X-ray detector of multi-channel type ionization chamber

An X-ray detector with a multi-channel type ionization chamber has plural signal plate electrodes and plural high voltage plate electrodes respectively disposed in parallel to and alternating with the signal plate electrodes all of the plate electrodes being mounted between a pair of insulators. A conductive rubber member is provided between one of the insulators and the high voltage plate electrodes, and a long conductive member is provided along the conductive rubber member at a position where the long conductive member contacts the rubber member, but does not contact the high voltage plate electrodes. Thereby, the amount of X-rays is detected accurately in respective channels in spite of the simple construction of the X-ray detector.

BACKGROUND OF THE INVENTION 
Present invention relates to an X-ray detector with a multi-channel type 
ionization chamber having a plurality of high voltage plate electrodes 
supplied with a high voltage and a plurality of signal plate electrodes 
for taking out a signal corresponding to an amount of detected X-rays, the 
high voltage plate electrodes and the signal plate electrodes being 
arranged in parallel to and alternating with each other. 
The high voltage plate electrodes are connected in parallel to an 
electrically conductive rubber member which is disposed in an arranging 
direction of the plate electrodes and is supplied with a high voltage, and 
at the same time, the high voltage plate electrodes are fixedly supported 
by disposing the conductive rubber member between the high voltage plate 
electrodes and an electrically insulating support member. 
Such electrical connection by use of a conductive rubber member makes it 
easy to assemble an X-ray detector having a fine construction, and an 
example of such a detector is described in Japanese Patent Laid-open No. 
58-168981 (1983) . 
However, in the X-ray detector having a construction as described above, a 
voltage drop in the high voltage plate electrode arises in relation to the 
distance from the end of the conductive rubber member which is connected 
to the high voltage source to a position at which the conductive rubber 
member is connected to the respective high voltage plate electrodes, 
because the conductive rubber has a significantly large resistance. 
Such a voltage drop causes generation of voltage differences between the 
high voltages applied to the respective plate electrodes and makes it 
difficult to take out a signal which accurately reflects the amount of the 
X-rays which should be detected. 
It is possible to decrease the resistance of the conductive rubber member; 
however, this creates the problem that the process for producing the 
conductive rubber member becomes complex and the elasticity of the rubber 
decreases so significantly that it becomes impossible to firmly support 
the plate electrodes on the insulating support member. 
SUMMARY OF THE INVENTION 
The present invention has been accomplished to overcome the above mentioned 
problem of the conventional technique. 
An object of the present invention is to provide an X-ray detector with a 
multi-channel type ionization chamber having a plurality of high voltage 
plate electrodes and a plurality of signal plate electrodes for detecting 
an amount of X-rays accurately by feeding a predetermined constant voltage 
to the high voltage plate electrodes in a simple way using a conductive 
rubber member. 
In order to attain the above object, in a X-ray detector with a 
multi-channel type ionization chamber having a plurality of high voltage 
plate electrodes supplied with a high voltage and a plurality of signal 
plate electrodes for taking out a signal corresponding to an amount of 
detected X-rays, which plate electrodes are arranged in parallel with each 
other, a pair of electrical insulators are provided to support the high 
voltage plate electrodes and the signal plate electrodes therebetween, and 
the high voltage plate electrodes are supplied with a high voltage through 
an electrically conductive rubber member and a further electrically 
conductive member connected to a high voltage source, both of which 
members are disposed between the high voltage plate electrodes and one of 
the insulators, .so as to electrically connect the high voltage plate 
electrodes in parallel with the further conductive member through the 
conductive rubber member. Thereby, any difference between the voltage 
drops for the plurality of high voltage plate electrodes caused by the 
resistance of the conductive rubber member becomes remarkably small, so 
that a predetermined consistent high voltage is respectively applied to 
all of the high voltage plate electrodes in the respective channels, and 
the amount of X-rays is detected accurately in each channel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIG. 2, showing a perspective view of the overall construction of an 
X-ray detector in accordance with the present invention, a pair of 
electrical insulators 1A, 1B, respectively shaped as plates, are disposed 
opposite each other in parallel relationship. The pair of insulators 1A, 
1B are made of ceramics, for example, and an assembly including a pair of 
insulators 1A, 1B mounting high voltage plate electrodes 2A and signal 
plate electrodes 2B is generally referred to as an electrode block. 
The high voltage plate electrodes 2A and signal plate electrodes 2B are 
supported between the pair of insulators 1A, 1B and are disposed in 
parallel and alternate with one another. The two spaces on either side of 
one of the signal plate electrodes 2B and between two successive high 
voltage plate electrodes 2A on opposite sides of the one signal plate 
electrode form one channel of the X-ray detector. 
As the electrode block is disposed in Xenon gas, the spaces between the 
high voltage plate electrodes 2A and signal plate electrodes 2B are filled 
with Xenon gas. X-rays are irradiated into the spaces, as shown in FIG. 2 
with an arrow, and the energy of the X-rays is absorbed by the Xenon gas. 
Thereby, the Xenon gas is separated into electrons and positively charged 
particles according to the amount of X-rays. The electrons and positively 
charged particles are separated by a force of an electrical field between 
the high voltage plate electrodes 2A and the signal plate electrodes 2B, 
and the electrons are caused to move towards the high voltage plate 
electrodes 2A, which are charged positively, and the positively charged 
particles of the Xenon gas are moved towards the signal plate electrodes 
2B, which are charged negatively. Therefore, an electric current flows 
between the signal plate electrodes 2B and the high voltage plate 
electrodes 2A according to the amount of X-rays and an electric signal is 
taken out from the signal plate electrode 2B according to the magnitude of 
the detected electric current. 
The high voltage plate electrodes 2A are connected in parallel to a long 
electrically conductive rubber member 3, which extends in the longitudinal 
direction of the insulators 1A, 1B and is disposed in contact with a long 
conductive member 51 (not shown in FIG. 2), extending along the conductive 
rubber member 3. 
FIG. 1 shows a cross-sectional view of a section along line I--I' in FIG. 
2. 
A protruding portion 20 is integrally formed on an upper side of each high 
voltage plate electrode 2A, a protruding portion 10 is integrally formed 
on one side of the insulator 1A, and the conductive rubber member 3 is 
disposed between each protruding portion 10 and the protruding portion 20. 
On an inner corner formed by the protruding portion 10, where an upper 
side of the conductive rubber member 3 is disposed, a wire-like conductive 
member 51 is provided in close contact with the conductive rubber member 3 
so as to be held in position by the protruding portions 10 and the 
conductive rubber member 3. 
In FIG. 3, which shows a partial cross-sectional view of an another 
embodiment of an X-ray detector in accordance with the present invention, 
a conductive member 52, shaped like a long plate, is disposed on the under 
side of the protruding portion 10 of the insulator 1A so as to contact the 
conductive rubber member 3. The plate-like conductive member 52 is 
connected to a high voltage source which is not shown in the figure and 
the conductive rubber member 3 is disposed in close contact with both the 
plate-like conductive member 52 and the protruding portion 20 of the high 
voltage plate electrode 2A. Therefore, the high voltage plate electrodes 
2A are connected by the plate-like conductive member 52 in parallel 
through the conductive rubber member 3. 
The plate-like conductive member 52 may be made of gilt formed by an 
electric gilding method. 
In FIG. 4, which shows a partial cross-sectional view of another embodiment 
of an X-ray detector in accordance with the present invention, a wire-like 
conductive member 53 is buried in the conductive rubber member 3 along a 
central axis thereof and is connected to a high voltage source which is 
not shown in the figure. The conductive rubber member 3 is closely 
inserted between the protruding portion 10 of the insulator 1A and the 
protruding portion 20 of each high voltage plate electrode 2A. Therefore, 
the high voltage plate electrodes 2A are connected by the conductive 
member 53 in parallel through the conductive rubber member 3 in the same 
way as the previous embodiments. 
In FIG. 5, which shows a partial cross-sectional view of a further 
embodiment of an X-ray detector in accordance with the present invention, 
a long plate-like conductive member 54 is fixed by a screw to a side of 
the protruding portion 10 of the insulator 1A so as to restrain the 
conductive rubber member 3 and is connected to a high voltage source which 
is not shown in the figure. The conductive rubber member 3 is closely 
fixed in position between the protruding portion 10 of the insulator 1A 
and the protruding portion 20 of each high voltage plate electrode 2A by 
the conductive member 54 so as to prevent it from being pulled out. 
Therefore, the high voltage plate electrodes 2A are connected by the 
conductive member 54 in parallel through the conductive rubber member 3 in 
the same way as the other embodiments. 
In the embodiment shown in FIGS. 1, 3, 4, 5, the electric resistances 
between the high voltage plate electrodes and the conductive members 51, 
52, 53, 54 are constant and small in spite of the large resistance of the 
conductive rubber member, because the distance along the conductive rubber 
member between the high voltage plate electrodes and the further 
conductive member is are constant and short. 
Therefore, fluctuation of the signal level generated by the voltage drops 
caused by the large resistance of the conductive rubber member is avoided 
and consistent voltages are applied to the high voltage plate electrodes 
in all channels which are respectively formed between respective pairs of 
high voltage plate electrodes. Thereby, the amount of X-rays is detected 
accurately in respective channels of the X-ray detector. 
Further, in FIG. 6, a protruding portion 10' is formed separately and is 
mounted on one side of the insulator 1A. The conductive rubber member 3 is 
inserted between the protruding portion 10' and the protruding portions 20 
of the high voltage plate electrodes 2A. 
Further, the conductive member may be a metal wire, disposed along the 
conductive rubber member 3 at a lower side portion thereof and in contact 
with the conductive rubber member 3 and, but not in contact with the high 
voltage plate electrodes directly, so as to be connected to the high 
voltage plate electrodes 2A only through the conductive rubber member 3. 
As stated above, in accordance with the present invention, the amount of 
X-rays is detected accurately in respective channels in spite of the 
simple construction of the X-ray detector.