JPH09184884A - Radiation detector and radiation distribution meter with the use of it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate radiation measurement in water or narrow places. SOLUTION: An SOF2 doped with scintillator in the core of an optical fiber and a normal optical fiber OF30 not doped are arranged side by side. Photomultipliers OMT 4 and 6 are connected at the same ends of both ones. To the other ends, a prism 32 is connected to make a transmission path of light from SOF2 to OF30. When radiation comes in a specific location from a radiation source, part of the light goes directly to PMT6 and other part goes to PMT4 by way of the prism 32. From the arrival time differences of these and count values, spacial distribution of radiation is known.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation detector and a radiation distribution measuring instrument. The present invention particularly relates to a radiation detector and a radiation distribution measuring instrument that include a scintillator and photoelectric conversion means and detect radiation and measure a spatial distribution.

[0002]

2. Description of the Related Art Radiation detectors or radiation distribution measuring instruments are used in particle accelerators, nuclear reactor facilities, nuclear fuel specification facilities, etc. for radiation measurement, radiation control, and monitoring of nuclear materials.

FIG. 1 is a block diagram of a conventional general radiation distribution measuring instrument. This measuring instrument detects radiation (eg, gamma rays) as light once by scintillation and converts it into an electric signal.
It is derived by the OF method (Time Of Flight).

[Structure] In the figure, a scintillation optical fiber (hereinafter referred to as SOF) 2 is an elongated fiber of several meters in order to cover a wide space to some extent. The width is often a few millimeters. Photomultiplier tubes (hereinafter referred to as PMTs) 4 and 6 for converting scintillation light into an electric signal are provided at both ends of the both ends. In this case, a delay device 8 is inserted in the path of the PMT 4 on the left side. PM
The output signals of T4 and T6 are input to the time-to-peak converter (hereinafter, TAC) 10 (via the delay device 8 in the former case).
The delay of the delay device 8 is set so that the output of the PMT 6 reaches the TAC 10 earlier than that of the PMT 4 even when the radiation enters the position closest to the PMT 4. The conversion result of TAC10 is the wave height analyzer (MCA)
It is input to 12 and the initial radiation distribution measurement is performed. It should be noted that the figure shows that the radiation is incident from the radiation source 16 to the specific portion 18 of the SOF 2.

[Operation] When the radiation enters the specific place 18, scintillation light is generated, of which those exceeding the critical angle of the fiber propagate toward both sides of the SOF 2. These lights are converted into electric signals by the PMTs 4 and 6 (amplified as needed at this time). P at this stage
The MT4 outputs the signal first, but this is the delay unit 8
Since it is delayed sufficiently by, the order is reversed when TAC10 is reached. When the signal from the PMT 6 reaches the TAC 10, this triggers to start time counting at the TAC 10, and when the signal arrives from the delay device 8, the time counting is stopped.

From this time difference and the delay time set in the delay device 8, the time difference when the scintillation light first reaches the PMTs 4 and 6 can be known. From this, the position of the specific portion 18 is known. On the other hand, the wave height at that time (which is proportional to the radiation count value) is analyzed by the MCA 12, and the analysis result can be plotted with the wave height value (ch) as the horizontal axis and the count value (count) as the vertical axis. . FIG. 2 is a diagram showing a plot example of the analysis result of the MCA 12. The spatial distribution of radiation can be known from this figure.

[0007]

As described above, according to the conventional radiation distribution measuring instrument, the following problems can be considered.

(1) Due to the need to supply power to the PMTs 4 and 6, it was difficult to install the entire measuring instrument in water. When installing, it was necessary to provide a separate waterproof mechanism.

(2) Overall shape, especially PMTs 4, 6
Since the diameter of the is generally larger than that of SOF2, it was difficult to install the measuring instrument in a narrow place.

(3) PMTs 4 and 6 are provided on both ends of the long SOF2.
Therefore, a long signal cable is required to guide signals from these to the TAC 10, and there is room for improvement in terms of installation space of the device.

[Purpose] An object of the present invention is to solve the above problems. For this reason, the radiation detector of the present invention takes measures to arrange the two PMTs on the same end side of the SOF, preferably adjacent to each other.

[0012]

A radiation detector for radiation is composed of an elongated scintillator, an elongated light guide means arranged along the scintillator, one end of the scintillator (hereinafter this end is referred to as a "folded end") and Connection means for connecting one end (also a folding end) of the near light guide means, and an optical path changing means for bending the path of the light emitted by the scintillator and passing the light through the connection means to the light guide means. , A first photoelectric conversion means attached to the other end of the scintillator (since it is the target direction of light, it will be referred to as a “target end” hereinafter),
The other end of the light guide unit (also this target end) includes a second photoelectric conversion unit attached at a position close to the first photoelectric conversion unit.

According to this structure, light is transmitted from the scintillator to the light guide means through the folded end. The scintillation light is composed of a component directly advancing to the target end and a component advancing to the folding end of the scintillator, and the latter also returns to the target end side via the light guide means. Therefore, it is possible to arrange the two PMTs close to each other. Further, at this time, the characteristic of the shape of the detector is that the folded end is the protruding end portion of the entire detector.

In one aspect of the radiation detector of the present invention, the scintillator is a scintillation optical fiber, and the light guiding means is an optical fiber. This is because it is a material suitable for realizing an elongated shape.

In one aspect of the radiation detector of the present invention, the folded end of the scintillator and the folded end of the light guiding means are adjusted so as to be located on the same plane. For example, the end faces of the folded end of the scintillator and the light guide means may be aligned so that the (unshaved) ends of the two pencils are aligned. At this time, the connecting means is a prism in which the inclined surface portion is in contact with both end surfaces, and this prism may also serve as the optical path changing means.

In the radiation detector of the present invention, the connecting means is a transparent member that smoothly connects the folded end of the scintillator and the folded end of the light guiding means, and the optical path changing means is a reflecting material formed around this transparent member. May be The transparent member may be plastic, glass or the like. As the reflecting material, there are silver coated on a transparent member, a mirror standing around the transparent member, and the like.

On the other hand, the radiation distribution measuring instrument of the present invention has any one of the above radiation detectors as a main part of its configuration, and further measures the generation time difference of the electric signals converted by the first and second photoelectric conversion means. It is the one to which the timekeeping means to be added is added. This makes it possible to know the radiation distribution by the so-called TOF method.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The radiation detector of the present invention will be described first, and then the radiation distribution measuring instrument using the same will be described.

1. Radiation Detector FIG. 3 is a configuration diagram of the radiation detector 100 according to the present embodiment. In the figure, the same components as those in FIG.

[Structure] In this detector, the PMTs 4 and 6 are adjacent to each other. PMT6 is provided at one end (target end) of SOF2.
Is connected. SOF2 is an optical fiber (hereinafter "O
(F)) is doped with a scintillator. As an example of OF, polystyrene can be used for the core part and polymethylmethacrylate (PMMA) can be used for the clad part. The SOF2 has a length of up to about 10 meters and a thickness of several millimeters. On the other hand, the PMT 4 is connected to the OF 30 which does not dope the scintillator. The shapes of SOF2 and OF30 are exactly the same.

The SOF2 and OF30 are slightly bent so that they are adjacent to each other when they exit the PMTs 4 and 6. These extend to the target end while remaining adjacent. SOF2 and OF3
The end face of the folded end of 0 is a plane perpendicular to the side surface of each fiber, and they are adjusted so that they are in the same plane. Minute prisms 32 are connected to both end faces so that the sloped portions come into contact with each other without any gap. The shape of the prism 32 is
The light propagated from the SOF 2 is designed to be reflected and folded back in the axial direction of the OF 30. In addition, SOF2, O
The F30 and the prism 32 are covered with a light shielding material (black vinyl or the like) not shown.

[Operation] Radiation from the radiation source 16 is SOF.
When it is incident on the specific portion 18 of No. 2, scintillation light is generated. Naturally, scintillation light is not generated on the side of the OF 30 which is not the scintillator.

The scintillation light propagates toward both sides of SOF2. Light reaches PMT6 directly, but PM
The light whose path has been changed by the prism 32 and which has passed through the OF 30 reaches T4. These lights are converted into electric signals by the PMTs 4 and 6, and intended processing is performed by a circuit in the subsequent stage (not shown).

[0024] 2. Radiation Distribution Measuring Device FIG. 4 is a configuration diagram of the radiation distribution measuring device 200 according to the present embodiment. This measuring instrument uses the radiation detector 100 described above, but in the figure, only the PMTs 4 and 6 of the detector are drawn.

[Structure] The electric signals output from the PMTs 4 and 6 are "stop" and "start" of the TAC 10, respectively.
Is input to These inputs serve as instructions to stop and start timing, respectively. The output of TAC10 is input to MCA12.

[Operation] The path of the scintillation light always goes to the PMT 4 regardless of where the radiation enters. For example, if the specific point 18 is located at the center of SOF2, the route from the specific point 18 through SOF2 to PMT6 (path 1) and the specific point 1
Regarding the length of the path from 8 to the PMT 4 via the prism 32 (referred to as path 2), path 1: path 2 = 1: 3 holds (here, the path inside the prism 32 is ignored). Therefore, the position of the specific portion 18 can be easily found from the arrival time difference measured by the TAC 10. After that, the distribution of FIG. 2 is obtained through the analysis of the wave height.

The radiation measuring device 200 (radiation detector 10
0) has the following advantages from its configuration.

(1) Easier measurement in water FIG. 5 is a diagram showing a state of radiation measurement in water by this measuring device. In this way, the SOF2 and OF30 portions form the tips, and the PMTs 4 and 6 are concentratedly arranged on the target end side, which facilitates the measurement that was difficult in the past.

(2) Easy measurement in a narrow place FIG. 6 is a diagram showing a state of radiation measurement in a narrow place by the measuring instrument. In this way, SOF2 and OF30 can be inserted into a narrow groove or the like.

(3) Improvement of device installation space This is because the signal cables from the PMTs 4 and 6 to the TAC 10 are short and the lengths thereof may be the same.

(4) Other Advantages Since the OF 30 also serves as a delay device, the delay device which has been indispensable in the past becomes unnecessary.

The above is the outline of the radiation detector 100 and the radiation distribution measuring device 200. The following improvements or modifications can be considered in this embodiment.

1. Although the PMT is used for the photoelectric conversion unit, it may be configured by an avalanche photodiode (APD) or the like.

2. Although the prism 32 is used for connecting the SOF 2 and the OF 30 and changing the optical path, other structures may be used. FIG. 7 is an enlarged view showing another configuration example of the folded end. As shown in the figure, here, a transparent member such as glass or OF is adopted as the connecting member 40 for both members, and a reflective film 42 such as silver is coated on the periphery thereof.

3. FIG. 8 is an enlarged view showing still another configuration diagram of the folded end. In this way, the end faces of the SOF2 and OF30 may be cut at 45 °, and the two mirrors 50 and 51 may be stood there. In this case, since light crosses the adjacent surface of SOF2 and OF30, it is desirable to bond this portion with a transparent adhesive or the like for joining the plastic scintillator.

4. As a material for SOF2 and OF30, quartz glass fiber can be used in addition to plastic. Attenuation length of OF light of plastic itself (1
The length (falling to / e) is generally about 6 meters, and the silica glass fiber is about 20 meters, so it can be used properly according to the application.

5. In the present embodiment, the shapes of SOF2 and OF30 are the same, but this is not essential. This is because the TOF method can be used as long as the ratio is known even if the two have different lengths.

[0038]

According to the present invention, it becomes easy to measure radiation in water or in a narrow place. Moreover, the length of the signal cable for transmitting the electric signal can be minimized. Further, the delay device which was conventionally required is not required. As a result, it is possible to provide a compact radiation detector and a radiation distribution measuring instrument that solve the conventional problems and have excellent performance.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a conventional general radiation distribution measuring instrument.

FIG. 2 is a diagram showing a plot example of analysis results of MCA12.

FIG. 3 is a configuration diagram of a radiation detector 100 according to the embodiment.

FIG. 4 is a configuration diagram of a radiation distribution measuring instrument 200 according to the embodiment.

FIG. 5 is a diagram showing a state of radiation measurement in water by the measuring instrument.

FIG. 6 is a diagram showing a state of radiation measurement in a narrow place by the measuring instrument.

FIG. 7 is an enlarged view showing another configuration example of the folded end.

FIG. 8 is an enlarged view showing still another configuration example of the folded end.

[Explanation of symbols]

2 SOF, 4,6 PMT, 10 TAC, 12 M
CA, 30 OF, 32 prism, 40 connecting member,
42 reflective film, 50, 51 mirror.

Claims (5)

[Claims] 1. An elongated scintillator, an elongated light guide means arranged along the scintillator, a connecting means for connecting one end of the scintillator to one end of the light guide means close thereto, and light emitted from the scintillator. An optical path changing unit that bends the path of the light and passes the light through the connecting unit to the light guide unit; a first photoelectric conversion unit attached to the other end of the scintillator; and a first photoelectric conversion unit at the other end of the light guide unit. A second photoelectric conversion means attached at a position close to one photoelectric conversion means, and a radiation detector comprising: 2. The radiation detector according to claim 1, wherein the scintillator is a scintillation optical fiber, and the light guiding unit is an optical fiber. 3. The radiation detector according to claim 1, wherein one end of the scintillator and one end of the light guide unit are adjusted so as to be located on the same plane, and the connection unit is a sloped portion. Is a prism in contact with one end of the scintillator and one end of the light guide means, and the prism also serves as the optical path changing means. 4. The radiation detector according to claim 1, wherein the connecting unit is a transparent member that smoothly connects one end of the scintillator and one end of the light guiding unit, and the optical path change. The means is a radiation detector which is a reflector formed around the transparent member. 5. The radiation detector according to any one of claims 1 to 4, which is provided with a clocking means for measuring a generation time difference of the electric signals converted by the first and second photoelectric conversion means. Radiation distribution measuring instrument to measure the distribution of.