JPH056875B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an ionization chamber type The present invention relates to an ionization chamber type X-ray detector in which a conductive thin film with good radiation transparency is disposed opposite to the X-ray entrance window with a gap formed therebetween, and the conductive thin film is held at a predetermined potential.

(Prior Art) As is well known, an ionization chamber type X-ray detector of a computerized tomography apparatus has a configuration shown in FIG. In the figure, the X-ray detector consists of a signal electrode plate 2 inside a sealed case 1 filled with xenon gas, etc.
(hereinafter referred to as anode) and bias electrode plate 3
(hereinafter referred to as a cathode) is made approximately parallel to incident X-rays, and is provided with an array of electrode plates arranged alternately. The front face 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 the arrow 5). The sealed case 1 also has an X-ray entrance window 4.
It has an arch shape with the inner side.

On the other hand, the anodes 2 are individually connected to a current detection circuit (not shown), and the cathodes 3 are all commonly connected to the output end 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, in this type of ionization chamber type X-ray detector,
As shown in FIG. 3 (FIG. 3 is a longitudinal cross-sectional view of an ionization chamber type X-ray detector), the electrode plate array consisting of an anode 2 and a cathode 3 has its front edge 3A connected to an X-ray entrance window 4. About 1mm apart from (forming gap a)
It is fixed to two ceramic insulator supports (substrates) 6 (the electrode plate array has anodes and cathodes arranged alternately at predetermined intervals in a direction substantially perpendicular to the plane of the paper).

In the above configuration, an electric field is formed in the sealed case 1 based on the DC voltage applied between the anode and the cathode. The xenon gas is ionized by the X-rays incident through the X-ray entrance window 4, and the ionization current flows along the electric field line and is detected by the current detection circuit. This allows the amount of incident X-ray energy to be known.

By the way, maintaining the structure of the electrode plate array stably has an important meaning in terms of stabilizing the electric field distribution, electric field strength, etc. within the sealed case and stabilizing the detection sensitivity. Therefore, care is usually taken to fix the electrode plate arrangement and the sealed case is provided with sufficient mechanical strength.

(Problem to be Solved by the Invention) However, in the conventional ionization chamber type X-ray detector, when the X-ray entrance window is bent due to temperature change, etc., the Because the electric field distribution between the leading edges of the aligned body is disturbed and the electric field strength changes,
There was a problem that the detection sensitivity fluctuated. especially,
There was a problem in that changes in the deflection of the X-ray entrance window were small (high-frequency changes), and sensitivity changes were noticeable when the gap a in adjacent channels was different (if the change in deflection was gradual, the effect on sensitivity was is small).

(Means for solving the problems) The present invention has been made in view of the above,
The purpose is to provide an ionization chamber type X-ray detector that does not cause sensitivity changes due to fine (high-period) deflection of the X-ray entrance window.

The ionization chamber type X-ray detector of the present invention that achieves the above object includes a conductive thin film with good X-ray transparency formed between the X-ray entrance window and the electrode plate array, forming a gap between the X-ray entrance window and the electrode plate array. The conductive thin films are arranged to face each other and held at a predetermined potential.

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

FIG. 1 is a configuration diagram (vertical cross-sectional view of the ionization chamber type X-ray detector) showing the main parts of an ionization chamber type X-ray detector according to an embodiment of the present invention. In FIG. 1, the same reference numerals as in FIG. 3 are used with the same meanings, so a description thereof will be omitted here. The feature of this embodiment is that the conductive base 7 is integrated with each insulator support 6 and is held at ground potential, and the X-ray entrance window 4 is fixed to the conductive base 7 with a gap b formed between the conductive base 7 and the X-ray entrance window 4. The feature is that it is equipped with an aluminum thin film (conductive thin film) with a thickness of approximately 0.1 mm.

In the above configuration, the cathode 3 and the anode 2
The electric field line due to the DC voltage applied between
It is determined by the relative positional relationship of the cathode 3, anode 2, and conductive thin film 8.

On the other hand, due to the bending of the sealed case 1, the X-ray entrance window 4
Even if the conductive thin film 8 is bent, it does not affect the conductive thin film 8 in any way. That is, even if the X-ray entrance window 4 is bent, the electric field distribution will not be disturbed or the electric field strength will not change.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and the conductive thin film may be configured to cover the X-ray incident window side with an insulator and maintain the same potential as the cathode 3, that is, the bias potential. good. Further, the electrode plates may be aligned by a so-called double-sided independent signal plate method, in which an anode with electrode parts formed on both sides of an insulating plate is installed between cathodes installed at a predetermined interval. .

(Effects of the Invention) As explained above, according to the ionization chamber type X-ray detector of the present invention, between the X-ray entrance window and the electrode plate array,
A conductive thin film with good X-ray transparency is placed opposite the X-ray entrance window with a gap formed therein, and in order to maintain the conductive thin film at a predetermined potential, changes in sensitivity due to small deflections of the X-ray entrance window are prevented. It never occurs.

[Brief explanation of the drawing]

FIG. 1 shows an ionization chamber type X according to an embodiment of the present invention.
Figure 2 is a configuration diagram showing the main parts of a radiation detector. Figure 2 is a configuration diagram showing an ionization chamber type X-ray detector. Figure 3 is a configuration diagram showing the main parts of a conventional ionization chamber type X-ray detector. be. 1... sealed case, 2... anode, 3... cathode, 4... X-ray entrance window, 7... conductive base, 6... insulator support, 8... conductive thin film with good X-ray transparency.

Claims (1)

[Claims] 1. In an ionization box type X-ray detector equipped with an electrode plate array consisting of a large number of signal electrode plates and bias electrode plates installed in a direction substantially parallel to the X-rays incident from the X-ray entrance window. , between the X-ray entrance window and the electrode plate array,
An ionization chamber type X-ray detector characterized in that a conductive thin film with good radiation transparency is disposed opposite to the X-ray entrance window with a gap formed therebetween, and the conductive thin film is maintained at a predetermined potential. 2. The ionization chamber type X-ray detector according to claim 1, wherein the conductive thin film is maintained at a ground potential. 3. Claim 1, characterized in that the X-ray incident window side of the conductive thin film is coated with an insulator, and the conductive thin film itself is maintained at a bias potential.
Ionization chamber type X-ray detector.