JP2007026785A - Photoelectric face, as well as photomultiplier tube equipped with it, x-ray generator, ultraviolet ray image tube, and x-ray image intensifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photoelectric face having high characteristics, a photoelectron multiplier provided with it, an X-ray generator, an ultraviolet ray image tube, and an X-ray image intensifier. <P>SOLUTION: This photo electric face is that in which a mixed crystal layer of magnesium oxide and zinc oxide expressed by a composition formula Mg<SB>x</SB>Zn<SB>(1-x)</SB>O (0<x<1) is film formed on a substrate, and emit photoelectrons into vacuum. By this photoelectric face, (1) the photoelectric face of a large area is enabled, (2) a curved substrate and the photoelectric face on a curved face on a plano-convex face is fabricable, (3) it is fabricable at a low cost, and high characteristics are obtained. Moreover, compatibility is high since the photoelectrons are emitted into the vacuum, and a high photoelectric effect can be obtained since outer photoelectric effect is utilized. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a photocathode, and a photomultiplier tube, an X-ray generator, an ultraviolet image tube, and an X-ray image intensifier provided with the photocathode.

  For conventional ultraviolet detectors, crystal photocathodes made of Group III / V semiconductors and diamond have been used. These photocathodes are made by attaching several molecular layers of alkali metal to a P-type crystal to lower the surface affinity. However, since the film is formed on a single crystal, (1) the area of the photocathode is limited. There are problems that (2) the shape of the photocathode film is limited to a flat surface, and (3) the film forming cost is high, and photocathodes that are not based on Group III / V semiconductors and diamond are being proposed.

  As a photocathode made of an oxide, there are techniques described in Patent Document 1 and Non-Patent Document 1 below. In Patent Document 1, it is disclosed that two or more kinds of compounds including MgO and ZnO are combined to form a photocathode and used for an air cleaner. Further, Non-Patent Document 1 shows that a hexagonal structure type MgZnO mixed crystal using ZnO as a buffer layer is used as a photocathode, and a detector is made using the internal photoelectric effect.

Japanese Patent Publication No. 7-93098 Journal of Applied Electronic Properties, Vol. 11, No. 1, 2005

However, in the said patent document 1, since it was supposed to use in air | atmosphere like an air cleaner etc., the process which raises the photoelectric effect of the activity by an alkali metal could not be performed, and the expandability was scarce. In Non-Patent Document 1, since the internal photoelectric effect is used, the S / N ratio when a bias voltage of 5 V is applied is as low as about 10 ³ (see FIG. 5 in the same document), and a high photoelectric effect can be obtained. was difficult.

  The present invention has been made in view of the above problems, and provides a photocathode having high characteristics, a photomultiplier tube, an X-ray generator, an ultraviolet image tube, and an X-ray image intensifier including the photocathode. With the goal.

The first photocathode according to the present invention forms a mixed crystal layer of magnesium oxide and zinc oxide represented by the composition formula Mg _x Zn _{(1-x) 2} O (0 <x <1) on a substrate. A reflection type photocathode that emits photoelectrons in a vacuum.

  In the first photocathode, an MgO layer is preferably provided between the substrate and the mixed crystal layer, and it is also preferable that an alkali metal is attached to the mixed crystal layer and activated.

The second photocathode according to the present invention is a mixed crystal of magnesium oxide and zinc oxide represented by the composition formula Mg _x Zn _(1-x) O (0 <x <1) on a substrate that transmits ultraviolet rays. A transmission type photocathode having a layer formed thereon, wherein photoelectrons are emitted in a vacuum.

  Moreover, it is also preferable that the second photocathode is activated by attaching an alkali metal to the mixed crystal layer.

  A photomultiplier tube according to the present invention includes the photocathode, a multiplier for multiplying photoelectrons emitted from the photocathode, and an anode for collecting the multiplied electrons.

  An X-ray generation apparatus according to the present invention includes the second photocathode, and generates X-rays when photoelectrons emitted from the photocathode upon irradiation with ultraviolet rays collide with an X-ray target. And

  An ultraviolet image tube according to the present invention includes the second photocathode, and outputs image light when photoelectrons emitted from the photocathode upon irradiation with ultraviolet rays enter a phosphor. .

  Moreover, the X-ray image intensifier according to the present invention includes the second photocathode and a scintillator that generates ultraviolet rays by X-ray irradiation, and is irradiated from the photocathode by irradiation of ultraviolet rays generated by the scintillator. Image light is output when the emitted photoelectrons enter the phosphor.

  According to the first photocathode (reflection photocathode) according to the present invention, (1) a large area photocathode is possible, (2) a curved photocathode can be produced on a curved substrate or a planocon surface, 3) It can be manufactured at a low cost, and high characteristics can be obtained. In addition, since the photoelectrons are emitted in a vacuum, the expandability is higher than that of the above-mentioned Patent Document 1, and since the external photoelectric effect is used, a higher photoelectric effect than that of the Non-Patent Document 1 can be obtained.

  Further, by providing the MgO layer between the substrate and the mixed crystal layer, the crystallinity of the mixed crystal layer can be increased, and the photoelectric effect is further increased by attaching and activating an alkali metal to the mixed crystal layer. be able to.

  According to the second photocathode (transmission type photocathode) according to the present invention, (1) a large area photocathode is possible, (2) a curved photocathode can be produced on a curved substrate or a planocon surface, 3) It can be manufactured at a low cost, and high characteristics can be obtained. In addition, since the photoelectrons are emitted in a vacuum, the expandability is higher than that of the above-mentioned Patent Document 1, and since the external photoelectric effect is used, a higher photoelectric effect than that of the Non-Patent Document 1 can be obtained. Moreover, the photoelectric effect can be further enhanced by attaching and activating an alkali metal to the mixed crystal layer.

  The photomultiplier tube, the X-ray generator, the ultraviolet image tube, and the X-ray image intensifier according to the present invention include a first photocathode (reflection photocathode) and a second photocathode (transmission type) according to the present invention. Since the photocathode is used, higher performance can be obtained compared to the prior art.

  First, a photocathode according to the present embodiment and a method for manufacturing a side-on photomultiplier tube using the photocathode will be described with reference to the flowchart shown in FIG. 1 and the cross-sectional view shown in FIG. .

First, an MgO powder material with a purity of 99.9% is prepared and stored in a desiccator (S1), and a ZnO powder material with a purity of 99.99% is prepared and stored in a desiccator (S2). Each of MgO powder and ZnO powder is put into a measuring container, and a sample with a desired molar ratio is prepared with a precision electronic balance (S3). That is, in the composition formula Mg _x Zn _(1-x) O, when it is desired to set x = 0.5, the molar ratio of MgO: ZnO is 5: 5, and when x = 0.7 is desired, MgO: ZnO. The molar ratio is 7: 3. Next, pellets in the form of 2 mmφ to 5 mmφ and 1.5 mm to 4 mm in thickness are produced from each of the produced samples using a compression pellet manufacturing machine (S4). Each pellet-like tablet produced in this way is put in a heat-resistant container, kept in an electric furnace at a temperature of 1000 ° C. to 1500 ° C. in an air atmosphere, sintered for 60 minutes or more, slowly cooled to room temperature, taken out from the furnace, and placed in a desiccator Store (S5).

  On the other hand, a nickel metal plate having a thickness of 0.3 mm is pressed into a required shape on the photocathode as a substrate to prepare a film forming substrate (S6). In addition to nickel metal, another substrate that can be a vacuum material such as a SUS metal substrate or a tantalum metal substrate may be used. The pressed metal substrate is washed with a detergent to sufficiently remove oil, and further washed with pure water and stored in a clean storage (S7).

And MgO and ZnO are vapor-deposited and formed on a nickel metal substrate, and the photocathode 111 is produced (S8). Specifically, the substrate prepared in S7 is set in the substrate mounting jig in the vapor deposition apparatus, and the MgO and ZnO sintered body stored in S5 is set in the vapor deposition source jig to form Mg _x Zn _{(1-x )} Form an O layer. At this time, when the MgO layer is required, the MgO layer is formed before the Mg _x Zn _(1-x) O layer is formed, and the photocathode 110 is manufactured. After the film formation is completed, the vacuum of the vacuum device is closed after the temperature in the device is sufficiently lowered, dry nitrogen gas is introduced into the device, and after reaching atmospheric pressure, the formed photocathode is taken out and a nitrogen-substituted desiccator chamber Keep in.

  Since the photocathode according to the present embodiment has been produced through the above steps, a method for producing a side-on photomultiplier tube using this photocathode will be described. First, other materials such as a secondary electron multiplier electrode, an anode electrode, and a sealing system are prepared (S9), and the photocathode prepared in S8 is added thereto to assemble a stem of the photomultiplier tube (S10). . Specifically, as shown in the cross-sectional view of FIG. 3, the photocathode 11, the multistage dynodes 12-1 to 9, the anode electrode 13, the shield plate 14, the mesh electrode 15, and the like are arranged.

  At the same time, a sealing material is prepared (S11). As the photocathode entrance window material, UV transparent materials such as high purity synthetic quartz transparent face plate, calcium fluoride transparent face plate, barium fluoride transparent face plate, magnesium fluoride transparent face plate, artificial sapphire transparent face plate are prepared. . For fusion bonding of the vacuum valve 10 and the window material 16, high temperature fusion fusion using an indium seal, an aluminum crimp seal, and frit glass is used. Then, the stem of the photomultiplier tube assembled in S10 and the vacuum valve 10 are sealed (S12). Laser welding, resistance heating welding, helium arc welding, or the like is used for sealing welding.

  Thereafter, the photocathode is activated with an alkali metal (S13). Specifically, a vacuum evacuation device is attached to the photomultiplier tube, heated to 300 ° C. in an electric furnace, held for 3 hours or more, degassed to confirm a sufficiently high vacuum, and then the temperature of the electric furnace Is set to 150 ° C., the photocathode is irradiated with a mercury lamp, the photocurrent of the photocathode is measured with an ammeter, cesium metal is introduced, and when the photocurrent reaches the maximum value, the introduction of cesium metal is stopped, The temperature of the electric furnace is set to 140 ° C. to 110 ° C. and firing is performed for 30 minutes to 60 minutes, and then the electric furnace is gradually cooled. Then, after the photomultiplier tube in the electric furnace has dropped to approximately room temperature, the photomultiplier tube is chipped off from the exhaust device. Finally, a predetermined performance test and spectral sensitivity measurement are performed (S14), and the process is completed (S15). The method for producing the side-on photomultiplier tube using the first photocathode (reflection photocathode) according to the embodiment of the present invention has been described above. It is also possible to adopt a configuration having a photocathode (transmission photocathode).

Next, the result of the spectral sensitivity measurement of the photocathode according to the present embodiment by the present inventors will be shown. First, FIG. 4 is a semilogarithmic graph showing the spectral sensitivity before alkali activity when x = 1, 0.7, and 0.5 on the Mg _x Zn _(1-x) O photocathode. Compared to Example A (x = 1, ie, MgO), Example B (x = 0.7) and Example C (x = 0.5) are shown to have higher sensitivity in the ultraviolet wavelength region.

  FIG. 5 is a graph showing the spectral sensitivity after alkaline activity having an MgO layer. Examples D, E and F (above x = 0.7) as well as Examples G, H and I (above x = 0.5) are shown to provide higher sensitivity due to alkaline activity.

FIG. 6 is a graph comparing the spectral sensitivities of the Mg _x Zn _(1-x) O photocathode with x = 0.7 and 0.5 according to the presence or absence of the MgO layer. Example L (x = 0.7, with MgO layer) and Example M (x = 0) than Example J (x = 0.5, without MgO layer) and Example K (x = 0.7, without MgO layer) .5, with MgO layer) shows higher spectral sensitivity, indicating that the MgO layer is more useful for improving spectral sensitivity. This is because, in the 2θ-θ spectrum measurement by the X-ray diffraction method (XRD) shown in FIG. 7, a peak due to the MgO rock salt structure appears and a peak due to another crystal structure does not appear. It is speculated that the improvement in crystallinity contributed to the improvement in sensitivity.

  Finally, the X-ray generator, the ultraviolet image tube, and the X-ray image intensifier according to this embodiment using the above-described photocathode will be described.

FIG. 8 is a configuration diagram of the X-ray generator 20 according to the present embodiment. In this X-ray generator 20, an ultraviolet transmissive window 21 made of sapphire and a Mg _x Zn _(1-x) O photocathode 23 are sequentially arranged on one bottom surface in a cylindrical vacuum vessel 24, and beryllium is formed on the other bottom surface. An X-ray transmission window 27 and an X-ray target 26 are arranged in this order. Further, a gate electrode 28 and a focus electrode 29 are introduced from the side, and a voltage is applied to the Mg _x Zn _(1-x) O photocathode 23, the gate electrode 28, the focus electrode 29 and the X-ray target 26 by a driving power supply 25. It has a structure that can be added. In this X-ray generator 20, photoelectrons emitted from the photocathode 23 by the irradiation of ultraviolet rays through the ultraviolet transmission window 21 are accelerated and focused by the gate electrode 28 and the focus electrode 29 and collide with the X-ray target 26. As a result, X-rays are generated through the X-ray transmission window 27.

FIG. 9 is a configuration diagram of the ultraviolet image tube 30 according to the present embodiment. In this ultraviolet image tube 30, an ultraviolet transmissive window 31 made of synthetic quartz, a very thin MgO layer 32, and a Mg _x Zn _(1-x) O photocathode 33 are arranged in this order on one bottom surface in a cylindrical ceramic vacuum vessel 34. On the other bottom surface, an output window 37 made of Kovar glass and a phosphor 36 are arranged in this order. Further, focus electrodes 38 and 39 are introduced from the side surfaces, and the MgO layer 32, the focus electrodes 38 and 39, and the phosphor 36 are configured to be applied with a voltage by a drive power source 35. In the ultraviolet image tube 30, photoelectrons emitted from the photocathode 33 by the irradiation of ultraviolet rays through the ultraviolet transmission window 31 are focused by the focus electrodes 38 and 39 and incident on the phosphor 36, whereby the image light is output to the output window. 37 is output.

FIG. 10 is a configuration diagram of the X-ray image intensifier 40 according to the present embodiment. This X-ray image intensifier 40 has an X-ray transmission window 41 made of aluminum on one bottom surface in a metal vacuum vessel 44 having a curved bottom surface and a glass casing 45 and a convex portion on the other bottom surface, an ultraviolet scintillator 42, Mg _{The x} Zn _(1-x) O photocathode 43 is arranged in order, and an output window 48 made of Kovar glass and a phosphor 47 are arranged in order on the convex portions on the other bottom surface. A focus electrode 46 is introduced from the boundary with the convex portion on the other bottom surface. In the X-ray image intensifier 40, ultraviolet rays are irradiated from the ultraviolet scintillator 42 by X-ray irradiation through the X-ray transmission window 41, and photoelectrons emitted from the photocathode 43 receiving the ultraviolet rays are irradiated by the focus electrode 46. The light is focused and incident on the phosphor 47, whereby image light is output through the output window 48.

  As described above, according to the present embodiment, a photocathode having high characteristics, and a photomultiplier tube, an X-ray generator, an ultraviolet image tube, and an X-ray image intensifier including the photocathode can be provided. it can. The photocathode according to the present invention, and the X-ray generator, the ultraviolet image tube, and the X-ray image intensifier provided with the photocathode are not limited to the modes described in the above-described embodiments, but adopt various modifications. It is possible.

It is a flowchart explaining the manufacturing method of the photocathode which concerns on this embodiment, and the side-on type photomultiplier tube using this photocathode. It is sectional drawing of the photoelectric surface which concerns on this embodiment. It is sectional drawing of a side-on type photomultiplier tube. It is a graph which shows spectral sensitivity. It is a graph which shows spectral sensitivity. It is a graph which shows spectral sensitivity. It is a graph which shows the result of crystallinity measurement. It is a lineblock diagram of the X-ray generator concerning this embodiment. It is a block diagram of the ultraviolet image tube which concerns on this embodiment. It is a block diagram of the X-ray image intensifier which concerns on this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Vacuum valve, 11 ... Photocathode, 12 ... Dynode 12, 13 ... Anode electrode, 14 ... Shield plate, 15 ... Mesh electrode, 16 ... Window material, 20 ... X-ray generator, 21 ... Ultraviolet transmission window, 23 ... Photocathode, 24 ... Vacuum container, 25 ... Drive power supply, 26 ... X-ray target, 27 ... X-ray transmission window, 28 ... Gate electrode, 29 ... Focus electrode, 30 ... UV image tube, 31 ... UV transmission window, 32 ... MgO layer, 33 ... photocathode, 34 ... vacuum vessel, 35 ... drive power source, 36 ... phosphor, 37 ... output window, 38, 39 ... focus electrode, 40 ... X-ray image intensifier, 41 ... X-ray transmission window 42 ... UV scintillator, 43 ... Photocathode, 44 ... Vacuum container, 45 ... Glass casing, 46 ... Focus electrode, 47 ... Phosphor, 48 ... Output window

Claims (9)

A reflective photocathode in which a mixed crystal layer of magnesium oxide and zinc oxide represented by the composition formula Mg _x Zn _{(1-x) 2} O (0 <x <1) is formed on a substrate, in a vacuum A photocathode characterized in that it emits photoelectrons. The photocathode according to claim 1, wherein an MgO layer is provided between the substrate and the mixed crystal layer. 3. The photocathode according to claim 1, wherein an alkali metal is attached to the mixed crystal layer and activated. A transmission type photocathode in which a mixed crystal layer of magnesium oxide and zinc oxide represented by the composition formula Mg _x Zn _{(1-x) 2} O (0 <x <1) is formed on a substrate that transmits ultraviolet rays. A photocathode characterized by emitting photoelectrons in a vacuum. The photocathode according to claim 4, wherein an alkali metal is attached to the mixed crystal layer and activated. A photoelectron multiplier comprising the photocathode according to claim 1, a multiplier for multiplying photoelectrons emitted from the photocathode, and an anode for collecting the multiplying electrons. Double pipe. An X-ray generator comprising the photocathode according to claim 4 or 5, wherein photoelectrons emitted from the photocathode upon irradiation with ultraviolet rays collide with an X-ray target and generate X-rays. 6. An ultraviolet image tube comprising the photocathode according to claim 4 or 5, wherein photoelectrons emitted from the photocathode upon irradiation with ultraviolet rays enter the phosphor to output image light. A photocathode according to claim 4 or 5 and a scintillator that generates ultraviolet rays by X-ray irradiation, and photoelectrons emitted from the photocathode by irradiation of ultraviolet rays generated by the scintillator are incident on the phosphor. An X-ray image intensifier characterized by outputting image light.

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