invention comprises a first photoelectron generating means for generating photoelectrons by irradiation of incident light, and a photoelectron generating means for generating photoelectrons by the first photoelectron generating means. By providing at least light that does not contribute to the generation and providing the second photoelectron generating means for generating photoelectrons, not only the incident light is generated by the first photoelectron generating means, but also the first photoelectron generating means is provided. The second photoelectron generating means generates photoelectrons by light that does not contribute to the generation of photoelectrons by the photoelectron generating means so as to have high quantum efficiency. For example, after passing through the first photocathode member in the conventional example, the discarded light is guided to the first photocathode member or the like by a light reflecting mirror to generate photoelectrons, or the first photocathode member. The photoelectron generating means formed of a second photocathode member or the like different from the above is used to generate photoelectrons again, and the quantum efficiency is improved.

[0007]

Embodiments of the present invention will be specifically described below with reference to the drawings. 1 and 2 relate to a first embodiment of the present invention, FIG. 1 shows a schematic cross section of a photomultiplier tube of the first embodiment, and FIG. 2 shows a first photocathode film and a second photocathode film. The formed transmissive glass plate is shown.

As shown in FIG. 1, in the photomultiplier tube 1 of the first embodiment, a transparent circular plate 3 such as a glass plate for transmitting light is provided in one circular opening of a cylindrical and light-shielding housing 2, for example. Is attached to form a light incident window 4 through which light is incident. Inside the light entrance window 4, the transparent disc 3
A thin transmissive glass plate 5 is disposed, for example, in rotational symmetry with respect to the central axis O, and is opposed to the transmissive glass plate 5 and has a disk shape of, for example, substantially the same size as the transmissive glass plate 5. The light reflecting mirror 6 is arranged.

As shown in FIG. 2, the first photocathode film 7 and the second photocathode film are formed on both surfaces of the transmissive glass plate 5, that is, the surface facing the light incident window 4 and the surface facing the light reflecting mirror 6, respectively. 8 is formed by, for example, vapor deposition. The first photocathode film 7 and the second photocathode film 8 are formed of a substance having a high quantum efficiency that generates photoelectrons when irradiated with light. The first photocathode film 7 and the second photocathode film 8 are formed of a substance having a high light transmittance. These first photocathode film 7
The second photocathode film 8 is set to a zero potential, for example.

The first photocathode film 7 forms first photoelectron generating means for generating photoelectrons by incident light. Further, the second photocathode film 8 constitutes second photoelectron generation means for generating photoelectrons by light that does not contribute to the generation of photoelectrons in the first photocathode film 7. In the first embodiment, the light reflecting means is provided, the second photocathode film 8 constitutes the third photoelectron generating means, and the first photocathode film 7 constitutes the fourth photoelectron generating means.

A first mesh electrode 9 is provided between the transparent disc 3 and the transmission type glass plate 5 (that is, the first photocathode film 7).
And the second mesh-shaped electrode 1 between the transmissive glass plate 5 (that is, the second photocathode film 8) and the light reflecting mirror 6.
0 is placed. The first mesh-shaped electrode 9 and the second mesh-shaped electrode 10 have, for example, a conical shape rotationally symmetrical about the central axis O. That is, the first mesh electrode 9
The second mesh electrode 10 and the second mesh electrode 10 are arranged such that the distance from the first photocathode film 7 and the second photocathode film 8 increases as the distance from the central axis O increases.

The first mesh-shaped electrode 9 and the second mesh-shaped electrode 10 are meshes which hardly interfere with the progress of light. For example, the thickness of the mesh is reduced so that the area of the entire mesh portion per unit area is sufficiently smaller than that of the void portion other than the mesh portion. Further, instead of the mesh, a transparent electrode film that transmits light may be formed.

By setting the first mesh electrode 9 and the second mesh electrode 10 to a negative potential, the first mesh electrode 9
The photoelectrons generated in the photocathode film 7 and the second photocathode film 8 can be guided to the outside in the radial direction. Further, the cylindrical focusing electrode 11 covers the peripheral edges of the first mesh electrode 9 and the second mesh electrode 10.
Are arranged. The focusing electrode 11 is also formed in a mesh shape, and by setting the focusing electrode 11 at a positive potential, photoelectrons can be collected on the focusing electrode 11 side, that is, in the radial outside. Also in this focusing electrode 11, the ratio of the void portion of the mesh is made sufficiently wider than the mesh portion so that the photoelectrons are not captured so much. In addition, the periphery of the mesh forming the focusing electrode 11 may be covered with an insulator or the like to reduce the flow of current to the focusing electrode 11 and to increase the function of guiding the current to the first dynode 12 side after collision. ..

A first stage dynode 12 having a shape close to a cylinder or a cone whose diameter is expanded while bulging toward the front side (the traveling direction side of incident light) is arranged further outside the focusing electrode 11. A second stage dynode 13 is arranged adjacent to the first stage dynode 12, and the second stage dynode 13 is arranged so as to further guide the photoelectrons guided by the first stage dynode 12 to the third stage dynode 14. Has been done. The first, second and third dynodes 12, 13 and 14 are set to a positive potential.

The first-stage dynode 12 is a focusing electrode 11
By irradiating the photoelectrons passing through between the meshes, the photoelectrons are multiplied, reflected so that they are bent at about 90 °, advanced to the front side, and guided to the second stage dynode 13. The dynode 13 also serves to multiply photoelectrons by irradiation of photoelectrons, reflect the photoelectrons so that they are bent at about 90 °, and guide the photoelectrons to the third dynode 14 disposed inside the second dynode 13.

The photoelectrons irradiated to the third-stage dynode 14 and similarly multiplied by the latter-stage dynode (not shown) are input to a current measuring device or the like, and are made incident by the current value input to this current measuring device. The amount of light can be detected. The inside of the housing 2 is set to a vacuum.

In this embodiment, not only the first photoelectron generating means is formed by the first photocathode film 7, but also the light which has not contributed to the generation of photoelectrons by the first photoelectron generating means is generated by the second photoelectron generating means. Second photocathode film 8 as a means for generating photoelectrons
And use it to generate photoelectrons. Also, light that does not contribute to the generation of photoelectrons in the second photocathode film 8 is reflected on the front surface or the rear surface of the reflecting mirror 6 and is guided to the second photocathode film 8 that also functions as the third photoelectron generating means. .. Further, the third photoelectron generating means has a mechanism in which light that does not contribute to the generation of photoelectrons is guided to the first photocathode film 7 which also functions as the fourth photoelectron generating means. The operation of the first embodiment thus constructed will be described below.

The light passing through the light incident window 4 is irradiated on the first photocathode film 7 formed on the transmissive glass plate 5, and depends on the material forming the first photocathode film 7. Photoelectrons are generated with a probability of about several tens of percent. The photoelectrons are attracted to the focusing electrode 11 side by the electric field formed by the first mesh electrode 9 and the focusing electrode 11, and the photoelectrons passing through the mesh of the focusing electrode 11 are attracted and accelerated to the first dynode 12 side. .. The photoelectrons are multiplied by the first-stage dynode 1 and further multiplied by the second-stage dynode 1.
It is multiplied by the 3rd and 3rd stage dynodes 14, respectively. This action is similar to the conventional example.

The light that has been applied to the first photocathode film 7 and has passed through the first photocathode film 7 without generating photoelectrons is at least several times the light that contributed to the generation of photoelectrons, and this light is the second light. It is incident on the photocathode film 8 and photoelectrons are generated with a probability of, for example, about several tens of percent of the incidence. The photoelectrons are attracted to the focusing electrode 11 side by the electric field formed by the second mesh electrode 10 and the focusing electrode 11, etc., and the photoelectrons passing through the mesh of the focusing electrode 11 are attracted and accelerated to the first dynode 12 side. .. The subsequent operation is the same as described above. By this action, the quantum efficiency can be improved considerably (for example, about 70%) as compared with the conventional example.

Nearly 100% of the light which has been irradiated onto the second photocathode film 8 and which has passed through the second photocathode film 8 without generating photoelectrons is reflected by the light reflecting mirror 6 and the second photocathode film 8 again. The photoelectrons are generated with a probability of, for example, about several tens of percent. The photoelectrons are generated by the electric field formed by the second mesh-shaped electrode 10 and the focusing electrode 11, etc.
The photoelectrons that are attracted to the side and pass through the mesh of the focusing electrode 11 are attracted and accelerated toward the first-stage dynode 12 side.

The light that has been applied to the second photocathode film 8 and transmitted through the second photocathode film 8 without generating photoelectrons is incident on the first photocathode film 7 and, for example, has a probability of several tens of percent. To occur. The photoelectrons are attracted to the focusing electrode 11 side by the electric field formed by the first mesh electrode 9 and the focusing electrode 11, and the photoelectrons passing through the mesh of the focusing electrode 11 are attracted and accelerated to the first dynode 12 side. ..

According to the first embodiment which operates in this way,
The photoelectrons are generated by the light incident on the light incident window 4 as in the conventional example, and the light that does not contribute to the generation of the photoelectrons in the conventional example is guided to the next (second) photoelectron generating means to generate the photoelectrons. The light that is not used to generate photoelectrons is re-introduced to the second photoelectron generating means and the like by the light reflecting means, and the light that does not contribute to photoelectron generation is reused. Since it is also used for photoelectron generation by being guided to the photoelectron generation means, the quantum efficiency can be greatly improved compared to the conventional example.

Note that, in comparison with the conventional example in which photoelectrons are first generated only by the first photocathode film 7, this embodiment further generates photoelectrons by the light moving between the light reflecting mirror 6 and the transmissive glass plate 5. Therefore, the degree of time resolution is not much different from that of the conventional example, that is, the quantum efficiency can be significantly improved without significantly lowering the time resolution.

FIG. 3 shows a photomultiplier tube 21 according to the second embodiment of the present invention. In this embodiment, a first photocathode film 7 is formed by vapor deposition or the like on the inner surface of the transparent disk 3 forming the light incident window 4 as shown in an enlarged view in FIG. 4 (a). Photoelectrons are generated by the light incident on the first photocathode film 7. In addition, in front of the first photocathode film 7, a disk-shaped light reflecting mirror 6 having a size substantially equal to the size of the first photocathode film 7 is disposed so as to face the light incident window 4 side of the light reflecting mirror 6. The second photocathode film 8 is formed on the surface as shown in FIG.

Conical mesh electrodes 9 and 10 are disposed between the first photocathode film 7 and the second photocathode film 8 and are generated in the first photocathode film 7 and the second photocathode film 8, respectively. The photoelectrons are guided to the outside in the radial direction, and are attracted by the electric field of the focusing electrode 11 arranged on the outside, and are guided to the first dynode 12 arranged on the outside of the focusing electrode 11. The other structure is similar to that of the first embodiment, and the description thereof is omitted. The operation of the second embodiment will be described below.

The light that has passed through the light incident window 4 and is incident on the first photocathode film 7 is, for example, several tens at the first photocathode film 7.
%, Photoelectrons are generated with a probability of about%, and the photoelectrons are generated by the mesh-shaped electrode 9 and the focusing electrode 11 and the like.
Guided to 2. The light transmitted without contributing to the generation of photoelectrons in the first photocathode film 7 is incident on the second photocathode film 8, and photoelectrons are generated with a probability of, for example, about several tens of percent of the incident light. Is guided to the first dynode 12 by the mesh electrode 10, the focusing electrode 11 and the like.

The light transmitted without contributing to the generation of photoelectrons in the second photocathode film 8 is reflected by the light reflecting mirror 6 and returns to the second photocathode film 8 again, with a probability of, for example, about several tens of percent. Generate photoelectrons. The light transmitted without contributing to the generation of photoelectrons in the second photocathode film 8 returns to the first photocathode film 7 side and is used in the generation of photoelectrons in the first photocathode film 7. The second embodiment operating in this way has the same effect as the first embodiment.

FIG. 5 shows a photomultiplier tube 31 according to the third embodiment of the present invention. In this embodiment, for example, a conical surface-shaped transmissive glass plate 5 is arranged in place of the transmissive glass plate 5 in the first embodiment shown in FIG. It is arranged so that it is inclined to the opposite side. As shown in FIG. 6, that is, the first photocathode film 7 and the second photocathode film 8 are formed on both surfaces of the transmissive glass plate 5, as in the first embodiment.

Further, in this embodiment, a first-stage dynode 12 'is arranged in front of the transmission-type glass plate 5, for example, in parallel with the transmission-type glass plate 5, and the first-stage dynode 1 is further provided.
A first-stage dynode 12 is also arranged outside the transmissive glass plate 5 substantially parallel to 2 '. The first-stage dynode 12 has a truncated conical surface shape in which the top side of the conical surface is cut out, and the second-stage dynode 13 is arranged in front of this. A third dynode 14 is arranged inside the second dynode 13.

In this embodiment, the photoelectrons generated in the first photocathode film 7 or the second photocathode film 8 are the first stage dynode 1
The suction is accelerated to 2 or 12 '. In this case, after the photoelectrons attracted to the first-stage dynode 12 'are multiplied,
After being sucked toward the second stage dynode 13 and further multiplied, it proceeds to the third stage dynode 14 and further multiplied. This embodiment does not require a mesh electrode and a focusing electrode. The effect of this embodiment is almost the same as that of the first embodiment.

In this embodiment, instead of the first-stage dynodes 12 or 12 ', mesh-shaped electrodes 9 and 10 shaped like these dynodes may be used.
In that case, the light reflecting mirror 6 (indicated by a dotted line in FIG. 5) is attached. Then, photoelectrons generated in the photocathode film 7 and the photocathode film 8 are attracted to the second dynode 13 side by the mesh electrodes 9 and 10.

FIG. 7 shows a photomultiplier tube 41 according to the fourth embodiment of the present invention. In this embodiment, for example, in the first embodiment of FIG. 1, the light reflecting mirror 6 is arranged at the position of the transmissive glass plate 5.
As shown in FIG. 8, a first photocathode film 7 is formed on the surface of the light reflecting mirror 6 facing the light incident window 4, and is arranged between the light incident window 4 and the light reflecting mirror 6 in the first embodiment. The transparent glass plate 5 is not provided. In addition, this embodiment is based on one mesh electrode 9 of the first embodiment.
Are arranged. Other configurations are the same as those in the first embodiment.

In this embodiment, incident light generates photoelectrons in the first photocathode film 7 in front of it before being reflected by the light reflecting mirror 6, and light which does not contribute to the generation of this photoelectron is reflected by the light reflecting mirror 6. After that, photoelectrons are generated again in the first photocathode film 7. That is, in this embodiment, the light reflecting means is formed on the conventional one provided with the first photocathode film, and the light not contributing to the generation of photoelectrons is guided to the first photocathode film again to generate photoelectrons. is there. That is, this embodiment has a configuration having the functions of the first and second photoelectron generating means. This simple configuration has the advantage that the quantum efficiency can be improved to approximately 1 to 7 times that of the conventional example.

FIG. 9 shows a photomultiplier tube 51 which is a modification of the fourth embodiment. In this modified example, in FIG. 7, the light reflecting mirror 6 having the first photocathode film 7 formed thereon is arranged not to be parallel to the transparent disk 3 but to be inclined so as to substantially face the first-stage dynode 12, and further to have a mesh shape. The configuration is such that the electrode 9 and the focusing electrode 11 are omitted. In this modified example, as in the case of the fourth embodiment, incident light generates photoelectrons in the first photocathode film 7 in front of it before being reflected by the light reflecting mirror 6, and light that does not contribute to the generation of this photoelectron is reflected by the light. After being reflected by the mirror 6, photoelectrons are generated again by the first photocathode film 7. Then, the photoelectrons have a positive potential V1.
To the side of the first stage dynode 12 set to. First
The photoelectrons multiplied by the stage dynode 12 proceed to the side of the second stage dynode 13 set to the positive potential V2, and the photoelectrons multiplied by the second stage dynode 13 have a positive potential V3.
To the side of the third stage dynode 14 set to. The effects of this modification are similar to those of the fourth embodiment, and the configuration can be further simplified. In this modification, the potentials of the first stage dynode 12 to the third stage dynode 14 may be set to a common potential.

In this modification, the light reflecting mirror 6
Since light that is reflected by, and does not contribute to the generation of photoelectrons also travels to the first-stage dynode 12 side, instead of the first-stage dynode 12, a shape like this first-stage dynode 12,
A reflecting mirror formed with the second photocathode film may be used. In this case, an electrode is provided on the second photocathode film itself or on the back surface side thereof and set to a positive potential, and photoelectrons advancing there are reflected and guided to the second dynode 13 side.

In the modification shown in FIG. 9, for example,
Instead of the first photocathode film 7 provided on the light reflecting mirror 6, for example, a structure obtained by weaving a fiber such as an optical fiber having a photocathode film provided on the surface thereof is used as a multilayer structure The photocathode film may be formed later on, or the photocathode film may be formed on a porous transparent member later.), And the incident light is passed through this structure. By making the photocathode film a mechanism that can collide with fibers provided on the surface many times, it is possible to generate photoelectrons with high probability by multiple collisions, even when photoelectrons are not generated in one collision. Is also good.

In this case, the generated photoelectrons are attracted to the first dynode 12 side. In this case, the light reflecting mirror 6 is not always necessary. Further, an electrode set to a negative potential may be provided on the back side of the structure (the side opposite to the light incident window 4). Also with this configuration, higher quantum efficiency than the conventional example can be realized. In this structure, the structure itself constitutes a plurality of photoelectron generating means.

Further, instead of the above structure, a lattice member is arranged in parallel with the surface of the transparent disc 3 of the light incident window 4, and
A plurality of lattice-shaped members may be arranged in multiple layers at a constant pitch in the light incident direction. In this case, a light-reflecting film is formed on the surface of each wire-like member that forms a grid-like member such as a comb-like or mesh-like member, and a photocathode film is further formed on the light-reflecting film. The cross-sectional shape of the wire-shaped member is, for example, an isosceles triangle whose top is on the side of the light-incident window 4, and the light incident from the light-incident window 4 (most of which forms the first-layer lattice-shaped member). The wire-like member), so that photoelectrons can be generated in the photocathode film. When photoelectrons are not generated, they are reflected by the light reflection film and hit the photocathode film again to contribute to the generation of photoelectrons.

Even when the photoelectrons are not generated here, the photoelectrons are efficiently guided to the lattice-like member of the next layer and contribute to the generation of photoelectrons. Then, the first-stage dynodes may be arranged in front of these grid-like members, and the generated photoelectrons may be attracted to the first-stage dynodes. The photocathode film of the grid member is grounded by a lead wire that conducts at, for example, the outer peripheral side end of the grid member.

The present invention is not limited to the above-described one, but may be a structure in which the light reflecting mirror 6 is not provided in the first embodiment, for example. In this case, the functions of the first and second photoelectron generating means are provided as in the fourth embodiment.

Further, in the above description, for example, the second photoelectron generating means is described as generating photoelectrons by utilizing light that does not contribute to the generation of photoelectrons in the first photoelectron generating means.
By using a substance capable of generating photoelectrons even with low energy as the material forming the photocathode film, the photoelectrons are generated in the first photoelectron generating means, and the following second Two
The photoelectron generating means may be able to generate photoelectrons again.

In each of the above-mentioned embodiments, the shape and the like may be modified. Further, different embodiments can be formed by partially combining the above-described embodiments and the like, and these also belong to the present invention.

[0043]

As described above, according to the present invention, the first photoelectron generating means for generating photoelectrons by irradiation of incident light and at least the first photoelectron generating means do not contribute to the generation of photoelectrons. Since the second photoelectron generating means for generating photoelectrons by using light is provided, the quantum efficiency can be significantly improved as compared with the conventional example.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a photomultiplier tube according to a first embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of a transmissive glass plate on which a first photocathode film and a second photocathode film according to the first embodiment are formed.

FIG. 3 is a schematic sectional view of a photomultiplier tube according to a second embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a member having a first photocathode film and a second photocathode film formed in a second embodiment.

FIG. 5 is a configuration diagram showing a specific configuration of a third embodiment of the present invention.

FIG. 6 is an enlarged sectional view showing a transmissive glass plate on which a first photocathode film according to a third embodiment is formed.

FIG. 7 is a schematic sectional view of a photomultiplier tube according to a fourth embodiment of the present invention.

FIG. 8 is an enlarged cross-sectional view showing a light reflecting mirror on which a first photocathode film according to a fourth embodiment is formed.

FIG. 9 is a schematic sectional view of a photomultiplier tube of a modification of the fourth embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Photomultiplier tube 2 ... Housing 3 ... Transparent disc 4 ... Light entrance window 5 ... Transmission type glass plate 6 ... Light reflecting mirror 7 ... 1st photocathode film 8 ... 2nd photocathode film 9 ... 1st mesh shape Electrode 10 ... Second mesh electrode 11 ... Focusing electrode 12 ... First stage dynode 13 ... Second stage dynode 14 ... Third stage dynode

Claims (1)

[Claims] 1. A first photoelectron generating means for generating photoelectrons by irradiation of incident light, and a first photoelectron generating means for generating photoelectrons using at least light that does not contribute to the generation of photoelectrons by the first photoelectron generating means. 2. A photomultiplier tube, characterized in that it is provided with a photoelectron generating means (2).