JPS5850486A - Radiation detector - Google Patents

Abstract

PURPOSE:To increase a space resolving power and to obtain detection data of excellent quality by forming a conductive layer on electrode plates for detecting signals by a suspension substrate method utilizing plasma polymerization, and by earthing the conductive layer thus formed to use the same as guard electrodes. CONSTITUTION:Electrode plates 6 and 7 for high voltage and for detection of signals are arranged in plural at prescribed intervals by using the grooves of insulating supports 18. On the electrode plates 7 for detection of signals, insulating layers 7c and conductive layers 7d are formed at the parts of the plates inserted into the grooves of the supports 18, by a suspension substrate method utilizing plasma polymerization. The conductive layers 7d are earthed and used as guard electrodes.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a radiation detector used in a radiation tomography apparatus. 1 Combi 5. as one of the radiation tomography devices. -Computerized Tomogr4
There is a device U called aphy (hereinafter abbreviated as CT device). As shown in FIG. 1, this device includes, for example, an Xk source J that emits flat fan beam X-rays FX in a pulsed manner;
The X&! The source 1 and the radiation detector 2 are rotated around the subject 3 in the same direction and at the same angular velocity to collect X-ray absorption data in various directions of the cross section of the subject 3. After collecting sufficient data, this data is analyzed by a computer, the X-ray absorption rate for each position of the object cross section is calculated, and the object cross section is reconstructed with a gradation level corresponding to the absorption rate. (This allows analysis to be performed in as many as 2,000 gradations depending on the composition.)
Clear tomographic images can be obtained with 1 ranging from soft tissues to hard tissues.

Incidentally, the radiation detector 2 detects the energy/I/g of the X-rays transmitted through the cross section of the subject 3 as an ionizing current, and outputs this as X-ray absorption data.

In other words, in collecting this X-ray absorption j'-wave, the energy of the X-rays that have passed through the line connecting each radiation detection cell making up the ionization tank and the X source (this is called an X-ray nox) is collected. is detected as a low ionization current, this is integrated for a predetermined time, the integrated value is discharged in a discharge circuit with a predetermined time constant, and the discharge time value is used as X-ray absorption data.

Once the data collection for the X-ray path from one direction is completed, the data collection for the next direction begins. completely disappeared.

If it is not completed, errors will appear in the next data collection.

That is, the repetition period of X-ray beam exposure is generally limited by the recovery time of the radiation detector.

This is a factor that does not have a major impact on the data collection time (i.e., imaging time) per tomographic plane, and in today's world where shortening imaging time is required, it is necessary to shorten this as much as possible7.
That's right.

In addition, the resolution of the ladle-composed image is determined by the sensitivity and resolution of the radiation 1V transverse extractor, so in order to repair the damaged C1' device, it is necessary to use radiation that has a fast recovery time, high sensitivity, and high resolution. There is no strain when using the detector.

In order to obtain excellent spatial resolution, the total length of each radiation detection cell row must be set to 1.
(It is desirable that they be placed close to each other and uniformly self-installed.)
The detector detects a very weak current on the order of nanoamperes (nA) as a signal, so □ti
It is necessary to pay sufficient attention to the leakage current between the terminals.

The present invention has been made in view of the above-mentioned circumstances, and a large number of electrode plates for high voltage and for I= detection are arranged alternately at predetermined intervals, and the electrode plates for signal detection and the electrode plates for detecting the signal are respectively In a radiation detector with spatial position resolution, an insulating support with a plurality of grooves into which the ends of the electrode plate are inserted is used, and the electrode plate is inserted into the grooves. is inserted and held, and the electrode plate for signal detection is coated with plasma polymerization (.
``Kyo#) An extremely thin and precise insulating thin film on the order of microns, and a similarly thin film of conductive material formed on top of it,
By using this conductor while grounded, the influence of leakage current on the detection signal can be prevented, and the processing method described above can form a thin film with extremely high uniformity, resulting in a highly accurate and high quality detection element. It is an object of the present invention to provide a radiation detector which has uniform energy characteristics between elements, which are important as detector characteristics because groups can be formed, and which has high sensitivity and high resolution with small sensitivity deviations.

An embodiment of the present invention will be described below with reference to FIGS. 2 to 14.

As described above, the radiation detector is placed facing the X-ray source through the subject.

5- Since the Xi sources and radiation detectors placed facing each other rotate around the subject at arbitrary times,
The beam is emitted in a pulsed manner. The X-ray beam passes through the cross section of the object while expanding in a fan shape with an angle of expansion θ. And this Xtj! The beam is incident on the radiation detection cell array and is separated from INL in accordance with its energy. Thereby, the photon intensity at the leading edge of the xH beam is detected in the form of an ionization current by the electrode plate of the radiation detection cell into which it is incident, and is spatially identified.

As mentioned above, in order to obtain excellent spatial resolution, the electrode plates constituting each radiation detection cell row should be placed close to each other.
Increase the i-pass number (-7: Maybe this X-ray A'
It is desirable to arrange them at a constant pitch so that the width of the space is uniform.

In order to achieve this state, in the present invention, grooves with a minute pitch are formed on an insulating material (for example, ceramic, etc.), and along the grooves, an insulating material and a conductive material are formed on the high voltage electrode plate and the sides. Inserting a signal electrode plate having two layers of polymeric coating = 6- makes it easier to maintain the pitch accuracy of the stain electrode plates.

An embodiment of the present invention will be described below in order.

FIG. 2 is a perspective view showing the configuration of this device. In the figure, 4 is an arcuate box-shaped case that houses the electrode group and others, and 5 closes the opening side of this case 4 and mounts the electrode group and others. It is a lid.

These case 4 and lid 5 are bolted together to maintain sufficient strength and airtightness against the high pressure gas filled inside. In this radiation detector, the incidence portion 4b on the entrance surface side 4a is made thin in accordance with the spread angle θ of the fan beam X-rays FX, so that sufficient X-rays can be incident thereon.

Figure 3 is a plan view of this radiation detector, and Figure 4 is its front view. Become.

FIG. 5 is a sectional view taken along the line AA in FIG. 3.

As can be seen from the figure, the inside of the main body 4 is hollow, and eventually a group of electrode elements will be disposed therein. Furthermore, the X-ray incident portion 4b is made thin so that the amount of transmitted X-rays is increased.

FIG. 6 is a diagram showing how the electrode plates 6 and 7 are arranged in the case 4, and a pair of electrode plates 6 to 7 facing each other.
Each part consists of two radiation detection cells.

Actually, the electrode group is attached to the lid side that closes the case 4.

Fig. 7 shows a plate-like high voltage application using a suppressing material such as a gold case formed into an approximately rectangular shape (for example, !i 00 to 1oooV).
'it & plate 6, 6a is a tab protruding from one side. This tab is for connecting to a high voltage line that guides high voltage when using GaFiJ.

FIG. 8 shows a blank plate of the electrode plate 7 for signal detection for detecting ionizing current. As shown in the figure, the base plate is a rectangular plate made of a conductive material such as metal, and has three tabs 7a, 7b, and 7a' protruding from the negative side. Among these, the tabs 7a and 7a' are provided at both ends, and the tab 7b is provided in the middle, and the tab 7b is a wiring tab for extracting the ionizing current and transmitting it to the data processing system. ,7a
'' is a tab used to cause leakage current flowing from the high-voltage electrode plate 6 to the signal detection electrode plate 7 to earth. The tab side is the back surface, the side opposite to the side with the tab is the radiation incident side, that is, the front side, and the remaining two sides are the groove insertion portions.

Figure 9 shows the prongs (groove insertion part) at both ends of the electrode blank shown in Figure 8.
A strip-shaped insulating thin film 7c made of an insulating material is formed on the portion with a predetermined width using a plasma polymerization method, and further a conductive material is formed on the upper surface of the insulating thin film 7c with a narrower width f or a conductive material using a plasma polymerization method. This is an electrode plate for signal detection formed by producing a thin film 7d. These thin films on the electrode plate 7 have a thickness on the order of microns, and their width is slightly wider than the depth of the groove of the support for holding the electrode plate.

A thin film 7d made of a conductive material is insulated from the base plate 9-Ap1 on the insulating thin film 7c. This thin film 7d is 1
? -1 and serves as a guard electrode to prevent leakage current flowing into the high-voltage electrode plate 6 from flowing into the blank plate.

Here, the method of generating the guard pole will be explained using FIG. 1θ and FIG. 11.

This method is called a floating substrate method in which the substrate is electrically suspended and a film is generated by interaction between plasma and the substrate. According to this method, the substrate on which the film is formed can be made of any material. However, when the substrate to which the coating is attached is used as an electrode, its material is limited to a conductor.

Below, Zolazma, ■Skin 1 legal will be explained.

In FIGS. 10 and 11, 10 is a reaction chamber, and this reaction chamber 10 is an exhaust gas 71? 7°1 is connected,
Due to this exhaust bonder 11, the inside of the reaction chamber IQ is 10~In.
It is evacuated to about torr and the impurity gas inside is removed. A 10-substrate 12 is disposed within a plasma generation region A described later in the reaction chamber 10, but portions of the substrate 12 where film formation is not required are masked by an appropriate method to prevent the film from adhering. Make it.

The masked substrate 12 is set in the reaction chamber 10 in an electrically floating state. The reaction chamber 10 has an evaporator 1
3 is not connected, and this evaporator 13 has deposited substances (
monomer) is vaporized and sent into the evacuated reaction chamber 10. In addition, in the reaction chamber 10, a pair of electric currents %14,
15 are provided, and when a high frequency voltage (kHz = MHz) is applied between these electrodes 14 and 15 from an AC power source 16, a discharge is started between these electrodes 14 and 15. Then, the space A between the electrodes 14 and 15 in the reaction chamber 10 becomes in a plasma state. In plasma, the temperature of electrons is two to three orders of magnitude higher than that of ions, so electrons fly around at an extremely high speed compared to ions.

Therefore, when the electrically floating substrate 12 comes into contact with the plasma, the substrate 12 is mainly bombarded with electrons and becomes negatively charged, reaching a potential 9 negative compared to the plasma.

Therefore, in the vicinity of the substrate 12 placed in plasma, electrons are repelled, the electron density decreases, and the substrate 12 is surrounded by ions. Ion sheath (Ion 5eat)
h).

In the plasma, ions moving due to thermal diffusion join the ion sheath, then reach the substrate surface, where they recombine with electrons and form a single body. Then, it is further made into a polymer (monomer).

For example, the deposited material, i.e., I'i as a monomer, and dielectric insulating materials such as aluminum chloride and styrene.

Examples include tetratoxysilane and vinyl chloride, and generated polymers include aluminum oxide, styrene, and silicon oxide. Since silicon oxide and the like react with oxygen, an oxygen partial pressure of about 101 mHg must be taken into consideration.

Furthermore, as for conductive materials, thin films of copper, molybdenum, nickel, etc. may be formed. Formation of this thin film of conductive material is carried out by a method completely similar to the method described above, but it is also possible to use not only this method but also a vacuum evaporation method.

The rate of polymer formation depends on various factors, such as the pressure (degree of vacuum), temperature, AC power frequency, current density, etc. in the reaction chamber 10, but generally 'vrn1 n
Al on the level.

Note that the noah in FIGS. 1θ and 11 is a vacuum gauge for measuring the degree of vacuum within the reaction chamber 1θ.

The electrode plate 7 for signal detection shown in FIG. 9 is made in this way, and the tab 7a is formed on the thin film 7d made of a conductive material.

By connecting the lead wire at the position 7a/ and grounding it, it is possible to suppress leakage current from the high voltage electrode plate 6 from flowing into the electrode plate 7.

It should be noted that while the diagram in FIG. 10 shows the generation of one substrate, FIG. 11 shows the generation of a plurality of substrates.

A plurality of electrode plates 7 for signal detection formed in this manner and electrode plates 6 for surface pressure described above are prepared, and a plurality of grooves 13-1B& for electrode insertion are formed as shown in FIGS. 12 to 14. The electrode plates 6.7 are alternately inserted and arranged in a pair of provided supports 18 with their ends held in the grooves 18h.

That is, Fig. 12 is a partial view of the radiation 40-emitter seen from the back, Fig. 13 is a view indicated by the B-B arrow, and Fig. 14
The figure shows a perspective view, where 4 is the aforementioned case and 5 is the aforementioned lid. The support 18 is a plate-shaped member made of an insulating material, and the groove 18a is arranged at a pitch of the electrode plate I], 7.
1-1 are formed in the direction in which the electrode plates 6 and 7 are arranged.

This support 18 is provided in the case 4 with the grooves 18a facing each other, and the electrode plates 6 and 7 are inserted between these grooves 18h with their tabs on the back side. The electrode plate 7 for signal detection has a guide electrode, that is, a conductive thin film 7d formed on the insulating thin film zc, with a width slightly larger than the depth of the groove 18a. is inserted and held in the groove 18a in such a manner that it protrudes beyond the groove 18a. The groove 18a insertion portion of the electrode plates 6, 7 is bonded and fixed with an insulating adhesive 19 such as epoxy resin. Further, the tabs 6a of each high-voltage electrode plate 6 are connected to each other by a lead wire 20, and a high voltage (500 per 1 o o ov) is supplied through this lead wire 20.

In fact, the card electrode portions of each R4 detection electrode plate 7, that is, the conductive +H film 7d portion are connected to each other by a lead wire 2, and are grounded via this lead wire 2.

Further, the lid 5 is provided with terminals 22 for external signal extraction at positions corresponding to the electrode plates 7 for signal detection.
Each of these terminals 22 is connected to a tab 7 of a corresponding electrode plate 7.
3° connected to the lead wire 23 by the lead wire 23. In such a device, the grounded guard electrode is connected to the insulating thin film 7C.
The support 1 is formed on the supporting end side of the electrode plate 7 through the 9 high voltage electrode plate 6 due to the skin effect.
Leakage current flowing into the signal detection electrode plate 7 through the layer 8 and adhesive 19 is blocked by this guard electrode portion. Therefore, there is no leakage current in the electrode plate 7 for signal detection, and only the component f caused by ionization is detected.

In addition, this device is designed to form the guard electrode portion using a plasma polymerization floating substrate method that can form a thin film with high uniformity and thinness. It can be processed to a high degree of precision using numerically controlled machine tools, etc. In combination with I-r15-), a multi-channel radiation IA1 detector with high quality and uniform detection characteristics can be created.

As described in detail above, the present invention has two electrode plates for high voltage and signal detection; A plurality of the insulating sieves are arranged alternately at a predetermined interval, and a detection signal corresponding to the incident radiation is detected from each of the signal detection electrode plates. In a multi-channel radiation detector that has spatial resolution by using A44, the electrode plate for signal detection is coated with an insulating layer and a conductive layer in the portion to be inserted into the groove of the tube using a floating substrate method using plasma polymerization. Since the conductive layer is grounded and used as a guard electrode, the leakage current from the high voltage electrode plate is blocked by this guard electrode, and therefore it is used for signal detection. 1. Signal detection can be performed with high accuracy and sensitivity, and the insulating layer and conductive layer electrically float the electrode plate, which is disposed in the plasma, and each of the above Since each layer is formed by a floating substrate method using plasma polymerization by supplying the vapor of a substance that generates the layers, the insulating layer and conductive layer can be formed thinly and uniformly in thickness, and therefore the processing accuracy can be improved. Because you can keep
A detector with high dimensional accuracy can be obtained with a narrow electrode arrangement pitch,
Therefore, it is possible to provide a radiation detector that can obtain high quality detection data with high spatial resolution.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining the principle of a CT device, Fig. 2 is a perspective 17- view showing an example of a conventional radiation detector, Fig. 31 is a plan view thereof, and Fig. 4 is a front view of Fig. 2. , FIG. 5 is a sectional view taken along the line A-A in FIG. 3, FIG. 6 is a diagram showing the arrangement of the detection element group in the radiation detector, FIG. The figure shows the floor plate of the electrode plate for signal detection, and FIGS. Kawaguchi, Figures 1O and 11 are diagrams for explaining the floating substrate method using plasma polymerization used to form the guard electrode portion of the electrode plate for signal detection, and Figure 12.
FIGS. 13 and 14 are a rear view, a view taken along the H-11 arrow 1III, and a perspective view thereof, showing the state of a detection string assembly assembled using the electrode plate according to the present invention. 4... Case, 5... Lid, 6... Electrode plate for high voltage, 6a, 7a, 7a', 7b... Tab, 7... Electrode plate for signal detection, 7C... Insulation Thin film, 7d... Thin film made of conductive material, 18... Support, 18a... Groove, 1
9...Adhesive layer. =18- Figure 3 Figure 4 Figure 6 498- Figure 7 Figure 8

Claims (1)

[Claims] A plurality of electrode plates for high voltage and signal detection are inserted and held by using the grooves of an insulating support formed with electrode plate holding grooves formed at predetermined intervals. In a multi-channel radiation detector, the electrode plates are arranged alternately to form a group of detection elements, and a detection signal corresponding to incident radiation is obtained from each of the signal detection electrode plates,
The signal detection electrode plate has an insulating layer formed by a floating substrate method using plasma polymerization at least in the portion to be inserted into the groove of the support, and a p-conducting layer formed thereon by a floating substrate method using plasma polymerization or a vacuum evaporation method. A radiation detector characterized in that the conductive layer is grounded and used as a guard electrode.