JP2007234428A - Alkali metal generation material, alkali metal generator using the same, photoelectron discharge surface, and photomultiplier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alkali metal generation material capable of reducing a management load in a manufacturing process and forming a high-sensitivity photoelectric surface, to further provide an alkali metal generator using the alkali metal generation material, to provide a photoelectric surface formed by the alkali metal generation material, and to provide a photomultiplier using the photoelectric surface. <P>SOLUTION: The photoelectric surface is manufactured by using the alkali metal generation material, where cesium chromate (Cs<SB>2</SB>CrO<SB>4</SB>) and cesium molybdate (Cs<SB>2</SB>MoO<SB>4</SB>) are mixed as an oxidizing agent, for activation. In this case, setting the ratio of the cesium molybdate to 10-45% is preferable in a nondefective product rate and sensitivity. Further, setting the ratio to 20-50% is preferable since especially improved sensitivity can be obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an alkali metal generating material used for forming a photoelectron emitting surface that emits photoelectrons in response to incident light, an alkali metal generator used at the time of forming, and a photoelectron manufactured using the alkali metal generating material. The present invention also relates to a photomultiplier tube including the emission surface and the photoelectron emission surface.

  As a main part such as a photomultiplier tube, a phototube, an image intensifier, a streak tube, there is a photoelectron emission surface (photoelectric surface) that emits electrons (photoelectrons) in response to incident light. As the photocathode, a so-called transmissive photocathode formed on a transparent substrate and a so-called reflective photocathode formed on a metal substrate are known. Many of the photocathodes currently in practical use are formed by forming a photoelectron emission material containing an alkali metal on a substrate. As the photoelectron emission material, for example, an intermetallic compound of Cs or Sb or a compound semiconductor is used. ing.

Such a photoelectron emitting material generates an alkali metal vapor in an atmosphere maintained at a predetermined degree of vacuum (about 10 ⁻⁷ to 10 ⁻² Pa) and temperature, and reacts with a member formed on the substrate in advance. The method of forming with is known. For example, a method of forming an intermetallic compound layer by forming a vapor deposition film of Sb on a substrate, generating Cs vapor, and reacting with Sb of the vapor deposition film is known.

  Alkali metal itself is a very unstable substance in the atmosphere, so in order to generate alkali metal vapor, supply the alkali metal with a combination of oxidizing agent and reducing agent that can generate alkali metal by oxidation-reduction reaction. Used as a source. This supply source is called an alkali metal generating material.

The technique described in Patent Document 1 relates to this type of alkali metal generating material, and discloses a technique using molybdate as the alkali metal generating material. Since molybdate has a weaker oxidizing power than conventionally used chromate, the oxidation-reduction reaction with the reducing agent proceeds more slowly than when chromate is used. For this reason, it is described that the progress does not proceed rapidly, and it becomes easy to control the reaction rate by managing the reduction temperature.
International Publication No. 2004/066338 Pamphlet

  However, among the molybdates, cesium molybdate, which has good properties as an alkali metal generating material, has a problem that management in the manufacturing process becomes complicated because it is highly deliquescent. In addition, a photocathode formed with molybdate as an alkali metal generating material has a problem that its sensitivity is slightly lower than that of a photocathode formed with chromate.

  Therefore, the present invention reduces the management burden in the manufacturing process, and enables an alkali metal generator that can form a highly sensitive photocathode, and further, an alkali metal generator using the alkali metal generator, An object is to provide a photocathode formed thereby and a photomultiplier tube using the photocathode.

  In order to solve the above problems, an alkali metal generating material according to the present invention is an alkali metal generating material that serves as a supply source of an alkali metal used for forming a photoelectron emitting surface that emits photoelectrons in response to incident light. , Cesium molybdate and cesium chromate are mixed.

  In the process of investigating the optimum alkali metal source, the present inventors have mixed cesium molybdate and cesium chromate, and therefore, in the case of using cesium molybdate alone, management due to deliquescence becomes a problem. In addition to overcoming the problems, it is possible to overcome the problems of increasing the reduction temperature and the difficulty in controlling the reaction rate, which are problems when using cesium chromate alone, and compared to using each cesium chromate alone. It was found that improvement in sensitivity is also expected. The present invention is based on this finding.

  Here, the mixing ratio of cesium molybdate to cesium chromate is preferably 10% to 45%, more preferably 20% to 40%. When the mixing ratio is 10% to 45%, sufficiently higher photoelectric sensitivity can be realized than when each is used alone. When it is 20% to 40%, particularly good photoelectric sensitivity can be realized.

  An alkali metal generator according to the present invention is an alkali metal generator that generates an alkali metal used for forming a photoelectron emission surface that emits photoelectrons in response to incident light, and includes an accommodation space therein. And a case having a discharge port communicating with the housing space and the outside, the alkali metal generating material according to the present invention described above is housed in the housing space, and the alkali vapor generated from the alkali metal generating material is discharged to the discharge port. It is characterized by being released through.

  The photoelectron emission surface according to the present invention is a photoelectron emission surface that emits photoelectrons corresponding to incident light, and is activated by the alkali vapor generated from the alkali metal generating material according to the present invention described above. It is a feature.

  On the other hand, a photomultiplier tube according to the present invention is characterized by comprising the above-described photoelectron emission surface according to the present invention.

  If the alkali metal generator according to the present invention is used in the alkali metal generator according to the present invention, the photoelectron emission surface according to the present invention with excellent photoelectric sensitivity can be produced, and the photoelectron with excellent characteristics provided with this photoelectron emission surface. A multiplier tube can be obtained. At this time, since the management of the alkali metal generating material is easy and the control at the time of manufacture is easy, the effect of improving the yield at the time of manufacturing the product is also obtained.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. In order to facilitate the understanding of the description, the same reference numerals are given to the same components in the drawings as much as possible, and duplicate descriptions are omitted.

  FIG. 1 shows a perspective view of an embodiment of the alkali metal generating material according to the present invention. This alkali metal generating material 1 becomes a supply source of an alkali metal used for forming a photocathode according to the present invention described later. The alkali metal generating material 1 is molded into a disk-shaped pellet as shown in the figure. By using such a pellet, the handling property of the alkali metal generating material 1 is improved, and the work for producing a photocathode or the like by being accommodated in an alkali metal generator according to the present invention described later is facilitated.

This alkali metal generating material 1 contains at least an oxidizing agent and a reducing agent. As the oxidizing agent, an alkali metal salt having an alkali metal ion as a counter cation is used. In the present invention, cesium chromate (Cs ₂ CrO ₄ ) and cesium molybdate (Cs ₂ MoO ₄ ) are mixed at a predetermined ratio. Here, the weight of cesium molybdate relative to the total mass of cesium chromate and cesium molybdate, that is, the mixing ratio is preferably 10% to 45%, and more preferably 20% to 40%.

  Cesium molybdate has high deliquescence and is easy to deteriorate by absorbing water alone. By mixing this with cesium chromate, its storage and handling properties are improved, and deterioration of the product is suppressed. Moreover, as will be described later, by mixing the two at the above-mentioned mixing ratio, a photocathode having better performance than when used alone can be created.

  As the reducing agent of the alkali metal generating material 1, a compound having a property of starting an oxidation-reduction reaction with the above-described oxidizing agent at a predetermined temperature and reducing alkali metal ions is used. Various known compounds can be used as this type of compound, but one or more types from a group including Si, Zr, Al, W, and Ti may be used in any combination. In the following description, a case where Si is used as a reducing agent will be described as an example. When Si is used as a reducing agent, the alkali generation amount is saturated at about 900 ° C. For this reason, compared with other reducing agents, the amount of alkali generated with respect to the heating temperature can be easily controlled, and the reaction can be performed in a short time, which is suitable for mass production. Further, it is also suitable as a reducing agent when using a high-frequency heating reaction method in which fine temperature control is difficult.

In order to cause the oxidizing agent and reducing agent in the alkali metal generating material 1 to react, an atmosphere adjusted to a predetermined degree of vacuum (partial pressure of residual gas in the atmosphere is preferably 10 ⁻⁶ Pa to 10 ⁻¹ Pa, more preferably In an atmosphere of 10 ⁻⁶ Pa to 10 ⁻³ Pa) to carry out the reaction by heating to a predetermined temperature.

  Next, the manufacturing method of this alkali metal generating material 1 is demonstrated. FIG. 2 is a flowchart for explaining the manufacturing process. First, cesium molybdate and cesium chromate serving as oxidizing agents and Si serving as a reducing agent are prepared (steps S1 to S3). Each compound uses a high-purity compound of 99.9% or more, and is pulverized into fine particles. What was previously pulverized may be stored in a storage.

  Next, each compound is weighed using a precision electronic balance or the like (steps S4 to S6). After weighing, each compound is put into a stirrer and sufficiently stirred (step S7). Weigh the required amount according to the shape of the photocathode to be manufactured after stirring. After weighing, it is introduced into a compression pellet molding machine to produce compressed pellets having a diameter of 2 to 5 mm and a thickness of 1 to 3 mm (step S8). The size of the pellet is set according to the properties of the photocathode to be produced, that is, the required amount of alkali metal. In this way, the alkali metal generating material 1 shown in FIG. 1 can be manufactured.

  In addition, you may form the alkali metal generating material 1 concerning this invention not as a disk shaped pellet as mentioned above but as a pellet of another shape (for example, elongate column shape, prismatic shape, flat plate shape). Moreover, what was once formed in the pellet form may be crushed and used in a granular state, or the powder after stirring can be used as it is. However, in the case of pellets, handling is easier than in the case of powders and granules, and there is an advantage that the labor of weighing during use can be saved. In the following description, the description will be given only in the case of pellets, but the present invention can also be applied to the case of using powder or granules.

  FIG. 3 is a perspective view showing an alkali metal generator using the alkali metal generating material 1, and FIG. 4 is a sectional view taken along line IV-IV. The alkali metal generator 2 includes a case 20 made of metal (for example, nickel) and containing the alkali metal generator 1 in the form of pellets or powder.

  The case 20 has a recess 21 provided in the center, a housing member 22 having an annular flange portion around the upper end thereof, and a disc-shaped lid member 24 whose edge is welded to the flange portion of the housing member 22. Consists of. This welding may be performed by, for example, resistance heating by energization. The recess 21 surrounded by the lid member 24 and the housing member 22 becomes a housing space for housing the alkali metal generating material 1 pellets. The accommodation space is formed to be slightly larger than the pellet so as to accommodate the pellet, and preferably the inner shape thereof is substantially similar to the outer shape of the pellet. Thereby, the accommodated alkali metal generating material 1 is prevented from leaking outside.

  The flange portion of the housing member 22 and the edge portion of the lid member 24 are partially unwelded, and the unwelded portion communicates between the housing space and the outside and is discharged from the alkali metal generating material 1. It functions as a discharge port 23 for discharging the alkali metal to the outside of the alkali metal generator 2.

  The alkali metal generator 2 includes a heating device. When the case 20 is incorporated in the photomultiplier tube 7, the heating device has a high-frequency coil 25 and the coil from outside the photomultiplier tube. Heating can be performed by generating high-frequency electromagnetic waves in the case 20 by irradiating high-frequency electromagnetic waves with a device comprising a high-frequency power source 26 that supplies high-frequency current to 25. By supplying a high frequency current having a frequency of 1 MHz to 300 MHz to the coil 25, an eddy current is caused to flow to the conductor (alkali metal generator) by the coil 25 by the high frequency current. In this case, the alkali metal generator 2 and the alkali metal generating material 1 inside thereof are heated by direct electromagnetic wave irradiation. Further, since the case 20 of the alkali metal generator 2 is a metal case comprising a pair of a housing member 22 having an annular flange portion and a disc-like lid member 24, it efficiently absorbs high-frequency magnetic waves generated from the high-frequency coil 25. Direct heating that generates an eddy current in the metal case, which has little heat loss such as lead wires and high heating efficiency, is particularly suitable for heating in the low pressure state and vacuum state as described above.

  Next, the manufacturing method of this alkali metal generator 2 is demonstrated. FIG. 5 is a flowchart showing the manufacturing process of the alkali metal generator. First, nickel metal for vacuum material is prepared, and this is pressed into a predetermined shape, whereby the housing member 22 and the lid member 24 for housing the recess 21 are manufactured (step S11). Next, both processed members are washed with a solvent to perform a degreasing / cleaning process (step S12). In parallel with steps S11 and S12, a pellet-shaped alkali metal generating material 1 having a predetermined shape is prepared (step S13). And the prepared alkali metal generating material 1 is stored in the recessed part 21 of the accommodating member 22, and it covers with the cover member 24 (step S14). Next, the alkali metal generator 2 shown by FIG. 3, FIG. 4 is obtained by welding a required part (step S15).

  Then, the photomultiplier tube concerning this invention is demonstrated. FIG. 6 is a sectional view of an embodiment of the photomultiplier tube according to the present invention. This photomultiplier tube 7 is a head-on photomultiplier tube having a transmission type photocathode. More specifically, it has a line focus type electron multiplier. The photomultiplier tube 7 has a configuration in which a photocathode C7, an electron multiplier D7, a focusing electrode E7, an anode A7, and an alkali generator 2 as main components are housed in a glass side tube 72.

  The photocathode C7 is made of a film-like photoelectron emitting material (for example, an intermetallic compound or a compound semiconductor) that emits photoelectrons e1 corresponding to the incident light L1 on a light-transmitting substrate (face plate) C71 such as glass. A photoelectron emitting material layer C72 is provided.

  The photoelectron emitting material layer C72 contains alkali metal emitted from the alkali metal generating material 1 described above. That is, as the photoelectron emission material layer C72, for example, Sb—Cs, Sb—Rb—Cs, Sb—K—Cs, Sb—Na—K—Cs, GaAs (Cs), InGaAs (Cs), InP / InGaAs ( Cs), InP / InGaAsP (Cs), and the like. Here, (Cs) in the above notation indicates a material activated by Cs.

  As will be described later, the photoelectron emission material layer C72 is formed of a photoelectron emission material that reacts with an alkali metal such as antimony or a compound semiconductor. The photoelectron emission material layer C72 is formed on the back surface of the substrate C71 (on the side facing the tube when mounted on the photomultiplier tube 7). Surface) Obtained by forming on FC72 and subsequently reacting with alkali metal vapor.

  The side tube 72 is a cylindrical side tube made of, for example, Kovar glass or UV glass. Although it is made of glass here, a metal material such as Kovar metal or stainless steel may be used. The above-described photocathode C7 is fused and fixed to the opening 72a on one side (upper side in the drawing) of the side tube 72 with the light receiving surface FC71 facing outward.

  A stem plate 78 made of glass (for example, Kovar glass, UV glass, etc.) is welded and fixed to the other opening 72 b of the side tube 72. The stem plate 78 may also be formed of a metal material such as Kovar metal or stainless steel like the side tube 72. A sealed container is formed by the side tube 72, the photocathode C7, and the stem plate 78.

  A cylindrical exhaust pipe 73 extending to the opposite side of the side pipe 72 is fixed at the center of the stem plate 78. This exhaust pipe 73 is used in the process of manufacturing the photomultiplier tube 7 by discharging the air inside the sealed container constituted by the side tube 72, the photocathode C7, and the stem plate 78 by a vacuum pump to make a vacuum state. After that, the inside of the photomultiplier tube 7 is maintained in a vacuum state by being sealed.

  The electron multiplier D7 is composed of a first dynode D71 to a ninth dynode D79 each having a plurality of plate-like dynodes. Each of the first dynode D71 to the ninth dynode D79 is a film and has a film shape having a secondary electron emission surface FD7 which is disposed on the substrate and emits secondary electrons e2 using incident photoelectrons e1. And a layer made of a secondary electron emission material. Hereinafter, the layer made of the secondary electron emission material is referred to as a secondary electron emission material layer.

  Each of the first dynode D71 to the ninth dynode D79 is supported in the sealed container by, for example, a metal (for example, Kovar metal) stem pin 75 provided so as to penetrate the sealed container. The tip of the stem pin 75 on the support side is electrically connected to each of the corresponding first dynode D71 to ninth dynode D79 (illustration of the stem pin 75 in the pipe is omitted). The other end passes through a pin hole provided in the stem plate 78 and is exposed outside the tube. Each pin hole is filled with a tablet (for example, made of Kovar glass) used as a hermetic seal, so that each stem pin 75 is fixed to the stem plate 78 via the tablet. As the secondary electron emission material layer of each of the dynodes D71 to D79, the same material as the photoelectron emission material layer of the photocathode described above can be used.

  Between the electron multiplier D7 and the stem plate 78, an anode A7 supported by a dedicated stem pin 75 is disposed. On the other hand, a focusing electrode E7 is disposed between the electron multiplier D7 and the photocathode C7. In the center of the focusing electrode E7, an opening for guiding the focused photoelectron e1 flow toward the electron multiplier is formed.

  Each stem pin 75 is electrically connected to the voltage application portion at a portion exposed to the outside of the photomultiplier tube 7, whereby a predetermined voltage is supplied to the first dynode D71 to the ninth dynode D79 and the anode A7. The A predetermined voltage is also supplied to the photocathode C7 and the focusing electrode E7. Specifically, the photocathode C7 and the focusing electrode E7 are set to the same potential, and the first dynode D71 to the ninth dynode D79 and the anode A7 are set to have a high potential in order from the top in the figure, that is, the photocathode. The closer to C7 and the focusing electrode E7, the higher the potential is set.

  By setting the voltage in this way, when the light L1 enters the light receiving surface FC71 of the photocathode C7, the photoelectrons e1 are emitted from the opposite surface FC72. The emitted photoelectrons e1 are guided to the electron multiplier D7 by the focusing electrode E7, multistage multiplied by the first dynode D71 to the ninth dynode D79, incident on the anode A7, and the number of photoelectrons e1. That is, a current corresponding to the light intensity of the light L1 is output.

  Next, a method for manufacturing the photomultiplier tube 7 will be described. In this manufacturing method, conditions and procedures other than manufacturing the photocathode C7 and the first dynode D71 to the ninth dynode D79 according to the present invention using the alkali metal generator and the alkali metal generator according to the present invention are as follows. It is not limited to description of this, It is possible to manufacture by a well-known technique.

  FIG. 7 is a flowchart showing the manufacturing process of the photomultiplier tube 7. First, a glass tube to be the side tube 72 and a glass substrate to be the substrate C71 are prepared (step S21). At this time, the photoelectron emitting material layer C72 on the substrate C71 is in an incomplete state where alkali activation is not performed. Next, both are heated and integrated (step S22).

  Subsequently, the stem pin 75 is passed through the pin hole of the stem plate 78 and fixed by the tablet (step S23). Here, a cylindrical exhaust pipe 73 is connected to the center of the stem plate 78. The exhaust pipe 73 is in a state where both ends are open. Then, the anode A7, the focusing electrode E7, and the electron multiplier D7 are assembled by assembling each of the anode A7, the focusing electrode E7, the first dynode D71 to the ninth dynode D79 on the corresponding stem pin 75. Further, the alkali metal generator 2 manufactured in advance in the previous process is disposed and fixed at a position where high-frequency electromagnetic waves are easily absorbed (step S24). For example, it may be fixed by welding to the stem pin 75 or the like. At this stage, the secondary electron surfaces on the substrate on which the dynodes D71 to D79 are formed are in an incomplete state where alkali activation is not performed. The assembled electron multiplier D7 or the like (assembly) is inserted from the opening 72b side of the side tube 72 (step S25), and the stem plate 78 and the side tube 72 are heated and integrated to form a sealed container. (Step S26). However, the inside and outside of the pipe communicate with each other only through the exhaust pipe 73 described above.

  The alkali metal generator 2 used for forming the photocathode C7 of the photomultiplier tube 7 and the first dynode D71 to the ninth dynode D79 is the same as that shown in FIG. The photomultiplier tube 7 that has finished step S26 is connected to a glass tube connected to a vacuum pump (not shown) through the exhaust pipe 73 (step S27). At this time, the entire system connected to the vacuum pump is brought into an airtight state.

  First, after the exhaust system is heated and sufficiently degassed to obtain a high vacuum, the photomultiplier tube 7 itself is also heated to perform heat degassing (step S28). After the exhaust system reaches a sufficiently high vacuum, the photomultiplier tube 7 is once cooled to room temperature (step S29). And manganese is vapor-deposited on a window material by supplying with electricity to the manganese coil which is arranged in the system which is not illustrated (Step S30).

  After vapor deposition, high purity oxygen is introduced into the system (step S31). The pressure of the oxygen gas at this time is about several Pa to several tens Pa. In this state, a predetermined direct current or alternating voltage is applied to the photocathode C7 to oxidize the deposited manganese and make it transparent (step S32). After the transparency, the vacuum pump is operated to discharge the oxygen gas in the system, and the inside of the system is evacuated again (step S33).

When a predetermined degree of vacuum is reached, antimony is deposited on the manganese oxide by energizing an antimony coil (not shown) disposed in the system (step S34). Next, the photomultiplier tube 7 is heated to 150 ° C. to 200 ° C. by an electric furnace or the like (step S35). Thereafter, the alkali metal generator 4 arranged in the photomultiplier tube 7 is heated at high frequency (step S36). When the internal pellet 1A is sufficiently heated, the following oxidation-reduction reaction proceeds between Cs ₂ CrO ₄ and Cs ₂ MoO _{4 that} are oxidizing agents and Si that is a reducing agent.
4Cs ₂ CrO ₄ + 5Si → 5SiO ₂ + 8Cs + 2Cr ₂ O ₃ (1)
4Cs ₂ MoO ₄ + 5Si → 5SiO ₂ + 8Cs + 2Mo ₂ O ₃ (2)

At this time, even if the same Cs ⁺ is used as a counter cation, Cs ₂ MoO ₄ is weaker in oxidizing power than Cs ₂ CrO ₄ , and therefore the redox reaction with the reducing agent is performed in the reaction (2) in the reaction (2) than in the reaction (1). Progress slowly. For this reason, it becomes easier to control the reaction rate of the whole pellet compared with the case where Cs ₂ CrO ₄ is used alone as the oxidizing agent (only reaction (1)), and the alkali metal vapor is stably generated. Can do.

  When the alkali metal has been sufficiently reduced (a sufficient amount of alkali metal vapor has been generated), the high-frequency heating is stopped (step S37), and the photomultiplier tube 7 is heated to 120 ° C. to 180 ° C. with an electric furnace or the like. Heat and bake for 30 minutes to 2 hours (step S38). After firing, the photomultiplier tube 7 is returned to room temperature (step S39), and then the exhaust tube 73 is sealed and cut to be removed from the glass tube 76 (step S40). Thereafter, a performance test is performed (step S41), and a product satisfying the performance is shipped as an acceptable product.

  Here, a head-on type photomultiplier tube has been described as an example, but the present invention can also be suitably applied to a side-on type photomultiplier tube shown in FIG. In addition, a configuration having a similar photocathode can also be applied to a phototube having no multiplication section, an image intensifier having a microchannel plate as a multiplication section, or a streak tube.

  The inventors made photocathodes using various alkali metal generating materials having different mixing ratios of cesium chromate and cesium molybdate, and conducted comparative experiments to evaluate the performance.

  Note that Si is used as the reducing agent, the ratio of the oxidizing agent to the reducing agent is 2: 1 to 4: 1, and a constant temperature bath at a temperature of 30 ° C. and a humidity of 80% assuming a working environment in a high temperature and high humidity environment. The performance of a photomultiplier tube produced using an alkali metal generator stored for 24 hours was evaluated.

The evaluation results are shown in Tables 1 and 2 and FIGS. Table 1 shows cathode sensitivity (Sk: μA / μL), cathode blue sensitivity (Skb: μA), anode sensitivity (SP: μA / μL), and two types of dark currents (Idb: nA). The upper part of each column is the average value, and the lower part is the standard deviation. Table 2 shows the non-defective product ratio obtained from these characteristics and surface unevenness conditions as the non-defective products only that passed the standard. FIGS. 8 and 9 show the anode (anode) sensitivity as histograms for samples having the same mixing ratio. FIG. 10 is a graph in which the average value of the cathode sensitivity is plotted against the mixing ratio.

  From these results, it was confirmed that when the ratio of cesium molybdate in the oxidizing agent was 10% to 45%, the yield rate was 100%, and good characteristics were obtained. Furthermore, it was confirmed that the ratio of cesium molybdate in the oxidizing agent was 20% to 40%, which was more advantageous and preferable in terms of sensitivity. In the above ratio range, the cathode sensitivity Sk increases, but the dark currents Idb1 and Idb2 decrease, which is advantageous in terms of the S / N ratio. In addition, products with stable performance can be obtained with little variation among products.

  Thus, the reason why a better product is obtained when cesium molybdate is mixed than when cesium chromate alone is considered as follows. When a simple alkali salt is used as the oxidizing agent, the metal container containing the alkali source is heated by high-frequency heating, and the heat is transferred to the pellet, so that the pellet is heated from the peripheral part in contact with the metal container toward the center. Therefore, excessive heating is required to advance the reaction by heating to the reduction temperature.

  However, in the alkali metal generating material of the present invention, when the metal container is heated, the reaction of cesium molybdate having a low reduction temperature proceeds first, and due to the reaction heat generated from the inside of the pellet, the pellet is also from the inside. Since it is heated, the entire alkali pellet can be efficiently heated and the oxidation-reduction reaction can proceed without supplying excessive heat from the outside. As a result, generation of unnecessary gas released by excessive heating is suppressed, so that a high vacuum state can be maintained. Moreover, it is possible to realize a good function as an alkali metal generating material, such as prevention of oxidation and evaporation of the secondary electron surface forming material due to heating of the dynode electrode due to high frequency leakage during high frequency heating.

  The effect of the present invention is the combined effect of the high reduction temperature of cesium chromate and the low reduction temperature of cesium molybdate. Similar effects can be considered in other cesium oxide materials. For example, it can be inferred that the same effect can be obtained by combining cesium chromate with cesium tungstate having a lower reduction temperature.

  On the other hand, when the mixing ratio of cesium molybdate increases, the photocathode sensitivity decreases. When cesium molybdate has deliquescence and adsorbs a large amount of moisture, this moisture is heated inside the pellet by heating during reduction. This is considered to cause oxidation of more released and reduced alkali metal or Sb which is a photocathode forming material.

It is a perspective view of one embodiment of an alkali metal generating material concerning the present invention. It is a flowchart which shows the manufacturing process of the alkali metal generating material of FIG. It is a perspective view which shows the alkali metal generator using the alkali metal generating material of FIG. It is the IV-IV sectional view taken on the line of FIG. It is a flowchart which shows the manufacturing process of the alkali metal generator of FIG. 3, FIG. It is sectional drawing of one Embodiment of the photomultiplier tube concerning this invention. It is a flowchart which shows the manufacturing process of the photomultiplier tube of FIG. It is a histogram about the anode sensitivity of the photocathode sample manufactured when the alkali metal generating material of the same mixing ratio is used. It is another histogram about the anode sensitivity of the photocathode sample manufactured when the alkali metal generating material of the same mixing ratio is used. It is the graph which showed the cathode sensitivity (average value) with respect to mixing ratio. It is sectional drawing of another embodiment of the photomultiplier tube concerning this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1, 1A ... Alkali metal generating material, 2, 4 ... Alkali metal generator, 7 ... Photomultiplier tube, 20, 20A ... Case, 21 ... Recessed part, 22 ... Housing member, 23 ... Release port, 24 ... Cover member, 25 ... high frequency coil, 26 ... high frequency power source, 72 ... glass side tube, 72a, 72b ... opening, 73 ... exhaust pipe, 75 ... stem pin, 76, 77 ... glass tube, 78 ... stem plate, A7 ... anode, C7 ... Photocathode, C71 ... substrate, C72 ... photoelectron emission material layer, D7 ... electron multiplier, D71-D79 ... dynode, e1 ... photoelectron, e2 ... secondary electron, E7 ... focusing electrode, FC71 ... light receiving surface, FC72 ... opposite Surface, FD7 ... secondary electron emission surface, L1 ... light.

Claims (6)

An alkali metal generating material serving as a supply source of an alkali metal used for forming a photoelectron emitting surface that emits photoelectrons in response to incident light,
An alkali metal generating material characterized by using an oxidant mixed with cesium molybdate and cesium chromate.   2. The alkali metal generating material according to claim 1, wherein a mixing ratio of cesium molybdate in the oxidizing agent is 10% to 45%.   The alkali metal generating material according to claim 2, wherein a mixing ratio of cesium molybdate in the oxidizing agent is 20% to 40%. An alkali metal generator that generates an alkali metal used to form a photoelectron emission surface that emits photoelectrons in response to incident light,
It has a case with a storage space inside, and a discharge port that communicates the storage space with the outside.
An alkali characterized in that the alkali metal generating material according to any one of claims 1 to 3 is accommodated in the accommodation space, and alkali vapor generated from the alkali metal generating material is discharged through the discharge port. Metal generator. A photoelectron emission surface that emits photoelectrons in response to incident light,
5. A photoelectron emitting surface which is activated by alkali vapor generated from the alkali metal generating material according to claim 1.   A photomultiplier tube comprising the photoelectron emission surface according to claim 5.

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