JP3124306B2 - Distribution detector of the radiation material inside the pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detector for detecting the distribution of radioactive materials in a pipe wall, which is used, for example, for detecting contamination by radioactive materials in a pipe used in a nuclear power plant.

[0002]

2. Description of the Related Art As shown in FIG. 12, a conventional detector of this type includes a cylindrical plastic scintillator 1 and
A light guide 2 disposed inside the light guide 2, two light detectors 3 protruding from the base end of the light guide 2 and detecting light emitted from the base end of the light guide 2, and the two detectors 3 A signal processing circuit 5 for processing an output signal of the photodetector 3, a display device 6 for displaying a processing result of the signal processing circuit 5,
It is composed of

[0003] The plastic scintillator 1 and the photodetector 3 are housed in a case (not shown) having a radiation entrance window, and are used by being inserted into a tube to be measured.

The above-described detector is used for measuring α-rays and β-rays, and removes noise by simultaneously counting the outputs of the two photodetectors 3 in order to measure a low dose. I have to.

Further, in order to suppress the sensitivity to γ-rays,
The plastic scintillator 1 has a thin cylindrical shape. The size of the plastic scintillator 1 is for measuring a tube having an inner diameter of 4 to 6 cm.

[0006]

It is difficult to apply the above-described radioactive substance distribution detector on the inner wall of a pipe to the measurement of a pipe having a small inner diameter or a curved pipe, and it is possible to measure the distribution of radioactive substance in the axial direction of the pipe. However, there are problems such as the inability to measure the distribution in the circumferential direction and the insufficient removal of counts by γ-rays in the measurement of α-rays and β-rays when γ-rays are mixed.

The present invention has been made in view of the above-mentioned conventional problems, and has a radioactive substance distribution detector capable of measuring the radioactive substance distribution of a small-diameter pipe, for example, a pipe having an inner diameter of 5 mm or less. The purpose is to provide.

In the measurement of a curved tube, the measurement of the radioactive material distribution in the circumferential direction of the tube, or the measurement of α-rays and β-rays in the presence of γ-rays, the removal of the γ-ray count is sufficient. It is an object of the present invention to provide a distribution detector.

[0009]

SUMMARY OF THE INVENTION The present invention comprises a photodetector, a light guide section comprising an optical fiber for guiding light to the photodetector, and a small-diameter scintillator attached to the tip of the light guide section. In the distribution detector for the radioactive substance on the inner wall of the tube , the light guide section and the detection section
Consist of at least one scintillation fiber,
The light guide is covered with an α- and β-ray shielding outer coating,
The detection unit is configured in an exposed state to achieve the above object.

[0010]

[0011]

[0012] Further, according to claim 1, wherein the detection unit is formed by bundling a plurality of scintillation fibers,
The bundle of scintillation fibers is divided into an inner group of the bundle and an outer group surrounding the inner group, and the light guide unit and the photodetector are divided into the inner group and the outer group. An inner light guide and an outer light guide connected to each other, and an inner light detector and an outer light detector may be configured.

[0013] In the first aspect, the detection unit is formed by bundling a plurality of scintillation fibers,
A part of the scintillation fiber is covered by a shielding member that blocks α-rays and β-rays, and the light guide and the photodetector correspond to a part and the remaining part of the scintillation fiber. , A light guide unit and a photodetector separately connected to each other.

[0014]

[0015] In the first aspect , the detection unit may include a γ
Scintillation fibers may be arranged in a plurality of groups around a cylindrical holder made of a material having a high line shielding ability at appropriate intervals in the circumferential direction of the cylindrical holder.

According to a fourth aspect of the present invention, a plurality of the photodetectors and the light guides may be connected to each group of the scintillation fibers divided into the plurality of groups.

Furthermore, in claim 5 , the scintillation fibers of each group are divided into two bundles, and one bundle is covered with a material that blocks α-rays and β-rays, and the two bundles are separated. May be connected to a separate photodetector via the light guide section.

Further , according to any one of claims 4, 5 and 6 , the holder is provided with grooves in the outer periphery thereof at appropriate intervals in a circumferential direction, and the scintillation fibers are formed in each group. Each time, it may be arranged by fitting into the groove.

The scintillation fiber according to any one of claims 4, 5 and 6 , wherein the holder is provided at an inner position with respect to an outer peripheral surface thereof at appropriate intervals in a circumferential direction. An axial insertion hole into which each group can be inserted may be formed, and an entrance window communicating with the outer periphery of the holder may be formed in each insertion hole.

[0020]

According to the first aspect, the photodetector and the small-diameter scintillator are connected by an optical fiber, and the photodetector is disposed outside the tube to be measured , and is continuously connected to the scintillator.
Detecting part of the fiber and guide light to other part
Can be constructed as a part, the structure is simple, and the scintillator in a small diameter, can der measurement of distribution detection and bends of radioactive material thin tube is, also, the light guide portion is α ray and β
The light guide is covered with α-ray
And β-rays do not act to cause erroneous detection.

[0021]

[0022]

According to the second aspect , α-rays, β-rays and γ-rays are detected by the outer group of scintillation fibers, and in the inner group, most of the α-rays and β-rays are detected in the outer group. Because it is absorbed, mainly the gamma rays penetrating the outer group are detected, and the signals are sent to separate light guides and photodetectors, respectively, and the two signals are compared by a signal processing circuit. Accordingly, α rays, β rays, and γ rays can be discriminated and detected.

According to the third aspect , γ-rays are detected by scintillation fibers covered by a shielding member for shielding α-rays and β-rays, and α-rays and β-rays are detected by scintillation fibers not covered by the shielding members. And γ-rays are detected, output to separate light guides and photodetectors, respectively, and can be discriminated and detected by the signal processing circuit.

According to the fourth aspect of the present invention, the scintillation fiber is provided around the cylindrical holder to constitute the detecting section. Therefore, by changing the outer diameter of the cylindrical holder, it is made to correspond to the inner diameter of the pipe to be measured. be able to.
In addition, since the cylindrical holder is made of a material having a high γ-ray shielding ability, γ-rays are detected from the wall to which the scintillation fiber is approaching, and γ-rays do not reach other portions of the scintillation fiber. The accuracy of the line detection position can be improved.

According to the fifth aspect , the photodetector and the light guide are connected to the scintillation fibers arranged in a plurality of groups at appropriate intervals in the circumferential direction of the cylindrical holder. Therefore, it is possible to measure not only the distribution of the radioactive substance on the inner wall of the pipe in the pipe axis direction but also the distribution in the circumferential direction.

According to claim 6 , the scintillation fibers of each group around the cylindrical holder are composed of α rays, β rays.
It is divided into a bundle for detecting rays and γ-rays and a bundle for detecting only γ-rays, each of which is connected to a separate light guide and photodetector. It is possible.

According to the seventh aspect , since the scintillation fibers are fitted and arranged for each group in the groove on the outer periphery of the holder, the directivity of sensitivity to radiation can be enhanced.

Furthermore, according to claim 8, each group of scintillation fibers are inserted into the insertion hole of the holder periphery inward, since the entrance window that communicates with the holder outside the insertion hole is formed, according to claim 7 More than in the case of
Directivity of sensitivity to radiation can be improved.

[0030]

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

The detector 10 of the first embodiment shown in FIG.
Is a small-diameter cylindrical plastic scintillator 12, a light guide section 16 composed of an optical fiber connected to the base end of the scintillator 12, and a photodetector 18 for photoelectrically converting the light guided from the light guide section 16. And a signal processing circuit 20 for processing the output signal of the photodetector 18, and a display device 22 for displaying the processing result of the signal processing circuit 20.

In this embodiment, since the photodetector 18 is not directly attached to the plastic scintillator as in the conventional detector (FIG. 12), the outer diameter of the plastic scintillator 12 is The diameter can be reduced regardless of the size.

Further, since the photodetector 18 is not directly connected to the plastic scintillator 12, the overall length becomes shorter,
In addition, since the light guide 16 made of an optical fiber is freely bendable, a curved tube can be measured.

Next, a detector 24 according to the second embodiment shown in FIG. 2 will be described.

In the second embodiment, the tip of a continuous bundle of scintillation fibers 26 is used as a detector 28, the remaining portion is used as a light guide 16, and the light guide 16 is used for shielding α rays and β rays. It is covered with the outer coating 30.

Since the other structure is the same as that of the first embodiment, the description is omitted by giving the same reference numerals to the same parts.

The outer coating 30 is made of a material such as polyethylene, and has a thickness sufficient to shield β- and α-rays to be measured.

At the time of measurement, as shown in FIG.
It is inserted from the detection unit 28 into the tube 32 to be measured.

The inserted detecting section 28 receives a β ray or an α ray from a radioactive substance 33 attached to the inner wall of the tube 32,
The detecting unit 28 includes the exposed scintillating fiber 26
, Scintillation light is generated here.

The generated scintillation light propagates in the scintillation fiber 26, is detected by the photodetector 18 outside the tube 32, is photoelectrically converted here, is processed by the signal processing circuit 20, and is processed by the display device 22. The detection result is displayed.

Here, the position of the tube 32 of the radioactive substance in the longitudinal direction is calculated by the insertion length of the detection unit 28, and the position resolution in this case is determined by the length of the detection unit 28.

Next, a third embodiment of the present invention shown in FIG. 3 will be described.

The detector 34 of the third embodiment includes a detector 2
Reference numeral 8 denotes a scintillation fiber 26, and a space between the detection unit 28 and the photodetector 18 is constituted by an ordinary light guiding optical fiber 36. Here, the number of the scintillation fibers 26 and the number of the optical fibers 36 constituting the detection unit 28 are the same, and each is continuously optically connected.

In this embodiment, the portion of the optical fiber 36 is covered with an outer coating 38 for shielding light.

In this embodiment, compared to the second embodiment shown in FIG.
Since it is limited to 8, it is not necessary to cover with an outer coating for shielding β rays and α rays.

In particular, in this embodiment, the optical fiber 36
Since the detection by γ-rays at the site is almost negligible,
It is possible to detect not only β-rays and α-rays but also γ-rays.

Next, a fourth embodiment of the present invention shown in FIG. 4 will be described.

In the detector 40 according to the fourth embodiment, as in the case of the third embodiment of FIG. 3, the detector 28 is formed from the scintillation fiber 26, and the light guide 16 is formed from the optical fiber 36. Further, the outside of the light guide 16 is covered with an outer coating 30 that blocks α rays and β rays.

In the fourth embodiment, a plurality of scintillation fibers 26 constituting the detecting section 28 are bundled, and the inner group 26A of the bundle is the outer group 26B surrounding the inner group 26A. Each of the inner group 26A and the outer group 26B is independently provided with an inner light detector 18A via an inner light guide 16A and an outer light detector 18B via an outer light guide 16B. Are connected to each other. The inner group 26A includes, as shown in an enlarged view in FIG. 5, each of the scintillation fibers 26 has a shielding member 4 for shielding α rays and β rays.
Covered by two.

Therefore, in this embodiment, the scintillation fibers 26 of the outer group 26B are composed of α rays, β rays.
Are sensitive to all gamma and gamma radiation, and the scintillation fibers 26 of the inner group 26A
Only the lines will have sensitivity. Thus, γ-rays can be discriminated and detected from α-rays and β-rays based on the outputs of the inner light detector 18A and the outer light detector 18B.

Here, when the α-ray and the β-ray are weak or the outer group 26B is too thick to transmit through the outer group 26B, there is no need to provide the shielding member 42 of the inner group 26A.

That is, as shown in FIG. 6, although γ-rays have a high material transmittance, α-rays and β-rays have low material transmittances, so that they are blocked by the outer group 26B and become This is because only the γ-rays can reach the inner group 26A without reaching.

Next, a fifth embodiment of the present invention shown in FIG. 7 will be described.

The detector 44 according to this embodiment includes a detector 28
To a cylindrical holder 4 made of a material having a high γ-ray shielding ability.
The scintillation fibers 26 are provided around the plurality of groups 2 at appropriate intervals in the circumferential direction of the cylindrical holder 48.
7A to 27H.

Also in this embodiment, the light guide 16 is constituted by an optical fiber 36 connected to the scintillation fiber 26.

In the case of the fifth embodiment, the tube 3 to be measured is
This is useful when the inner diameter of the tube 2 is large, and the cylindrical holder 48 having a diameter suitable for the inner diameter of the tube can be used to measure tubes of various sizes.

Further, in this embodiment, the scintillation fiber 26 is
7A to 27H, the detection unit 28
The number of scintillation fibers to be used can be reduced as compared with the case where the whole is composed of scintillation fibers.

Further, since the scintillation fiber 26 is attached to the outer periphery of the cylindrical holder 48, it is possible to approach the inner wall surface of the tube 32 at the time of measurement, thereby improving the accuracy of the detection position of the radioactive substance. Can be planned.

Further, since the cylindrical holder 48 is made of a material capable of shielding γ-rays, for example, a metal, even if one of the groups 27A to 27H is close to the γ-ray radiation source, the other group will not. The scintillation fiber 26 is shielded by the cylindrical holder 48 and can shield γ-rays from other than the inner wall surface of the tube, so that the background caused by the γ-ray radiation source can be reduced.

Next, a sixth embodiment of the present invention shown in FIG. 8 will be described.

The detector 50 of the sixth embodiment is similar to that of FIG.
In the same manner as in the embodiment, outside the cylindrical holder 48, the groups 27A to 27A including the scintillation fibers 26 are formed.
27F are attached at appropriate intervals in the circumferential direction, and the detection unit 28 and the light guide unit 16 transmit the α-rays and β-rays, but block the normal light. And further, the groups 27A to 27F are connected to the photodetectors 54A via the independent light guides 17A to 17F, respectively.
To 54F and the signal processing circuits 20A to 20F.

In this embodiment, since the scintillation fiber groups 27A to 27F are independently connected to the photodetectors 54A to 54F, the circumferential distribution of the radioactive substance can be detected.

The outer cover 52 is for preventing the light generated from the individual fibers from being mixed.

Next, a seventh embodiment of the present invention shown in FIG. 9 will be described.

In the detector 56 of the seventh embodiment, groups 60A to 60D of γ-ray correction fibers to which α- and β-ray shielding caps 59 are attached are arranged adjacent to the scintillation fiber groups 27A to 27D. The photodetectors 54A to 54D are connected to the groups 27A to 27D where no cap is provided, and the photodetectors 62A to 62D are connected to the groups 60A to 60D of the γ-ray correction fibers. Each pair of photodetectors 54A,
62A..., 54D and 62D are the signal processing circuits 20 respectively.
A to 20D.

In this embodiment, α, β
By comparing the signal amount of the fiber with the line shielding cap and the signal amount of the fiber without the line shielding cap, it is possible to calculate the effect on the pair by the γ-ray.
Even in a line mixed field, detection of β-rays and α-rays is possible.

Next, an eighth embodiment of the present invention shown in FIG. 10 will be described.

The detector 64 according to the eighth embodiment has grooves 48A to 48A formed on the outer periphery of the cylindrical holder 48 at appropriate intervals in the circumferential direction.
48F are formed, and groups 27A to 27F of the scintillation fibers 26 are fitted and arranged in the grooves 48A to 48F for each group.

In the case of the eighth embodiment, the groups 27A to 27F of the scintillation fibers 26 are formed by the grooves 48A.
~ 48F, the cylindrical holder 48
This improves the directivity having sensitivity only to the radiation that goes from the radial outside to the center.

Next, a detector 66 according to the ninth embodiment of the present invention shown in FIG. 11 will be described.

In the ninth embodiment, the groups 27A to 27F of the scintillation fibers 26 can be inserted into the cylindrical holder 48 at a position close to the outer periphery and at appropriate intervals in the circumferential direction. Insertion hole 68A
To 68F are formed, and each of the insertion holes 68A to 68F has an entrance window 70A to 70F (7
0E and 70F are not visible).

The ninth embodiment is different from the eighth embodiment in FIG. 6 in that the group 2 of the scintillation fiber 26 is
Since most of the outer circumferences of 7A to 27F are embedded and only a part is exposed through the entrance windows 70A to 70F, FIG.
The directivity is further improved as compared with the embodiment.

[Brief description of the drawings]

FIG. 1 is a perspective view including a partial block diagram showing a first embodiment of a distribution detector for radioactive material on the inner wall of a pipe according to the present invention.

FIG. 2 is a perspective view including a partial block diagram showing the second embodiment.

FIG. 3 is a perspective view, including a partial block diagram, showing the third embodiment.

FIG. 4 is a perspective view including a partial block diagram showing the fourth embodiment.

FIG. 5 is an enlarged perspective view showing a main part of the embodiment.

FIG. 6 is an enlarged sectional view showing the operation of the embodiment.

FIG. 7 is a perspective view including a partial block diagram showing the fifth embodiment.

FIG. 8 is a perspective view including a partial block diagram showing the sixth embodiment.

FIG. 9 is a perspective view including a partial block diagram showing the seventh embodiment.

FIG. 10 is a perspective view showing a main part of the eighth embodiment.

FIG. 11 is a perspective view showing a main part of the ninth embodiment.

FIG. 12 is a perspective view including a partial block diagram showing a conventional distribution detector of radiation material on the inner wall of a tube.

[Explanation of symbols]

10, 24, 34, 40, 44, 50, 56, 64, 6
Reference numeral 6: detector, 12: plastic scintillator, 16, 17A to 17H: light guide, 16A: inner light guide, 16B: outer light guide, 18, 54A to 54F, 62A to 62D: light detector, 18A: Inside photodetector, 18B Outside photodetector, 20, 20A-20F ... Signal processing circuit, 22 ... Display device, 26 ... Scintillation fiber, 26A ... Inside group, 26B ... Outside group, 27A-27H ... Group, 28: detection unit, 30, 38: outer coating, 32: tube, 36: optical fiber, 42: shielding member, 48: cylindrical holder, 48A to 48F: groove, 59: α, β-ray shielding cap, 60A to 60D ... Gamma ray correction fiber group.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-24582 (JP, A) JP-A-2-190792 (JP, A) JP-A-3-242590 (JP, A) International Publication No. 88-6297 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01T 1/20 G01T 1/00 G01T 1/167

Claims (8)

(57) [Claims] 1. A light detecting device comprising: a light detector; a light guiding portion formed of an optical fiber for guiding light to the light detecting portion; and a detecting portion formed of a small-diameter scintillator attached to a tip of the light guiding portion. in the distribution detector comprising inner wall radioactive material, the light guide
Section and the detecting section are at least one continuous scintillation
Fiber, and the light guide section is composed of α rays and β rays.
The detection part was covered with a shielding outer coating, and the detection part was exposed.
A distribution detector for a radioactive substance on the inner wall of a pipe, characterized in that: 2. The device according to claim 1 , wherein the detecting unit is formed by bundling a plurality of scintillation fibers, and the bundle of scintillation fibers is an inner group of the bundle and an outer group surrounding the inner group. Divided into groups
The light guide unit and the photodetector are configured to include an inner light guide unit and an outer light guide unit connected to the inner group and the outer group, respectively, and an inner photodetector and an outer photodetector. Detector for distribution of radioactive material inside the pipe. 3. The detection unit according to claim 1 , wherein the detection unit is formed by bundling a plurality of scintillation fibers, and a part of the scintillation fibers is covered by a shielding member that blocks α rays and β rays. The light section and the light detector correspond to a part and the remaining part of the scintillation fiber, respectively, and are each constituted by a light guide part and a light detector separately connected thereto. Radioactive material distribution detector. 4. The apparatus according to claim 1 , wherein the detecting section comprises a plurality of groups of scintillation fibers arranged around a cylindrical holder made of a material having a high γ-ray shielding ability at appropriate intervals in a circumferential direction of the cylindrical holder. A distribution detector for a radioactive substance on the inner wall of a tube, wherein the distribution detector is configured to be arranged separately. 5. A tube inner wall radioactive element according to claim 4 , wherein a plurality of said photodetectors and said light guides are provided for each group of scintillation fibers divided into said plurality of groups. Substance distribution detector. 6. The scintillation fiber of claim 5 , wherein the scintillation fibers of each group are divided into two bundles, one bundle being covered with a material that blocks α and β rays, and the two bundles being separated. A distribution detector for the radioactive substance on the inner wall of the tube, wherein the distribution detector is connected to a separate photodetector via the light guide section. 7. The holder according to claim 4 , wherein grooves are formed on the outer periphery of the holder at appropriate intervals in a circumferential direction, and the scintillation fibers are provided for each group. A distribution detector for the radioactive substance on the inner wall of the tube, wherein the distribution detector is arranged so as to be fitted in the groove. 8. The holder according to claim 4 , wherein the holder is provided at a position inside the outer peripheral surface thereof.
An axial insertion hole into which each group of the scintillation fibers can be inserted is formed at appropriate intervals in the circumferential direction, and an entrance window communicating with the outer periphery of the holder is formed in each insertion hole. Distribution detector for radioactive material inside the pipe.