JPS6264041A - Ionization chamber type radiation detector - Google Patents

Abstract

PURPOSE:To improve the radiation transmitting rate, the sensibility of detector and the air-tightness by employing a complex member reinforced with highly strong carbon fiber reinforced resin at the radiation incident window section. CONSTITUTION:A container body 60 and a X-ray incident window section 61 are integrated through mechanical machining where the window section 61 is made as thin as 0.5mm while the window section 61 is provided with carbon fiber reinforced resin 62 at the inside and made as thick as 2mm. The body 60 and the resin 62 are secured through adhesive. In the resin 62, the fibers are arranged longitudinally in eight layers while laterally in two layers thus to form such X-ray incident window as having rational strength corresponding with the inner stress.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to an ionization chamber type radiation detector, and in particular,
The present invention relates to an ionization chamber type radiation detector with high detection efficiency and which is effective for obtaining good images in T apparatuses.

[Background technology]

The imaging method of conventional X-ray CT equipment uses an X-ray source that emits fan-shaped X-rays with an aperture angle of about 40° and a multi-element ionization chamber radiation detector (hereinafter referred to as the detector) at a distance of about 1 m. The X-ray source and detector are placed facing each other at a distance of X from multiple directions
This method irradiates X-rays, measures the X-ray intensity distribution, and obtains tomographic images by computer processing the signals. In this type of X@CT system, a xenon ionization phase detector is mainly used as a detector (Japanese Patent Application Laid-Open No.
17889, JP-A-54-89791).

Conventional detectors of this type are shown in FIGS. 3 and 4.

In FIGS. 3 and 4, an electrode plate assembly 5 is housed in a sealed space formed by the container body 1, M2, and bolt 3. As shown in FIG. Electrode plate assembly 5
The support frame 6 has signal electrode plates 51 and bias electrode plates 52 held alternately and parallel to each other. This electrode plate assembly 5 is sealed in a container body l along with xenon gas, is electrically connected to a conductor formed on one gasket 4, and is used to extract detection signals from the electrodes to the outside. . The incidence of X-rays from the X-ray entrance window 11 causes an ionization effect on the xenon gas, and the electrode plate assembly 5 outputs an electrical signal according to the amount of incident X-rays.

Since the container body 1 and the lid 2 are under high pressure of xenon gas, they are usually made of an aluminum alloy having a sufficient thickness to cope with the high pressure.

However, in such a detector, the front wall of the container body 1 is made thin and an X-ray entrance window 11 is provided through which X-rays enter, but the container body 1 and the lid 2 are pressure vessels. Therefore, it is not possible to make the radiation entrance window 11 thinner than a certain limit).

Figure 5 shows a cross section of the pressure vessel deformed when xenon gas is filled, and the window part of the X-ray entrance window 11 (window part 4 mm, other 1
5 mm), the deformation here is the largest (reference numeral 20 in FIG. 5), and the tensile stress in the vertical direction in the figure is the largest. If the window is made even thinner, the tensile stress on the aluminum alloy will exceed the allowable stress, and there is a risk of breakage.

On the other hand, aluminum alloy exhibits a transmittance as shown in FIG. 6 for X-rays with an average energy of 70 KeV, which is often used in x-mar devices. By the way, as a result of actual measurements and calculations, at 4mm+thickness, the transmittance is 78%, that is, 22%.
It is attenuated by the line entrance window 11 and does not contribute to the output. Because it is not possible to further increase the transmittance of X-rays in the entrance window due to the intensity, this is a factor that makes it difficult to further improve the efficiency of X-ray utilization.

In addition, constructing the entire container body 1 from carbon fiber-reinforced resin has superior X-ray usage efficiency compared to aluminum alloy, but it also has long-term effects such as the xenon gas inside the container leaking out and the internal pressure decreasing (years). There are problems with the airtightness and workability of the product. moreover.

Even when only the X-ray entrance window 11 is made of carbon fiber-reinforced resin and the other parts are made of aluminum alloy and are bonded (adhered) to form the container body 1, there is a problem with the airtightness of the joint part and the carbon fiber-reinforced resin. there were.

[Purpose of the invention]

An object of the present invention is to provide an ionization box-type radiation detector that improves the sensitivity of the detector by increasing the radiation transmittance at the radiation entrance window and has excellent airtightness.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

(Summary of the Invention) A brief outline of one typical invention disclosed in this application is as follows.

In other words, in order to maintain airtightness, the container body is made of a mechanically strong and easy-to-process metal such as aluminum alloy.
The radiation entrance window structure has excellent X-ray transmittance by making the wall thickness of the radiation entrance window much thinner than before, and by using a composite material that reinforces areas where strength is insufficient with higher strength carbon fiber reinforced resin. That is.

[Structure of the invention]

Hereinafter, the present invention will be explained using examples and drawings.

In all figures for explaining the embodiments, parts having the same functions are denoted by the same reference numerals, and repeated explanations thereof will be omitted.

FIG. 1 shows the structure of a container body of an ionization chamber type radiation detector according to an embodiment of the present invention.

In FIG. 1, the container body 6o and the X-ray entrance window 61 are
Made of a mechanically strong and easy-to-work metal such as an aluminum alloy, it is made in one piece by machining (mainly milling). Then, the thickness of the X-ray entrance window 61 is set to 0.5 m.
It is very thin and has a thickness of m.

The window width W is 25 mm, and the width of the X-ray entrance window 61 is 25 mm.
The lower end 61A is rounded with a circular arc having a radius of 3 mm to avoid concentration of stress. A carbon fiber reinforced resin 62 is provided inside the X-ray entrance window 61 to reinforce it, and its thickness is 2 mm. The container body 60 and the carbon fiber reinforced resin 62 are fixed with an adhesive. Specifically, the bonding surfaces of the container body 60 made of an aluminum alloy and the carbon fiber reinforced resin 61 are polished with sandpaper, degreased with a solvent, and then epoxy adhesive is applied to the bonding surfaces of both to a thickness of 30 to 50 μm. Coat as shown, put both sides together, apply pressure (approx. 5 kg/cJ), and heat (approx. 50 layers)
After waiting for the adhesive to harden, a container body 60 is created as shown in FIG. 1(b). At this time, pay attention to the fiber direction and arrangement of the carbon fiber reinforced resin 62. The carbon fiber reinforced resin 62 has anisotropy in which the tensile strength in the fiber direction and the tensile strength in the direction perpendicular to the fiber direction are significantly different.

Generally, the tensile strength of carbon fiber reinforced resin is about 150 kg/mm in the fiber direction, while it is about 5 kg/mm in the direction perpendicular to this. The former is 30 times stronger than the latter. The carbon fiber reinforced resin having a thickness of 2 ml is constructed by stacking, for example, 10 layers of carbon fiber reinforced resin having a thickness of -M0.2 mm using unidirectional fibers.

Now, as shown in FIG. 5, when the internal pressure of the container body 1 is applied, the tensile stress in the downward direction (vertical direction) in the figure becomes about four times as large as the horizontal direction tensile stress. Therefore, the fiber direction of the carbon fiber reinforced resin 62 can be oriented in such a way that eight layers are oriented in the vertical direction and two layers are oriented in the horizontal direction, thereby constructing an X-ray entrance window that has a reasonable strength that matches the internal stress that occurs. can. Note that one carbon fiber is a very thin filament with a diameter of 7 to 10 μm, so regardless of the internal pressure of the container body, it can be woven like a 4:1 textile in advance to achieve the required anisotropy. It is also possible to give it a gender. The tensile strength in the longitudinal direction at this time is approximately 80 kg/rn r
d eThe horizontal direction is about 20 kg/mnr, and if it is 2H thick, it has a structure that can sufficiently withstand an internal pressure of 30 kg/d.

The carbon fiber reinforced resin 62 has a density (f) of 1.6.
, with an X-ray absorption coefficient (μ) of 0.26c+a, the X-ray transmittance for that thickness is shown in Figure 6 (
It becomes the curve b).

Therefore, the overall transmittance of the X-ray entrance window in this example is 92% of the product of 97% of the aluminum alloy with a thickness of 0 and 5 mm and 95% of the carbon fiber reinforced resin with a thickness of 2 mm. The attenuation is 14% lower than the transmittance of 78% for the four-layered lens. In addition, the container body 6
Regarding the airtightness at the X-ray entrance window 61, since it is made of a single piece of aluminum alloy, the xenon gas inside the container will not leak to the outside and the internal pressure will not drop.

FIGS. 2(a) and 2(b) show a container body of an ionization chamber-type radiation detector according to another embodiment.

In FIGS. 2(a) and 2(b), the container body 7° has a shape substantially similar to the container body 60 of the embodiment shown in FIG.
Made of aluminum alloy, etc. X-ray entrance window 61
The width of the top and bottom of the window is 2m each.
m, which is wider than the embodiment shown in FIG.

The carbon fiber reinforced resin 72 has a thickness of 2 mm, as shown in FIG.
), and is preformed so as to fit into the X-ray entrance window 71 of the container body 70. The fiber orientation and arrangement of the carbon fiber reinforced resin 72 are also the same as in the previous embodiment. When molding the carbon fiber reinforced resin 72, the corners are rounded to avoid stress concentration during pressurization. In machining the container body 70, use an end mill with rounded corners to achieve the same roundness.
Make sure there are no gaps. The container body 70 and the carbon fiber reinforced resin 72 are bonded together in the same manner as described above.

By making the container body 70 have such a structure, it is possible to realize an ionization box-type radiation detector with excellent X-ray transmittance while maintaining airtightness.

Furthermore, although not shown, FIGS. 1(a) and (b) and the second
Composite structures as shown in Figures (a) and (b) are also possible. At this time, by creating a sandwich structure with 1 mm thick carbon fiber reinforced resin on the inside and outside of the aluminum alloy X-ray entrance window (0 and 5 mm thick), X-ray This is to maintain and strengthen the X-ray transmittance of the entrance window. In this structure, the container body is made up of three parts (the other parts are two parts), but it is the most superior method for reinforcing aluminum alloy in terms of strength.

The present invention has been specifically explained above using examples, but
It goes without saying that the present invention is not limited to the embodiments described above, and can be modified in various ways without departing from the spirit thereof.

For example, the X-ray entrance window of the container body was made to have a thickness of 0.5 mm, and the carbon fiber reinforced resin was made to have a thickness of 211II11, but the present invention
Of course, the present invention is not limited to this, and can be applied to other thickness combinations.

[Effects] As explained above, according to the present invention, the container body has
An ionization chamber-type radiation detector with high X-ray utilization efficiency can be realized.

As a result, a large output current can be obtained for the same dose of X-ray input, and the S/N ratio of the ionization chamber radiation detector is improved, so that an X-ray 01 image with excellent concentration resolution can be obtained.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) are diagrams showing the configuration of a container body of an ionization chamber-type radiation detector according to an embodiment of the present invention;
is its sectional view, and (b) is its perspective view. FIGS. 2(a) and 2(b) are diagrams showing the structure of the container body of an ionization chamber-type radiation detector according to another embodiment of the present invention;
) is its cross-sectional view, (b) is its perspective view, Figure 3 is a perspective view of all 11 units of the conventional ionization chamber type radiation detector, and Figure 4 is the ionization chamber type radiation detector of Figure 3. A cross-sectional view of the detector; Figure 5 is a cross-sectional view showing the deformation of the container during pressurization of the ionization chamber radiation detector shown in Figure 3; Figure 6 shows the relationship between material thickness and X-ray transmittance. FIG. In the figure, 60.70--container body, 61.71-X-ray entrance window section, 62.72--carbon fiber reinforced resin for reinforcement.

Claims (5)

[Claims] (1) In an ionization box-type radiation detector in which a lid is placed on a box-shaped container body in which a radiation entrance window is formed to form a sealed space, and an electrode plate assembly is housed within the sealed space,
The container body and the radiation entrance window are integrally made of mechanically strong metal that is easy to process, the radiation entrance window is formed thin, and the radiation entrance window is reinforced with carbon fiber reinforced resin. An ionization chamber type radiation detector characterized by: (2) The ionization box-type radiation detector according to claim 1, wherein the container body is made of an aluminum alloy. (3) The ionization box-type radiation detector according to claim 1, wherein the radiation entrance window portion is reinforced with carbon fiber reinforced resin from the inside thereof. (4) The ionization box-type radiation detector according to claim 1, wherein the radiation entrance window portion is reinforced from the outside with carbon fiber reinforced resin. (5) The ionization box-type radiation detector according to claim 1, characterized in that the radiation entrance window portion is reinforced by sandwiching it with carbon fiber reinforced resin from both the inside and outside thereof. .