JPH07294653A - High-sensitivity/large-area scintillation detector - Google Patents

Abstract

PURPOSE:To rapidly and accurately detect radioactivity from a wide measurement range with a high sensitivity by expanding a total effective area by aligning scintillators with a certain effective area adjacently in parallel and at the same time adding the detection signals of the adjacent scintillators. CONSTITUTION:Scintillators C1-C5 with a certain effective area A are laid out adjacently with the incidence surface being aligned and an emission phenomenon by the radioactive rays of the scintillators C1-C5 is detected individually by photomultipliers P1-P5 and is converted into an electrical signal, is multiplied, and is output. With this configuration, even if, for example, radioactive rays from a radioactive contamination surface Q with 100cps at a boundary region are measured for 70cps and 30cps by the scintillators C2 and C3, respectively, they are added by an addition circuit S2 and are outputted as a signal with 100cps, thus accurately detecting signals. Since the number of scintillators C can be increased, a total effective area can be freely increased and the detection sensitivity of a detector constituted by two scintillators C does not decrease to 3X(2Nb)<1/2> or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scintillation detector comprising a scintillator and a photoelectron multiplying device which detects a light emission phenomenon of the scintillator due to radiation, photoelectrically converts the amplified light and outputs the amplified light. The present invention relates to a scintillation detector capable of detecting with high sensitivity over a wide measurement range without increasing the background even if the total effective area of the data area is widened.

[0002]

2. Description of the Related Art Generally, a scintillation detector detects a scintillator and a light emission phenomenon (scintillation) due to radiation in the scintillator, performs photoelectric conversion, and outputs a photomultiplier tube as an electric signal. , And there are three types of scintillators: solid, liquid and gas.

The detection sensitivity of such a scintillation detector is defined by a significant signal amount (eg, count rate or current value) that can be evaluated by the detector, and the smaller the value, the higher the detection sensitivity. Is evaluated as high. That is, since the scintillator in the detector picks up radiation coming from other than the sample to be measured, for example, radiation from cosmic rays and natural radioactivity as the background, the detection sensitivity is the natural counting rate of the detector. (Background count rate, hereinafter referred to as BG value), which is the standard deviation σ of the BG value
It is defined as 2 to 3 times (2 to 3σ) of (σ = √ (Nb)). Therefore, a detector with a large BG value has a lower detection sensitivity than a detector with a small BG value.

By the way, the magnitude of the BG value is generally proportional to the effective area of the incident surface of the scintillator in the detector. For example, if the effective area is doubled, the BG value is also doubled. Since the BG value becomes 5 times when doubled, the detection sensitivity qualitatively decreases if the effective area is simply increased. For example, if the detection sensitivity of a scintillator detector having a certain effective area is 3 × √ (Nb), the detection sensitivity of a detector in which the effective area of the scintillator is simply multiplied by 5 is 3 × √ ( 5Nb) and the detection sensitivity is √
(5) It decreases by a factor of 2. Therefore, the smaller the effective area,
That is, the smaller the significant signal amount is, the higher the detection sensitivity is evaluated.

[0005]

However, in practical measuring devices, it is often required to increase the effective area of the scintillator while maintaining the detection sensitivity at a certain value. For example, at the time of loading and unloading radioactive materials to and from nuclear power facilities, or at the time of unloading scaffolding members, equipment, tools, etc. used at the time of inspecting the facilities inside the nuclear power plant, from the power plant. When people try to detect the degree of radioactive contamination when entering and exiting with a detector formed of a scintillator with a small effective area, the range that can be measured at one time is limited. Accurate detection measurement may not be possible. Although some detectors have a scintillator with a large effective area, the detection sensitivity cannot be expected so much. At present, a detector in which the size of the incident surface of one scintillator is about 40 × 30 cm in length and width is mainly used, and the scintillator portion of the detector is relatively moved to cover a wide range. The reality is that you are measuring
At present, no detector has a satisfactory detection sensitivity for a wide range of measurement targets.

Therefore, the problem to be solved by the present invention is to have a scintillator part having a wide total effective area for rapidly and accurately detecting and measuring the radioactivity of an object having a wide measurement range. It is an object of the present invention to provide a new scintillation detector in which the detection sensitivity does not decrease due to the increase in the total effective area of the scintillator portion.

[0007]

SUMMARY OF THE INVENTION The structure of the present invention, which has been made for the purpose of solving the above problems, detects a scintillator having a certain effective area and its light emission phenomenon and converts it into an electric signal to increase it. A plurality of scintillation detectors each comprising a photomultiplier for multiplying, a scintillator portion in which the respective scintillators are adjacent to each other, and the incident surfaces are aligned, and the scintillator. It is characterized in that it comprises an addition arithmetic circuit for adding signals output from the photomultipliers respectively attached to two adjacent scintillators in the section and outputting as a detection signal.

[0008]

The total effective area of the scintillator portion is expanded by aligning the scintillators having a certain effective area and arranging them next to each other. Since the signals respectively detected from the two matching scintillators are added and output as a detection signal, the detection measurement region can be expanded without increasing the BG value.

[0009]

Embodiments of the present invention will now be described with reference to FIGS. FIG. 1 is a block diagram for explaining the principle of a high-sensitivity, large-area scintillation detector, which is an example of an embodiment of the present invention formed by arranging five scintillation detectors side by side in a row. FIG. 2 is a perspective view of another example of the detector of the present invention in which the scintillators in a plurality of scintillation detectors are formed by arranging the front faces of the scintillation detectors side by side and adjoining each other in a grid pattern. 3 is a plan view of an example of an auxiliary detector in the detector shown in FIG.

In FIG. 1, reference numeral 1 denotes a detector of the present invention, which is a scintillator C ₁ having a constant effective area as shown by a broken line A, and an emission phenomenon due to radiation in this scintillator C _1. Is formed, and five scintillation detectors, each of which is a minimum constitutional unit composed of a photomultiplier tube P ₁ for detecting and converting the signal into an electric signal and multiplying the signal, are arranged side by side. C is 5
Scintillation detector scintillators C ₁ , C ₂ ,
This is a scintillator portion in which C ₃ , C ₄ , and C ₅ are adjacent to each other and the incident surfaces are aligned. Here, the scintillation - all the effective area of the capacitor C ₁ -C ₅ are are the same.

Each of the scintillators C _{1 to} C ₅ constituting the scintillator portion C has a photomultiplier tube P ₁ , P ₂ , P respectively.
₃ , P ₄ , P ₅ are attached, and each scintillator C ₁ ~
The light emission phenomenon due to radiation at C ₅ is individually detected by each of these photomultiplier tubes P _{1 to} P ₅ , converted into an electric signal, and multiplied and output. Here, the light emission phenomenon at the scintillator C ₁ in the scintillation detector of the minimum constitutional unit indicated by the broken line A is detected by the photomultiplier tube P ₁ , and its detection sensitivity is the scintillator C ₁ B
If the standard deviation of the G value is σ (σ = √ (Nb)), then 2-3
Double (2 to 3σ), that is, 2 × √ (Nb) to 3 × √ (Nb). The other four scintillation detectors have the same detection sensitivity as the scintillation detector of the minimum structural unit indicated by the broken line A.

By the way, in the detector of the present invention of the above example, the total effective area of the scintillator portion C is determined by the scintillators C ₁ to C ₁ .
The area is the sum of the effective areas of C ₅ , but if one scintillator with the same effective area as the total effective area is used and the light emission phenomenon is detected by one photomultiplier tube, the detection sensitivity is The detection sensitivity of the scintillation detector indicated by the broken line A is reduced to a value obtained by multiplying √ (5). Therefore, in order to increase the total effective area of the scintillator portion without lowering the detection sensitivity, scintillators of a size equal to the required area are arranged side by side and the light emission phenomenon in each scintillator is reduced. If each is detected, a wide measurement area can be secured without increasing the BG value.

However, in the case of the above configuration, for example, 100 cps (counts per unit time) of radiation from a certain radioactive contamination surface acts entirely on one scintillator C _1. And the scintillator C ₁ is 100c
There is no problem when measuring ps radiation, but there is a 100 cps radioactive contamination surface on the boundary between two adjacent scintillators C ₁ and C ₂ , and there are two scintillators C ₁ and C ₂ . When the acting radiation is measured with each scintillator C ₁ and C ₂ as 50 cps, the radioactivity on the radioactively contaminated surface cannot be accurately detected. For example, as shown in FIG. 1, about 70% of the area on the boundary between _two scintillators C ₂ and C ₃ where the radioactively contaminated surface Q emitting 100 cps of radiation is adjacent to the scintillator C ₂ side. When it is located, the scintillator C ₂ side measures 70 cps and the scintillator C ₃ side measures 30 cps.

In order to solve the problem in the boundary region between such two scintillators, the present invention has a scintillator in which the scintillators are arranged in a horizontal direction or a vertical direction or which will be described later in a grid pattern. In the touch panel, two scintillators that are adjacent to each other in the front-back direction in the horizontal direction, the vertical direction, or the vertical and horizontal directions.
Each set of two scintillators has a signal to be detected added thereto and output as a detection signal. By doing so, for example, the radiation from one radioactive ray contaminated surface of 100 scps located in the boundary area of two scintillators adjacent to each other in front and back is 30
Even when measured as cps and on the other hand as 70 cps, they are added and output as a detection signal of 100 cps, so an accurate detection output signal can be obtained.

In FIG. 1, S ₁ detects the light emission phenomenon in the adjacent scintillators C ₁ and C _{2 by} the photomultiplier tubes P ₁ and P ₂ , respectively, and the electric output signals thereof are added and calculated. Similarly, S ₂ is an addition arithmetic circuit provided for the photomultiplier tubes P ₂ , P ₃ attached to the scintillators C ₂ , C ₃ , and S ₃ is also a scintillator C. _The photomultiplier tubes P ₃ and P ₄ attached to the photomultiplier tubes ₃ and C ₄ , and the addition arithmetic circuit S ₄ are the scintillators C ₄ and C ₄ .
₅ is an addition arithmetic circuit provided in the photomultiplier tubes P ₄ and P ₅ attached to ₅ . In addition, these addition arithmetic circuits S ₁ ,
In S _2, S _3, S _4, two adjacent scintillation - for summing also each BG level of data, the detection sensitivity of the present invention, scintillator indicated by the dashed line A - data C ₁ and the photomultiplier Tube P
_When compared with the detection sensitivity of the scintillation detector composed of ₁ , the detection sensitivity is reduced by √ (2) times. However, since the number of scintillators can be increased in units of two adjacent scintillators,
The total effective area of the scintillator section can be freely expanded to the required area, and the detection sensitivity of the scintillation detector composed of two scintillators is 3 × √.
It does not fall below (2Nb).

Next, referring to FIG. 2, a detector 2 according to another example of the present invention will be described. This detector 2 is composed of a scintillator having a constant effective area and a photomultiplier tube.
The scintillation detectors are arranged side by side in the vertical and horizontal directions, and the incident surfaces of the scintillators CN _{1 to} CN ₉ are aligned, so to speak, so that they are arranged side by side in a grid pattern, so that the scintillator portion CN is formed.
And each scintillator CN _{1 of} this scintillator portion CN
Each with attaching the photomultiplier tube PN ₁ to PN ₉ to -CN _9, are formed by attaching a 12 addition operation circuit SU ₁ to SU _12. If the scintillators CN _{1 to} CN ₉ in the detector 2 shown in FIG. 2 are the same scintillators used in the detector 1 shown in FIG. When moving in the horizontal or vertical direction within the width of the scintillator, as in the detector 1 shown in FIG.
It can be measured with a detection sensitivity of × √ (2Nb). Therefore, the detector 2 of another example of the present invention shown in FIG.
9 pieces of scintillator CN ₁ with a certain effective area
The total effective area is doubled, and in the horizontal and vertical directions, the signals respectively detected from two scintillators adjacent to each other in the front and rear are added and output as a detection signal.
The measurement detection range can be expanded vertically and horizontally without lowering the detection sensitivity.

However, in the scintillator portion CN of the detector 2 shown in FIG. 2, a radioactive contamination surface (not shown) is present.
Is located in an area on the boundary in the central portion of the four scintillators, for example, four scintillators C
When a radioactive contamination surface (not shown) is located in the area on the boundary Y indicated by the broken line in the central portion of N ₁ , CN ₂ , CN ₄ , and CN ₅ , the scintillation phenomenon causes four scintillation phenomena. Ta C
N ₁ , CN ₂ , CN ₄ , CN ₅ occur simultaneously, which is detected by the respective photomultiplier tubes PN ₁ , PN ₂ , PN ₄ , PN ₅ and converted into an electrical signal, and their output signals are vertically The detection signals are simultaneously output from the _four addition operation circuits SU ₁ , SU ₃ , SU ₄ , SU ₆ after being added in the horizontal and horizontal directions. However, these addition arithmetic circuits SU ₁ , S
The outputs from U ₃ , SU ₄ , and SU ₆ do not accurately output the intensity of the radioactivity on the surface contaminated with radiation, and the output from the addition arithmetic circuits SU ₃ and SU ₄ is added or arithmetically operated. Even if the outputs from the circuits SU ₁ and SU ₆ are added and calculated, the detection sensitivity only drops to √ (4).

Therefore, in the present invention, as shown in FIG. 3, the auxiliary detector 3 is formed in the scintillator portion CN. That is, 4 arranged vertically and horizontally next to each other
The scintillators CN ₁ , CN ₂ , CN ₄ , and CN ₅ are used as a unit (each combination has four sets when nine scintillators are arranged in a grid), and each scintillator is used as a unit. C
N ₁ , CN ₂ , CN ₄ , CN ₅ are equally divided into left and right (not actually cut and divided) by dividing lines indicated by broken lines l ₁ and l ₂ , and the boundary portion of these divided scintillators is divided. Auxiliary photomultiplier tubes PM ₁ , PM ₂ ,
PM _4, fitted with a PM _5, each scintillator - motor CN _1, CN _2,
Only the scintillation phenomenon on the divided side of CN ₄ and CN ₅ including the boundary Y side of the scintillator is detected, and the BG value in each divided region is not divided. It is set to 1/2 of the value.

Thus, auxiliary photomultiplier tubes P adjacent to each other
When the outputs from M ₁ and PM ₂ are added by the addition operation circuit SM _1, and the outputs from the adjacent auxiliary photomultipliers PM ₄ and PM ₅ are added by the addition operation circuit SM ₂ , the addition operation circuit SM _{2 is} added. The detection sensitivity from ₁ and SM ₂ is 3 × √ (N
b). Therefore, when the auxiliary addition operation circuit SX ₁ is provided and the detection output signals from these addition operation circuits SM ₁ and SM ₂ are added and calculated, the detection sensitivity output from this auxiliary addition operation circuit SX ₁ is 3 × √ (2Nb). Becomes The addition arithmetic circuit SM ₁ is an addition circuit for the auxiliary photomultipliers PM ₁ , PM ₄ , and the addition arithmetic circuit SM ₂ is for the auxiliary photomultipliers PM ₂ , PM.
_{Even with} the adder circuit of ₅ , the same detection result as above can be obtained. Also, each scintillator CN ₁ , CN ₂ , CN ₄ , CN ₅
May be equally divided vertically. The detector shown in FIG. 2 is provided with four such auxiliary detectors 3.

Here, the auxiliary detector 3 is, in the example shown in FIG. 3, four auxiliary photomultiplier tubes PM ₁ , PM ₂ , P.
The operation is performed when electric signals are simultaneously output from M ₄ and PM ₅ , and at the same time, addition operation circuits SU ₁ , SU ₃ , and S _{5 are} simultaneously activated.
The outputs from U ₄ and SU ₆ are not handled as detection signals, but other signal processing means may be used.

The present invention is not limited to the above embodiment, but the number of scintillators having a certain effective area (that is, the number of scintillation detectors as constituent units) is required. Can be increased according to the total area of
In that case, the number of auxiliary detectors, that is, the number of auxiliary addition arithmetic circuits also increases according to the number of scintillators. For example, when 16 scintillators having a constant effective area are used and arranged in a regular lattice, 24 adder arithmetic circuits and 9 auxiliary adder arithmetic circuits are required. Moreover, when 16 scintillators are arranged in two rows and arranged side by side,
Two addition arithmetic circuits and seven auxiliary addition arithmetic circuits are required.

Further, the total effective area of the scintillator portion can be set by adjusting the size of the scintillator which is a constituent unit. Incidentally, a square or rectangular scintillator formed by adjusting the length and width of each scintillator within the range of 20 cm to 40 cm can be used. The length and width of the scintillator can be set to 10 cm or less, but in that case, the detection sensitivity is less deteriorated, but the number of sheets used to satisfy the required area is large, and therefore the addition arithmetic circuit and auxiliary addition are performed. The number of arithmetic circuits also increases considerably.

In the detector of the present invention, the detection signals output from the addition operation circuit and the auxiliary addition operation circuit are processed by a computer (not shown), and the scintillator section of the detected scintillator is processed. It is also possible to measure the positional relationship in, the direction in which adjacent scintillators are arranged for detection, the strength of the radioactively contaminated surface, its moving direction, the moving speed, and the like.

The detector of the present invention is as described in each of the above embodiments, but the scintillator constituting the scintillator portion includes a plastic scintillator, ZnS.
(Ag), CsI (Tl), BGO, NaI (Tl), Lil (Eu),
Anthracene or the like can be appropriately used depending on the measurement target.

[0025]

The present invention is as described above. In the detector of the present invention, the scintillator portions having a certain effective area are aligned next to each other by aligning the front surfaces of the scintillator portions so that the scintillator portion is integrated. As the effective area is increased, the light emission phenomenon in each scintillator is detected, and the signals detected from the adjacent scintillators are added and output as a detection signal, so that the BG value is not increased. The detection and measurement area can be expanded. That is, since the number of scintillators can be increased in units of two adjacent scintillators, the total effective area of the scintillator portion can be freely expanded to a required area, and its detection sensitivity is also increased. Does not fall below the detection sensitivity of a scintillation detector composed of two scintillators.

Further, since the detector of the present invention has a wide range of measurable objects, if it is arranged at the entrance / exit where radioactive materials are carried into nuclear power facilities and used radioactive pollutants are carried out, the detectors can be carried out. You can quickly catch the situation of entering. In addition, when the scaffolding members, equipment, tools, etc. used during the inspection of the facilities inside the nuclear power plant are carried out or when workers are in and out, the degree of radioactive contamination should be detected quickly and accurately at one time. You can

[Brief description of drawings]

FIG. 1 is a block diagram illustrating the principle of a high-sensitivity, large-area scintillation detector according to an example of the present invention.

FIG. 2 is a perspective view of a detector according to another example of the present invention.

FIG. 3 is a plan view of an example of an auxiliary detector in the detector shown in FIG.

[Explanation of symbols]

1 Detector of one example of the present invention C _{1 to} C ₅ scintillator P _{1 to} P ₅ Photomultiplier tube S _{1 to} S ₄ Addition arithmetic circuit Q Radioactive contamination surface 2 Detector of another example of the present invention CN ₁ ~ CN ₉ scintillator PN ₁ ~ PN ₉ photomultiplier tube SU ₁ ~ SU ₁₂ addition arithmetic circuit 3 auxiliary detector PM ₁ , PM ₂ , PM ₄ , PM ₅ auxiliary photomultiplier tube SM ₁ , SM ₂ addition operation Circuit SX ₁ Auxiliary addition operation circuit l ₁ , l ₂ Dividing line

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomoji Harada 8-9-23 Okamura, Isogo-ku, Yokohama, Kanagawa Prefecture (72) Kenichi Sato 2-13-11 Toyohachi, Shinagawa-ku, Tokyo

Claims (4)

[Claims] 1. A plurality of scintillation detectors comprising a scintillator having a constant effective area and a photoelectron multiplying device for detecting a light emission phenomenon thereof, converting the light emission phenomenon into an electric signal and multiplying the electric signal. From the scintillator portion in which the respective scintillators are adjacent to each other and the incident surfaces are aligned, and from the photomultipliers respectively attached to the two adjacent scintillators in the scintillator portion. A high-sensitivity, large-area scintillation detector comprising an addition arithmetic circuit for adding output signals and outputting as a detection signal. 2. The high-sensitivity, large-area scintillation detector according to claim 1, wherein the scintillator portion is formed by arranging a plurality of scintillators adjacent to each other in one row or in two or more rows in the horizontal or vertical direction. 3. The scintillator portion is formed by arranging a plurality of scintillators adjacent to each other in the vertical and horizontal directions.
High-sensitivity, large-area scintillation detector. 4. A scintillator part in which a plurality of scintillators are arranged side by side in the vertical and horizontal directions, and in regard to four scintillators which are adjacent to each other in the vertical and horizontal directions, each of the four scintillators is provided. , An auxiliary photomultiplier is attached to almost half of the area on the side of contact with the boundary, and an addition arithmetic circuit that adds signals output from adjacent auxiliary photomultipliers and outputs as a detection signal is added. The high-sensitivity, large-area scintillation detector according to any one of claims 1 to 3, further comprising an auxiliary addition arithmetic circuit which is provided to perform an arithmetic operation on the outputs from these addition arithmetic circuits.