JP4459635B2 - Electron tube and manufacturing method thereof - Google Patents

Description

  The present invention relates to an electron tube having a photocathode that emits photoelectrons by light incident from the outside and a method for manufacturing the same.

Conventionally, a photocathode used for detecting light incident from the outside and an electron tube equipped with the photocathode are known. Since such a photocathode is generally made of a P-type semiconductor and has a relatively high electric resistance, a technique for maintaining photosensitivity by providing a thin film such as a metal oxide along the photocathode. Is used (see, for example, Patent Document 1 and Patent Document 2).
Japanese Examined Patent Publication No. 62-20654 Japanese Patent Publication No. 29-524

  However, in the above-described conventional technology, the resistance value of the photocathode increases at the time of measurement in a low temperature environment, and the photosensitivity tends to decrease. That is, the P-type semiconductor used as the photocathode material and the metal oxide used as the thin film both have negative resistance characteristics with respect to temperature.

  In particular, in the recent measurement of cosmic rays in the field of astrophysics, measurement using liquid argon or a scintillator is performed. As a result of an increase of several orders of magnitude, the overall photosensitivity of the electron tube decreases.

  Therefore, the present invention has been made in view of such problems, and an object thereof is to provide an electron tube capable of sufficiently maintaining photosensitivity even in a low temperature environment and a method for manufacturing the same.

  The electron tube of the present invention is a container having a light-transmitting light incident surface, a conductive layer provided on the inner side of the light incident surface, and provided on the conductive layer, and is incident from the outside through the container and the conductive layer. A photocathode that emits photoelectrons by light, and the conductive layer is formed on the light incident surface, and is made of a metal film made of a platinum group metal and a metal formed in a linear pattern along the light incident surface. And a conductor.

  The method of manufacturing an electron tube according to the present invention includes a step of depositing a platinum group metal on the inner side of a light-transmitting light incident surface of a container to form a metal film, and a slit having a predetermined shape on the inner side of the light incident surface of the container. After providing a mask and depositing a metal, the method includes forming a conductor by removing the mask and forming a photocathode on a conductive layer including the metal film and the conductor.

  In such an electron tube and an electron tube manufactured by such an electron tube manufacturing method, light incident from the light incident surface into the container passes through the conductive layer and hits the photoelectric surface to emit photoelectrons. At this time, by providing a metal film made of a platinum group metal and a conductor having a linear pattern along the photocathode, the conductivity of the entire photocathode is improved even in a low temperature environment, and the light in the conductive layer is also increased. Is sufficiently secured.

  In addition, the conductor is preferably formed radially from the center of the light incident surface. With such a configuration, the conductivity of the entire photocathode is effectively increased.

  Furthermore, it is preferable that the conductor is further formed in an annular shape on the light incident surface. In this case, the conductivity can be made more uniform on the photocathode.

  Furthermore, the conductor is preferably made of aluminum. In this way, the conductor can be easily formed, and even when the conductor is miniaturized due to its low resistivity, the light transmittance in the conductive layer is maintained while maintaining the conductivity of the photocathode. Enhanced.

  According to the electron tube of the present invention, the photosensitivity can be sufficiently maintained even in a low temperature environment.

  Hereinafter, preferred embodiments of an electron tube and a manufacturing method thereof according to the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. Further, the dimensional ratios in the drawings do not necessarily match those described.

  FIG. 1 is a side view showing a preferred embodiment of an electron tube according to the present invention. As shown in the figure, a photomultiplier tube 1 which is an electron tube according to the present invention is a device for emitting photoelectrons by light incident from the outside and outputting the photoelectrons as a current. The photomultiplier tube 1 includes a glass bulb (container) 5 having a translucent dome-shaped light incident surface 3, a photocathode 7, a contact film 9, an electron multiplier 11, an anode 12, And a socket 13.

  The glass bulb 5 has a cylindrical convex portion 15 projecting outward on one end side of a substantially spherical container, and is made of a translucent material such as glass. In addition, an electron multiplying unit 11 is installed in the center of the glass bulb 5. The glass bulb 5 as a whole has translucency, but only the light incident surface 3 may be formed of a translucent material.

  An aluminum contact film 9 for supplying a voltage of a predetermined potential to the photocathode 7 is formed on the surface of the crow bulb 5 other than the region where the photocathode 7 is formed. The contact film 9 is electrically connected to a conductive layer (details will be described later) formed in the photocathode 7.

  The electron multiplying unit 11 is for multiplying photoelectrons emitted from a photocathode 7 (details will be described later) provided in the vicinity of the light incident surface 3 and collecting it as a current. A dynode (not shown) which is a multi-stage electrode for multiplying photoelectrons emitted from the cathode 7 is provided. Also, an anode 12 for collecting photoelectrons multiplied by the dynode is installed in the vicinity of the electron multiplier 11 on one end side in the glass bulb 5. Further, a focusing electrode (not shown) for efficiently allowing photoelectrons emitted from the photocathode to enter the electron multiplier 11 at a predetermined position between the electron multiplier 11 and the photocathode 7 in the glass bulb 5. Are arranged in an annular shape.

  A socket 13 is attached to the end surface 19 of the convex portion 15 of the glass bulb 5, and a conductive wire 17 extending from the inside of the glass bulb 5 passes through the socket 13 and the end surface 19. The conductive wire 17 is used to supply a voltage having a predetermined potential to each electrode in the glass bulb 5 or to take out a current flowing between the photocathode 7 and the anode. Furthermore, the conductive line 17 is electrically connected to the contact film 9 and supplies a voltage to the photocathode 7 through the contact film 9.

  As described above, the photocathode 7 is formed in a dome shape inside the light incident surface 3 on the other end side of the glass bulb 5. FIG. 2 is an end view taken along the axis of the light incident surface and the photocathode of FIG. As shown in the figure, the photocathode 7 is formed by forming a conductive layer 21 and a photocathode 23 on a glass bulb 5 in this order. The conductive layer 21 includes a metal film 21a formed along the light incident surface 3 and a conductor 21b formed in a linear pattern on the metal film 21a.

  The metal film 21a is mainly composed of a platinum group metal such as ruthenium, rhodium, palladium, osmium, iridium, or platinum. Among such platinum group metals, platinum is more preferably used from the viewpoint of its chemical stability in the process of photocathode processing.

  The conductor 21b is made of a metal such as aluminum, chromium, silver, gold, or a platinum group metal. Among these metal materials, aluminum is preferably used because of its high workability and high conductivity, and chromium is preferably used because of its high strength, but aluminum is more preferably used because it has a lower melting point and is easy to process. .

  The conductor 21b is formed on the metal film 21a in a predetermined linear pattern. 3A is a diagram illustrating an example of a conductor formation pattern viewed from the light incident surface side, and FIG. 3B is a diagram illustrating another example of the conductor formation pattern viewed from the light incident surface side. is there. Referring to FIG. 3A, the conductor 21b includes eight curve patterns P1 extending in a radial pattern from the vicinity of the center of the light incident surface 3 to the edge, and two adjacent conductors 21b. The curved line pattern P2 extends radially to the edge between the curved line patterns P1, and is shorter than the curved line pattern P1 on the center side. Further, as shown in FIG. 3B, the conductor 21b has the axis of the glass bulb 5 so as to short-circuit adjacent curve patterns P1 and P2 in order to make the conductivity of the entire photocathode 7 uniform. Further, it may be formed with an annular curve pattern P3 centering on.

  In addition, each curve pattern P1, P2, P3 has a film thickness of several μm and a line width of about 2 mm in order to reduce the electrical resistance of the conductor 21b and at the same time not reduce the light transmittance in the photocathode 7. Provided. The curved patterns P1 and P2 may be formed so as to extend from the edge of the light incident surface 3 onto the contact layer 9. In this case, the electric potential of the entire photocathode 7 is more uniformly maintained by electrically connecting the conductor 21b and the contact layer 9.

The photocathode 23 emits photoelectrons toward the electron multiplying unit 11 by light incident from the outside through the glass bulb 5 and the conductive layer 21. The photocathode 23 is made of a P-type semiconductor whose main component is SbCs ₃ , SbK ₂ Cs or the like that is an alkali metal. Among these P-type semiconductors, SbK ₂ Cs is more suitable as a material for the photocathode 23 in terms of spectral sensitivity characteristics similar to those of scintillators used for cosmic ray observation and the like. Here, the scintillator emits fluorescence having a certain decay time by the incidence of radiation. This scintillator is used in combination with the photomultiplier tube 1 to detect radiation such as cosmic rays.

  In the photomultiplier tube 1 described above, light incident on the glass bulb 5 from the light incident surface 3 passes through the conductive layer 21 and hits the photocathode 23 to emit photoelectrons. At this time, the conductive layer 21 is provided with a metal film 21 a made of a platinum group metal and a conductor 21 b having a linear pattern along the photocathode 23. Here, the metal film 21a of the photomultiplier tube 1 is formed so as to transmit light having a wavelength of 170 nm to 650 nm with a transmittance of 75% or more, and the photosensitivity of the photomultiplier tube 1 is high. Sufficiently secured. In addition, the metal film 21a is formed so as to transmit light having a wavelength of 170 nm to 650 nm with a transmittance of 90% or less, and the resistance value of the entire photocathode 7 is a constant value even in an extremely low temperature state. It is suppressed to the following. For example, when the platinum film is used as the material of the metal film 21a, the film thickness that satisfies the above light transmittance is not less than 10 mm (1 nm) and not more than 50 mm (5 nm). Thus, even when the metal film 21a is thinned to ensure 90% of the light transmittance of the metal film 21a, the entire resistance value of the photocathode 7 is reduced due to the presence of the conductor 21b.

  Further, in the case where only the conductive lines are provided on the substrate as in the photocathode described in JP-A-54-146952, it is difficult to miniaturize the conductive lines in order to maintain the conductivity of the photocathode. is there. On the other hand, since the metal film 21a and the conductor 21b are complementary to each other in terms of conductivity, the conductor 21b can be miniaturized, and as a result, the transmittance of light incident on the photocathode 23 is increased. be able to. Therefore, the conductivity of the entire photocathode 7 is enhanced even in a low temperature environment, and the light transmittance in the conductive layer 21 is sufficiently ensured.

4 and 5 show experimental results relating to the linearity of the anode output current of the photomultiplier tube 1. FIG. 4 is a graph showing the linearity of the anode output current of a conventional product measured in an environment of room temperature (25 ° C.) and low temperature (−10 ° C.), and FIG. 5 is a graph showing room temperature (25 ° C.) and liquid argon 3 is a graph showing the linearity of the anode output current of the photomultiplier tube 1 of the present invention measured in an environment of a cryogenic temperature (−196 ° C.), which is a temperature (in the conventional product, an extreme of −196 ° C. is shown). At low temperatures, the anode output current was below the detection limit, making it impossible to measure linearity.) In this case, as the photomultiplier tube 1, a glass bulb 5 having a maximum diameter of about 20.3 cm (8 inches), a platinum metal film 21a having a film thickness of about 30 mm, and a line as shown in FIG. Used was a conductor 21b made of aluminum having a pattern, and a photocathode 23 having SbK ₂ Cs as a main material and a manganese oxide film as a base. As a conventional product, a photomultiplier tube having the same configuration as that of the photomultiplier tube 1 was used except that the conductive layer was not provided.

  Here, the linearity of the anode output current was measured as follows. First, a shielding plate having four shutter holes was installed between the measurement light source and the light incident surface 3 perpendicular to the axis of the photomultiplier tube 1. The ratio of the anode output current when each shutter was opened separately and the anode output current when all the shutters were opened simultaneously was calculated as a current ratio. The same measurement was performed by changing the light amount of the measurement light source. The change in the light amount of the measurement light source corresponds to the change in the anode output current on the horizontal axis in FIGS.

  As shown in FIGS. 4 and 5, in the conventional product in which the conductive layer 21 does not exist in a room temperature environment, the anode output current is saturated near 10 nA and the linearity is deteriorated, whereas the photoelectron increase. In the double tube 1, it can be seen that the output current has a good linearity up to about 5 μA. Furthermore, in the low temperature environment of −196 °, the linearity of the conventional product is greatly deteriorated, but the anode output current of the photomultiplier tube 1 has a good linearity up to about 5 μA. In general, when the resistance of the photocathode is high, the anode output current with respect to the incident light intensity tends to saturate. Therefore, these measurement results show that the conductivity of the entire photocathode 7 is not only in a room temperature environment but also at a low temperature. It shows that the environment is improving.

  Next, the manufacturing method of the photomultiplier tube by this invention is demonstrated.

First, the glass bulb 5 is housed in a bell jar (vacuum deposition apparatus), and the inside of the bell jar is depressurized with a vacuum pump until the pressure becomes 1 × 10 ⁻³ to 1 × 10 ⁻⁶ Pa. Thereafter, aluminum is vacuum-deposited in a region other than the light incident surface 3 in the glass bulb 5 to form a contact film 9. Further, platinum is vacuum-deposited on the inner side of the light incident surface 3 of the glass bulb 5 until the film thickness is about 10 to 50 mm to form the metal film 21a. Here, the contact film 9 and the metal film 21a are formed so as to be in electrical contact with each other at their boundaries.

Next, the inside of the bell jar is once returned to atmospheric pressure, and a mask having a slit having a predetermined shape as shown in FIG. 3 (a) or 3 (b) is provided on the surface on which the metal film 21a is formed. The inside of the bell jar is depressurized until the pressure becomes 1 × 10 ⁻³ to 1 × 10 ⁻⁶ Pa. The conductor 21b is formed by vacuum-depositing aluminum to a thickness of several μm and then removing the mask. The conductor 21b may be provided until it extends on the contact film 9.

Furthermore, after the electron multiplier 11 and the focusing electrode are attached in the glass bulb 5, the glass bulb 5 is connected to an exhaust device for photocathode activation prepared separately. Then, after the inside of the glass bulb 5 is depressurized to 1 × 10 ⁻⁵ Pa or less by the exhaust device, a predetermined film thickness is obtained from the manganese vapor deposition coil provided on the focusing electrode to the metal film 21b in the glass bulb 5. Until vacuum deposition (not shown). Then, after evacuation is stopped and oxygen gas is introduced into the glass bulb 5, manganese on the metal film 21b in the glass bulb is oxidized.

  Next, after the pressure inside the glass bulb 5 is reduced again to a sufficient atmospheric pressure, the antimony is formed on the conductive layer 21 composed of the metal film 21a and the conductor 21b in the glass bulb 5 so as to obtain an optimum film thickness. Is vacuum deposited. Thereafter, after the glass bulb 5 is housed in the electric furnace, the temperature in the electric furnace is raised. Then, in a state where the inside of the glass bulb 5 is maintained at a predetermined temperature, the photocathode 23 is formed by reacting antimony on the conductive layer 21 with an alkali metal. Further, the photocathode 23 is stabilized by leaving the glass bulb 5 at a predetermined temperature for a predetermined time in an electric furnace. After the photocathode 23 is stabilized, the glass bulb 5 is gradually cooled to room temperature, and at the same time, the exhaust device is removed from the glass bulb 5.

  Finally, after attaching the socket 13 and the conductive wire 17 to the end surface of the convex portion 15 of the glass bulb 5, measurement of predetermined items for performance confirmation is performed.

The present invention is not limited to the embodiments described above, for example, as the material of the photomultiplier tube 1 of the photocathode 23, SbCs 3, _SbK 2 P-type semiconductor such as _Cs has been used However, you may use what contains other alkali metals, such as sodium and rubidium.

  In the photocathode 7, the conductor 21b is provided on the metal film 21a. However, as shown in FIG. 6, the conductor 21b and the metal film 21a are provided on the glass bulb 5 in this order. May be. In this case, in the step of forming the metal film 21a and the conductor 21b, the metal film 21a may be formed after the conductor 21b is formed on the glass bulb 5.

  In the photomultiplier tube 1 according to the present embodiment, the photocathode 7 is provided in the photomultiplier tube. However, the photomultiplier tube is not limited to the photomultiplier tube, and is not limited to the photomultiplier tube. A photocathode 7 may be provided.

1 is a side view showing a preferred embodiment of an electron tube according to the present invention. FIG. 2 is an end view along an axis of a light incident surface and a photocathode in FIG. 1. (A) is a figure which shows an example of the conductor formation pattern seen from the light-incidence surface side of FIG. 1, (b) shows another example of the conductor formation pattern seen from the light-incidence surface side of FIG. FIG. It is a graph which shows the linearity of the anode output current of the conventional product measured in the environment of room temperature (25 degreeC) and low temperature (-10 degreeC). It is a graph which shows the linearity of the anode output current of the photomultiplier tube of this invention measured in the environment of room temperature (25 degreeC) and cryogenic temperature (-196 degreeC). It is an end elevation which shows another embodiment of the light-incidence surface and photocathode concerning this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Photomultiplier tube (electron tube), 3 ... Light incident surface, 5 ... Glass bulb (container), 7 ... Photocathode, 9 ... Contact film | membrane, 11 ... Electron multiplier part, 13 ... Socket, 17 ... Conductive wire, 21 ... conductive layer, 21a ... metal film, 21b ... conductor, 23 ... photocathode.

Claims (5)

A container having a light-transmitting light incident surface;
A conductive layer provided inside the light incident surface;
A photocathode that is provided on the conductive layer and emits photoelectrons by light incident through the container and the conductive layer;
With
The conductive layer is formed on the light incident surface, and includes a metal film made of a platinum group metal and a metal conductor formed in a linear pattern along the light incident surface.
An electron tube characterized by that. The conductor is formed radially from the center of the light incident surface.
The electron tube according to claim 1, wherein: The conductor is further formed in an annular shape on the light incident surface.
The electron tube according to claim 2, wherein: The conductor is made of aluminum.
The electron tube according to claim 1, wherein: Forming a metal film by depositing a platinum group metal inside the light-transmitting light incident surface of the container; and
Providing a mask having a slit having a predetermined shape inside the light incident surface of the container and depositing a metal, and then forming the conductor by removing the mask; and
Forming a photocathode on a conductive layer including the metal film and a conductor;
An electron tube manufacturing method comprising:

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