JPH04345741A - Phototube - Google Patents

Abstract

PURPOSE:To provide a phototube having high possibility of collecting photoelectrons, generated in a photocathode, in an anode despite an outside strong magnetic field, and good photo detecting efficiency. CONSTITUTION:Photoelectrons are generated when a photocathode 13 receives light. The photoelectrons generated in the photocathode 13 are collected with an anode 14. These photocathode 13 and anode 14 are provided in a transmittable glass bulb 12. The photoelectron collecting surface of the anode 14 has an area larger than that of the photoelectron generating surface of the photocathode 13 opposite to the photoelectron collecting surface. Moreover the photoelectron collecting surface of the anode 14 is provided near to the photoelectron generating surface of the photocathode 13.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phototube that can operate even in strong magnetic fields, and is particularly useful in the field of high-energy physics.

0002

2. Description of the Related Art Conventionally, this type of phototube has a cross-sectional structure shown in FIG. A photocathode 2 is formed on the inner wall surface of the glass container 1 facing the light entrance surface 1a, and light arriving from the entrance surface 1a is converted into photoelectrons at the photocathode 2. The converted photoelectrons are attracted by the electric field E to an anode 3 provided opposite the photocathode 2 and captured by the anode 3.

0003

However, in the conventional phototube 4, the strong magnetic field B is applied in a direction perpendicular to the plane of the paper that is perpendicular to the electric field E, in other words, in a direction perpendicular to the normal direction of the light incident surface 1a. In this case, a phenomenon occurs in which photoelectrons generated at the photocathode 2 are no longer captured by the anode 3. In other words, the photoelectrons generated at the photocathode 2 perform a cycloidal motion due to this strong magnetic field B, and perform a circular motion returning to the photocathode 2 as shown by the arrow.

At this time, the trajectory of the photoelectrons generated at the end of the photocathode 2 is outside the space sandwiched between the photocathode 2 and the anode 3, as indicated by the arrow in the longitudinal cross-sectional view of FIG. 6(a). and moves away from the anode 3. FIG. 2B is a cross-sectional view of this phototube, and arrows indicate the trajectory of the photoelectrons generated at the end of the photocathode 2. From the figure, it can be understood that photoelectrons generated at the end of the photocathode 2 move away from the anode 3. Note that in FIGS. 6A and 6B, the same parts as in FIG. 5 are designated by the same reference numerals.

Therefore, in the phototube 4 of the conventional structure,
Photoelectrons generated in the photocathode 2 due to the strong magnetic field B perpendicular to the electric field E may not be captured by the anode 3 as described above. For this reason, the photodetection efficiency of the phototube 4 was reduced. This phenomenon of decrease in detection efficiency appears prominently when the direction of the strong magnetic field B is perpendicular to the normal direction of the light entrance surface 1a, and decreases as the direction of the strong magnetic field B approaches the normal direction of the light entrance surface 1a. do.

[0006]

[Means for Solving the Problems] The present invention has been made to solve the above problems, and the photoelectron collecting surface of the anode has a larger area than the photoelectron generating surface of the photocathode facing thereto, and , the photoelectron collecting surface of the anode is provided in close proximity to the photoelectron generating surface of the photocathode.

Furthermore, in such a phototube, the peripheral edge of the photoelectron collecting surface of the anode is formed closer to the peripheral edge of the photoelectron generating surface of the photocathode.

[0008]

[Operation] Even if photoelectrons generated at the photocathode move outside the space sandwiched between the photocathode and the anode, the anode exists outside this space, so the photoelectrons are likely to be captured by the anode. If the peripheral edge of the photoelectron collecting surface of the anode is formed closer to the photoelectron generating surface of the photocathode, the trajectory of photoelectrons generated at the edge of the photocathode will be extremely close to the peripheral edge of the anode. Therefore, photoelectrons are particularly easy to capture. Also,
Even if a photoelectron moves in a cycloidal motion, moving away from the photocathode and returning again, the anode is close to the photocathode, so the photoelectron is more likely to be captured by the anode at this distance.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view showing a phototube according to an embodiment of the present invention.

The phototube 11 is constructed within a cylindrical glass bulb 12. The top and bottom surfaces of the glass bulb 12 are hermetically sealed, and the interior thereof is maintained in a vacuum state. Further, this glass bulb 12 is made of a transparent material, and its upper surface serves as a light incident surface 12a, forming a translucent airtight container. This glass bulb 12
A photocathode 13 that generates photoelectrons when exposed to light is formed on the inner wall surface facing the light incident surface 12a. Furthermore, an anode 14 that collects photoelectrons generated at the photocathode 13
A photoelectron collecting surface is provided in close proximity to the photoelectron generating surface of the photocathode 13, and the collected photoelectrons are transferred to the lead portion 1.
4a to the outside of the glass bulb 12. This lead portion 14a also serves to hold the anode 14. Further, the photoelectron collecting surface of the anode 14 has a larger area than the photoelectron generating surface of the photocathode 13 facing thereto.

In such a structure, the light incident surface 12a
The light arriving from the photocathode 13 collides with the photocathode 13, where it is converted into photoelectrons. The generated photoelectrons are drawn toward the anode 14 by the electric field E generated between the photocathode 13 and the anode 14, and are captured by the anode 14.

According to the phototube 11 of this embodiment, even if a strong magnetic field B perpendicular to the electric field E is applied, photoelectrons generated at the photocathode 13 are collected at the anode 14 with a high probability. That is, since the photoelectron collecting surface of the anode 14 is larger than the photoelectron generating surface of the photocathode 13, the anode 14 also exists outside the space sandwiched between the photocathode 13 and the anode 14. Therefore, even if the photoelectrons generated at the end of the photocathode 13 undergo cycloidal motion and move out of the space between the photocathode 13 and the anode 14 due to the application of the strong magnetic field B as described above, the photoelectrons will not move out of this space. The probability of being captured by the anode 14 present in the area increases. Furthermore, even if the photoelectrons generated at the photocathode 13 make a cycloidal motion and take a trajectory that once moves away from the photocathode 13 and then returns again, the anode 14
Since the anode 14 is located close to the anode 14, the probability that photoelectrons will be captured by the anode 14 at this far distance is extremely high.

Therefore, according to the phototube 11 according to the present embodiment, even if a strong magnetic field B is applied in a direction perpendicular to the normal direction of the light incident surface 12a and the photoelectrons generated in the photocathode 13 undergo cycloidal motion, the anode The probability of being collected on 14 is extremely high. As a result, the photodetection efficiency of the phototube 11 is not affected by the external magnetic field B and is always maintained in a good state.

FIG. 2 is a sectional view showing the structure of a phototube according to another embodiment of the present invention. In the phototube 21 according to this embodiment, the inner wall cross section of the glass bulb 22 on the light incident surface 22a side is formed in a convex shape, and the photocathode 23 is formed on this convex surface. The anode 24 is provided close to the photocathode 23 and has a photoelectron collecting surface 24a having a larger area than the photoelectron generating surface of the photocathode 23. Furthermore, a side wall 24b that is closer to the peripheral end of the photoelectron generating surface of the photocathode 23 is formed at the peripheral end of the photoelectron collecting surface 24a. That is, this side wall 24b is formed so as to surround the peripheral end of the photocathode 23.

According to this embodiment, in addition to the same effects as the above embodiment, the following effects are also achieved. In other words, the electric field E generated between the photocathode 23 and the anode 24
A strong magnetic field B is applied in the direction perpendicular to the photocathode 23, and the photoelectrons generated at the end of the photocathode 23 move in a cycloid and move toward the anode 24.
Even if the photoelectrons try to move away from the anode 24, the trajectory of the photoelectrons collides with the side wall 24b at the peripheral end of the anode 24. Therefore, most of the photoelectrons generated at the end of the photocathode 23 are transferred to the side wall 24b.
Becomes captured by. Therefore, the phototube 21 according to this embodiment has a higher light detection efficiency than the phototube 11 according to the above embodiment.

FIG. 3(a) shows a photocell 21 according to this embodiment.
3 is a graph showing a change in photodetection sensitivity with respect to a change in the direction of an external magnetic field B. FIG. The horizontal axis of the graph indicates the incident angle θ[°\] of this external magnetic field B. In the same figure (b), this incident angle θ is
This is the angle that the magnetic field B makes with respect to the normal direction of a. Also,
The vertical axis of the graph shows the detection sensitivity S of the optical signal input to the light incidence surface 22a when the external magnetic field B is applied at an incident angle of θ°, and the detection sensitivity S when the external magnetic field B is applied at the incident angle of 0°. It represents the value S/S (0°) normalized by the detection sensitivity S (0°) of the optical signal input to . This detection sensitivity S(0
°) is the detection sensitivity when the photoelectrons generated at the photocathode 23 are least influenced by the external magnetic field B.

A characteristic curve a shown by a solid line shows the characteristics obtained with the phototube 21 according to this embodiment, and a characteristic curve b shown by a dotted line shows the characteristics obtained by the phototube 4 of the conventional structure shown in FIG. ing. As can be understood from the graph, in the phototube 4 of the conventional structure, the photodetection sensitivity begins to deteriorate when the incident angle θ of the magnetic field B is around 50°.
In the phototube 21 according to this embodiment, the light detection sensitivity begins to deteriorate when the incident angle θ of the magnetic field B is around 75°. That is, in the phototube 21 according to this embodiment, even if the incident angle θ of the external magnetic field B becomes a steep angle, the photodetection sensitivity is less degraded. That is, since the photocathode 23 and the anode 24 are close to each other, the photoelectron collection surface of the anode 24 is large, and the side wall 24b is formed at the peripheral end of the anode 24, the direction of application of the external magnetic field B is directed to the light entrance surface 22a. Even when approaching the direction parallel to the photocathode 23, the probability that the photoelectrons generated at the photocathode 23 will be collected at the anode 24 is extremely high.

FIG. 4 is a sectional view showing the structure of a phototube according to another embodiment of the present invention. In the phototube 31 according to this embodiment, the cross section of the inner wall surface on the light incident surface 32a side of the glass bulb 32 is formed in a convex shape as in the above embodiment, and the photocathode 33 is formed on this convex surface. The anode 34 is formed on the inner wall surface of the glass bulb 32, which faces closely to the photocathode on which the photocathode 33 is formed. This anode 34 has a photoelectron collecting surface 34a having a larger area than the photoelectron generating surface of the photocathode 33, and
The peripheral end portion 34b of is located closer to the photocathode 33.

The phototube 31 according to this embodiment has almost the same structure as the phototube 21 according to the above embodiment, and has the same effects as the above embodiment.

[0020]

As explained above, according to the present invention, even if photoelectrons generated at the photocathode move outside the space sandwiched between the photocathode and the anode, the anode also exists outside this space, so the photoelectrons are becomes easily captured by this anode. If the peripheral edge of the photoelectron collecting surface of the anode is formed closer to the photoelectron generating surface of the photocathode, the trajectory of photoelectrons generated at the edge of the photocathode will be extremely close to the peripheral edge of the anode. Therefore, photoelectrons are particularly easy to capture. Furthermore, even if a photoelectron makes a cycloidal motion and takes a trajectory that once moves away from the photocathode and returns again, the anode is close to the photocathode, so the photoelectron is more likely to be captured by the anode at this distance.

Therefore, the probability that photoelectrons generated at the photocathode will be collected at the anode regardless of an external strong magnetic field is increased, and a phototube with good photodetection efficiency can be provided.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the structure of a phototube according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the structure of a first phototube according to another embodiment of the present invention.

FIG. 3 is a diagram showing a change in photodetection sensitivity with respect to a change in the direction of the external magnetic field B of the phototube shown in FIG. 2.

FIG. 4 is a cross-sectional view showing the structure of a second phototube according to another embodiment of the present invention.

FIG. 5 is a diagram showing the structure of a conventional phototube.

FIG. 6 is a diagram for explaining the trajectory taken by photoelectrons generated at the end of a photocathode in a conventional phototube.

[Explanation of symbols]

11...Phototube 12...Glass bulb 12a...Light incidence surface 13...Photocathode (photoelectron generation surface) 14...Anode (photoelectron collection surface) 14a...Lead part

Claims (3)

[Claims] 1. A phototube comprising a photocathode that generates photoelectrons when exposed to light, and an anode that collects photoelectrons generated at the photocathode, wherein a photoelectron collecting surface of the anode is arranged on the photoelectron collecting surface. A phototube having a larger area than the photoelectron generating surface of the opposing photocathode, and wherein the photoelectron collecting surface of the anode is provided close to the photoelectron generating surface of the photocathode. 2. The phototube according to claim 1, wherein the peripheral edge of the photoelectron collecting surface of the anode is formed closer to the peripheral edge of the photoelectron generating surface of the photocathode. 3. The phototube according to claim 1, wherein the anode is formed integrally with a photocathode and a translucent sealed container housing the anode.