1. Field of the Invention
The present invention relates to a photomultiplier and a sensor module including the same.
2. Related Background Art
Japanese Patent No. 4640881 (Japanese Patent Application Laid-Open Publication No. 2002-42719) discloses a photomultiplier having a glass container the interior of which is maintained in a vacuum state, and an electron multiplier unit housed in the glass container. In this photomultiplier, the electron multiplier unit is held at a predetermined position in the glass container in a state in which it is supported by lead pins extending from a bottom (stem) of the glass container.
The Inventors examined the conventional photomultiplier and found the problem as described below. Specifically, in the conventional photomultiplier the relative position of the electron multiplier unit to the glass container is maintained by only the lead pins extending from stem pins. For this reason, when we assume that the photomultiplier is used under severe environments, e.g., in underground resource exploration, the conventional photomultiplier had a possibility of failing to maintain sufficient durability and high reliability.
For example, when the photomultiplier is assumed to be used in a high-temperature, high-pressure environment, the glass container can possibly fail to provide sufficient durability. In addition, the position of the electron multiplier unit relative to the glass container varies with intense vibration in the structure where the electron multiplier unit is held at the predetermined position in the glass container, and thus the reliability can also possibly degrade. Particularly, in the ordinary configuration wherein the glass container and a part of the electron multiplier unit are held by springs on the inner wall of the glass container, if unwanted gas is produced in the glass container because of friction by vibration, the photomultiplier will inevitably undergo degradation of reliability (reduction in measurement sensitivity, malfunction, and so on).
The present invention has been accomplished in order to solve the problem as described above and it is an object of the present invention to provide a photomultiplier capable of maintaining excellent durability and reliability even in the use under high-temperature, high-pressure environments and, particularly, to provide a photomultiplier with a structure for improvement in anti-vibration performance when compared with the conventional technology and a sensor module including the photomultiplier.
In order to solve the above-described problem, a photomultiplier according to an embodiment of the present invention, as a first aspect, comprises: a sealed container the interior of which is maintained in a predetermined vacuum state; a photocathode housed in the sealed container and configured to emit photoelectrons into the sealed container in response to light of a predetermined wavelength; an electron multiplier unit housed in the sealed container; and a structure for fixing an installation position of the electron multiplier unit in the sealed container. It is noted that in the present specification the vacuum state refers to a state achieved by evacuating gas in the sealed container by means of a vacuum pump or the like, in which the degree of vacuum represented by pressure of residual gas in the sealed container is maintained at 10−1 Pa or less (note: the artificially possible pressure at present is approximately 10−10 Pa).
In the foregoing first aspect, the sealed container includes a first ceramic side tube and a second ceramic side tube arranged in order along a first tube axis of the sealed container, on the assumption of use under high-temperature, high-pressure environments. The electron multiplier unit is comprised of a dynode unit, an anode, a pair of insulating support members integrally grasping these dynode unit and anode, and a focusing electrode fixed to the pair of insulating support members. The dynode unit includes multi-stage dynodes for emitting secondary electrons in response to the photoelectrons arriving from the photocathode and successively cascade-multiplying the emitted secondary electrons. The anode extracts secondary electrons resulting from the cascade multiplication by the dynode unit, as a signal. The focusing electrode is disposed between the photocathode and the dynode unit in a state in which it is fixed to the pair of insulating support members. Furthermore, the focusing electrode has a through hole for letting the photoelectrons from the photocathode pass through.
The structure for fixing the installation position of the electron multiplier unit in the sealed container is realized by a fixing member forming a part of the sealed container. Specifically, the fixing member has an aperture for defining an installation position of the focusing electrode, an inside end defining the aperture, and an outside end surrounding the inside end. Furthermore, the outside end is grasped by the first ceramic side tube and the second ceramic side tube whereby the fixing member is fixed to the sealed container. On the other hand, the inside end of the fixing member located in the sealed container is fixed to the focusing electrode. This configuration fixes the installation position of the electron multiplier unit relative to the sealed container, thereby to achieve drastic improvement in anti-vibration performance of the photomultiplier.
As a second aspect applicable to the first aspect, the sealed container may further comprise a stem portion, and a metal side tube for defining an installation position of the stem portion. Specifically, the stem portion is comprised of a ceramic pedestal for, with a plurality of stem pins penetrating through, holding these stem pins, and a metal reinforcement member covering at least a side face of the ceramic pedestal. Furthermore, the metal side tube is located opposite to the first ceramic side tube with the second ceramic side tube in between, and one end thereof is fixed to the second ceramic side tube. In this configuration, the metal reinforcement member of the stem portion is fixed to the metal side tube.
As a third aspect applicable to at least either one of the first and second aspects, the fixing member may have a plurality of through holes provided between the inside end and the outside end. Each of these through holes establishes communication between a space where the dynode unit exists and a space where the photocathode exists. The luminescent phenomenon occurs in the anode with increase in electron density and light from the anode, if reaching the photocathode, would be reflected as noise component in the signal extracted from the anode. On the other hand, the photocathode is formed by supplying an alkali metal vapor from the stem portion side toward the photocathode side and, for this reason, a gap in some width is needed between the side tubes and the electron multiplier unit inside the sealed container in the vacuum state. In the third aspect, therefore, a light shield function is realized by the fixing member with the inside end located inside the sealed container and the outer peripheral portion of the focusing electrode, while a flow path for the alkali metal vapor is secured by the plurality of through holes provided in the fixing member. As a fourth aspect applicable to the third aspect, the plurality of through holes in the fixing member are preferably arranged so as to surround the first tube axis of the sealed container.
The photomultiplier according to at least any one of the first to fourth aspects can be applied to a sensor module used under high-temperature, high-pressure environments, for example, in underground resource exploration.
Specifically, as a fifth aspect, a sensor module according to an embodiment of the present invention comprises: the photomultiplier having the structure as described above (the photomultiplier according to the embodiment of the present invention); and a case for housing the photomultiplier. The case of the sensor module has openings at two ends thereof and has a shape extending along a second tube axis.
As a sixth aspect applicable to the fifth aspect, the sensor module may further comprise a positioning spacer for defining an installation position of the photomultiplier in the case, the positioning spacer being installed in the case. Furthermore, as a seventh aspect applicable to the sixth aspect, the positioning spacer preferably has a taper face with which a part of the photomultiplier is in contact. In this case, it becomes feasible to adjust a posture of the photomultiplier relative to the second tube axis of the case, in a state in which the stem portion of the photomultiplier is in contact with the positioning spacer (i.e., in a state in which posture stability of the photomultiplier in the case is ensured). Specifically, as an eighth aspect applicable to at least either one of the sixth and seventh aspects, the photomultiplier can be stably kept and fixed in the case, even in a state in which the first tube axis of the sealed container and the second tube axis of the case are out of alignment.
Each of embodiments according to this invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings. These embodiments are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of this invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, and it is apparent that various modifications and improvements within the spirit and scope of the invention will be obvious to those skilled in the art from this detailed description.
Various embodiments of the photomultiplier and sensor module 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 portions and the same elements will be denoted by the same reference signs, without redundant description.
As shown in
The sealed container 100A is composed of a head portion 200, a body portion 300, and a stem portion 400 arranged along a tube axis AX1 (first tube axis) thereof. The head portion 200 is composed of a glass faceplate 210 having a light entrance face 210a and a back face 210b opposed to the light entrance face 210a, and a Kovar flange 220. The back face 210b of the glass faceplate 210 is a curved surface defining an interior space of the sealed container 100A and the photocathode 230 is provided on this back face 210b. The body portion 300 is composed of a Kovar flange 310, a first ceramic side tube 330a, a fixing metal flange 320, a second ceramic side tube 330b, and a metal side tube 340, which are arranged in order from the head portion 200 toward the stem portion 400 along the first tube axis AX1. The stem portion 400 is fixed to the metal side tube 340 in a state in which at least a part thereof is housed in the metal side tube 340. Furthermore, the stem portion 400 is composed of a ceramic pedestal 410 holding a plurality of stem pins 430 in a state in which the stem pins 430 penetrate through, and a metal reinforcement member 420 for protecting the side face of the ceramic pedestal 410. A plurality of electrodes forming the electron multiplier unit 500 (including a dynode unit and an anode) are electrically connected through a plurality of connection pins (lead pins) corresponding to the respective electrodes, to a plurality of stem pins 430 fixed to the ceramic pedestal 410. By this configuration, the electron multiplier unit 500 is held at a predetermined position in the sealed container 100A, in a state in which it is supported by the connection pins extending from the respective stem pins 430.
The exhaust tube 600 extending along the first tube axis AX1 is fixed to the center of the ceramic pedestal 410. The exhaust tube 600 is composed of a metal pipe 610 one end of which is brazed to the ceramic pedestal 410 with an Ag—Cu alloy, and a glass pipe 620 fixed to the other end of the metal pipe 610. The glass pipe 620 is collapsed after evacuation of the interior of the sealed container 100A, whereby the interior of the sealed container is maintained in a constant degree of vacuum. Furthermore, the sealed container 100A shown in
The electron multiplier unit 500 is composed of a focusing electrode disc 510, a dynode unit 550, and an anode 520 arranged inside the dynode unit 550. The focusing electrode disc 510 is an electrode for altering the trajectory of photoelectrons emitted from the photocathode 230, so as to focus them toward the dynode unit 550, which is arranged between the photocathode 230 and the dynode unit 550 and which has a through hole 510a for letting the photoelectrons from the photocathode 230 pass through. The dynode unit 550 is composed of multi-stage dynodes Dy1 to Dy10 for successively cascade-multiplying secondary electrons emitted in response to the photoelectrons arriving via the focusing electrode disc 510 from the photocathode 230. In addition, the electron multiplier unit 500 further has a pair of insulating support members 530a, 530b for integrally grasping the focusing electrode disc 510, the dynode unit 550 composed of the multi-stage dynodes Dy1-Dy10, and the anode 520 for extracting secondary electrons resulting from the cascade multiplication by the multi-stage dynodes Dy1-Dy9 and secondary electrons from the inverting dynode Dy10 as a signal. The anode 520 is arranged on the trajectory of secondary electrons traveling from the ninth-stage dynode Dy9 to the inverting dynode Dy10. In the dynode unit 550, the inverting dynode Dy10 is a dynode for receiving secondary electrons passing through the anode 520 among the secondary electrons emitted from the ninth-stage dynode Dy9 and for again emitting secondary electrons toward the anode 520.
The electron multiplier unit 550 housed in the sealed container 100A is arranged, as shown in
Furthermore, the photomultiplier 100 has the structure (the pair of insulating support members) for integrally holding at least the focusing electrode disc 510, the dynode unit 550, the anode 520, and the light shield member 540, in a state in which at least the first-stage dynode Dy1 and the second-stage dynode Dy2 in the dynode unit 550 are directly opposed to the focusing electrode disc 510 without any conductive member in between. As a result, variation in electron transit time is drastically reduced in a process of travel from the photocathode 230 via the first-stage dynode Dy1 to the second-stage dynode Dy2 because a metal disc set at the same potential as the first-stage dynode Dy1 and directly supporting the first-stage dynode Dy1 as in the conventional photomultiplier, is not interposed between the focusing electrode disc 510 and the dynode unit 550.
Next, manufacturing processes of the respective parts in the photomultiplier 100 according to the present embodiment will be described in detail using
As shown in
Furthermore, there are also fixing pieces 520a, 520b provided at two ends of the anode 520, the fixing piece 520a is inserted into a corresponding installation hole 534a of the first insulating support member 530a, and a projecting portion thereof from the installation hole 534a is welded and fixed to a connection pin 550a. In similar fashion, the fixing piece 520b provided at the other end is also inserted into a corresponding installation hole 534b of the second insulating support member 530b and a projecting portion thereof from the installation hole 534b is welded and fixed to a connection pin 550b. The inverting dynode Dy10 is also provided with fixing pieces Dy10a, Dy10b at its two ends. The fixing piece Dy10a is inserted into a corresponding installation hole 533a of the first insulating support member 530a and a projecting portion thereof from the installation hole 533a is welded and fixed to a connection pin 550a. The fixing piece Dy10b is inserted into a corresponding installation hole 533b of the second insulating support member 530b and a projecting portion thereof from the installation hole 533b is welded and fixed to a connection pin 550b. In addition, the light shied member 540 is attached to the first and second insulating support members 530a, 530b so as to surround the anode 520. The anode 520 can become luminescent with increase in electron density. If such light from the anode 520 reaches the photocathode 230, it will be reflected as noise component in the signal extracted from the anode 520. Then, the light shield member 540 is installed so as to surround the anode 520, whereby it functions to prevent the unwanted light from the anode 520 from reaching the photocathode 230.
Each of the first and second insulating support members 530a, 530b is provided with projections 531a, 531b in the upper part (on the photocathode side). Each of the projections 531a of the first insulating support member 530a is inserted into an installation hole 511a of the focusing electrode disc 510, while each of the projections 531b of the second insulating support member 530b is inserted into an installation hole 511b of the focusing electrode disc 510. By this configuration, the focusing electrode disc 510 is fixed to the first and second insulating support members 530a, 530b grasping the dynode unit 550 including the anode 520. Holes 512 provided in the focusing electrode disc 510 are holes for letting a lead pin 513 for supporting a metal material of the photocathode 230 which will be formed after the interior of the sealed container 100A has become maintained in the vacuum state, pass through. The lead pin 513 is not used after formation of the photocathode 230.
Through the above assembly process, each of the members constituting the electron multiplier unit 500, such as the focusing electrode disc 510, the first- to ninth-stage dynodes Dy1-Dy9, the anode 520, the inverting dynode Dy10, and the light shield member 540, is integrally and stably held by the first and second insulating support members 530a, 530b.
On the other hand, the stem portion 400 located opposite to the photocathode 230 with the electron multiplier unit 500 in between has the ceramic pedestal 410 to the center of which the exhaust tube 600 is attached and which holds the plurality of stem pins 430 arranged so as to surround the aperture of the exhaust tube 600, and the metal reinforcement member 420 covering at least the side face of the ceramic pedestal 410. The exhaust tube 600 is composed of the metal pipe 610, and the glass pipe 620 fused and spliced to one end of the metal pipe 610, and the glass pipe 620 is sealed after completion of evacuation for the interior of the sealed container 100A (in the state in which the interior of the sealed container 100A is maintained in the vacuum state).
In the stem portion 400, the metal pipe 610 of the exhaust tube 600 is brazed and fixed to the ceramic pedestal 410 with the Ag—Cu alloy. In addition, the plurality of stem pins 430 are also brazed and fixed to the respective through holes of the ceramic pedestal 410 with the Ag—Cu alloy. Furthermore, the metal reinforcement member 420 is also brazed and fixed to the side face of the ceramic pedestal 410 with the Ag—Cu alloy. In addition, the other end of a corresponding one of the connection pins 550a, 550b is welded and fixed to each of the plurality of stem pins 430 each one of which is held in a penetrating state by the ceramic pedestal 410.
Through the above assembly process, the electron multiplier unit 500 supported by the stem portion 400 through the connection pins 550a, 550b is obtained, as shown in
Next, the assembly processes of the head portion 200 and the body portion 300 each forming a part of the sealed container 100A will be described in detail using
The head portion 200, as shown in
The body portion 300, as shown in
In the body portion 300 in
The focusing electrode disc 510 fixed to the fixing metal flange 320 shown in
As shown in the development view (top plan view and side view) of
As shown in the development view (side view, top plan view, and bottom plan view) of
Each of the plurality of through holes 322 establishes communication between the two spaces separated by the focusing electrode disc 510 and the fixing metal flange 320, i.e., between the space where the dynode unit 550 exists and the space where the photocathode 230 exists. The anode 520 can possibly become luminescent with increase in electron density. The light generated in the anode 520 is blocked to some extent by the light shield member 540 but it cannot be said enough. If the light from the anode 520 leaking from the electron multiplier unit 500 reaches the photocathode 230, it will be reflected as noise component in the signal extracted from the anode 520. On the other hand, the photocathode 230 is formed by supplying the alkali metal vapor from the stem portion 400 side toward the photocathode 230 side, and thus it is necessary to provide a gap in some width between the body portion 300 and the electron multiplier unit 500 in the sealed container 100A in the vacuum state. Then, the fixing metal flange 320 in the present embodiment is provided with the plurality of through holes 322.
The below will describe a process for finally manufacturing the photomultiplier 100 of the present embodiment with the sectional structure shown in
First, the electron multiplier unit 500 and the stem portion 400 (internal unit) obtained through the assembly process in
The fixing of the electron multiplier unit 500 and the stem portion 400 to the body portion 300 is carried out in a state in which the electron multiplier unit 500 supported by the stem portion 400 through the connection pins 550a, 550b is inserted in the body portion 300, as shown in
Furthermore, as shown in
It is noted that no change is allowed for the order of welding and fixing the electron multiplier unit 500 and the stem portion 400 to the body portion 300. This is attributed to the step (
In the present embodiment, for solving the problem in manufacture associated with the fixing of the installation position of the focusing electrode disc 510, the metal side tube 340 is provided on the opening end face 330b-2 side of the second ceramic side tube 330b. Since this metal side tube 340 has the space for housing the stem portion 400 as shown in
The photomultiplier 100 with the structure as described above can be applied to various sensor modules used under high-temperature, high-pressure environments, e.g., in underground resource exploration. As an example,
In
The sensor module 700 shown in
Next, control of the posture of the photomultiplier 100 in the sensor module 700 according to the present embodiment (a method of installing the photomultiplier 100 in the metal case 710) will be described using
The head portion 200 of the photomultiplier 100 housed in the metal case 710 is composed of the glass faceplate 210 and the Kovar flange 220 and, normally, the light entrance face 210a of the glass faceplate 210 can be inclined at angle θ to the first tube axis AX1 of the sealed container 100A, as shown in
In the present embodiment, therefore, the positioning spacer 730 is arranged in the metal case 710 and between the housed photomultiplier 100 and the socket 740. This positioning spacer 730 has the taper face 730a with which the stem portion 400 of the photomultiplier 100 is brought into contact, and can function to maintain the posture of the photomultiplier 100 in the metal case 710. Namely, the photomultiplier 100 is brought into contact with the taper face 730a of the positioning spacer 730, whereby the posture of the photomultiplier 100 can be kept stable, in a state in which the first tube axis AX1 and the second tube axis AX2 are out of alignment so as to keep the light entrance face 210a of the glass faceplate 210 and the opening face (aperture 710a) of the metal case 710 parallel to each other. As a result, we obtain the sensor module 700 with sufficient durability ensured and with excellent anti-vibration performance.
As described above, the photomultiplier according to the present embodiment realizes the structure resistant to use under high-temperature, high-pressure environments and the anti-vibration performance thereof is drastically improved when compared with the conventional technology. Furthermore, the sensor module according to the present embodiment also allows the posture of the photomultiplier to be kept stable in the case and the anti-vibration performance thereof is drastically improved when compared with the conventional technology.
From the above description of the present invention, it will be obvious that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all improvements as would be obvious to those skilled in the art are intended for inclusion within the scope of the following claims.
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Entry |
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“The Chinuchi Shimbun,” Nov. 12, 2013, including English-language translation. |
Number | Date | Country | |
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61921119 | Dec 2013 | US |