JPH04242040A - Alkali source - Google Patents

Abstract

PURPOSE:To make an alkali source small-sized in order to perform heating reduction of required alkaline metal gas with lower heating quantity by forming an alkaline metal gas generating agent into a pellet shape to make it contact with a plate heater to seal it with a sealing member. CONSTITUTION:An alkali source 6 consists of pellets 67, 68 for alkaline metal gas generation arranged above and below a nichrome-made plate long heater 63 in contact therewith and the upper and lower caps 61 and 62 for sealing these tightly. When a heater 63 is electrified, alkaline metal gas is heated and reduced from the pellets in contact therewith. The sealing members 61, 62 generate a little gap due to heating to leak out heated and reduced gas for filling, for instance, a photoelectron doubler tube and being absorbed by a photoelectric surface formation part wherein Sb and the like is sticking so as to form a photoelectric surface. Because of pellets, an alkali source can be small-sized and its component quantity also can be correctly managed so that a loss of heating quantity of the heater can be reduced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkali source that generates an alkali metal gas contained in an electron tube such as a photomultiplier tube or an image tube by heating and reducing the alkali metal gas that forms a photocathode.

0002

2. Description of the Related Art Photomultiplier tubes, image tubes, and the like are provided with a photocathode that emits photoelectrons in response to incident light. The photocathode, for example, is made by forming an antimony (Sb) layer on the inner wall of the tube head of a photomultiplier tube, and then mixing cesium chromate (Cs3 CrO4) and silicon (Si) in a vacuum and reducing them by heating. Cs is evaporated and this Cs gas is absorbed into the Sb layer to form a photocathode made of SbCs3.

A conventional method for forming a photocathode will be described with reference to FIG. In the figure, three sleeves 21 to 23 are inserted along the axial direction inside the photomultiplier tube. For example, as shown in the cross section of FIG. 7, the sleeve 22 is formed as a triangular nichrome tube 22a with a hollow interior, and an alkali metal gas generating agent 22b containing a powdered alkali metal compound in the inner cavity. is included. The alkali metal gas generating powders sealed in the three nichrome sleeves 21 to 23 may be the same, or may be different alkali metal gas generating powders. sleeve 2
The alkali metal gas generating powder sealed in 1 to 23 is heated and reduced by heating the nichrome sleeves 21 to 23 that function as heaters, and the heated and reduced alkali metal gas is heated to the upper part of the powder. Sb
is absorbed by the attached photocathode forming portion 2 to form a photocathode.

0004

[Problems to be Solved by the Invention] The photocathode forming method described above has the following problems. Since the powdered alkali metal gas generating agent is sealed in the inner cavity of the nichrome sleeve, the amount of the alkali metal gas generating agent required for forming the photocathode cannot be accurately controlled. Since the total volume of the inner cavity of the nichrome sleeves 21 to 23 is small, the length of the nichrome sleeves 21 to 23 has to be long in order to enclose the necessary alkali metal gas generating powder, and the length of the photomultiplier tube has to be increased. The length becomes longer. If the length is not increased, it is necessary to increase the number of pipes, and the diameter of the pipe becomes thicker. Since the outer surfaces of the nichrome sleeves 21 to 23 are exposed inside the photoelectron tube, there is a large heat loss on the outer surfaces, and it is necessary to generate more heat than is necessary for thermal reduction of the alkali metal gas, and a large current must be applied. It won't happen. Therefore, the feeder lines 25 to 27 inserted into the photomultiplier tube become thicker, or
Multiple feeder lines must be installed. As the surface area of the nichrome sleeves 21 to 23 increases, the amount of heat generated increases, and as mentioned above, since the outer surfaces are exposed,
The heat from the dynode (
(not shown), etc. When the amount of alkali metal gas generating powder enclosed is increased, the outer dimensions of the nichrome sleeves 21 to 23 also become larger, and the amount of heat generated increases. As a result, the negative effect on the dynode and the like becomes even greater. Furthermore, although the calorific value increases, a very large amount of electric power is required to reach the temperature at which the alkali metal gas is reduced, which is inefficient. The work of inserting the alkali metal gas generating powder into the inner cavity of the sleeve is troublesome, and the processing of the sleeve is also troublesome. As a result of the above, the price will be higher overall.

The above-mentioned problems exemplified with respect to photomultiplier tubes are also encountered in other electron tubes such as image tubes which require an alkaline source. Therefore, an object of the present invention is to provide an alkali source that efficiently forms a photocathode.

[0006]

[Means for Solving the Problems] In order to solve the above problems, the present invention solidifies an alkali metal gas generating agent containing an alkali metal into pellets, brings the pellets into contact with a flat heater, and connects them to a sealing member. The alkali metal gas is heated and reduced using a flat plate heater. That is,
The alkali source of the present invention includes a flat plate heater, pellets that are in contact with the heater and solidify an alkali metal gas generating agent containing an alkali metal, and a plate heater that is connected to the heater while partially exposing both ends of the flat plate heater. and a sealing member for sealing the pellet in contact with the pellet.

[0007]

[Operation] When power is supplied by connecting power lines to both ends of the heater,
Alkali metal gas is heated and reduced from the alkali metal gas generating pellets that come into contact with this heater. Although the sealing member seals the alkali gas generating pellets, a slight gap is created due to heating, and the heated and reduced alkali metal gas leaks from the gap. The leaked alkali metal gas fills the photomultiplier tube, for example, and is absorbed by the photocathode forming portion to which Sb or the like is attached, forming a photocathode.

[0008]

[Embodiment] As an embodiment of the alkali source of the present invention, a case where it is applied to forming a photocathode in a photomultiplier tube will be illustrated below.

FIG. 1 is a perspective view of a photomultiplier tube containing an alkali source according to this embodiment, and FIG.
FIG. 2 is a cross-sectional view of a photomultiplier tube in FIG. Note that in these drawings, the cathode, focus electrode, dynode, anode, etc. necessary for the photomultiplier tube are omitted for illustration purposes.

In FIGS. 1 and 2, a photocathode 2 to which Sb is attached is provided on the inner surface of a glass surface 1 of the tube head of a photomultiplier tube. A diffusion disk 3 is supported by a disk support line 15 between the focus electrode and the dynode in the axial direction of the photomultiplier tube. The lower part of the diffusion disk 3,
Three alkaline sources 6 to 8 are placed along the inner wall of the glass tube side wall 4.
One end is supported by a return line 10, and the other end is supported by feed lines 11 to 13, respectively. As shown in FIG. 2, these alkali sources 6 to 8 are arranged outside the dynode arrangement region 20 and near the inner wall of the glass tube side wall 4. The return wire 10 and the feeder wires 11 to 13 are connected to external connection pins 16 and 17 via a socket portion 5 provided at the bottom of the photomultiplier tube.
~19 is connected.

Detailed views of the alkali source 6 are shown in FIGS. 3 and 4. 3 is a sectional view of the alkali source 6 taken along line H2-H2 in FIG. 1, and FIG. 4 is an exploded view of the alkali source 6 shown in FIG. The alkali source 6 includes a long flat plate heater 63 made of nichrome, and alkali metal gas generating pellets 67 and 68 disposed above and below the heater 63 in surface contact with the heater 63.
, an upper cap 61 and a lower cap 62 that seal the heater 63 and the alkali metal gas generating pellets 67, 68 are integrally constructed. The alkali metal gas generating pellets 67 and 68 are made by kneading and solidifying cesium chromate and Si in order to reduce the alkali metal gas by heating. The alkali metal gas generating pellets 67 and 68 can also be formed by kneading cesium chromate and Si and adding aluminum Al or the like. The alkali metal gas generating pellets 67 are inserted into the recesses of the upper cap 61 and are in surface contact with the heater 63. The alkali metal gas generating pellets 68 are inserted into the recessed portion of the lower cap 62 and are in surface contact with the heater 63. Projections are formed at both ends of the upper cap 61. The protrusion on the right side is welded to the return wire 10. One end of the heater 63 on the right side in the figure has the same length as the lower cap 62, and an insulator 65 is attached to the other end, and the tip thereof is welded to the power supply line 11. The insulator 65 is a material that does not change mechanically or electrically even when heated, for example,
It is made of mica or ceramic and is coated on the surface of the long flat heater 63.

Since the heater 63 is a long flat plate made of nichrome, its cross-sectional area in the longitudinal direction is small, its resistance value is large, and the amount of heat generated is large. Also, since it is a flat plate, the surface area is large. Since the alkali metal gas generating pellets 67 and 68 are solidified into pellets, their volumes are small and their amounts can be measured accurately. Alkali metal gas generation pellets 67,
By reducing the volume of the heater 68 and the size of the heater 63, the alkali source 6 can be made smaller as a whole. As a result, the dynode arrangement area 20 and other members (not shown) housed within the photomultiplier tube can be arranged with sufficient margin. Further, in the axial direction of the photomultiplier tube, only the diameter of the alkali sources 6 to 8 plus the distance between them is required, so that the length of the photomultiplier tube in the longitudinal direction is shortened.

Hereinafter, the alkali sources 6 to 8 are heated to produce an alkali metal, that is, cesium (in this example).
The operation of thermally reducing Cs) and absorbing it into Sb formed on the photocathode 2 will be described. Connection pin 17~
19, current flows through the alkali sources 6 to 8 between the power supply lines 11 to 13 and the return line 10, or more precisely, to the heaters of these alkaline sources 6 to 8. These heaters heat the alkali metal gas generating pellets 67, 68 which are in surface contact with both surfaces of the pellets, thereby reducing Cs gas. This heating temperature is sufficient to reduce Cs in the vacuum photomultiplier tube. The heated and reduced Cs gas leaks out from the gap between the upper cap 61 and the lower cap 62, which are sealed. The leaked Cs gas fills the photomultiplier tube and is absorbed by Sb attached to the photocathode 2. As a result, a photocathode 2 having a predetermined photoelectric conversion performance is formed.

Note that when the upper cap 61 and the lower cap 62 are completed as a single alkali source, the alkali metal gas generating pellets 67, 68 and the heater 63 are completely sealed. This is also to suppress the reaction of chemically active alkali metals in the atmosphere. However, this sealed state is broken as the upper cap 61 and lower cap 62 are slightly deformed due to thermal distortion caused by heating of the heater 63 inside the photomultiplier tube, and the gap between the upper cap 61 and the lower cap 62 is broken. A slight gap is created between the two, and the heated and reduced Cs gas flows out from the gap.

Further, the diffusion disk 3 diffuses the Cs gas filling the photomultiplier tube so that it is uniformly absorbed by the photocathode 2 to which Sb is attached.

As described above, the heater 63 has a small longitudinal cross-sectional area and a large resistance value. Therefore, the amount of heat generated is large relative to the supplied current, and there is little wasteful heat relative to the reduction temperature. As a result, not only the dynodes disposed in the dynode disposing area 20 but also other objects contained within the photomultiplier tube are less adversely affected by heat.

EXAMPLE The results of a comparison between this example having the above configuration and the case where a conventional alkali source is applied to a photomultiplier tube under the same conditions as this example are shown below. Current capacity: reduced by almost half. Length of photomultiplier tube (alkaline source attached part): Approximately 1/4
was shortened to Heater heat output: reduced by about half. Price: A fraction of the price.

As mentioned above, it is preferable for the heater to contact the alkali metal gas generating pellets 67, 68 over as wide an area as possible so as to have a large resistance value. FIG. 5 shows the flat plate long heater 63 shown in the above embodiment.
A modification example is shown below. This flat plate heater 63' has a circular plane that is bent so as to be in wide surface contact with the alkali metal gas generating pellets 67 and 68, and is designed to have a cross-sectional area in the axial direction as small as possible in order to increase the resistance value. It is made into a thin flat plate. Therefore, the heat generation efficiency of this flat heater 63' is further improved than that described above. Furthermore, the alkali metal gas generating pellets 67 and 68 can be heated to a predetermined reduction temperature with less electric power.

Pellet for generating alkali metal gas 67,6
8 can be attached to only one side of the flat plate heater 63. Note that the size of the alkali metal gas generating pellets 67, 68 is determined by the amount of alkali metal gas to be generated. Similarly, the number of alkali sources 6 to 8 is determined by the total amount of alkali metal gas to be generated or the type of alkali metal gas to be generated. The latter case involves generating different alkali metal gases. Note that the above-mentioned materials for the alkali metal gas generating agent, the material for the flat plate heater, and the material for the insulator 65 are merely examples, and other materials may be used.

As shown in FIG. 1, the alkali sources 6 to 8 are arranged not only along the inner wall of the glass side wall 4 in the axial direction of the photomultiplier tube, but also above the socket part 5. ，
They can also be arranged circumferentially along the inner wall of the glass side wall 4. With this arrangement, the alkali sources 6 to 8 are 1
Since only the stage occupies a position in the tube axis direction, the axial length of the photomultiplier tube is further reduced.

Although the alkali source of the present embodiment is applied to a photomultiplier tube as an example above, the alkali source of the present invention can also be used when enclosed in various other electron tubes to reduce alkali metal gas by heating. can also be used.

[0022]

As described above, according to the alkali source of the present invention, the alkali metal gas generating pellets are enclosed in the sealing member together with the heater, so that the loss of calorific value is small. In addition, since the alkali metal gas can be sufficiently reduced even with a small amount of excess heat, the
For example, the thermal effect on dynodes in photomultiplier tubes is small. In addition, since it is only necessary to supply the power necessary for approximately the reduction temperature, the power supply line to the heater can also be made thinner. Furthermore, by solidifying the alkali metal gas generating agent containing an alkali metal and forming it into pellets, the volume of the alkali metal gas generating agent becomes smaller, and it can be accommodated.
For example, the size of photomultiplier tubes can be reduced. Furthermore, according to the present invention, the amount of alkali metal can also be accurately controlled. Furthermore, according to the present invention, processing operations are simplified and costs are reduced.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a photomultiplier tube to which an alkali source according to an embodiment of the present invention is applied.

FIG. 2 is a cross-sectional view of the photomultiplier tube taken along line H1-H1 in FIG. 1;

FIG. 3 is a cross-sectional view of the alkali source taken along line H2-H2 in FIG. 1;

FIG. 4 is an exploded view of the alkali source of FIG. 3.

FIG. 5 is a diagram showing a modification of the heater shown in FIG. 4;

FIG. 6 is a perspective view of a conventional alkali source inserted into a photomultiplier tube.

7 is a cross-sectional view of the sleeve in which the alkali source of FIG. 6 is enclosed and heated to be reduced; FIG.

[Explanation of symbols]

1. Phototube head glass surface, 2. Photocathode, 3. Disk for diffusion, 4. Glass side wall, 5. Disc support line, 6 to 8.
... Alkali source, 10... Return line, 11-13... Power supply line, 16-19... Connection pin, 20... Dynode arrangement area, 61... Upper cap, 62... Lower cap, 6
3... Flat plate heater, 65... Insulator, 67, 68... Pellet for generating alkali metal gas.

Claims (1)

[Claims] 1. A flat plate heater, solidified alkali metal gas generating pellets containing an alkali metal in contact with the heater, the heater and an alkali metal gas generating pellet in contact with the heater with both ends of the flat plate heater partially exposed. and a sealing member for sealing gas generating pellets.