JP2003004886A - Article radiation detector and article radiation detection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve measurement efficiency by simultaneously measuring radiation of inside and surface of an article. SOLUTION: A thin plastic scintillator detector 1 having a detector thickness capable of capturing β-ray radiated from an article 20 and transmitting γ-ray radiated from an article 20 and counting β-ray from the article surface 21a, γ-ray from the article surface 21a and total count rate of γ-ray from the article surface 21b is provided. A thick NaI(TI) scintillator detector 2 whose detection surface is arranged overlapping to almost coincide with the outward form of the detection surface of the detector 1 and having a detector surface capable of capturing γ-ray radiated from the article 20 and transmitting the detector 1 and coming in, and counting the total count rate of γ-ray from the article surface 21a and total count of γ-ray from the article surface 21b is provided. A count rate operation circuit 12 for obtaining the count rates of β-ray from the article surface 21a and γ-ray from the article surface 21a is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention simultaneously measures the radiation emitted from the inside and the surface of an article, and counts the gamma rays emitted from the inside, the counting rate from the beta rays emitted from the surface, and the surface. TECHNICAL FIELD The present invention relates to an article radioactivity detection device and an article radioactivity detection system that can be applied to the measurement of a low radioactivity level that can separately obtain and obtain the counting rates by the γ-rays emitted from the.

[0002]

2. Description of the Related Art When an article that has been carried into a radioactively controlled area such as a nuclear power plant is to be taken out of the radioactively controlled area again, the radioactive contamination level of the article should be measured and there should be no radioactive contamination. Alternatively, it is necessary to confirm that the amount of radioactivity is below a predetermined standard value.

[0003] In addition, a drum can that is possibly contaminated by radioactivity, such as a drum can containing low-level radioactive waste to be buried, is stored inside, and the surface of the drum can itself is also radioactive. For potential contamination, both internal and surface radioactivity should be measured.

In order to confirm this, conventionally, the surface activity (β activity and γ activity) of an article is measured by an article unloading monitor as shown in FIG.
In the radioactive waste carry-out inspection device shown in Fig. 1, the radioactivity on the surface of the drum and the internal radioactivity (γ-activity) of the drum can are measured.

In the article unloading monitor shown in FIG.
The belt 5 is conveyed by the belt conveyor 26 between a pair of detectors 27 provided above and below the conveying path, and the radiation emitted from the surface of the article 25 is detected by the detector 27. A plastic scintillator, for example, is applied to the detector 27. Then, the detection signal detected by the detector 27 is processed by the signal processing circuit 28,
The presence or absence of surface contamination of the article 25 is determined based on the processing result.

In the radioactive waste carry-out inspection apparatus shown in FIG. 11, an article 25 such as a drum can is placed on a turntable 30, and γ-rays emitted from the inside of the article 25 are measured by a Ge detector 31. A collimator 32 is provided between the article 25 and the Ge detector 31, and only radiation emitted from a specific part of the article 25 is detected. Further, the turntable 30 moves the article 25 up and down,
Alternatively, by rotating and moving, the measurement from various parts of the article 25 can be performed, and the radioactivity distribution inside the article 25 can be obtained based on the measurement. The radioactivity on the surface of the drum can is obtained by wiping measurement with a smear.

[0007]

However, in the case of measuring surface contamination radioactivity and internal radioactivity (activated radioactivity) of an article such as waste from a decommissioning furnace, such a conventional article radioactivity detection method is used. Then, there are the following problems.

That is, in the conventional method for detecting radioactivity of articles as described above, there is no apparatus for simultaneously measuring the surface radioactivity of an article and the internal radioactivity of the article at the same time. Must be measured.

For this reason, not only the setting of the article to be measured in the device but also the measurement must be performed for each device, which is time-consuming and time-consuming.
There is a problem that the measurement work efficiency is low.

Therefore, it is desired to develop an article radioactivity detection method capable of improving the measurement work efficiency by simultaneously measuring both the internal radioactivity and the surface radioactivity.

The present invention has been made in view of such circumstances, and it is possible to simultaneously measure both the internal radioactivity and the surface radioactivity of an article to be measured, thereby improving the measurement work efficiency. An object of the present invention is to provide an article radioactivity detection device and an article radioactivity detection system.

[0012]

In order to achieve the above object, the present invention takes the following means.

That is, in the article radioactivity detection apparatus of the first aspect of the invention, the article radioactivity detection device is arranged with the detection surface facing the article to be measured, and it is possible to capture β rays emitted from the article. And has a detection part thickness that allows transmission of γ-rays emitted from the article, the counting rate by β-rays emitted from the surface of the article (K3), the counting rate by γ-rays emitted from the surface of the article ( K1), and γ emitted from inside the article
Total count rate (P = K1 +
K3 + K4) has a first radiation detector and a detection surface having substantially the same size and shape as the detection surface of the first radiation detector, and this detection surface is a non-article of the detection surface of the first radiation detector. Is placed on the side surface so as to substantially match the outer shape of the detection surface of the first radiation detector, and is emitted from the article,
The detector has a thickness capable of capturing γ-rays transmitted through the first radiation detector and incident, and the counting rate (K2) by γ-rays emitted from the surface of the article and the emission from the inside of the article Based on the second radiation detector for counting the total counting rate (Q = K2 + K5), which is the sum of the counting rates (K5) by the γ-rays, and the counting rate counted by the first and second radiation detectors. Count to obtain the counting rate (K3) by β rays emitted from the surface of the article, the counting rate (K5) by γ rays emitted from the inside of the article, and the counting rate (K2) by γ rays emitted from the surface of the article And rate calculation means.

According to a second aspect of the invention, in the article radioactivity detecting apparatus of the first aspect of the invention, the counting rate calculating means counts the γ rays emitted from the surface and inside of the article by the second radiation detector. The ratio of the counting rate counted by the first radiation detector to the counted rate K (K = K1 / K2
= K4 / K5), the count rate (K3) by the β rays emitted from the surface of the article is obtained according to K3 = P−Q * K, and the nuclide that emits β and γ rays from the surface of the article is specified. The constant J determined by
Using (J = K1 / (K1 + K3)), the count rate (K5) by the γ-rays emitted from the inside of the article is calculated according to K5 = Q−K3 * J / ((1-J) × K), and K2 = Q-K5, the count rate (K2) by the γ rays emitted from the surface of the article is obtained.

According to a third aspect of the invention, in the article activity detecting apparatus according to the first or second aspect of the invention, the first radiation detector includes a plastic scintillator including a scintillator which emits fluorescence when receiving energy of radiation. A NaI including a NaI (Tl) scintillator, which has a thickness larger than that of a plastic scintillator radiation detector and emits fluorescence when receiving energy of radiation, as a second radiation detector while applying the detector.
(Tl) Apply scintillator detector.

According to a fourth aspect of the invention, in the article radioactivity detecting apparatus of the third aspect of the invention, the scintillator which is arranged between the plastic scintillator detector and the NaI (Tl) scintillator detector and is included in the plastic scintillator detector. When the scintillator emits fluorescence when receiving energy from the fluorescence emitted by the scintillator, when the scintillator emits fluorescence, the first fluorescent optical fiber that propagates this fluorescence to the end side and NaI (Tl )
It is placed on the non-article side surface of the scintillator detector, and NaI
(Tl) NaI (Tl) contained in scintillator detector
The scintillator includes a scintillator that emits fluorescence when receiving energy from the fluorescence emitted by the scintillator. When the scintillator emits fluorescence, a second fluorescent optical fiber that propagates this fluorescence to the end side, , Which is provided at both ends of the fluorescent optical fiber, converts the fluorescence propagated by the first fluorescent optical fiber into an electric signal, and counts the converted electric signal as a count rate counted by the plastic scintillator detector. And a pair of first photomultiplier tubes for outputting to, and fluorescent light propagated by the second fluorescent optical fiber, which is provided at both ends of the second fluorescent optical fiber, respectively, is converted into an electric signal, and the converted electric signal To the count rate calculation means as a count rate counted by the NaI (Tl) scintillator detector. Adding a photomultiplier tube.

According to a fifth aspect of the present invention, in the article radioactivity detection apparatus according to the third aspect of the invention, the scintillator which is disposed between the plastic scintillator detector and the NaI (Tl) scintillator detector and is included in the plastic scintillator detector. When the scintillator emits fluorescence when receiving energy from the fluorescence emitted by the scintillator, when the scintillator emits fluorescence, the first fluorescent optical fiber that propagates this fluorescence to the end side and NaI (Tl )
It is placed on the non-article side surface of the scintillator detector, and NaI
(Tl) NaI (Tl) contained in scintillator detector
The scintillator includes a scintillator that emits fluorescence when receiving energy from the fluorescence emitted by the scintillator. When the scintillator emits fluorescence, a second fluorescent optical fiber that propagates this fluorescence to the end side, A pair of first photomultiplier tubes, which are provided at both ends of the fluorescent optical fiber, convert the fluorescence propagated by the first fluorescent optical fiber into an electric signal, and output the converted electric signal; And a pair of second photomultiplier tubes provided at both ends of the fluorescent optical fiber for converting the fluorescence propagated by the second fluorescent optical fiber into an electric signal and outputting the converted electric signal, The electric signals output from the first photomultiplier tubes are compared with each other, and only the electric signals generated at the same time are counted by the first radiation detector. As a second radiation detection, the first simultaneous measurement circuit for outputting to the counting rate calculating means and the electric signals respectively output from the pair of second photomultiplier tubes are compared, and only the simultaneously generated electric signals are detected in the second radiation detection. A second simultaneous measurement circuit that outputs the count rate to the count rate calculation means as the count rate counted by the instrument is added.

In the article radioactivity detection system of the sixth aspect of the present invention, a plurality of article radioactivity detection devices of any one of the first to fifth aspects of the present invention are provided around the article and provided around the article. Based on the count rate measured by each article radioactivity detection device, the radioactivity distribution information in the article is acquired.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) A first embodiment of the present invention will be described with reference to FIGS. 1 to 5.

FIG. 1 is a structural conceptual view showing an example of an article radioactivity detecting apparatus according to the first embodiment.

That is, the article radioactivity detection apparatus according to the present embodiment has a thin plastic scintillator detector 1 having a detection surface facing the article 20 to be measured as a radioactivity detection section, and the detection surface thereof. Is approximately the same size as the detection surface of the thin plastic scintillator detector 1, and is provided with a thick NaI (Tl) scintillator detector 2 arranged so as to overlap the thin plastic scintillator detector 1. The thin plastic scintillator detector 1 has a thickness of about 0.1 to 0.3 mm.
On the other hand, the thickness of the thick NaI (Tl) scintillator detector 2 is about 1 cm.

On the other hand, when surface contamination 21a is present on the surface of the article 20, β is directed from there to the article radiation detector.
Rays and gamma rays are emitted. In addition, β-rays and γ-rays are also emitted when there is internal contamination 21b inside the article 20, but since the β-rays have a weak penetrating power, they cannot pass through the article 20 and only γ-rays are emitted. It is emitted toward the article radioactivity detection device. As a typical nuclide in the surface contamination 21a,
For example, there is cobalt 60 (Co-60). Cobalt 6
0 is a radionuclide that emits β and γ rays. Typical nuclides in the internal pollution 21b include manganese 54 (Mn-54) and iron 59 (Fe-59) in addition to the above-mentioned cobalt 60. Both manganese 54 and iron 59 are nuclides that emit γ rays.

The β-rays and γ-rays thus emitted toward the article radioactivity detecting device first reach the detection surface of the thin plastic scintillator detector 1, of which γ
Since the line has a strong penetrating power, most of it passes through the thin plastic scintillator detector 1 and the thick Na
It reaches the detection surface of the I (Tl) scintillator detector 2.
Since the thin plastic scintillator detector 1 includes a scintillator that emits fluorescence when receiving energy from radiation, this scintillator emits fluorescence by receiving energy from β rays and γ rays. The β rays that have reached the thin plastic scintillator detector 1 are deprived of their energy and their penetrating power is weakened there.
l) The scintillator detector 2 cannot be reached.

On the other hand, most of the γ-rays pass through the thin plastic scintillator detector 1 and the thick NaI (T
l) Reach the detection surface of the scintillator detector 2. Thick N
The aI (Tl) scintillator detector 2 also includes a scintillator that emits fluorescence when receiving energy from radiation. Thick NaI (Tl) scintillator detector 2
Is designed to have a thickness that can efficiently receive the energy of γ-rays, so that the γ-rays that reach the thick NaI (Tl) scintillator detector 2 are thick NaI (Tl)
l) Energy is taken by the scintillator detector 2, and fluorescence is emitted by this energy.

In this manner, the thin plastic scintillator detector 1 emits fluorescence upon receiving the energy of β rays and γ rays emitted from the surface contamination 21a of the article 20 and the γ rays emitted from the internal contamination 21b. Further, the thick NaI (Tl) scintillator detector 2 emits fluorescence upon receiving the energy of the γ-ray emitted from the surface contamination 21a and the internal contamination 21b of the article 20.

Each plastic scintillator detector 1, 2
A large number of fluorescent optical fibers 3 and 4 are arranged on the upper surface of the with a substantially constant pitch. Fluorescent optical fiber 3,4
Includes in the core 13 a scintillator that emits fluorescence at an energy lower than that of fluorescence emitted by each of the plastic scintillator detectors 1 and 2. Therefore, FIG.
, Each plastic scintillator detector 1,
When fluorescence is emitted at 2, the energy scatters the scintillator 15 contained therein. Then, this fluorescence is confined in the core 13 and propagates toward the end while refracting.

For example, when the thin plastic scintillator detector 1 receives energy from radiation, about 410
a scintillator 14 that emits fluorescence of nm is included,
When the fluorescent optical fiber 3 arranged on the upper surface of the thin plastic scintillator detector 1 receives energy from the light, the scintillator 15 emits fluorescence of about 520 nm.
Will be described using the case where is included. In this case, when the energy of radiation (β-rays and γ-rays) is absorbed by the thin plastic scintillator detector 1, the scintillator 1
4 fluoresces at about 410 nm. The energy of this fluorescence excites the scintillator 15 contained in the fluorescent optical fiber 3 arranged on the upper surface of the thin plastic scintillator detector 1 to emit fluorescence of about 520 nm.

In this way, the surface contamination 21 of the article 20
Radiation emitted from a or the internal pollution 21b is converted into fluorescence in the fluorescent optical fibers 3 and 4. Figure 1
, Each plastic scintillator detector 1,
2 has a wide detection surface so that even a large size article 20 can be detected, these fluorescent optical fibers 3 and 4 are connected to the plastic scintillator detectors 1 and 2, respectively.
By arranging over the entire upper surface of 2, it is possible to capture the fluorescence emitted over the entire detection surface and convert it into the fluorescence within the fluorescent optical fiber 3.

Photomultiplier tubes 5 and 6 are connected to both ends of the fluorescent optical fibers 3 and 4, respectively. The photomultiplier tubes 5 and 6 are several fluorescent optical fibers 3 and 4, respectively.
Is connected to convert the fluorescence propagated by the fluorescent optical fibers 3 and 4 into an electric signal, and outputs the converted electric signal to the simultaneous measurement circuits 7 and 8.

That is, the fluorescent optical fiber 3 propagates the fluorescence corresponding to the energy of the radiation detected by the thin plastic scintillator detector 1 to the photomultiplier tube 5, and the photomultiplier tube 5 sends this fluorescence to an electric signal. To the simultaneous measurement circuit 7. On the other hand, the fluorescent optical fiber 4 is the thick NaI (Tl) scintillator detector 2
The fluorescence corresponding to the energy of the radiation detected by is propagated to the photomultiplier tube 6, the photomultiplier tube 6 converts this fluorescence into an electric signal, and outputs it to the simultaneous measurement circuit 8. It is a schematic diagram which shows the signal waveform of the electric signal output to the simultaneous measurement circuit 7 (# 1) from the multiplier 5 (# R1, # L1).

As shown in FIG. 3, the photomultiplier tube 5 (# R1) connected to the right end of the fluorescent optical fiber 3 and the photomultiplier tube 5 (# L1) connected to the left end of the fluorescent optical fiber 3 are as shown in FIG. Noise signal N as well as electrical signal S converted from fluorescence
Is output to the simultaneous measurement circuit 7 (# 1).
However, as shown in FIG. 3, the photomultiplier tube 5 (#
R1) and the electric signal S output from the photomultiplier tube 5 (# L1) have the same timing, but the photomultiplier tube 5
The timing of the noise signal N output from (# R1) and the photomultiplier tube 5 (# L1) does not match. The simultaneous measurement circuit 7 (# 1) uses this fact to make noise signal N
And the electric signal S are separated, the noise signal N is removed, only the electric signal S by the detector is extracted, and the result is output to the adding circuit 9. The method of removing the noise signal N in this way is called a simultaneous measurement method.

When the radiation signal is large and the electric signal S can be sufficiently discriminated from the noise signal N, the noise removal by the simultaneous measurement circuits 7 and 8 is not necessarily performed. good. In general, the energy of γ-ray is large and the signal of the thick NaI (Tl) scintillator is also large, so that the electric signal S output from the photomultiplier tube 6 is sufficiently larger than the noise signal N. Therefore, regarding the fluorescent optical fiber 4, the simultaneous measurement circuit 7
Is omitted, and the photomultiplier tube 6 is provided only at either the left end portion or the right end portion, and the electric signal S output from the photomultiplier tube 6 is discriminated from the electric noise according to the wave height to be directly supplied to the addition circuit 11. You may make it output.

The adder circuit 9 has an electric signal S output from the simultaneous measurement circuit 7 (# 1) and the simultaneous measurement circuit 7 (# 2).
Are respectively added, and the count rate as the addition result is output to the count rate calculation circuit 12. The addition circuit 11 also adds the electric signals S output from the simultaneous measurement circuit 8 (# 1) and the simultaneous measurement circuit 8 (# 2), respectively, and outputs the count rate as the addition result to the count rate calculation circuit 12. To do.

Incidentally, in FIG. 1, each of the adder circuits 9 and 11 is
Two simultaneous measurement circuits 7 (# 1, # 2), 8 (#
It is assumed that the electric signal S output from the terminals 1 and # 2) is received, but the number of the simultaneous measurement circuits 7 and 8 is not limited to two and may be more. For example, three pairs of photomultiplier tubes 5 connected to the ends of a predetermined number of fluorescent optical fibers 3 are provided, and three simultaneous measurement circuits 7 for outputting electric signals from the photomultiplier tubes 5 of each pair are also provided. You may do it.

The counting rate calculation circuit 12 performs the following calculation based on the counting rate output from the adding circuit 9 and the counting rate output from the adding circuit 11 to obtain the article 20.
The counting rates from the β rays and γ rays emitted from the surface contamination 21a and the γ rays emitted from the internal contamination 21b of the article 20 are separately obtained.

FIG. 4 shows the counting rate of β-rays and γ-rays emitted from the article 20 detected by the thin plastic scintillator detector 1 and the thick NaI.
It is a schematic diagram for demonstrating the relationship with the count rate counted by being detected by (Tl) scintillator detector 2.

That is, from the surface contamination 21a of the article 20, β rays and γ rays are emitted toward the article radioactivity detection apparatus as described above, and the β rays and γ rays are the thin plastic scintillator detector 1. It is absorbed by and emits fluorescence. Further, the γ-rays pass through the thin plastic scintillator detector 1 and are absorbed by the thick NaI (Tl) scintillator detector 2 to emit fluorescence. The β rays pass through the thin plastic scintillator detector 1 and the thick NaI
(Tl) Scintillator detector 2 is not reached. Further, from the internal contamination 21b of the article 20, γ-rays are emitted toward the article radioactivity detection device as described above, but the γ-rays are absorbed by the thin plastic scintillator detector 1 and emit fluorescence. Further, the γ-rays pass through the thin plastic scintillator detector 1 and are absorbed by the thick NaI (Tl) scintillator detector 2 to emit fluorescence.

Therefore, the count rate P by the thin plastic scintillator detector 1 is γ from the surface contamination 21a.
Counting rate K1 caused by lines and surface contamination 21a
Is the sum of the counting rate K3 caused by the β rays from and the counting rate K4 caused by the γ rays from the internal contamination 21b, and the following equation (1) is established. P = K1 + K3 + K4 (1) Further, the counting rate Q by the thick NaI (Tl) scintillator detector 2 is the counting rate K2 caused by the γ rays from the surface contamination 21a and the γ from the internal contamination 21b. It becomes the sum with the counting rate K5 caused by the line, and the following equation (2) is established. Q = K2 + K5 (2) Further, in the case of the surface contamination 21a, β in the thin plastic scintillator detector 1 for a specific contamination nuclide.
The ratio (J) of the count rate of γ rays to the total count rate of rays and γ rays is constant. Therefore, when the contaminated nuclide is known, the following equation (3) is obtained. J = K1 / (K1 + K3) (3) Furthermore, the counting rate of γ rays in the thin plastic scintillator detector 1 and the counting rate of γ rays in the thick NaI (Tl) scintillator detector 2 Since the ratio is constant (K), the following equation (4) is obtained. K1 / K2 = K4 / K5 = K (4) Using the above equations (1) to (4), surface contamination 21
The counting rate K3 counted in the thin plastic scintillator detector 1 by the β-rays from a is calculated in the thick NaI (Tl) scintillator detector 2 by the γ-rays from the internal contamination 21b from the equation (5) below. From the equation (6) showing the counting rate K5, the surface contamination 21
The counting rate K2 counted in the thick NaI (Tl) scintillator detector 2 by the γ-ray from a is obtained from the following equation (7).

K3 = P-Q * K ... (5) K5 = Q-K3 * J / ((1-J) * K) ... (6) K2 = Q-K5. (7) The article radioactivity detection apparatus according to the present embodiment has the counting rate of β rays emitted from the surface contamination 21a of the article 20 and the emission from the surface contamination 21a as described above. The counting rate by the γ-rays and the counting rate by the γ-rays emitted from the internal contamination 21b are simultaneously acquired. Furthermore, a constant rate library that stores constants such as the detection efficiency according to the shape of the article 20, the surface area of the article 20, and the weight of the article 20 is provided in the counting rate calculation circuit 12, and the constants stored in this constant library are used as appropriate. It is also possible to calculate the surface contamination density and the activated radioactivity concentration of the article 20.

The flow of such arithmetic processing will be described with reference to the operation flow chart shown in FIG. That is, the radiation emitted from the article 20 is simultaneously measured by the thin plastic scintillator detector 1 and the thick NaI (Tl) scintillator detector 2 (S1), and based on the simultaneous measurement result,
The counting rate calculation circuit 12 acquires the β ray counting rate (S2) due to the surface contamination 21a and the γ ray counting rate (S3) due to the internal contamination 21b, respectively. Further, the counting rate calculation circuit 1
On the basis of these results, 2 performs calculation using constants such as the detection efficiency according to the shape of the article 20, the surface area of the article 20 and the weight of the article 20 from the constant library (S4), and the surface contamination density (S5) and Each of the activated radioactivity concentrations (S6) is acquired.

Next, the operation of the article radioactivity detecting apparatus according to the present embodiment configured as described above will be described.

That is, when the article 20 to be measured is placed at a predetermined position of the article radioactivity detecting apparatus according to the present embodiment, β rays and γ are emitted from the surface contamination 21a of the article 20.
When the radiation is internal contamination 21b, γ rays are emitted from the radiation to the article radioactivity detection device. In addition,
Even when β rays are emitted from the internal pollution 21b,
Since β rays have a weak penetrating power, they cannot penetrate the article 20, and only the γ rays are emitted from the internal contamination 21b toward the article radioactivity detection device.

Β released toward the article radioactivity detector
Rays and γ rays first reach the detection surface of the thin plastic scintillator detector 1, and among them, γ rays have a strong penetrating power, so most of them pass through the thin plastic scintillator detector 1 It reaches the detection surface of the NaI (Tl) scintillator detector 2. The scintillator included in the thin plastic scintillator detector 1 receives energy from these β rays and γ rays and emits fluorescence.

On the other hand, the β rays that have reached the detection surface of the thin plastic scintillator detector 1 are deprived of their energy here and their penetrating power is weakened, and do not reach the detection surface of the thick NaI (Tl) scintillator detector 2. Therefore, only the γ-ray reaches the detection surface of the thick NaI (Tl) scintillator detector 2, and the thick NaI (Tl) scintillator detector 2
Then, the γ-ray energy causes fluorescence to be emitted.

On the upper surface of each scintillator detector 1, 2,
A large number of fluorescent optical fibers 3 and 4 are arranged at a substantially constant pitch over almost the entire area. Since the fluorescent optical fibers 3 and 4 include a scintillator that emits fluorescence at a lower energy than the energy of fluorescence emitted from each scintillator detector 1 and 2, in the core 13, as shown in FIG. When the scintillator 14 included in the detectors 1 and 2 fluoresces, the scintillator 1 included in the core 13 is caused by the fluorescence energy.
5 fluoresces, and this light propagates through the core 13 to the end side.

Photomultiplier tubes 5 and 6 are connected to both ends of the fluorescent optical fibers 3 and 4, respectively. Several fluorescent optical fibers 3 and 4 are connected to the photomultiplier tubes 5 and 6, respectively. Then, the fluorescence propagated by the fluorescent optical fibers 3 and 4 is transferred to the photomultiplier tube 5,
6 is converted into an electric signal, and the simultaneous measurement circuit 7,
8 is output.

Since a high voltage is applied to the photomultiplier tubes 5 and 6, a signal including not only the electric signal S but also the noise signal N is output to the simultaneous measuring circuit 7. The noise signal N is removed by the simultaneous measurement circuit 7 using the simultaneous measurement method. As a result, only the electric signal S is extracted,
The result is output to the adder circuit 9.

In the adding circuit 9, the simultaneous measuring circuit 7 (# 1)
And the electric signal S output from the simultaneous measurement circuit 7 (# 2) is added, and the count rate as the addition result is output to the count rate calculation circuit 12. Also in the adder circuit 11,
Simultaneous measurement circuit 8 (# 1) and simultaneous measurement circuit 8 (# 2)
The electric signals S output from each are added, and the count rate as the addition result is output to the count rate calculation circuit 12.

In the counting rate calculation circuit 12, based on the counting rate output from the adding circuit 9 and the counting rate output from the adding circuit 11, β rays and γ rays emitted from the surface contamination 21a of the article 20, And the count rate from the γ-rays emitted from the internal contamination 21b of the article 20 is calculated.

Furthermore, the surface contamination density and the radioactive activity concentration of the article 20 can also be obtained by performing calculations using data such as the detection efficiency according to the shape of the article 20, the surface area of the article 20, and the weight of the article 20. .

As described above, in the article radioactivity detecting apparatus according to the present embodiment, the above-described operation causes
The internal radioactivity and the surface radioactivity of the article 20 to be measured can be separately measured at the same time. Γ-radioactivity can be separately measured for internal radioactivity, and both γ- and β-radioactivity can be separately measured for surface radioactivity.

As a result, not only the measurement time can be shortened, but also the surface contamination measurement and the internal radioactivity measurement, or the setting to another device depending on the radiation quality, becomes unnecessary. It is possible to significantly improve the measurement work efficiency.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIGS. 6 to 9.

That is, the article radioactivity detection system according to the present embodiment, as shown in FIG.
6f is provided on the six sides of the article 20 to be measured.

As shown in FIG. 7, the detecting section 16 is a portion formed by stacking the thin plastic scintillator detector 1, the fluorescent optical fiber 3, the thick NaI (Tl) scintillator detector 2 and the fluorescent optical fiber 4 shown in FIG. Equivalent to. Therefore, the detection units 16a to 16f shown in FIG.
1 includes photomultiplier tubes 5 and 6, simultaneous measurement circuits 7 and 8, adder circuits 9 and 11, and a count rate calculation circuit 12, as shown in FIG. Is omitted. As shown in the cross-sectional view of FIG. 8, this detection unit 16 is arranged with the surface on the thin plastic scintillator detector 1 side facing the surface of the article 20 to be measured.

When the radioactivity of the article 20 is measured, the article 2 is placed on the tray 18 on the conveyor 17 as shown in FIG.
0 is set and set in the operating range of the detector 16 (position where the detector 16 can approach). The article 2 is detected by the detection units 16a and 16b.
The upper and lower surfaces of 0 are measured by the detectors 16c and 16d on the left and right surfaces, and the front and rear surfaces by the detectors 16e and 16f. If the article 20 is long, the article 20 is moved and measured. When the measurement is completed, it is carried out from the place where the detector 16 is arranged by the conveyor 17.

The detector 16a located on the upper surface of the article 20,
The detection units 16c and 16d located on the left and right, the detection unit 16e located on the front surface, and the detection unit 16f located on the rear surface are
It is configured such that it can be moved by an elevating means (not shown) as shown by the arrow in FIG.

With the above-described structure, the article radioactivity detection system according to the present embodiment has the following effects in addition to the effects obtained in the first embodiment. be able to.

That is, since the detectors 16 are arranged on the top, bottom, left, right, and front of the article 20, the articles 20 having various shapes can be measured. In particular, article 2
The detector 16a located on the upper surface of 0 is the up-down direction, the detectors 16c and 16d located on the left and right are the left-right directions, the detector 16e located on the front and the detector 16 located on the rear.
Since f is movable in the vertical direction, the detection unit 16a,
By measuring while moving 16c, 16d, 16e, and 16f, even a long article 20 can be measured over the entire height direction.

Further, by comparing the measurement results measured by the detection units 16a to 16f, it is possible to determine not only the presence or absence of contamination but also the location of contamination.
Furthermore, it is also possible to evaluate the uneven distribution of radioactivity from the distribution of count rates calculated based on the measurement results of the detection units 16a to 16f.

Furthermore, a weight scale for measuring the weight of the article 20 and a shape measuring device for measuring the shape of the article 20 by using, for example, a laser beam are appropriately added, and the weight of the article 20 measured by the weight scale, By using the shape data of the article 20 measured by the shape measuring device, it is possible to calculate the radioactivity concentration and the radioactivity distribution.

The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such configurations. Within the scope of the technical idea of the invention as claimed in the claims, those skilled in the art can come up with various modifications and modifications, and the modifications and modifications are also within the technical scope of the present invention. Be understood to belong to.

[0064]

As described above, according to the present invention,
It is possible to realize both an article radioactivity detection device and an article radioactivity detection system capable of simultaneously measuring both the internal radioactivity and the surface radioactivity of an article to be measured and thereby improving the measurement work efficiency. it can.

[Brief description of drawings]

FIG. 1 is a configuration conceptual diagram showing an example of an article radioactivity detection device according to a first embodiment.

FIG. 2 is a schematic diagram for explaining the principle of light conversion by a fluorescent optical fiber.

FIG. 3 is a schematic diagram showing a signal waveform of an electric signal output from a photomultiplier tube to a simultaneous measurement circuit.

FIG. 4 is a count rate of β rays and γ rays emitted from an article by a thin plastic scintillator detector and thick Na
Schematic diagram for explaining the relationship with the count rate by the I (Tl) scintillator detector

FIG. 5 is an operation flow chart for explaining a step of calculating a surface contamination density or an activated radioactivity concentration based on a count rate.

FIG. 6 is a perspective view showing an arrangement example of detection units of the article radioactivity detection system according to the second embodiment.

FIG. 7 is a configuration conceptual diagram showing an example of each detection unit.

FIG. 8 is a sectional view of a detection unit.

FIG. 9 is a conceptual diagram of loading of articles at the time of measurement

FIG. 10 is a conceptual diagram of an article unloading monitor.

FIG. 11 is a perspective view of a radioactive waste discharge inspection device.

[Explanation of symbols]

1. Thin plastic scintillator detector 2. Thick NaI (Tl) scintillator detector 3,4 ... Fluorescent optical fiber 5, 6 ... Photomultiplier tube 7, 8 ... Simultaneous measurement circuit 9, 11 ... Adder circuit 12 ... Count rate calculation circuit 13 ... Core 14, 15 ... Scintillator 16 ... Detector 17 ... Conveyor 18 ... Tray 20, 25 ... Goods 21a ... Surface contamination 21b ... Internal pollution 26 ... Belt conveyor 27 ... Detector 28 ... Signal processing circuit 30 ... turntable 31 ... Ge detector 32 ... Collimator

Continued front page    (72) Inventor Eiji Ochiai             2-5-3 Marunouchi, Chiyoda-ku, Tokyo             Hishi Heavy Industries Ltd. (72) Inventor Katsumi Urayama             12 D, 622, Ishikawa, Funaishi, Tokai-mura, Naka-gun, Ibaraki Prefecture             Within Clear Development Co., Ltd. (72) Inventor Nobuyuki Imai             12 D, 622, Ishikawa, Funaishi, Tokai-mura, Naka-gun, Ibaraki Prefecture             Within Clear Development Co., Ltd. (72) Inventor Hideo Doi             12 D, 622, Ishikawa, Funaishi, Tokai-mura, Naka-gun, Ibaraki Prefecture             Within Clear Development Co., Ltd. F term (reference) 2G075 AA01 AA18 CA48 DA08 FA18                       FB07 FC14 GA15 GA16                 2G088 EE06 EE17 FF04 FF05 GG11                       GG15 GG18 JJ01 KK28 KK29

Claims (6)

[Claims] 1. A measurement surface is disposed on the side of an article to be measured, which is capable of capturing β rays emitted from the article and transmitting γ rays emitted from the article. With a detection part thickness capable of being detected, the counting rate by the β rays emitted from the surface of the article (K3), the counting rate by the γ rays emitted from the surface of the article (K1), and from the inside of the article. A first radiation detector that counts a total counting rate (P = K1 + K3 + K4) that is a total of counting rates (K4) of emitted γ rays; and detection of substantially the same size and shape as the detection surface of the first radiation detector. A detection surface of the first radiation detector and a non-article side surface of the detection surface of the first radiation detector, and the detection surface of the first radiation detector is placed so as to substantially match the outer shape of the detection surface of the first radiation detector. ,
The counting rate (K2) by the γ-rays emitted from the surface of the article has a detection portion thickness capable of capturing the γ-rays emitted from the article and transmitted through the first radiation detector and incident. ), And the total counting rate (Q = K2 +) of the counting rate (K5) by the γ rays emitted from the inside of the article.
A second radiation detector for counting K5), and a counting rate (K3) by β rays emitted from the surface of the article based on the counting rates counted by the first and second radiation detectors, Γ emitted from inside the article
An article radioactivity detection device comprising: a counting rate (K5) by a ray and a counting rate calculation means for obtaining a counting rate (K2) by a γ ray emitted from the surface of the article. 2. The article radioactivity detection device according to claim 1, wherein the counting rate calculation means counts gamma rays emitted from the surface and inside of the article by the second radiation detector. The ratio of the counting rate counted by the first radiation detector to the counting rate K (K = K1 / K2 = K4 / K
5) is used to determine the count rate (K3) by β rays emitted from the surface of the article according to K3 = P−Q * K, and specify the nuclide that emits β rays and γ rays from the surface of the article. Using a constant J (J = K1 / (K1 + K3)) determined by: K5 = Q-K3 * J / ((1-J) * K) An article radioactivity detection device, characterized in that a rate (K5) is obtained, and a counting rate (K2) by γ rays emitted from the surface of the article is obtained according to K2 = Q−K5. 3. The article radioactivity detection apparatus according to claim 1 or 2, wherein a plastic scintillator detector including a scintillator that emits fluorescence when receiving energy of radiation is applied as the first radiation detector. In addition, as the second radiation detector, NaI (Tl) scintillator detection including a NaI (Tl) scintillator whose thickness is thicker than that of the plastic scintillator radiation detector and emits fluorescence when receiving energy of radiation. An article radioactivity detector characterized by applying a container. 4. The article radioactivity detection device according to claim 3, wherein the plastic scintillator detector and the NaI (T
l) A scintillator which is disposed between the scintillator detector and emits fluorescence when receiving energy from the fluorescence emitted by the scintillator included in the plastic scintillator detector, and when the scintillator emits fluorescence, A first fluorescent optical fiber that propagates this fluorescence to the end side, and a NaI (Tl) included in the NaI (Tl) scintillator detector, which is arranged on the non-article side surface of the NaI (Tl) scintillator detector. ) A scintillator that emits fluorescence when receiving energy from the fluorescence emitted by the scintillator, and when the scintillator emits fluorescence, a second fluorescent optical fiber that propagates this fluorescence to the end side, and The first fluorescent optical fiber is provided at both ends of the first fluorescent optical fiber. A pair of first photomultiplier tubes for converting the fluorescence propagated by the electric signal to an electric signal and outputting the converted electric signal to the count rate calculating means as a count rate counted by the plastic scintillator detector; Two fluorescent optical fibers are provided at both ends of the fluorescent optical fiber, and the fluorescent light propagated by the second fluorescent optical fiber is converted into an electric signal.
An article radioactivity detecting apparatus further comprising a pair of second photomultiplier tubes for outputting to the counting rate calculation means as a counting rate counted by the aI (Tl) scintillator detector. 5. The article radioactivity detection device according to claim 3, wherein the plastic scintillator detector and the NaI (T
l) A scintillator which is disposed between the scintillator detector and emits fluorescence when receiving energy from the fluorescence emitted by the scintillator included in the plastic scintillator detector, and when the scintillator emits fluorescence, A first fluorescent optical fiber that propagates this fluorescence to the end side, and a NaI (Tl) included in the NaI (Tl) scintillator detector, which is arranged on the non-article side surface of the NaI (Tl) scintillator detector. ) A scintillator that emits fluorescence when receiving energy from the fluorescence emitted by the scintillator, and when the scintillator emits fluorescence, a second fluorescent optical fiber that propagates this fluorescence to the end side, and The first fluorescent optical fiber is provided at both ends of the first fluorescent optical fiber. A pair of first photomultiplier tubes for converting the fluorescent light propagated by the electric signal into an electric signal and outputting the converted electric signal; and a second fluorescent light provided at both ends of the second fluorescent optical fiber. The fluorescent light propagated by the optical fiber and converts the fluorescence into an electric signal, and outputs the converted electric signal. A pair of second photomultiplier tubes and an electric signal output from the pair of first photomultiplier tubes are provided. A first simultaneous measurement circuit that compares and outputs only the electrical signals generated at the same time to the count rate calculation means as the count rate counted by the first radiation detector; and the pair of second photoelectron multipliers. A second electrical signal output from the double tubes is compared, and only electrical signals generated at the same time are output to the counting rate computing means as a counting rate counted by the second radiation detector. An article radioactivity detection device, characterized in that a simultaneous measurement circuit is added. 6. A plurality of article radioactivity detection devices according to claim 1, which are provided around the article, and are measured by the article radioactivity detection devices provided around the article. An article activity detection system, characterized in that the activity distribution information of the article is acquired based on the counting rate.