JPS6224549A - Ion chamber type x-ray detector - Google Patents

Abstract

PURPOSE:To suppress influence of leakage currents from cathodes, by providing anodes with guards, which are connected to a reference potential point in a circuit, so that leakage currents flowing from cathodes can be made to flow into the reference potential point in the circuit. CONSTITUTION:Each terminal of bases and guards on all anodes is jointed to a common electroconductive member such as a band-shaped material made of electroconductive rubber, and connected a reference potential point in a circuit. Terminals 17A and 17B at electrode parts are individually connected to current-detection circuits. And, cathodes 3 are provided with external-circuit- connection-terminals 19, and connected to a d-c voltage power supply. During measurement, output of the d-c voltage power supply is applied across the cathode 3 and anode 11 (base 12). Then, leakage currents, flowing into the anode 11 side through conduction passages of adhesive 7, are made flow into the reference potential point from guards 15A1, 15A2, 15B1, and 15B2, not coming to electrode parts 14A and 14B. Therefore, leakage current elements are not contained in the signal detected by the current-detection circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an ionization chamber type X-ray detector for a computer tomography apparatus, and more specifically, a signal electrode plate (hereinafter referred to as an anode) is provided with a circuit. The present invention relates to an ionization box type X-ray detector that is equipped with a guard connected to a reference potential point of a circuit, and is configured to allow leakage current flowing from a bias electrode plate (hereinafter referred to as a cathode) to flow to a reference potential point of the circuit.

(Prior art) As is well known, the ionization chamber type
The line detector has the configuration shown in FIG. In the figure, the X-ray detector has an anode 2 and a cathode 3 placed approximately parallel to incident X-rays, and an array of electrode plates placed alternately in a sealed case 1 filled with xenon gas or the like. I am prepared. The front part 4 of the sealed case 1 is made of a material with good X-ray transparency, such as an aluminum thin film, and serves as an X-ray entrance window (X-rays enter from arrow X). Further, the sealed case 1 has an arch shape with the X-ray entrance window 4 facing inside.

On the other hand, the anode 2 is connected to an individual current detection circuit (not shown).
Furthermore, all the cathodes 3 are connected in common to the output ends of a DC voltage source (not shown).

Note that the X-ray entrance window 4 is normally connected to a reference potential point (ground potential) of a current detection circuit or a DC voltage source.

Conventionally, the anode 2 in this type of ionization chamber type X-ray detector
and the cathode 3 as shown in FIG.
2), two ceramic insulator supports (substrates) 6 with grooves 5 spaced apart and an epoxy adhesive 7 (the adhesive 7 has a thickness of approx. .5M (covering the creeping surface 8 between the anode and cathode).

In the above configuration, when X-rays enter the X-ray detector,
The xenon gas is ionized and the l1lift flow flows to the anode 2.
A current flows between the current and the cathode 3 and is detected by the current detection circuit. This allows the amount of incident X-ray energy to be known.

(Problems to be solved by the invention) However, in conventional ionization chamber type X-ray detectors, the adhesive may contain impurities or be poorly cured, resulting in poor adhesion.) , the insulation resistance between the anode and cathode becomes low, and leakage current flows from the cathode 3 to the anode 2 and is detected together with the ionization current, reducing the detection characteristics and, in turn, adversely affecting the image quality of the computerized tomography R imaging device. There was a problem with the impact.

(Means for Solving the Problems) The present invention has been made in view of the above, and an object thereof is to provide an ionization chamber type X-ray detector that improves the influence of leakage current from the cathode. .

The ionization chamber type X-ray detector of the present invention that achieves the above object includes a guard connected to the reference potential point of the circuit on the anode,
The leakage current flowing from the cathode is directed to the reference potential point of the circuit.

(Example) Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIGS. 1(A) to 1(C) are block diagrams showing one embodiment of the present invention; FIG. 1(A) is a cross-sectional view showing the main parts of an ionization chamber type , a perspective view of the anode, (c),
FIG. 2 is a perspective view of a cathode.

The same reference numerals in each figure as those shown in FIG. 6 are used with the same meaning. The features of this embodiment are that the anode 11 includes a flat base 12 made of molybdenum and a highly insulating plastic plate covering both sides of the base 12 (
flexible printed circuit boards) 13A and 13B, electrode parts 14A and 14B formed on the plate surfaces of plastic plates 13A and 13B, and guards 15A and 15A
, 15B1 and 15B2 (each electrode part and each guard are formed by adhering plastic plates 13A and 13B to both sides of the base 12 and etching them). The electrode portion 14A is located on the plastic plate 13A and is spaced apart from the support locations at both ends of the anode 11. (located in the center not in contact with adhesive 7). On the other hand, the guards 15A1 and 15A2 are configured to be electrically insulated from the electrode portion 14A near the support portion of the anode 11. Further, the electrode part 14B and the guards 15B1 and 15B2 are also arranged on the plastic plate 13B. Circuit connection terminal 16.
17A, 17B, 18A1.18A2.18B1 and 1
It is equipped with 8B2. The base and guard terminals of all the anodes are connected to a common conductive member, such as a conductive rubber strip (not shown), and are connected to a reference potential point of the circuit (grounded). ing). Further, terminals 17A and 17B of the electrode portion are individually connected to a current detection circuit (not shown). Furthermore, the cathode 3 is also the first
As shown in Figure (c), it is provided with an external circuit connection terminal 19 and is connected to a DC voltage source (not shown).

In the above configuration, the output of the DC voltage source is applied between the cathode 3 and the anode 11 (base 12) during measurement. At this time, the leakage current that flows into the anode 11 side as the adhesive 7 is a conduction path is caused by the guard 15A1.15A2.1.
5B1 or 15B2 to the reference potential point, and the electrode part 1
4A or 14B is not reached. Therefore, the signal detected by the current detection circuit does not include a leakage current component.

Figures 2 (a) and (b) are configuration diagrams showing other embodiments of the present invention, in which (a) is a cross-sectional view of the main part of the ionization chamber type X-ray extractor; FIG. 75 is a perspective view of the cathode. The same reference numerals in each figure as in FIGS. 1 and 6 are used with the same meaning. The feature of this embodiment is that the anode 11 is constructed in the same manner as in the previous embodiment, and the cathode 21 has a flat base 22 made of molybdenum.
Highly insulating plastic plates (flexible printed circuit boards) 23A and 23B cover both sides of the base, and electrode portions 24A and 24. are formed on the surfaces of each plastic plate away from the support points at both ends of the cathode 21. (Each electrode part is formed by adhering flexible printed boards to both sides of the base 22 and etching them.) The electrode portions 24A and 24B are provided with external circuit connection terminals 25A and 25B, as shown in FIG. 2(B), and are individually connected to the output terminal of the DC voltage source via each terminal.

In the above configuration, the insulation resistance of the plastic plates 23A and 23B of the cathode 21 is generally the same as that of the adhesive 7.
It can be said that it is stable compared to .

Therefore, when the output of the DC voltage source is applied to each electrode portion of the cathode 21, almost no leakage current flows through the conductive path on the surface of the plastic plate 23Δ or 23B. Furthermore, even if a leakage current flows, it will flow through each guard of the anode 11 to the reference potential point and will not reach the electrode portion 14A or 14B of the anode 11.

FIG. 3 is a configuration diagram (cross-sectional view of the X-ray detector) showing the main parts of an ionization chamber type X-ray detector according to still another embodiment of the present invention. Each reference numeral in the figure has the same meaning as in each of the above figures. The feature of this embodiment is that the cathode is
The anode 31 includes an electrode portion 34A and a guard 35A, an electrode portion 34B and a guard on each plate surface of plastic plates 33A and 33B that cover both sides of the base 32. 35B. The end of each electrode part reaches one support point of the anode 31, and the end of each guard reaches one support point of the anode 31.
The structure is such that it reaches the other support point of No. 1. Further, the base, each electrode portion, and each guard are connected to an external circuit in the same manner as the base, each electrode portion, and each guard in the 7 nodes 11.

In the above configuration, the electrical characteristics of the cathode 21 are the same as those in FIG. 2. Therefore, the cathode 21
There is almost no leakage current from the anode 31 to the anode 31. or,
Even if a leakage current flows, the leakage current flowing into the guards 35A and 35B is based on the base 21! Detection characteristics are improved since the current is applied to a potential point.

Note that the present invention is not limited to the above embodiment, and may be a combination of the anode 31 and cathode 3. or,
As shown in FIG.
The guard 15Δ and 15B2 may be electrically connected to the M1 potential point via the base. Furthermore, the anode and cathode bases are electrically conductive and
Other materials that do not transmit X-rays, such as tungsten, may also be used.

(Effects of the Invention) As explained above, according to the ionization chamber type X-ray detector of the present invention, the circuit base 11! Since a guard connected to the potential point is provided so that leakage current flowing from the cathode flows to the reference potential point of the circuit, the influence of leakage current from the cathode can be improved.

[Brief explanation of drawings]

Figures 1 (a), (b), and (c) are block diagrams showing one embodiment of the present invention, and Figures 2 (a) and (b) are block diagrams showing another embodiment of the present invention. , FIG. 3 is a block diagram showing still another embodiment of the present invention, FIG. 4 is a block diagram showing still another embodiment of the present invention, and FIG. 5 shows an ionization chamber type X-ray detector. The configuration diagram, FIG. 6, is a configuration diagram showing a conventional example. 2.11.31... Anode, 3.21... Cathode, 6... Insulator support, 7... Adhesive, 12.
22.32...Base, 13A, 13B, 23A, 2
3B, 33A, 33B... Plus deck board, 14. A
, 14B, 24A, 24B, 34Δ, 34B...electrode portion, 15A, 15A, 15B, 15B2.
35A, 35B...guard, 40...'F4 electrical adhesive.

Claims (3)

[Claims] (1) Ionization chamber type equipped with an electrode plate array consisting of a large number of signal electrode plates and bias electrode plates arranged in a direction substantially parallel to the X-rays incident from the X-ray entrance window and supported at both ends by insulator supports. In the X-ray detector, the signal electrode plate is provided with a guard that allows leakage current flowing from the bias electrode plate to flow to a reference potential point of the circuit.
line detector. (2) The ionization chamber according to claim 1, wherein the guard is configured to be electrically insulated from the electrode portion of the signal electrode plate in the vicinity of support points at both ends of the signal electrode plate. type X-ray detector. (3) The ionization chamber according to claim 1, wherein the guard is configured to be electrically insulated from the electrode portion of the signal electrode plate near a support point at one end of the signal electrode plate. type X-ray detector.