JP2001228255A - Radiation detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a large area detector which can reduce background and secure a detection efficiency. SOLUTION: This detector has a plurality of scintillators 11 arranged to divide an area to be measured to a plurality of areas, light-collecting parts 12a, 12b, etc., 13a, 13b, etc., optically connected to the scintillators 11 for totally introducing the light from the scintillators 11 by every row and every column to optical detectors 14a, 14b, etc., the optical detectors 14a, 14b, etc., for converting the collected light to electrical signals and generating electric pulse signals at every emission, a counting circuit 16 for processing the signals and counting the number of optical pulses from each of the scintillators, an emission position-recognizing circuit 17 for judging from which scintillators the signals are outputted and storing the counted value from each scintillator to a set place, a storage device 18 for storing the counted values from the scintillators to set places, and a switching circuit 19 for sequentially switching the storage places of the counted values every time a set time passes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation detector using a scintillator used in, for example, a nuclear facility, and more particularly to a radiation detector capable of measuring an object larger than each scintillator.

[0002]

2. Description of the Related Art In a nuclear facility such as a nuclear power plant, radiation detection using a large-area scintillator has been conventionally performed in order to detect contamination of a person who has entered the facility and has performed some work, used tools and clothes. Vessel is used.

FIG. 11 is a diagram showing the structure of a radiation detector of this type. A detector scintillator 1 coated with a light-reflective paint has a planar scintillator 2 and a plurality of photoelectric converters having a relatively large photoelectric surface. An element 3 is provided, and the scintillation light generated in the planar scintillator 2 is irregularly reflected on the wall surface of the detector container 1 and collected, and then converted into an electric signal by the plurality of photoelectric conversion elements 3 for measurement. I am trying to do it.

At the time of measurement, coincidence measurement is performed on output signals from a plurality of photoelectric conversion elements 3 by a coincidence circuit in order to improve the S / N ratio and increase the radiation detection sensitivity. Further, extraneous light is blocked by a light-shielding film, and only radiation is incident on the flat scintillator 2. When a large area is required as the effective area of the radiation detector, the required area is realized by arranging a plurality of the radiation detectors.

[0005]

When a long measurement time is required when the object to be measured is large or when the object to be measured is moving, the area of the scintillator may be increased. However, when the area of the scintillator is increased, the counting efficiency for gamma rays, cosmic rays, and the like from radioisotopes contained in the ground and buildings increases, and as a result, the background count increases. Then, as a countermeasure against this, a method of dividing and measuring the scintillator is considered.

However, in the conventional radiation detector, the S / N ratio increases as the amount of light converted by the photoelectric conversion element 3 increases, and a high detection sensitivity can be obtained as a radiation detector.
Therefore, unless the area of the light receiving surface of the photoelectric conversion element 3 is increased, the amount of received light cannot be secured. In the current photoelectric conversion element, when the area of the light receiving surface is increased, the size of the entire element is also increased, and it is necessary to secure a space for light reflection. Therefore, even if the scintillator is divided, even if the scintillator is divided, The detector for detecting light becomes large. Therefore, there is a problem that a gap is generated between the divided scintillators and the detection efficiency of the detector as a whole decreases.

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to provide a large-area detector capable of reducing background and ensuring detection efficiency.

[0008]

According to a first aspect of the present invention, a plurality of scintillators having an area smaller than the area to be measured are arranged so as to divide the area to be measured into a plurality of areas,
A light-collecting unit optically connected to each of the scintillators for summing light from the scintillator for each row and each column and guiding the light to a photodetector, and converting the collected light into an electric signal to emit light. A photodetector that generates an electric pulse signal, a counting circuit that processes the signal from the photodetector and counts the number of light pulses from each scintillator, and determines which scintillator is the signal from each. A light emitting position recognizing circuit for distributing the count value from the scintillator to a predetermined location, and a storage device for storing the count value from each scintillator at the predetermined location.

According to a second aspect of the present invention, in the first aspect, the whole or most of the radiation detector having the scintillator and the photodetector is surrounded by lead, and a plastic scintillation detector is disposed outside the radiation detector. An anti-simultaneous measurement circuit for anti-simultaneous measurement of the count pulse from the radiation detector and the count pulse from the plastic scintillation detector is connected.

According to a third aspect of the present invention, there are provided a plurality of scintillators which are arranged so as to divide an area to be measured into a plurality of areas and which have areas smaller than the area to be measured and which emit light of different colors from each other. A photodetector having a corresponding transmission frequency band, a counting circuit that processes signals from the photodetector and counts the number of light pulses from each scintillator, and whether there is contamination of the device under test based on the output of the counting circuit. And an output device for transmitting the photodetector that has detected the contamination to a human or a management device.

According to a fourth aspect of the present invention, there is provided a first scintillator having a thickness enough to stop radiation to be measured, a second scintillator emitting light at a wavelength different from that of the first scintillator, and a first scintillator. An optical filter that transmits light but does not transmit synthesized light when the first and second scintillators emit light simultaneously, converts the light transmitted through the optical filter into an electric signal, and generates an electric pulse signal every time light is emitted. Generating a photodetector and processing a signal from the photodetector;
And a counting circuit for counting the number of light pulses from the scintillator.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a view showing a first embodiment of a radiation detecting apparatus according to the present invention. In a detector container 10 provided with a light-shielding member which allows radiation of a desired radiation but blocks external light. A plurality of scintillators 11 having an area smaller than the area to be measured are vertically and horizontally arranged so as to divide the area to be measured. These scintillators 11 have an area of about 15 cm × 15 cm and a thickness of about 0.5 mmt, and are formed extremely thin as compared with the area.

Both end faces in the horizontal direction of all the scintillators 11 arranged in the horizontal direction, ie, the row direction, are made of, for example, an acrylic prism-shaped condensing section 12 extending in parallel with the row direction.
a, 12b,... and all scintillators 11 arranged in the vertical direction, that is, in the column direction.
Are optically joined to other acrylic prismatic light collectors 13a, 13b,... Extending parallel to each other in the column direction. The condensing portions 12a, 12b,... And 1
Are joined to photodetectors 14a, 14b,... Or 15a, 15b,... Outside the effective surface formed by the vertically and horizontally arranged scintillators 11, respectively. 12a, 12b, ..., 13a, 13
b,... are collected by the respective photodetectors 14a, 14b,.
, 15a, 15b, ... are converted into electric signals,
An electrical pulse signal is output each time light is emitted.

The scintillator 11, the light condensing parts 12a, 1
, 13, 13b, ... and photodetectors 14a, 14
, 15a, 15b,... are housed in the detector container 10, and the photodetectors 14a, 14b,.
The outputs of a, 15b,... are provided outside the detector container 10 and counted by a counting circuit 16 for counting the number of light pulses from each scintillator.

The output of the counting circuit 16 determines from which scintillator the signal is output, and distributes the count value from each scintillator to a predetermined location.
The light emission position is assigned to the counter, and the count output to which the light emission position is assigned is stored in a predetermined location of the storage device 18. The storage location of the stored count output is sequentially switched by the switching circuit 19 every time a predetermined time elapses. Then, the count value at the storage location on the storage device 18 corresponding to the light emitting location of the scintillator is read out by the contamination determination circuit 20, and the contamination determination of the measurement object at that location is performed. The result is output by the output device 21 to a human or a monitoring computer.

That is, when one of the divided scintillators 11 emits light upon incidence of radiation, the light is emitted by two sets of condensers, for example, 12a, 12b and 13a, 13b, which are optically joined to the scintillator 11. The light is guided to the photodetectors 14a, 14b, 15a, and 15b, where the incident light is converted into an electric pulse signal. In the counting circuit 16, the photodetectors 14a, 14b, 15
The number of times of light emission from the scintillator 11 is counted while discriminating the outputs of a and 15b from noise pulses due to causes other than radiation incidence. In this case, information indicating which photodetector is the output signal is added to the count data, and time information such as a measurement time is also added as necessary.

In the light emitting position recognizing device 17, photodetectors 14a, 14a corresponding to signals input simultaneously in the row direction and the column direction are provided.
The coordinates of the scintillator that has emitted light are determined by specifying 14b, 15a, and 15b, and the coordinate information is added to the signal from the counting circuit 16. In the storage device 18, the count value data to which the coordinates of the scintillator 11 are added by the light emission position recognition device 17 is stored in the storage area. The stored count value data can be moved at intervals determined by the switching circuit 19. This corresponds to, for example, switching the scintillator for measuring the location of the measurement target in accordance with the movement of the measurement target when the measurement target is moving.

As shown in FIG. 2, the count value data is switched while averaging adjacent scintillators so as to prevent a place where measurement cannot be performed at the time of switching.
Switching of the count value data will be described with reference to FIG.

It is assumed that the radiation detector is composed of four divided scintillators A, B, C and D. An object flowing in the direction of the scintillator A → B → C → D is measured by the scintillators A, B, C, D, and the result is stored in the storage area 1,
Consider the case of storing in 2, 3, 4,... Simultaneously with the start of the measurement, the signals from the scintillators A, B, C, D,. Since the time required for the measurement object to move by half the length of the scintillator has elapsed, the average value of the scintillators A and B is the storage area 1, the average of the scintillators B and C is the storage area 2,
The average value of the scintillators C and D is stored in the storage area 3, the value of the scintillator D is stored in the storage area 4, and the value of the scintillator A is stored in the storage area 5. After a lapse of time required for the measurement object to move further by half the length of the scintillator, the value of the scintillator B is stored in the storage area 1, the value of the scintillator C is stored in the storage area 2, and the value of the scintillator D is stored in the storage area. 3. The value obtained by adding the value of the storage area 5 to the value of the scintillator A is stored in the storage area 4. The value in the storage area 5 is deleted after being added to the storage area 4. After a further time has elapsed, the above operation is repeated. By a series of these operations, the position of the measurement object and the location of the storage area correspond to each other, and it is as if the measurement object enters the measurement surface of the scintillator A and then leaves the measurement surface of the scintillator D. Can be treated as if it were measured with a detector of

Thus, in this embodiment,
Regardless of whether the detection surface is composed of multiple divided scintillators, the same detection is performed from when the object enters the upstream detection surface until it exits the most downstream detection surface. It can be treated as if it were measured with a device. In addition, since the scintillator is divided, the background count is reduced, and the light emitted from the scintillator is guided to the photodetector via the light collector. Therefore, it is necessary to provide a photoelectric conversion element having a large light receiving surface area. Instead, the size of the detector itself can be made compact.

FIG. 3 is a view showing another embodiment of the present invention. An optical fiber 31 is optically bonded to the end face of the scintillator 11 with its cut surface facing the end face of the scintillator 11. The condensing part 12 is formed by the optical fiber 31.
a, 12b,..., 13a, 13b,.

In this case, however, the optical fiber 31
However, since it is thinner and easier to bend than an acrylic light guide, the gap between the divided scintillators can be made smaller than in the embodiment shown in FIG. 1, the dead area can be reduced, and the detection efficiency can be improved.

Further, as shown in FIG. 4, a wavelength conversion fiber 32 may be used as a light collecting section. That is, the side surfaces of the wavelength conversion fiber 32 may be optically joined to the end face of the scintillator 11 along the rows and columns. In this case, since the wavelength conversion fiber 32 is relatively thin and has higher light transmission efficiency than the optical fiber, the gap between the scintillators can be reduced, the amount of condensed light increases, and the detection efficiency can be improved.

In the above embodiment, the wavelength conversion fiber is used as the light collecting section.
A light guide using a wavelength conversion material may be used.

FIG. 5 is a view showing still another embodiment of the present invention. A plate 33 which is transparent to light is disposed on one surface of the scintillator 11 and optically joined to each other. The light condensing part 12 is optically joined to two mutually opposed sides of the plate 33, and the light condensing part 13 is optically joined to the other two mutually opposed sides.

In this embodiment, however, the light collectors 12 and 13 can be joined even to the thin scintillator 11 to which the light collector cannot be attached, and a thin scintillator can be used. Measurement in low background is possible. Therefore, high detection sensitivity can be obtained while keeping the dead area of the detector small.

FIG. 6 is a view showing another embodiment of the present invention. The area to be measured is divided into only one row, and the scintillators 11 are arranged in only one row. Other points are the same as those shown in FIG. Thus, in this case, the sensitivity required for each of the scintillators 11 is reduced twice. Therefore, although the degree of freedom of the area to be measured is reduced, higher detection sensitivity can be achieved.

FIG. 7 is a view showing still another embodiment of the present invention. In the apparatus shown in FIG. 1, the entire detector container 10 is covered with a lead plate 34, and a scintillator 35 is provided outside the lead plate 34. And a second detector container 37 having a photodetector 36 built therein. Then, the photodetector 36
Are sequentially connected to a wave height discriminating circuit 38 and an anti-simultaneous measuring circuit 39, and the anti-simultaneous measuring circuit 39 is connected to the counting circuit 16.

When the light from the scintillator 35 is detected by the wave height discriminating circuit 38, the anti-simultaneous measuring circuit 39 outputs a veto signal.
When the signal is input to the anti-simultaneous measurement gate input of No. 6, the counting operation of the counting circuit 16 is stopped.

Therefore, the counting circuit 16 is prevented from performing the counting operation by the background of the high energy particles penetrating the lead plate 34, and the background can be reduced.

FIG. 8 is a view showing another embodiment of the present invention, in which a detector container 10 having a light-shielding material is provided.
A plurality of scintillators 40 that are divided and emit light of different colors
a, 40b, 40c, 40d are arranged, and optical filters 41a, 41 having transmission frequency bands respectively corresponding to the emission colors of the scintillators 40a, 40b,.
, and the photodetectors 42a, 42b,.
0a, 40b,... Are arranged at positions where light from the light sources can be collected. The signals from the photodetectors 42a, 42b,... Are input to a counting circuit 16 having the same function as that shown in FIG. The detection data is output via 21.

Therefore, the photodetectors 42a, 42b,.
Can be recognized from which scintillator the light is emitted from even if they are physically separated from the scintillators 40a, 40b,..., Even when the device to be measured and the device for measurement must be set apart. Position discrimination becomes possible.

FIG. 9 is a view showing another embodiment of the present invention. In the detector container 10, a first scintillator 4 having a thickness enough to stop radiation to be measured is provided.
3. The second scintillator 44, which emits light at a wavelength different from that of the first scintillator 43, the light from the first scintillator 43 is transmitted, but the first and second scintillators 43, 4
An optical filter 45 that does not transmit the combined light when 4 emits light at the same time, and a photodetector 46 that detects light transmitted through the optical filter 45 are provided. When light is detected by the photodetector 46, a counting circuit (not shown) is operated.

However, light is detected by the photodetector 46 only when the first scintillator 43 emits light, and becomes insensitive to background radiation outside the measurement object.
Detection efficiency can be improved.

FIG. 10 is a view showing another embodiment shown in FIG. 9. The detector container 10 further has a thickness enough to stop the radiation of the measurement object transmitted through the first scintillator 43. A transparent shielding plate 47 having the following is provided.

Accordingly, also in this case, light is detected by the photodetector 46 only when the first scintillator 43 emits light, and the light is insensitive to background radiation outside the measurement object.

[0038]

Since the present invention is configured as described above, a sufficiently large detection area is ensured for a wide-area object to be measured or a moving object to be measured, high detection efficiency is maintained, and background is sufficiently reduced. Can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment of a radiation detection apparatus of the present invention.

FIG. 2 is a diagram illustrating the operation of the radiation detecting apparatus shown in FIG.

FIG. 3 is a diagram showing a schematic configuration of another embodiment of the radiation detecting apparatus shown in FIG. 1 of the present invention.

FIG. 4 is a diagram showing a schematic configuration of still another embodiment of the radiation detecting apparatus shown in FIG. 1 of the present invention.

5 is a diagram showing a schematic configuration of another embodiment of the radiation detecting apparatus shown in FIG. 1 of the present invention.

FIG. 6 is a diagram showing a schematic configuration of another embodiment of the radiation detecting apparatus shown in FIG. 1 of the present invention.

FIG. 7 is a diagram showing a schematic configuration of still another embodiment of the radiation detecting apparatus shown in FIG. 1 of the present invention.

FIG. 8 is a diagram showing a schematic configuration of another embodiment of the radiation detection apparatus of the present invention.

FIG. 9 is a diagram showing a schematic configuration of still another embodiment of the radiation detection apparatus of the present invention.

FIG. 10 is a diagram showing a schematic configuration of another embodiment of the radiation detection apparatus shown in FIG. 9;

FIG. 11 is a diagram showing a schematic configuration of a conventional radiation detection apparatus.

[Explanation of symbols]

10 Detector container 11, 35, 40a, 40b, ... Scintillator 12a, 12b, 12c ... 13a, 13b, 13c ...
Condenser 14a, 14b, 14c ... 15a, 15b, 15c ... 3
46, 42a, 42b,... 46 Photodetector 16 Counting circuit 17 Emission position recognition circuit 18 Storage device 19 Switching circuit 20 Contamination determination circuit 21 Output device 31 Optical fiber 32 Wavelength conversion fiber 33 Transparent plate 34 Lead plate 37 Second Detector container 38 Wave height discrimination circuit 39 Anti-simultaneous measurement circuit 41a, 41b... 45 Optical filter 43 First scintillator 44 Second scintillator

Claims (11)

[Claims] 1. A plurality of scintillators arranged so as to divide an area to be measured into a plurality of areas and having an area smaller than the area to be measured, and light from the scintillator is summed for each row and each column. A light-collecting unit optically connected to each of the scintillators for guiding the light to a detector, a light detector that converts the collected light into an electric signal and generates an electric pulse signal each time light is emitted, and a light detector for detecting the light. Counting circuit that processes the signal from the vessel and counts the number of light pulses from each scintillator, and recognizes the light emission position that determines which scintillator the signal is from and distributes the count value from each scintillator to a predetermined location A circuit, a storage device for storing the count value from each scintillator in a predetermined location,
A radiation detection device comprising: a circuit for determining the presence or absence of contamination of an object to be measured from an output of the storage device; and an output device for outputting which scintillator has detected contamination. 2. The radiation detecting apparatus according to claim 1, further comprising a switching circuit for sequentially switching a storage location of the count value every time a predetermined time elapses. 3. The radiation detecting apparatus according to claim 1, wherein the light collecting section is an optical fiber optically connected to each scintillator. 4. The radiation detecting apparatus according to claim 1, wherein the light collecting section is a wavelength conversion fiber optically connected to two opposite sides of each of the two scintillators. 5. The radiation detecting device according to claim 1, wherein the light condensing unit is a light guide using a wavelength conversion material optically connected to two opposite sides of each of the two scintillators. apparatus. 6. The light collecting section is a wavelength conversion fiber optically connected to the scintillator and optically connected to two opposite sides of two sets of plates transparent to light from the scintillator. The radiation detection apparatus according to claim 1, wherein 7. The radiation detecting apparatus according to claim 1, wherein the area to be measured is divided into only one line, and a plurality of scintillators are arranged in one line. 8. A radiation detector having a scintillator and a photodetector is entirely or largely surrounded by lead, and a plastic scintillation detector is disposed outside the radiation detector. The counting pulse from the radiation detector and the plastic scintillation are provided. 2. The radiation detecting apparatus according to claim 1, wherein an anti-simultaneous measurement circuit for performing anti-simultaneous measurement of the count pulse from the detector is connected. 9. A plurality of scintillators which are arranged so as to divide the area to be measured into a plurality of areas and which have areas smaller than the area to be measured and have mutually different luminescent colors, and transmissions respectively corresponding to the luminescent colors of the scintillators. A photodetector having a frequency band, a counting circuit that processes signals from the photodetector and counts the number of light pulses from the respective scintillators, and determines whether or not there is contamination of the device under test from the output of the counting circuit. A radiation detection device comprising: a circuit; and an output device that communicates which photodetector has detected contamination to a human or management device. 10. A first scintillator having a thickness enough to stop radiation to be measured, a second scintillator emitting light at a wavelength different from that of the first scintillator, and light from the first scintillator is transmitted. However, an optical filter that does not transmit the combined light when the first and second scintillators emit light simultaneously, and a light detection that converts the light transmitted through the optical filter into an electric signal and generates an electric pulse signal for each light emission A radiation detection apparatus comprising: a detector; and a counting circuit that processes a signal from the photodetector and counts the number of light pulses from the first scintillator. 11. The radiation detecting apparatus according to claim 10, wherein a transparent plate is interposed between the first scintillator and the second scintillator.