JP5604751B2 - Particle beam image detector with pixel electrode using high resistance electrode - Google Patents

Description

  The present invention relates to an improvement in operational stability of a particle beam image detector having a pixel electrode structure.

As a common direction in the currently planned high-energy physics experiments and beam experiments (such as synchrotron radiation and neutron beams) that are in operation and planned for material structure analysis, we aim to discover new phenomena and improve accuracy. An increase in brightness using a stronger beam can be mentioned.
On the other hand, in order to obtain results using these high-intensity particle beams effectively, a corresponding particle beam detector is required. Gas detectors such as wire chambers have been widely used as particle beam detectors because of their excellent position resolution and temporal resolution for individual incident particles. However, those using a wire for reading cannot cope with high-frequency incident particles of approximately 10 ⁴ counts / mm ² or more.

As a gas detector that exceeds this limit, a micro pattern gas detector using microfabrication technology supported by integrated circuit (IC) and electronic circuit board fabrication technology
(MPGD) has been researched and developed. A typical example of such a micro pattern gas detector is a strip type electrode detector MSGC (Micro Strip Gas).
GEM (Gas Electron), which was developed by Chamber (microstrip gas chamber) and CERN (European Elementary Particle Research Organization) and is entering the mass production stage in recent years.
(See, for example, Patent Document 1 and Patent Document 2). These are several hundred μm
It has the following extremely high detection position resolution and is characterized by having a particle beam incidence frequency tolerance of several hundred times or more compared to a wire type gas detector. For example, a substance using high-intensity X-rays It is used for structural analysis and has achieved certain results.

On the other hand, conventional MPGD because generally the electrode is large portion in contact with the insulator, the signal amplification factor of the comparable wire chamber in alone (10 ⁵ or more) be difficult to obtain, in the amplification factor of the increase, the electrode destruction by discharge It was mentioned as a drawback that the phenomenon tends to occur. In order to remedy these weaknesses, the inventor has so far improved μ-PIC which has greatly improved the electrode structure of the strip electrode detector (MSGC).
(Micro
(Pixel Chamber; micropixel chamber)
(Patent Document 3). This is a detector that realizes an electric field structure that does not cause a discharge phenomenon as much as possible while obtaining a high gas amplification factor by devising an electrode structure. In addition to high position resolution, the μ-PIC has an advantage that the dead time is extremely short as a gas amplifier, and is highly expected as a detector for a high-intensity particle beam.

In addition, at present, it has been confirmed that μ-PIC has no problem in operation even under a luminance of 10 ⁷ counts per square mm per second or more in a test using X-rays. Something that can withstand continuous operation of a certain degree is made.
However, in the development for practical use, in order to ensure a sufficient amplification factor and operational stability, GEM (Gas Electron)
At present, it must be combined with other detectors such as Multiplier.

Japanese Patent Laid-Open No. 10-300856 JP 2000-214264 A JP 2002-6047 A

  However, one of the biggest challenges in putting the above-described MSGC and μ-PIC into practical use is the destruction of the electrodes due to the discharge between the electrodes. In the above-mentioned MSGC, a voltage is applied between the electrodes with an interval of 50 μm or less, so if a high voltage is applied to obtain a high gas amplification factor, a large current flows between the electrodes, and the electrode strip is cut by the heat from the discharge. In many cases, the failure of conducting between the electrodes has occurred frequently, for example, due to the adhesion of the fragments to the surface insulating layer.

As for the mu-PIC, although the discharge between the electrodes as compared to the MSGC has become considerably suppressed are as in required particle beam track detection is 10 ⁴ or more gas amplification factor, such as electrons, also discharge Electrode destruction at a large current due to was a problem. In μ-PIC, ionization due to incident particles is very large, or discharge is often generated between electrodes due to accidental factors, which is a major cause of damage to the detector itself and the readout electronic circuit. It was.

  In view of the above problems, the present invention provides a pixel-type particle beam image detector capable of spontaneously suppressing a discharge phenomenon in which a large current flows locally between electrodes and improving operational stability. The purpose is to do.

In order to achieve the above object, the particle beam image detector of the present invention has a cylindrical anode electrode that penetrates the insulator substrate and whose upper end surface is exposed on the surface of the insulator substrate, and is formed on the back surface of the insulator substrate. And a cathode electrode pattern having a circular opening around the upper end surface of the cylindrical anode electrode and formed on the surface of the insulator substrate. In the container, the entire surface of the cathode electrode pattern is covered with a highly resistive conductor having a specific resistance of 10 Ω · m to 1000 Ω · m.

According to such a configuration, a discharge phenomenon in which a large current flows locally between the electrodes can be suppressed spontaneously by the voltage drop effect, and the operational stability can be improved.
The entire surface of the cathode electrode pattern is covered with a highly resistive conductor having a specific resistance of 10 Ω · m or more and 1000 Ω · m or less to avoid electrode damage due to self-sustained discharge in which a large current flows locally between the electrodes. . The high resistance material coated on the surface of the cathode electrode pattern spontaneously suppresses the discharge due to the voltage drop action. In this way, the discharge is suppressed spontaneously, and the stable operation of the detector is realized.
The range of the specific resistance of the conductor having high resistance is 10 Ω · m or more and 1000 Ω · m or less. If the specific resistance is less than 10 Ω · m, there is a possibility that a sufficient voltage drop cannot be obtained during discharge. Yes, it is not suitable for suppressing discharge spontaneously due to the voltage drop action, and when the specific resistance is larger than 1000 Ω · m, there is a possibility that a voltage drop may occur even in the detection of a normal particle beam and a sufficient signal cannot be obtained. Because. . The range of the specific resistance of the conductor having high resistance is more preferably in the range of 50 Ω · m to 500 Ω · m when the thickness of the material is 25 μm.

Here, the conductor having high resistance is preferably in contact with the insulator substrate. By not exposing the anode electrode part, it is possible to make the discharge more difficult to occur.

In addition, the conductive material having high resistance is preferably a conductive polyimide or a thin film containing conductive polyimide. The sudden voltage drop on the surface of the highly resistive conductor due to the discharge forms a very high electric field inside the highly resistive conductor itself. Therefore, a high dielectric breakdown resistance is required for such a highly resistive conductor . In general, polyimide is known to have excellent resistance to dielectric breakdown, and conductive polyimide in which carbon or the like is dissolved in polyimide is suitable for use as a conductor having high resistance in the present invention.

Furthermore, the film thickness of the high-resistance conductor coating film is specifically set to 1 to 100 μm.
Since the circular diameter of the opening of the cathode electrode is 200 to 300 μm, the film thickness is appropriate.
In addition, the range of the film thickness of the coating film of the conductor having high resistance is more preferably in the range of 1 to 30 μm.

According to the particle beam image detector according to the present invention, a large current is locally generated between the electrodes by covering the cathode electrode of the pixel-type electrode structure with a conductive material having high resistance such as a film-like polyimide. Can be suppressed spontaneously by the voltage drop action, and the operation can be stabilized.

Structural schematic diagram of particle beam image detector of pixel-type electrode of Example 1 Operation explanatory diagram of the particle beam image detector of Embodiment 1 Sectional view of the structure of the pixel electrode particle beam image detector of Example 1 Illustration of the surface shape of the pixel electrode The graph which measured the correlation of the applied voltage and gas amplification factor by the particle beam image detector of Example 1

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The scope of the present invention is not limited to the following examples and illustrated examples, and many changes and modifications can be made.

FIG. 1 shows a structural schematic diagram of a particle electrode image detector of a pixel type electrode according to the first embodiment.
In the particle beam image detector of the present invention, the cathode electrode pattern 14 and the anode electrode pattern 12 are formed on the front surface and the back surface of the insulator substrate 11, respectively.
The anode electrode pattern 12 has a cylindrical anode electrode 13 that penetrates the insulator substrate 11 and has an upper end surface exposed at the surface of the insulator substrate 11.
Moreover, the cathode electrode pattern 14 has a circular opening 16 around the upper end surface of the cylindrical anode electrode 13, and the surface of the cathode electrode pattern has a specific resistance of 10 Ω · m to 1000 Ω · m. It is covered with a high resistance material 15 having
As the high resistance material covering the cathode electrode pattern, a conductive polyimide sheet manufactured by DuPont is used.

Moreover, as a material of the insulator substrate 11, for example, an insulating material polyimide is used.
In addition, a drift electrode 17 is disposed at a predetermined interval above, and a chamber in which a gas composed of argon and ethane flows is formed.

  As shown in FIG. 1, the cathode electrode pattern 14 has openings 16 at predetermined intervals. At the center of the opening 16, there is an upper end portion of the cylindrical anode electrode 13 connected to the anode electrode on the back surface. The cylindrical anode electrode 13 is referred to as a pixel type electrode.

The size scale of the pixel-type electrode of Example 1 will be described with reference to FIG.
First, the diameter D1 of the pixel-type electrode, that is, the cylindrical anode electrode 13 is about 50 μm. The diameter D1 of the cylindrical anode electrode 13 is determined in the range of 40 to 100 μm. The height of the cylindrical anode electrode 13 can be appropriately set in the range of 50 to 150 μm according to the height of the double-sided substrate 11. The interval D3 between the cylindrical anode electrodes 13 is about 400 μm.
Further, the thickness D2 of the insulating substrate 11 is about 100 μm. The height D4 of the cylindrical anode electrode 13 is about 100 μm (corresponding to the thickness of the double-sided substrate 11).
The anode electrode pattern 12 has a width of 300 μm. The width of the anode 12 is determined in the range of 200 to 400 μm. The diameter of the circular opening 16 of the cathode electrode pattern 14 is about 250 μm. The diameter of the opening 16 is determined in the range of 200 to 300 μm.
The thickness D5 of the high-resistance material covering the cathode electrode pattern 14 is about 25 μm.

In an actual particle beam image detector, the insulator substrate 11 and the electrodes (12, 14) on both sides are placed in a pixel chamber, that is, a gas atmosphere based on a rare gas. By arranging the drift electrode 17 in an appropriate position (actually several mm to several cm) in parallel with the insulator substrate 11, μ-PIC
And particle beam image detection.

FIG. 2 is a diagram for explaining the operation of the particle beam image detector of the present invention.
Electrons e− ionized in the gas by the incident particle beam are drifted to the pixel electrode (cylindrical anode electrode 13) in the direction of the detector surface by the drift electric field. In the vicinity of the pixel electrode, a voltage of, for example, 500 V is applied between the cylindrical anode electrode and the cathode electrode, and the electron amplifies the gas avalanche by the strong electric field between the cylindrical anode electrode and the cathode electrode. Wake up. The resulting + ions drift quickly to the surrounding cathode electrode.

In this process, electric charges that can be observed on the electric circuit are generated in both the cylindrical anode electrode and the cathode electrode. The position of the incident particle beam can be observed by observing the positions of the anode electrode and the cathode electrode where the observable charges are generated.
As a circuit system for reading a signal and obtaining a two-dimensional image, a circuit system developed for a conventional μ-PIC can be used as it is.

FIG. 3 is a structural cross-sectional view of the pixel electrode particle beam image detector of the first embodiment.
The high resistance material covering the anode electrode causes a voltage drop from the interface between the cathode electrode and the high resistance material to the surface of the high resistance material for a large charge transfer such as discharge. As a result, large charge transfer such as discharge can be suppressed spontaneously.

FIG. 4 is an explanatory diagram of the surface shape of the pixel-type electrode. As shown in the drawing, the opening of the cathode electrode is covered with a conductive polyimide sheet made of a high-resistance material up to a 25 μm portion (D6) of the edge of the opening. The conductive polyimide sheet at the edge portion is brought into contact with the insulator substrate so that the cathode portion is not exposed.
In addition, between the patterns of the cathode electrode pattern 14, a portion (D7) corresponding to 25 μm of the edge is covered with a conductive polyimide sheet made of a high resistance material.

  FIG. 5 is a graph obtained by actually measuring the correlation between the applied voltage and the gas amplification factor by the particle beam image detector of Example 1. In FIG. 5, the horizontal axis represents the applied voltage (V) between the cathode and the pixel type electrode, and the vertical axis represents the gas amplification factor. In this measurement, a drift electric field of 2 kV / cm is applied, and a gas (circular pressure) in which argon and ethane are mixed in a one-to-one relationship as a gas flowing through the chamber.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

The particle beam image detector of the present invention is useful as a general-purpose two-dimensional particle beam image detector or three-dimensional charged particle track detector. As a specific application field, it can be used for a material structure analysis apparatus using X-rays or neutron beams, a medical diagnostic apparatus using radiation, a gamma ray camera, a particle beam momentum measurement apparatus, and the like.
Further, it is considered that operation in Geiger-Muller mode is possible depending on how to select the working gas and the resistance value of the high-resistance material. In this case, an image detector can be realized with a particle beam excellent in handling.

DESCRIPTION OF SYMBOLS 11 Insulator board | substrate 12 Anode electrode pattern 13 Cylindrical anode electrode 14 Cathode electrode pattern 15 High-resistance material 16 Opening 17 Drift electrode 20 Discharge

Claims (4)

A cylindrical anode electrode penetrating the insulator substrate and having an upper end surface exposed on the surface of the insulator substrate; an anode electrode pattern formed on the back surface of the insulator substrate; and an upper end surface of the columnar anode electrode In a pixel-type electrode particle beam image detector comprising a cathode electrode pattern having a circular opening around and formed on a surface of the insulator substrate,
A particle beam image detector, wherein the entire surface of the cathode electrode pattern is coated with a highly resistive conductor having a specific resistance of 10 Ω · m to 1000 Ω · m. The particle beam image detector according to claim 1 , wherein the high-resistance conductor is in contact with the insulator substrate. 2. The particle beam image detector according to claim 1, wherein the conductive material having high resistance is a conductive polyimide or a thin film containing conductive polyimide. 3. 2. The particle beam image detector according to claim 1, wherein the coating film of the conductive material having high resistance is 1 to 100 μm.