JP2007157442A - Photomultiplier tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photomultiplier tube for detecting ultraviolet light which is capable of having solar-blind characteristics highly accurately. <P>SOLUTION: A photomultiplier tube 1 comprises: a vacuum container 10 having a light receiving plate 11 for receiving light to be detected; a photoemissive face 20 which is formed in the vacuum container 10 and emits photoelectrons by converting light to be detected into electrons; a plurality of stages of dynodes 25a-25h which are arranged in the vacuum container 10, and each of them has a secondary electron emitting face, wherein the photoemissive surface 20 includes AL<SB>X</SB>Ga<SB>1-X</SB>N (0≤X<1); and a series of cascading dynodes 25a-25d which are included in the plurality of stages of dynodes 25a-25h in an electron multiplier 24 and include a first-stage dynode 25a for receiving photoelectrons emitted from the photoemissive face 20, and each of them has a beryllium copper alloy substrate and a secondary electron emission surface which is formed on the beryllium copper alloy substrate containing beryllium oxide. <P>COPYRIGHT: (C)2007,JPO&INPIT

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 is composed of a vacuum envelope (vacuum container), a transparent face plate (window member) provided at one end of the vacuum envelope, and a photoelectron emission cathode (photovoltaic) formed on the inner surface of the face plate. Surface) and a plurality of dynodes. Each dynode has a so-called box shape, and is arranged so that photoelectrons from the photoelectron emission cathode are transferred between the dynodes.

JP-A-60-262341

  In the output characteristics of photomultiplier tubes, the sensitivity wavelength limit on the long wavelength side (long wavelength side cutoff wavelength) is determined by the sensitivity wavelength range of the photocathode, and the sensitivity wavelength limit on the short wavelength side (short wavelength side cutoff wavelength) is It is determined by the cutoff wavelength of the window member. However, when a part of the incident light taken in from the window member slightly passes through the photocathode and reaches another part (for example, dynode) in the vacuum vessel, the constituent material at that part receives the incident light and receives photoelectrons. May be released. At this time, if the cut-off wavelength on the long wavelength side of the constituent material of the part is longer than that of the photocathode, an unintended long wavelength sensitivity characteristic different from the spectral sensitivity characteristic of the photocathode will occur in the output of the photomultiplier tube. . As a result, a noise component is added to the output of the photomultiplier tube, which contributes to a decrease in the S / N ratio.

  Here, FIG. 6 is a graph showing the spectral sensitivity characteristics of alkali antimony (Cs—K—Sb) generally used as a material for the secondary electron emission surface of the dynode. As shown in FIG. 6, the spectral sensitivity characteristic of alkali antimony extends to a wavelength of 750 nm that is a visible region. Therefore, even when a photocathode having a solar blind characteristic with extremely low sensitivity to the visible range, where the long wavelength cut-off wavelength is included in the ultraviolet range (wavelength 350 nm or less), is incident as described above. When part of the light reaches the dynode, photoelectrons corresponding to the wavelength component in the visible range are emitted from the dynode. As a result, the sensitivity wavelength range of the photomultiplier tube extends to the visible range, and the solar blind characteristics deteriorate.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a photomultiplier tube capable of realizing solar blind characteristics with high accuracy in a photomultiplier tube for detecting ultraviolet light.

  In order to solve the above problems, a configuration of the photomultiplier tube according to the present invention will be described. In the following description, the sensitivity wavelength limit on the long wavelength side means a wavelength at which the spectral sensitivity falls to 1% of the maximum spectral sensitivity.

A first photomultiplier tube according to the present invention includes a vacuum container having a window member for taking in incident detected light, and a photoelectric surface provided in the vacuum container for photoelectrically converting the detected light to emit photoelectrons. And a plurality of dynodes having a secondary electron emission surface disposed in a vacuum vessel, and an electron multiplier for multiplying photoelectrons emitted from the photocathode by secondary electrons. At least two stages including Al _X Ga _1-X N (0 ≦ X <1) and including a first dynode that receives photoelectrons from the photocathode among a plurality of dynodes of the electron multiplier section The secondary electron emission surface of the dynode includes a material whose sensitivity wavelength limit on the long wavelength side does not exceed the sensitivity wavelength limit on the long wavelength side of Al _X Ga _1-X N.

Some incident light that has passed through the photocathode mainly reaches the first dynode that receives electrons from the photocathode, but may reach the second dynode via the first dynode. is there. Here, Al _X Ga _1-X N used for the photocathode has sensitivity to light having a wavelength of 155 nm to 350 nm included in the ultraviolet region. Further, in the first photomultiplier tube described above, the sensitivity wavelength limit on the long wavelength side of the material contained in the secondary electron emission surface of at least two dynodes continuous including the first dynode is, The sensitivity wavelength limit (350 nm) on the long wavelength side of the photocathode material (Al _X Ga _1-X N) is not exceeded. That is, the sensitivity wavelength limit on the long wavelength side of the dynode in the range where the incident light reaches does not exceed the sensitivity wavelength limit on the long wavelength side of the photocathode material. Thus, according to a first photomultiplier tube described above, the sensitivity characteristics on the long wavelength side in the photomultiplier tube is substantially coincident with the spectral sensitivity characteristics of the photoelectric surface _{(Al X Ga 1-X N} ), Al X Good solar blind characteristics of Ga _1-X N can be used without deteriorating as sensitivity characteristics of the photomultiplier tube. Thereby, the solar blind characteristic can be realized with high accuracy.

Further, the first photomultiplier tube has a secondary electron emission surface with beryllium oxide, MgO, Cs-I, diamond, Cs-Te, Cs-Br, Na-Br, K-Br, Li-Br, Rb. including -I, K-I, Na- I, Li-I, MgZnO, Al 2 O 3, SiO 2, ZnO, NiO, Rb-Te, at least one kind of material out of the K-Te, and Na-Te This may be a feature. Each of the materials described above preferably functions as a secondary electron emission surface, and the sensitivity wavelength limit on the long wavelength side in the spectral sensitivity characteristic does not exceed the sensitivity wavelength limit on the long wavelength side of Al _X Ga _1-X N ( For example, beryllium oxide: 160 nm, MgO: 250 nm, Cs-I: 200 nm, diamond: 250 nm, Cs-Te: 320 nm). Therefore, according to the first photomultiplier tube, it is possible to suitably realize a secondary electron emission surface including a material whose sensitivity wavelength limit on the long wavelength side does not exceed the sensitivity wavelength limit on the long wavelength side of the photocathode material.

In the first photomultiplier tube, the window member may include at least one material of sapphire and AlN. Al _X Ga _1-X N used for the photocathode has sensitivity to light with a wavelength of 155 nm to 350 nm. Moreover, since the cut-off wavelength of sapphire and AlN used for the window member is shorter than 350 nm, light in part or all of the long wavelength side in the wavelength range in which the photocathode has sensitivity is suitably transmitted. it can. Therefore, according to this photomultiplier tube, it is possible to suitably detect ultraviolet light having a wavelength of 350 nm or less.

A second photomultiplier tube according to the present invention is provided in a vacuum container having a window member for taking in incident detected light, and in the vacuum container, and photoelectrically converts the detected light to emit photoelectrons. A photocathode, and a multi-stage dynode having a secondary electron emission surface and disposed in a vacuum vessel, and an electron multiplier for multiplying photoelectrons emitted from the photocathode by secondary electrons. The sensitivity wavelength limit on the long wavelength side of the surface is included in the ultraviolet region, and at least two continuous dynodes including the first dynode that receives photoelectrons from the photocathode among the multiple dynodes of the electron multiplier section are included. The secondary electron emission surface in the dynode is MgO, Cs-I, diamond, Cs-Te, Cs-Br, Na-Br, K-Br, Li-Br, Rb-I, KI, Na-I, Li _{-I, MgZnO, Al 2 O 3} , SiO 2, ZnO , NiO, Rb—Te, K—Te, and Na—Te.

  Each of the above materials preferably functions as a secondary electron emission surface, and the sensitivity wavelength limit on the long wavelength side in the spectral sensitivity characteristic does not exceed the ultraviolet region (for example, MgO: 250 nm, Cs-I: 200 nm, diamond : 250 nm, Cs-Te: 320 nm). In addition, as described above, part of the incident light transmitted through the photocathode may reach the second dynode via the first dynode. In the second photomultiplier tube described above, the secondary electron emission surface of at least two stages of dynodes including the first stage dynode includes at least one of the above materials. . Therefore, according to the second photomultiplier tube described above, the sensitivity wavelength limit on the long wavelength side in the dynode in the range where the incident light reaches does not exceed the ultraviolet region, so that the solar blind characteristic of the photocathode has high accuracy. realizable.

In the second photomultiplier tube, the photocathode includes CsI, the window member includes at least one material of MgF ₂ , CaF ₂ , BaF ₂ , LiF, quartz, and sapphire, and includes at least two stages. The secondary electron emission surface of the dynode may include at least one material of MgO, Cs-I, Cs-Br, Rb-I, KI, Na-I, and Li-I. Good. Cs-I used for the photocathode has sensitivity to light having a wavelength of 115 nm to 200 nm included in the ultraviolet region. Further, since MgF ₂ , CaF ₂ , BaF ₂ , LiF, quartz, and sapphire used for the window member have a cutoff wavelength shorter than 200 nm, a part on the long wavelength side in the wavelength range in which the photocathode has sensitivity. Alternatively, light in the entire wavelength range can be suitably transmitted. Therefore, according to this photomultiplier tube, ultraviolet light having a wavelength of 200 nm or less can be suitably detected. Further, the sensitivity wavelength limit on the long wavelength side of each material used for the at least two-stage dynodes is sensitive to a wavelength longer than the sensitivity wavelength limit (200 nm) on the long wavelength side of Cs-I which is a photocathode material. Extremely small enough to be ignored. For example, the sensitivity wavelength limit of MgO on the long wavelength side is longer than Cs-I (250 nm), but its sensitivity (quantum efficiency) is extremely small. In addition, the sensitivity wavelength limit on the long wavelength side of Cs-I, Cs-Br, Rb-I, KI, Na-I, and Li-I exceeds the sensitivity wavelength limit on the long wavelength side of Cs-I, respectively. Absent. Therefore, according to this photomultiplier tube, the sensitivity characteristic on the long wavelength side in the photomultiplier tube substantially coincides with the spectral sensitivity characteristic of the photocathode (Cs-I). Can be used without degrading the sensitivity characteristic of the photomultiplier tube. Thereby, the solar blind characteristic can be realized with higher accuracy.

  In addition, the first or second photomultiplier tube has a secondary electron emission surface in another dynode arranged on the rear side of at least two dynodes among the plurality of dynodes, and the alkali metal and Sb. It may be characterized by containing a compound consisting of. A compound composed of an alkali metal and Sb (for example, Cs—K—Sb) has higher secondary electron emission efficiency than MgO, Cs—I, diamond, Cs—Te and the like described above. Therefore, among the dynodes in a plurality of stages, the dynodes on the front stage (including the first stage dynode) where the incident light is likely to reach have long wavelengths such as MgO, Cs-I, diamond, and Cs-Te. Adopting a secondary electron emission surface whose sensitivity wavelength limit on the side does not exceed the ultraviolet region, and a dynode on the rear stage side where incident light is less likely to reach, a secondary electron emission surface containing a compound comprising an alkali metal and Sb Should be adopted. Thereby, the solar blind characteristic can be realized with high accuracy, and a sufficient secondary electron multiplication factor can be secured in the electron multiplication unit.

  A third photomultiplier tube according to the present invention is provided in a vacuum container having a window member for taking in incident detected light, and in the vacuum container, and photoelectrically converts the detected light to emit photoelectrons. A photocathode, and a multi-stage dynode having a secondary electron emission surface and disposed in a vacuum vessel, and an electron multiplier for multiplying photoelectrons emitted from the photocathode by secondary electrons. The sensitivity wavelength limit on the long wavelength side of the surface is included in the ultraviolet region, and at least two continuous dynodes including the first dynode that receives photoelectrons from the photocathode among the multiple dynodes of the electron multiplier section are included. The secondary electron emission surface in the dynode contains beryllium oxide, and the secondary electron emission surface in another dynode arranged on the rear side of at least two dynodes contains a compound composed of an alkali metal and Sb. And butterflies.

  Beryllium oxide suitably functions as a secondary electron emission surface, and the sensitivity wavelength limit (160 nm) on the long wavelength side in the spectral sensitivity characteristics does not exceed the ultraviolet region. In addition, as described above, part of the incident light transmitted through the photocathode may reach the second dynode via the first dynode. In the third photomultiplier tube described above, the secondary electron emission surface of at least two successive dynodes including the first dynode contains beryllium oxide. Therefore, since the sensitivity wavelength limit on the long wavelength side in the dynode in the range where the incident light reaches does not exceed the ultraviolet region, the solar blind characteristic of the photocathode can be realized with high accuracy. Furthermore, in the third photomultiplier tube described above, the secondary electron emission surface in another dynode arranged on the rear stage side with respect to the at least two dynodes contains a compound composed of an alkali metal and Sb. A compound composed of an alkali metal and Sb (for example, Cs—K—Sb) has higher secondary electron emission efficiency than beryllium oxide. Therefore, according to the third photomultiplier tube described above, the solar blind characteristic can be realized with high accuracy, and a sufficient secondary electron multiplication factor can be secured in the electron multiplier section.

In the third photomultiplier tube, the photocathode includes CsI, and the window member includes at least one material of MgF ₂ , CaF ₂ , BaF ₂ , LiF, quartz, and sapphire. Also good. When the photocathode contains Cs-I and the window member contains at least one material of MgF ₂ , CaF ₂ , BaF ₂ , LiF, quartz, and sapphire, ultraviolet light having a wavelength of 200 nm or less can be obtained as described above. It can detect suitably. Further, the sensitivity wavelength limit (160 nm) on the long wavelength side of beryllium oxide used in the at least two-stage dynodes does not exceed the sensitivity wavelength limit (200 nm) on the long wavelength side of Cs-I that is the photocathode material. Therefore, according to this photomultiplier tube, the sensitivity characteristic on the long wavelength side in the photomultiplier tube substantially coincides with the spectral sensitivity characteristic of the photocathode (Cs-I). Can be used without degrading the sensitivity characteristic of the photomultiplier tube. Thereby, the solar blind characteristic can be realized with higher accuracy.

In the second or third photomultiplier tube, the photocathode includes CsTe, and the window member includes at least one material selected from MgF ₂ , CaF ₂ , BaF ₂ , LiF, quartz, sapphire, and diamond. It may be characterized by including. Cs-Te used for the photocathode has sensitivity to light with a wavelength of 115 nm to 320 nm included in the ultraviolet region. In addition, since MgF ₂ , CaF ₂ , BaF ₂ , LiF, quartz, sapphire, and diamond used for the window member have a cutoff wavelength shorter than 320 nm, the photocathode has a sensitivity on the long wavelength side in the wavelength range. Light in a part or all of the wavelength range can be suitably transmitted. Therefore, according to this photomultiplier tube, it is possible to suitably detect ultraviolet light having a wavelength of 320 nm or less. Further, the sensitivity wavelength limit of each material used for the at least two-stage dynodes on the long wavelength side (for example, beryllium oxide: 160 nm, Mg—O: 250 nm, Cs—I: 200 nm, diamond: 250 nm, Cs—Te: 320 nm) ) Does not exceed the sensitivity wavelength limit (320 nm) on the long wavelength side of CsTe, which is a photocathode material. Therefore, according to this photomultiplier tube, the sensitivity characteristic on the long wavelength side in the photomultiplier tube substantially coincides with the spectral sensitivity characteristic of the photocathode (Cs-Te), so that the good solar blind characteristic possessed by Cs-Te. Can be used without degrading the sensitivity characteristic of the photomultiplier tube. Thereby, the solar blind characteristic can be realized with higher accuracy.

  In the first to third photomultiplier tubes, a plurality of dynodes of the electron multiplier section are formed in a plate shape and stacked together, and a secondary electron emission surface is formed on the inner wall in a predetermined direction. It may have a plurality of electron multiplier holes formed side by side, and the first stage dynode may be arranged to face the photocathode. In such a so-called metal channel type photomultiplier tube, since plate-like dynodes are stacked in the incident direction of incident detection light, the incident light transmitted through the photocathode is in the first stage dynode. It is easy to reach the dynodes in the second and subsequent stages through. Therefore, in the photomultiplier tube having such a dynode structure, the solar blind characteristics can be realized with higher accuracy by adopting the structures such as the first to third photomultiplier tubes described above.

  According to the present invention, solar blind characteristics can be realized with high accuracy in a photomultiplier tube that detects ultraviolet light.

  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. The photomultiplier tube of the present embodiment is a photomultiplier tube having a solar blind characteristic that has sensitivity to ultraviolet detection light and extremely low sensitivity to visible light. FIG. 1 shows an XYZ orthogonal coordinate system 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 detected 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 is formed on the inner surface 11b of the light receiving face plate 11 inside the vacuum vessel 10, 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 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 multiplying portion 24 is a metal channel type dynode 25a to 25a in which a plurality of electron multiplying 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 multiplying hole 28. 25h is stacked in a plurality of stages in the Z-axis direction. The plurality of electron multiplying holes 28 extend along the Y-axis direction, and are arranged in a slit shape along the X-axis direction (predetermined direction). Of the plurality of stages of dynodes 25a to 25h, the first stage dynode 25a located at the uppermost part (the endmost part in the Z-axis positive direction) is disposed to face the photocathode 20. In addition, an anode electrode 26 and a final stage dynode 27 are sequentially disposed below the dynode 25 h (Z-axis negative direction). A focusing electrode 21 for focusing photoelectrons from the photocathode 20 toward the first stage dynode 25a is disposed between the photocathode 20 and the first stage dynode 25a.

  A stem 17 serving as a base is penetrated by a pin 17 that is connected to an external voltage terminal and applies a predetermined voltage to the focusing electrode 21 and the dynodes 25a to 25h, 27, and the like. Each pin 17 is fixed to the stem 13 by a tapered hermetic glass 18. The above-described electron multiplier 24 is placed on the stem 13.

Here, the constituent materials of the light receiving face plate 11, the photocathode 20, and the dynodes 25a to 25h will be described. The photocathode 20 is sensitive to ultraviolet light to be detected and has no sensitivity to visible light (that is, a material whose long wavelength side sensitivity wavelength limit is included in the ultraviolet region), such as Al _X It is configured to include at least one material of Ga _1-X N (0 ≦ X <1), Cs—Te, and Cs—I. The light-receiving face plate 11 is made of a material whose cut-off wavelength on the short wavelength side is shorter than the sensitivity wavelength on the long wavelength side of the photocathode 20, for example, MgF ₂ , CaF ₂ , BaF ₂ , LiF, quartz (synthetic quartz or fused quartz). , Sapphire, diamond, and AlN.

Among the dynodes 25a to 25h, at least two continuous dynodes including the first dynode 25a (for example, four continuous dynodes 25a to 25d) are connected to the beryllium copper alloy substrate and the beryllium copper alloy substrate. A secondary electron emission surface including beryllium oxide formed on the inner wall of the formed electron multiplying hole. Alternatively, these four-stage dynodes 25a to 25d include a stainless (SUS) substrate and MgO, Cs-I, diamond, Cs-Te, Cs-Br, Na-Br, K-Br, formed on the stainless steel substrate, Material group consisting of Li—Br, Rb—I, KI, Na—I, Li—I, MgZnO, Al ₂ O ₃ , SiO ₂ , ZnO, NiO, Rb—Te, K—Te, and Na—Te And a secondary electron emission surface including at least one material. In this case, the secondary electron emission surfaces of the dynodes 25a to 25d are formed on the inner wall of the electron multiplying hole 28 formed in the stainless steel substrate. The other dynodes 25e to 25h arranged on the rear side of the at least two dynodes (dynodes 25a to 25d) are preferably selected with an emphasis on secondary electron emission ability. And a secondary electron emission surface containing a compound (for example, Cs—K—Sb, Cs—Sb, etc.) made of alkali metal and Sb formed on the substrate. The secondary electron emission surfaces of the dynodes 25e to 25h are formed on the inner wall of the electron multiplying hole 28 formed in the substrate.

Table 1 is a table showing suitable combinations of constituent materials in the photocathode 20, the light-receiving face plate 11, and the substrates and secondary electron emission faces of the dynodes 25a to 25d.

  The beryllium copper alloy mentioned as the substrate material of the dynodes 25a to 25d functions suitably as a secondary electron emission surface when the surface is oxidized (beryllium oxide). Further, by using a non-magnetic beryllium copper alloy substrate for the dynodes 25a to 25d, electrons (photoelectrons and secondary electrons) can fly stably in the electron multiplier 24.

  Here, the graph G1 in FIG. 2 shows the spectral sensitivity characteristic of the oxidized beryllium copper alloy, that is, beryllium oxide. As shown in FIG. 2, the sensitivity wavelength limit on the long wavelength side in the spectral sensitivity characteristics of beryllium oxide is about 160 nm and does not exceed the ultraviolet region. The same applies to the beryllium copper alloy that is the substrate material. That is, the sensitivity of the dynodes 25a to 25d with respect to visible light is extremely small enough to be ignored. Therefore, even when a part of incident light transmitted through the photocathode 20 reaches the dynodes 25a to 25d, beryllium copper alloy is used as the substrate material of the dynodes 25a to 25d, and the secondary electron emission surface is oxidized. By using beryllium, the solar blind characteristics of the photomultiplier tube 1 can be realized with high accuracy.

  Further, a part of the incident light transmitted through the photocathode 20 mainly reaches the first stage dynode 25a that receives photoelectrons from the photocathode 20. Depending on the conditions of the incident light such as the incident angle, the first stage The second dynode 25b may be reached via the second dynode 25a. In the photomultiplier tube 1, at least two dynodes (in this embodiment, four dynodes 25a to 25d) including the first dynode 25a are connected to a beryllium copper alloy substrate and the beryllium copper alloy. And a secondary electron emission surface containing beryllium oxide formed on the substrate. Therefore, according to the photomultiplier tube 1 of the present embodiment, since the sensitivity wavelength limit on the long wavelength side in the dynodes 25a to 25d in the range where the incident light reaches does not exceed the ultraviolet region, the solar blind characteristics can be made more accurate. realizable.

  Here, the graph G2 in FIG. 3A is a photomultiplier in which AlGaN is used as the material of the photocathode 20, beryllium copper alloy is used as the substrate material of the dynodes 25a to 25d, and the secondary electron emission surface is beryllium oxide. 4 is a graph showing sensitivity characteristics of the tube 1. Note that alkali antimony (Cs—K—Sb) is used for the secondary electron emission surfaces of the dynodes 25e to 25h. For comparison, a graph G3 in FIG. 3B shows sensitivity characteristics in a photomultiplier tube in which AlGaN is used for the photocathode and Cs—K—Sb is used for the secondary electron emission surfaces of all dynodes. It is a graph. In FIG. 3B, a graph G4 shows the spectral sensitivity characteristic of the AlGaN photocathode.

  As shown in the graph G3 in FIG. 3B, all dynodes are obtained even when AlGaN having a good solar blind characteristic (very low sensitivity to visible light longer than 350 nm) is used as the photocathode. When Cs—K—Sb is used for the secondary electron emission surface, the sensitivity to visible light is increased, and the solar blind characteristics of the photomultiplier tube are deteriorated. This is because photoelectrons are emitted from the Cs—K—Sb secondary electron emission surface when the visible wavelength component transmitted through the photocathode reaches the dynode. The spectral sensitivity characteristic of Cs—K—Sb is as shown in FIG.

  On the other hand, when a beryllium copper alloy is used as the substrate material of the dynodes 25a to 25d and the secondary electron emission surface is beryllium oxide, the sensitivity of the dynodes 25a to 25d with respect to visible light becomes extremely small to a negligible level. Even if the visible wavelength component transmitted through the surface 20 reaches the dynodes 25a to 25d, the solar blind characteristics of the photomultiplier tube 1 are not deteriorated. Therefore, as shown in FIG. 3A, the sensitivity characteristic in the photomultiplier tube 1 of the present embodiment is a good solar blind characteristic.

As described above, the secondary electron emission surfaces of the dynodes 25a to 25d are Cs-I, Cs-Te, MgO, diamond, Cs-Br, Na-Br, K-Br, Li-Br, Rb-I. , K-I, Na-I , Li-I, MgZnO, Al 2 O 3, at least one material of SiO 2, ZnO, NiO, material group consisting of Rb-Te, K-Te, and Na-Te May be used. Here, graphs G5 and G6 in FIG. 4 are graphs showing the spectral sensitivity characteristics of Cs-I and Cs-Te, respectively. A graph G7 in FIG. 5A is a graph showing the spectral sensitivity characteristic of MgO, and a graph G8 in FIG. 5B is a graph showing the spectral sensitivity characteristic of diamond.

As shown in graphs G5 to G8 in FIGS. 4 and 5A, 5B, the sensitivity wavelength limit on the long wavelength side in the spectral sensitivity characteristics of Cs-I, Cs-Te, MgO, and diamond is 200 nm, respectively. 320 nm, 250 nm, and 250 nm, which do not exceed the ultraviolet region. That is, the sensitivity of the dynodes 25a to 25d with respect to visible light is extremely small enough to be ignored. Although not shown, Cs—Br, Na—Br, K—Br, Li—Br, Rb—I, KI, Na—I, Li—I, MgZnO, Al ₂ O ₃ , SiO ₂ , ZnO, The same applies to NiO, Rb-Te, K-Te, and Na-Te. Accordingly, even when a part of incident light transmitted through the photocathode 20 reaches the dynodes 25a to 25d, the photoelectrons can be obtained by using at least one material of the above material group for the dynodes 25a to 25d. The solar blind characteristic of the multiplier 1 can be realized with high accuracy. In particular, Cs-I, Cs-Te, MgO, and diamond are easy to manufacture and are suitable as secondary electron emission surfaces. In addition, as described above, depending on the incident light conditions such as the incident angle, the second dynode 25b may be reached via the first dynode 25a. Therefore, the solar blind characteristic can be realized with higher accuracy by forming the secondary electron emission surface in at least two stages of dynodes (dynodes 25a to 25d) using at least one kind of material of the material group. .

  Further, when the above material group other than beryllium oxide is used as the secondary electron emission surface, a stainless steel substrate may be used for the dynodes 25a to 25d. By using a non-magnetic stainless steel substrate, electrons (photoelectrons and secondary electrons) can fly stably in the electron multiplier 24. Stainless steel also has good solar blind properties.

Further, as shown in Table 1, when the photocathode 20 is configured to include Cs-I, the constituent material of the light receiving face plate 11 is at least one of MgF ₂ , CaF ₂ , BaF ₂ , LiF, quartz, and sapphire. One type is preferred, and MgF ₂ is most preferred. Cs-I used for the photocathode 20 has sensitivity to light with a wavelength of 115 nm to 200 nm included in the ultraviolet region. In addition, since MgF ₂ , CaF ₂ , BaF ₂ , LiF, quartz, and sapphire used for the light receiving face plate 11 have a cutoff wavelength shorter than 200 nm, the photocathode 20 (Cs-I) has a sensitivity in the wavelength range. Among them, light in a part or all of the wavelength range on the long wavelength side can be suitably transmitted. Accordingly, ultraviolet light having a wavelength of 200 nm or less can be suitably detected by such a combination.

  Further, when Cs-I is used as the photocathode 20, the substrate material and the secondary electron emission surface in the dynodes 25a to 25d are sensitive to wavelengths longer than the sensitivity wavelength limit (200 nm) on the long wavelength side of Cs-I. It is preferable that it is not at all or extremely small so as to be negligible. For example, when beryllium oxide is used for the dynodes 25a to 25d, the sensitivity wavelength limit (160 nm) on the long wavelength side of beryllium oxide is the sensitivity wavelength limit (200 nm) on the long wavelength side of Cs-I that is the material of the photocathode 20. Shorter than. Therefore, the sensitivity characteristic on the long wavelength side in the photomultiplier tube 1 can be matched with the spectral sensitivity characteristic of the photocathode 20 (Cs-I), so that the good solar blind characteristic possessed by Cs-I can be increased. The sensitivity characteristics of the double tube 1 can be used without being deteriorated.

  When Cs-I is used as the photocathode 20, Cs-I, MgO, Cs-Br, Rb-I, KI, Na-I, and Li are used as secondary electron emission surfaces in the dynodes 25a to 25d. At least one material of -I may be used. When Cs-I is used as the secondary electron emission surface, the sensitivity wavelength limit on the long wavelength side of the secondary electron emission surface is the same as that of the photocathode (Cs-I). The sensitivity wavelength limit of MgO on the long wavelength side is longer than Cs-I (250 nm) as shown in graph G7 in FIG. 5A, but its sensitivity (quantum efficiency) is compared with Cs-I. And very small. Further, the sensitivity wavelength limits on the long wavelength side of Cs—Br, Rb—I, KI, Na—I, and Li—I are shorter than Cs—I, respectively. Accordingly, at least one material of Cs-I, MgO, Cs-Br, Rb-I, KI, Na-I, and Li-I is used as the secondary electron emission surface in the dynodes 25a to 25d. As a result, the sensitivity characteristic on the long wavelength side of the photomultiplier tube 1 can be made to substantially coincide with the spectral sensitivity characteristic of the photocathode 20 (Cs-I). Thereby, since the favorable solar blind characteristic which Cs-I has can be used as the sensitivity characteristic of the photomultiplier tube 1 without deteriorating, the solar blind characteristic can be realized with high accuracy.

As shown in Table 1, when the photocathode 20 includes Cs—Te, the constituent material of the light receiving face plate 11 is MgF ₂ , CaF ₂ , BaF ₂ , LiF, quartz, sapphire, and diamond. At least one of them is preferable, and MgF ₂ is most preferable. Cs-Te used for the photocathode 20 has sensitivity to light having a wavelength of 115 nm to 320 nm included in the ultraviolet region. In addition, since MgF ₂ , CaF ₂ , BaF ₂ , LiF, quartz, sapphire, and diamond used for the light receiving face plate 11 have a cutoff wavelength shorter than 320 nm, the photocathode 20 (Cs-Te) has a sensitive wavelength. Light in a part or all of the wavelength range on the long wavelength side in the range can be suitably transmitted. Accordingly, ultraviolet light having a wavelength of 320 nm or less can be suitably detected by such a combination.

Further, when Cs-Te is used as the photocathode 20, the substrate material and the secondary electron emission surface in the dynodes 25a to 25d are sensitive to wavelengths longer than the sensitivity wavelength limit (320 nm) on the long wavelength side of Cs-Te. It is preferable that it is not at all or extremely small so as to be negligible. For example, the above materials used for the secondary electron emission surface (beryllium oxide, Cs—I, Cs—Te, MgO, diamond, Cs—Br, Na—Br, K—Br, Li—Br, Rb—I, K -I, Na-I, Li- I, MgZnO, Al 2 O 3, SiO 2, ZnO, NiO, Rb-Te, K-Te, and Na-Te) on the long wavelength side of the sensitivity wavelength limit (e.g., oxide (Beryllium: 160 nm, MgO: 250 nm, Cs-I: 200 nm, diamond: 250 nm, Cs-Te: 320 nm) is the same as the sensitivity wavelength limit (320 nm) on the long wavelength side of Cs-Te that is the material of the photocathode 20 Shorter than that. Therefore, the sensitivity characteristic on the long wavelength side in the photomultiplier tube 1 can be matched with the spectral sensitivity characteristic of the photocathode 20 (Cs-Te), so that the good solar blind characteristic of Cs-Te can be increased. The sensitivity characteristics of the double tube 1 can be used without being deteriorated. Thereby, the solar blind characteristic can be realized with high accuracy.

Further, as shown in Table 1, when the photocathode 20 includes Al _X Ga _1-X N (0 ≦ X <1), the constituent material of the light-receiving face plate 11 is at least one of sapphire and AlN. The type is preferable, and sapphire is particularly preferable from the viewpoint of cost. Al _X Ga _1-X N used for the photocathode 20 has sensitivity to light having a wavelength of 155 nm to 350 nm included in the ultraviolet region. Moreover, since the sapphire and AlN used for the light-receiving surface plate 11 have a cut-off wavelength shorter than 350 nm, a part on the long wavelength side in the wavelength range in which the photocathode 20 (Al _X Ga _1-X N) is sensitive or Light in the entire wavelength range can be suitably transmitted. Accordingly, ultraviolet light having a wavelength of 350 nm or less can be suitably detected by such a combination.

Further, when Al _X Ga _1-X N is used as the photocathode 20, the substrate material and the secondary electron emission surface in the dynodes 25a to 25d have a sensitivity wavelength limit (350 nm on the long wavelength side of Al _X Ga _1-X N). It is preferred that there is no sensitivity to wavelengths longer than (1) or very small enough to be ignored. For example, the above materials used for the secondary electron emission surface (beryllium oxide, Cs—I, Cs—Te, MgO, diamond, Cs—Br, Na—Br, K—Br, Li—Br, Rb—I, K -I, Na-I, Li- I, MgZnO, Al 2 O 3, SiO 2, ZnO, NiO, Rb-Te, K-Te, and Na-Te) on the long wavelength side of the sensitivity wavelength limit (e.g., oxide Beryllium: 160 nm, MgO: 250 nm, Cs—I: 200 nm, diamond: 250 nm, Cs—Te: 320 nm) are sensitivity wavelength limits (350 nm) on the long wavelength side of Al _X Ga _1-X N that is the material of the photocathode 20. Shorter than). Therefore, since the sensitivity characteristic on the long wavelength side in the photomultiplier tube 1 can be matched with the spectral sensitivity characteristic of the photocathode 20 (Al _X Ga _1-X N), Al _X Ga _1-X N has. Good solar blind characteristics can be used without deteriorating as sensitivity characteristics of the photomultiplier tube 1. Thereby, the solar blind characteristic can be realized with high accuracy.

Further, as in the present embodiment, the multistage dynodes 25a to 25h of the electron multiplying unit 24 may be so-called metal channel dynodes. In the photomultiplier tube 1 having a metal channel type dynode, since the dynodes 25a to 25h are stacked in the incident direction of the incident detection light, the incident light transmitted through the photocathode 20 is the first stage dynode 25a. It is easy to reach the second and subsequent dynodes (for example, dynodes 25b to 25d) by passing through. Therefore, as in this embodiment, the secondary electron emission surface of at least two successive dynodes including the first dynode 25a is the material group (beryllium oxide, Cs—I, Cs—Te, MgO, Diamond, Cs—Br, Na—Br, K—Br, Li—Br, Rb—I, KI, Na—I, Li—I, MgZnO, Al ₂ O ₃ , SiO ₂ , ZnO, NiO, Rb— By including at least one material of Te, K-Te, and Na-Te), the solar blind characteristics can be realized with high accuracy in the metal channel type photomultiplier tube 1.

  Further, as in the present embodiment, among the plurality of dynodes 25a to 25h, secondary electron emission surfaces in the other dynodes 25e to 25h arranged on the rear stage side with respect to the dynodes 25a to 25d are alkali metals and Sb. It is preferable that the compound which consists of (for example, Cs-K-Sb, Cs-Sb etc.) is included. The compound composed of alkali metal and Sb has higher secondary electron emission efficiency than the above-described beryllium oxide, MgO, Cs-I, diamond, Cs-Te, and the like. Accordingly, among the dynodes 25a to 25h in a plurality of stages, the dynodes 25a to 25d on the front stage side where incident light is likely to reach has a secondary electron emission surface including at least one kind of material in the material group, for example. Adopting secondary electron emission surfaces including compounds composed of alkali metals and Sb may be employed for the dynodes 25e to 25h on the rear stage side where the possibility of incident light reaching is low. Thereby, the solar blind characteristic can be realized with high accuracy, and a sufficient secondary electron multiplication factor can be secured in the electron multiplication unit 24. If Cs-Sb containing no K is used as the secondary electron emission surface in the dynodes 25e to 25h, the secondary electron emission surface can be formed simultaneously with the photocathode 20 made of Cs-I or Cs-Te. It is. Further, if Cs—K—Sb is used as the secondary electron emission surface in the dynodes 25e to 25h, the dark current on the secondary electron emission surface can be reduced.

  Here, an example of a method for manufacturing the photomultiplier tube 1 according to the above embodiment will be described. First, an AlGaN crystal film is epitaxially grown by MOCVD on the inner surface 11b of the light-receiving face plate 11 made of sapphire. Next, the surface of the AlGaN crystal film is cleaned by chemical etching, and the light receiving face plate 11 is introduced into the transfer vacuum apparatus.

  Subsequently, a beryllium copper alloy substrate serving as a substrate for the dynodes 25a to 25h is prepared, and the beryllium copper alloy substrate serving as the preceding dynodes 25a to 25d is exposed to an oxygen atmosphere while being heated at a high temperature. Beryllium oxide is formed on the surface (including the inner wall of the electron multiplier hole 28). On the other hand, Sb is vapor-deposited on the surface of the stainless steel substrate (including the inner wall of the electron multiplying hole 28) to be the subsequent dynodes 25e to 25h. Then, these substrates are assembled on the stem 13 together with the anode electrode 26 and the focusing electrode 21 and the metal side tube 12 is welded, and the substrate is introduced into the transfer vacuum apparatus. Similarly, a seal member obtained by fusing the indium seal 14 to the inner periphery of the holding ring 14a is also introduced into the transfer vacuum apparatus.

  Subsequently, each part introduced into the transfer vacuum apparatus is degassed by baking. The AlGaN crystal film of the light receiving face plate 11 is subjected to heat cleaning at a high temperature of about 700 ° C. to remove contaminants on the crystal surface at the atomic level. Thereafter, cesium and oxygen are vapor-deposited on the surface of the AlGaN crystal film and activated to have a negative electron affinity, whereby the AlGaN photocathode 20 is completed. Further, the surface including the inner wall of the electron multiplying hole 28 is exposed to the stainless steel substrate to be the subsequent dynodes 25e to 25h by first exposing to a potassium atmosphere while maintaining a temperature of about 300 ° C. and then to a cesium atmosphere. A secondary electron emission surface made of Cs—K—Sb is formed.

  Finally, the sealed vacuum container 10 is formed by joining the metal side tube 12 and the light receiving face plate 11 via the indium seal 14 in the transfer vacuum apparatus. The photomultiplier tube 1 is completed through the above steps.

  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 dynode having a slit-shaped electron multiplier hole. However, the present invention is also applicable to a dynode having a matrix-shaped electron multiplier hole, for example. In addition to the metal channel type, the present invention is also applicable to a photomultiplier tube having another dynode configuration such as a mesh type.

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 graph which shows the spectral sensitivity characteristic of beryllium oxide. (A) It is a graph which shows the sensitivity characteristic of the photomultiplier tube which used AlGaN as a material of a photocathode, used beryllium copper alloy as a substrate material of the dynode of the front | former stage, and used the beryllium oxide as the secondary electron emission surface. (B) Graph G3 is a graph showing sensitivity characteristics in a photomultiplier tube using AlGaN for the photocathode and Cs-K-Sb for the secondary electron emission surfaces of all dynodes. Graph G4 is a graph showing the spectral sensitivity characteristics of the AlGaN photocathode. Graphs G5 and G6 are graphs showing the spectral sensitivity characteristics of Cs-I and Cs-Te, respectively. (A) It is a graph which shows the spectral sensitivity characteristic of MgO. (B) It is a graph which shows the spectral sensitivity characteristic of a diamond. It is a graph which shows the spectral sensitivity characteristic of the alkali antimony (Cs-K-Sb) generally used as a material of the secondary electron emission surface of a dynode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Photomultiplier tube, 10 ... Vacuum container, 11 ... Light-receiving surface plate, 12 ... Metal side tube, 13 ... Stem, 14 ... Indium seal, 14a ... Holding ring, 17 ... Pin, 18 ... Hermetic glass, 20 ... Photocathode , 21 ... focusing electrode, 24 ... electron multiplier, 25a to 25h ... dynode, 26 ... anode electrode, 27 ... final stage dynode, 28 ... electron multiplier hole.

Claims (10)

A vacuum container having a window member for taking in incident detected light;
A photocathode provided in the vacuum vessel and photoelectrically converting the detected light to emit photoelectrons;
An electron multiplier that includes a plurality of dynodes having a secondary electron emission surface and disposed in the vacuum vessel, and an electron multiplier for multiplying the photoelectrons emitted from the photoelectric surface;
The photocathode contains Al _X Ga _1-X N (0 ≦ X <1),
Of the plurality of dynodes of the electron multiplier section, the secondary electron emission surface in at least two dynodes continuous including the first dynode receiving the photoelectrons from the photocathode is long. A photomultiplier tube comprising a material whose sensitivity wavelength limit on the wavelength side does not exceed the sensitivity wavelength limit on the long wavelength side of Al _X Ga _1-X N. The secondary electron emission surface is beryllium oxide, MgO, Cs-I, diamond, Cs-Te, Cs-Br, Na-Br, K-Br, Li-Br, Rb-I, KI, Na-I. ₂ , comprising at least one material of Li—I, MgZnO, Al ₂ O ₃ , SiO ₂ , ZnO, NiO, Rb—Te, K—Te, and Na—Te. The photomultiplier tube described.   The photomultiplier tube according to claim 1, wherein the window member includes at least one kind of material selected from sapphire and AlN. A vacuum container having a window member for taking in incident detected light;
A photocathode provided in the vacuum vessel and photoelectrically converting the detected light to emit photoelectrons;
An electron multiplier that includes a plurality of dynodes having a secondary electron emission surface and disposed in the vacuum vessel, and an electron multiplier for multiplying the photoelectrons emitted from the photoelectric surface;
The sensitivity wavelength limit on the long wavelength side of the photocathode is included in the ultraviolet region,
Of the plurality of dynodes of the electron multiplier section, the secondary electron emission surface in at least two dynodes continuous including the first dynode receiving the photoelectrons from the photocathode is MgO. , Cs-I, diamond, Cs-Te, Cs-Br , Na-Br, K-Br, Li-Br, Rb-I, K-I, Na-I, Li-I, MgZnO, Al 2 O 3, A photomultiplier tube comprising at least one material selected from SiO ₂ , ZnO, NiO, Rb—Te, K—Te, and Na—Te. The photocathode includes Cs-I, the window member includes at least one material of MgF ₂ , CaF ₂ , BaF ₂ , LiF, quartz, and sapphire, and the secondary electrons in the at least two-stage dynodes. 5. The emission surface according to claim 4, wherein the emission surface includes at least one material of MgO, Cs-I, Cs-Br, Rb-I, KI, Na-I, and Li-I. Photomultiplier tube.   Of the plurality of dynodes, the secondary electron emission surface of another dynode disposed on the rear side of the at least two dynodes includes a compound composed of an alkali metal and Sb. The photomultiplier tube according to any one of claims 1 to 5. A vacuum container having a window member for taking in incident detected light;
A photocathode provided in the vacuum vessel and photoelectrically converting the detected light to emit photoelectrons;
An electron multiplier that includes a plurality of dynodes having a secondary electron emission surface and disposed in the vacuum vessel, and an electron multiplier for multiplying the photoelectrons emitted from the photoelectric surface;
The sensitivity wavelength limit on the long wavelength side of the photocathode is included in the ultraviolet region,
Of the plurality of dynodes of the electron multiplier section, the secondary electron emission surface of at least two dynodes including the first dynode receiving the photoelectrons from the photocathode is continuous with beryllium oxide. And the secondary electron emission surface of another dynode arranged on the rear side of the at least two dynodes includes a compound comprising an alkali metal and Sb. . The photocathode comprises a Cs-I, the window member is characterized in that it comprises _{MgF 2, CaF 2, BaF 2} , LiF, quartz, and at least one kind of material of the sapphire, according to claim 7 Photomultiplier tube. The photocathode includes Cs-Te, and the window member includes at least one material of MgF ₂ , CaF ₂ , BaF ₂ , LiF, quartz, sapphire, and diamond. 8. The photomultiplier tube according to 7. The plurality of dynodes of the electron multiplier section are formed in a plate shape and stacked on each other, and the secondary electron emission surface is formed on the inner wall, and a plurality of electron multiplier holes formed in a predetermined direction. The photomultiplier tube according to any one of claims 1 to 9, wherein the first stage dynode is disposed so as to face the photocathode.

Images