JP5255736B1 - Radioactive contamination inspection device, inspection method and inspection program - Google Patents

Abstract

Provided is a radioactive contamination inspection technique having a determination accuracy independent of the distance between a radiation sensor and a subject surface.
The inspection apparatus for radioactive contamination has a radiation dose rate detection signal S (S ₁ , S ₁ , S ₂ , 21 _n ) by a plurality of radiation sensors 21 (21 ₁ , 21 ₂ ,. S ₂ ,... S _n ), a section period T (= L / V) based on the length in the moving direction of the unit section partitioning the surface of the subject 11 and the velocity information V of the subject 11. ), A calculation unit 34 for calculating the addition average value A (A ₁ , A ₂ ,... A _n ) of the detection signal S for each division period T, and the movement direction or the vertical direction. A derivation unit 35 for deriving the determination threshold value D based on the ratio of the addition average values indicated by the two unit sections arranged, and whether or not to output the warning signal W based on the addition average value A and the determination threshold value D The determination part 36 to be provided is provided.

Description

  The present invention relates to a technique for examining whether or not a subject is contaminated with radioactivity.

In each country, export and import safety management systems have been incorporating radiation measurement into cargo inspection containers.
The standard method for inspecting the container for radioactive contamination is to scan the portable survey meter at a distance of about 2 cm from the surface of the container by the operator.

However, in the radioactive contamination inspection using this survey meter, since the processing speed is slow, it is difficult to inspect all of the containers to be inspected, and there is a situation in which it is necessary to rely on a sampling inspection.
In view of this, for the purpose of inspecting the presence or absence of radioactive contamination of the container, a method has been proposed in which the container is sequentially moved to the vicinity of the stationary radiation detector for measurement (for example, Patent Document 1).

JP 2011-257400 A

However, according to the method using a stationary radiation detector, it is necessary to provide a distance of about several tens of centimeters between the container passing therethrough and the radiation detector.
In consideration of point contamination on the container surface, it is known that the attenuation rate of the radiation dose rate is proportional to the square of the distance to the radiation detector.
For this reason, in the method using a stationary radiation detector, it is necessary to set the threshold of the radiation dose rate, which serves as a reference for contamination determination, smaller than in the method using a survey meter.

On the other hand, when a wide range of contamination on the container surface is taken into account, in the method using a stationary radiation detector, radiation is incident on this detector from a wide range as compared with the method using a survey meter.
For this reason, there is a concern that the stationary radiation detector detects the radiation dose rate exceeding the threshold value and makes a black determination even if the survey meter is low-concentration contamination that is determined as white.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a radiological contamination inspection technique having a determination accuracy that does not depend on the distance between the radiation sensor and the surface of the subject.

  In the radioactive contamination inspection apparatus, a receiving unit that receives detection signals of a radiation dose rate by a plurality of radiation sensors arranged in a direction perpendicular to a moving direction of a subject, and a unit section that partitions the surface of the subject A setting unit that sets a division period based on the length in the movement direction and the velocity information of the subject, a calculation unit that calculates an addition average value of the detection signals for each division period, and the movement direction or the vertical direction A deriving unit for deriving a determination threshold value based on a ratio of the addition average values indicated by the two unit sections arranged in the block, and determining whether to output an alarm signal based on the addition average value and the determination threshold value And a determination unit.

  The present invention provides an inspection technique for radioactive contamination having a determination accuracy that does not depend on the distance between the radiation sensor and the subject surface.

(A) External view showing an embodiment of an inspection apparatus for radioactive contamination according to the present invention, (B) External view showing an arrangement of radiation sensors applied to this embodiment, (C) Other arrangement of radiation sensors FIG. The functional block diagram of the inspection apparatus of the radioactive contamination which concerns on this embodiment. (A) The figure which shows the surface of the subject whose local range was radioactively contaminated with high concentration, (B) The graph which shows the result of having measured the radiation dose rate with the survey meter. (A) The figure which shows the surface of the test object in which the wide range was radioactively contaminated by low concentration, (B) The graph which shows the result of having measured the radiation dose rate with the survey meter. (A) The figure which applied the inspection apparatus of the radioactive contamination which concerns on this embodiment, measured the test subject which the local range was radioactively contaminated to high concentration, and displayed the surface distribution of the radiation dose rate as luminance. The graph which shows distribution of the radiation dose rate in the moving direction of a sample. (A) The figure which applied the inspection apparatus of the radioactive contamination which concerns on this embodiment, measured the object which was radioactively contaminated to the low density | concentration in the wide range, and the surface display of the radiation dose rate was displayed as a brightness | luminance, (B) Subject The graph which shows distribution of the radiation dose rate in the moving direction of.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
As shown in FIG. 1 (A), the radioactive contamination inspection apparatus 10 according to the embodiment has a pair of detections installed at intervals at which a trailer loaded with a container 11 (subject 11) can travel and pass. Units 20, 20, a data processing unit 30 that processes data signals transmitted from the detection unit 20, an input unit 12 for the operator 14 to input conditions and the like to the data processing unit 30, and data to the operator 14 And a display unit 13 for displaying the processing result of the processing unit 30.

As shown in FIG. 1B, a plurality of radiation sensors 21 (21 ₁ , 21 ₂ ,... 21 _n ) are arranged in the detection unit 20 in the direction Y perpendicular to the moving direction X of the subject 11. . The detection unit 20 is further provided with a speed sensor 22.
The detection unit 20 is installed on the left and right side surfaces of the container 11 as close as possible to the extent that they are not in direct contact.

Each of the plurality of radiation sensors 21 in FIG. 1B shows a case where the detection sensitivity is the same for uniformly incident radiation.
As another example shown in FIG. 1C, the detection unit 20 may be provided with a plurality of radiation sensors 21 (21 ₁ , 21 ₂ , 21 ₃ ) having different detection sensitivities to radiation. included.

  Further, as another configuration example (not shown) of the detection unit 20, the plurality of arranged radiation sensors 21 are classified into several groups grouped together by adjacent ones, and the radiation of the subject 11 is set as a unit. Sometimes the quantity rate is detected.

As shown in FIG. 2 (see FIG. 1 as appropriate), the data processing unit 30 of the radioactive contamination inspection apparatus according to this embodiment includes a plurality of units arranged in a direction Y perpendicular to the moving direction X of the subject 11. A unit that partitions the surface of the subject 11 and a receiving unit 31 that receives a detection signal S (S ₁ , S ₂ ,... S _n ) of a radiation dose rate from the radiation sensor 21 (21 ₁ , 21 ₂ ,... 21 _n ). A setting unit 33 that sets a section period T (= L / V) based on the length L of the section 15 (FIG. 5A) in the movement direction X and the velocity information V of the subject 11, and the section period T A calculation unit 34 for calculating the addition average value A (A ₁ , A ₂ ,... A _n ) of the detection signal S and two unit sections 15 (15 _n ^m−1) arranged in the movement direction X or the vertical direction Y. When 15 _n ^m or 15 ^{_n-1 m} and 15 _n ^m) the ratio of the average value shown by FIG. 5 or FIG. 6] A deriving unit 35 for deriving the decision threshold D based on ^{_{A n m-1 / A n}} m or ^{_{A n-1 m / A n}} m), a warning signal W on the basis of the average value A and the determination threshold value D And a determination unit 36 for determining whether or not to output.

As the radiation sensor 21 (21 ₁ , 21 ₂ ,... 21 _n ), a method capable of measuring at least γ rays, such as an ionization chamber type, a GM type, a semiconductor type, a scintillator type, or the like is employed.
A plurality of radiation sensors 21 (21 ₁ , 21 ₂ ,... 21 _n ) arranged in the vertical direction Y are moved by a trailer loaded with the container 11 (the subject 11) traveling in the moving direction X at a constant speed. 11 surfaces will be scanned.

Each of the radiation dose rate detection signals S (S ₁ , S ₂ ,... S _n ) output from the radiation sensors 21 (21 ₁ , 21 ₂ ,... 21 _n ) is subjected to data processing via a cable. The signal is received by the receiving unit 31 of the unit 30.

The speed information V of the container 11 in the movement direction X is measured by the speed sensor 22 and the data signal is acquired by the acquisition unit 32.
When the container 11 is moving at a controlled known speed, the speed sensor 22 is unnecessary and the speed information V is a setting condition input from the input unit 12.
In the present embodiment, the case where the radiation sensor 21 is fixed and the subject 11 moves is illustrated, but conversely, the subject 11 may be fixed and the radiation sensor 21 may be moved.

The detection of the radiation dose rate on the surface of the container 11 is performed for each unit section 15 in which the surface is partitioned in a mesh shape, as shown in FIG.
The length X in the X direction and the length H in the Y direction of the unit section 15 are setting conditions input from the input unit 12.
Among these, the length H in the Y direction of the unit section 15 is set from the interval between the radiation sensors 21 (21 ₁ , 21 ₂ ,... 21 _n ) arranged.
As described in another configuration example (not shown) of the detection unit 20, when the plurality of radiation sensors 21 are classified into groups, the length H in the Y direction of the unit section 15 is set with this group as a unit. .

Then, the setting unit 33 sets the section period T (= L / V) based on the length L in the X direction of the unit section 15 and the velocity information V of the subject 11.
Calculation unit 34, the operation for each of the received detection signal _{S (S 1, S 2,} ... S n), for each partition period T set, average value _{A (A 1, A 2,} ... A n) the To do.
Thus arithmetic unit 34, the radiation sensor _{21 (21 1, 21 2,} ... 21 n) average value of the detection signal S corresponding to each of the _{A (A 1, A 2,} ... A n) a partition period T Output at intervals.
Here, the average value A _n that are discretely output at intervals of the partition period T, A _n ^m-1, A _n ^m, show ... as.

FIG. 3 (A) shows the surface of the container 11 where the local area is radioactively contaminated with high concentration, and FIG. 4 (A) shows the surface of the container 11 where the wide area is radioactively contaminated with low concentration. .
The graph of FIG. 3 (B) shows the result of measuring the radiation dose rate of the high-concentration local contamination of FIG. 3 (A) with a survey meter as a comparative example.
The graph of FIG. 4 (B) shows the result of measuring the radiation dose rate of the low-concentration wide-range contamination of FIG. 4 (A) with a survey meter as a comparative example.

The radioactive contamination measurement by the survey meter scans (within about 2 cm) without leaving a large gap with the surface of the container 11, so the radiation dose corresponding to the contamination concentration is not dependent on the size of the contamination range. The rate can be detected.
For this reason, in the radioactive contamination measurement by the survey meter, determination of black determination in the case of FIG. 3 and white determination in the case of FIG. 4 is made using a fixed threshold value.

  On the other hand, FIG. 5 shows the result of measuring the radiation dose rate of high-concentration local contamination (in the case of FIG. 3A) in this embodiment, and FIG. 6 shows the radiation dose rate (Fig. 6) of low-concentration wide-range contamination in this embodiment. 4 (A)) is measured.

Since the detection unit 20 of the radioactive contamination inspection apparatus 10 needs to be arranged at a distance (several tens of centimeters) from the surface of the container 11, the radiation emitted from the contaminated part is compared with that by a survey meter. Thus, it will be detected after attenuation.
For this reason, in the radioactive contamination measurement in this embodiment, it is necessary to estimate the threshold value D lower than in the case of using a survey meter.

Furthermore, in this embodiment, due to the increased distance between the detection unit 20 and the surface of the container 11, the radiation emitted from the contaminated portion is detected after being diffused as compared with the case using the survey meter. Will be.
For this reason, the radiation sensor 21 detects not only the contaminated part immediately below but also the radiation emitted from the surrounding contaminated part.
Therefore, the detection value (FIG. 5B) of the radiation dose rate of the high-concentration local contamination (FIG. 3A) and the detection value of the radiation dose rate of the low-concentration wide-range contamination (FIG. 4A) (FIG. 6). With (B)), a significant difference may not be obtained when only peak values are compared.

Therefore, the deriving unit 35 (FIG. 2), 5 and 6, the ratio of the average value indicated by the two unit sections 15 (15 _n ^m and 15 _n ^m-1) arranged in the X direction ( A determination threshold value D is derived based on ₍ A _n ^m / A _n ^m-1 ).
More specifically, a correlation table is created between the pattern of radioactive contamination constructed in a simulated manner and the ratio of the addition average value derived from this radioactive contamination experimentally or by simulation analysis.

Further, a radioactive contamination pattern having a concentration at which a threshold value is counted by the measurement by the survey meter is assumed, and the radiation dose rate measured in the present embodiment for the assumed radioactive contamination pattern is set as the determination threshold value D.
That is, if the lead ratio of average value indicated by the two unit sections 15 (15 _n ^m and ^{_{15 n m-1) (A}} n m / A n m-1) is the pattern of radioactive contamination is estimated is not determined threshold D _n ^m is derived from the pattern of the estimated radioactive contamination.

The holding unit 39 (FIG. 2) holds a table indicating the correlation between the ratio of the average addition value in the X direction and the determination threshold value D, and when the addition average value _An ^m is calculated, the ratio with the previous value is calculated. A determination threshold value D _n ^m corresponding to (A _n ^m / A _n ^m-1 ) is presented.
Then, the determination unit 36 performs a white determination if the addition average value A _n ^m is less than the determination threshold D _n ^m , and performs a black determination if the addition average value A _n ^m is greater than or equal to the determination threshold D _n ^m to notify the alarm output unit 16 of an alarm signal. W is output.

In the above description, the arrangement in the X direction has been examined. However, the deriving unit 35 calculates the ratio (A _n ) of the addition average values indicated by the two unit sections 15 (15 _n ^m and 15 _n-1 ^m ) arranged in the Y direction. it is also possible to derive a determination threshold value D on the basis of the ^{_{m / a n-1 m)}} .
In this case, the holding unit 39 holds a table indicating a correlation between the ratio of the average value of the unit sections 15 in the Y direction and the determination threshold value D.
Thus, by examining the arrangement in the Y direction, it is possible to determine whether or not to output the warning signal W in a shorter time.

In the above description, the determination threshold value D is derived based on the correlation table. However, the determination threshold value D may be derived by calculation using a function having the ratio of the addition average value (A _n ^m / A _n-1 ^m ) as a variable. .

The display signal output unit 42 displays a luminance signal corresponding to the addition average value A in order to display the image shown in FIGS. 5A and 6A on the display unit 13. B is output.
Further, the display signal output unit 42 displays the addition average value A indicated by a plurality of unit sections arranged in one direction in order to cause the display unit 13 to display the graphs as shown in FIGS. 5B and 6B. A graph signal G indicating the distribution and a signal of the determination threshold value D overwritten on the distribution are output.

Next, as shown in FIG. 1C, when a plurality of radiation sensors 21 (21 ₁ , 21 ₂ , 21 ₃ ) having different detection sensitivities are installed, two unit sections arranged in the Y direction Consider a case in which the determination threshold value D is derived based on the ratio of the addition average value indicated by 15.
The detection sensitivity of the radiation sensor 21 is proportional to the incident area of radiation, and may be different based on differences in sensor specifications.

The correction processing unit 38 multiplies each detection signal S (S ₁ , S ₂ , S ₃ ) by an appropriate coefficient and depends on the difference in detection sensitivity of the radiation sensor 21 (21 ₁ , 21 ₂ , 21 ₃ ). The deviation of the added average value A (A ₁ , A ₂ , A ₃ ) is corrected.
These coefficients can be obtained from reference data stored in the storage unit 37 by measuring a uniform subject 11 with a known contamination concentration.
As this reference data, background data that is the detection signal S received in a blank state excluding the subject 11 can be used.

  According to the radioactive contamination inspection apparatus of at least one embodiment described above, the radiation dose rate on the surface of the subject is detected separately in unit sections, and thus does not depend on the distance between the radiation sensor and the subject surface. It becomes possible to inspect radioactive contamination with judgment accuracy.

Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, changes, and combinations can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.
The components of the radioactive contamination inspection apparatus can also be realized by a processor of a computer, and can be operated by a radioactive contamination inspection program.

DESCRIPTION OF SYMBOLS 10 ... Radioactive contamination inspection apparatus, 11 ... Container (subject), 12 ... Input part, 13 ... Display part, 14 ... Operator, 15 ... Unit division, 16 ... Alarm output part, 20 ... Detection unit, 21 ... Radiation Sensor 22 ... speed sensor 30 ... data processing unit 31 ... detection signal reception unit 32 ... speed information acquisition unit 33 ... compartment cycle setting unit (setting unit) 34 ... addition average value calculation unit (calculation unit) 35: Determination threshold deriving unit (derivation unit), 36: Determination unit, 37 ... Reference data storage unit (storage unit), 38 ... Correction processing unit, 39 ... Correlation table storage unit (storage unit), 42 ... Display signal output unit , A (A _n , A _n ^m−1 , A _n ^m , A _n−1 ^m )... Addition average value, B... Luminance signal, D... Judgment threshold, G. L, length of unit section in X direction, S (S ₁ , S ₂ ,... S _n ) ... detection Signal, T ... partition period, V ... speed information, W ... alarm signal.

Claims (10)

A receiving unit for receiving detection signals of radiation dose rates by a plurality of radiation sensors arranged in a direction perpendicular to the moving direction of the subject;
A setting unit that sets a division cycle based on the length in the moving direction of the unit section that partitions the surface of the subject and the velocity information of the subject;
An arithmetic unit that calculates an average value of the detection signals for each partition period;
A derivation unit for deriving a determination threshold based on a ratio of the addition average values indicated by the two unit sections arranged in the movement direction or the vertical direction;
A radiological contamination inspection apparatus comprising: a determination unit that determines whether or not to output an alarm signal based on the addition average value and the determination threshold value.   The radioactive contamination of claim 1, further comprising a holding unit that holds a table indicating a correlation between the ratio of the addition average value in the moving direction or the vertical direction in which the unit sections are arranged and the determination threshold value. Inspection device.   3. The radioactive contamination according to claim 1, further comprising: a correction processing unit that corrects a deviation of the addition average value depending on the differences when detection sensitivities of the plurality of radiation sensors are different. Inspection equipment.   The radiological contamination inspection apparatus according to claim 3, wherein the correction is performed based on background data that is the detection signal received in a blank state excluding the subject.   The radioactive contamination inspection apparatus according to claim 1, further comprising an acquisition unit configured to acquire a measurement signal of a speed sensor as the speed information.   The radioactive contamination inspection apparatus according to claim 1, further comprising a display signal output unit that outputs a luminance signal for displaying the unit section at a luminance corresponding to the addition average value. . The display signal output unit
A graph signal indicating a distribution of the addition average value indicated by the unit sections arranged in a plurality in one direction;
The radiological contamination inspection apparatus according to claim 6, wherein the determination threshold signal that is overwritten and displayed on the distribution is output. The plurality of radiation sensors are classified into several groups grouped together by adjacent ones,
The radiological contamination inspection apparatus according to claim 1, wherein a length of the unit section in the vertical direction is set in units of the group. Receiving a radiation dose rate detection signal from a plurality of radiation sensors arranged in a direction perpendicular to the moving direction of the subject;
Setting a partition period based on the length in the moving direction of the unit section partitioning the surface of the subject and the velocity information of the subject;
Calculating an average addition value of the detection signals for each partition period;
Deriving a determination threshold based on a ratio of the addition average values indicated by the two unit sections arranged in the moving direction or the vertical direction;
And a step of determining whether or not to output an alarm signal based on the addition average value and the determination threshold value. On the computer,
Receiving a radiation dose rate detection signal from a plurality of radiation sensors arranged in a direction perpendicular to the moving direction of the subject;
Setting a section period based on the length in the moving direction of the unit section partitioning the surface of the subject and the velocity information of the subject;
Calculating an addition average value of the detection signals for each partition period;
Deriving a determination threshold based on a ratio of the addition average values indicated by the two unit sections arranged in the movement direction or the vertical direction;
An inspection program for radioactive contamination, wherein a step of determining whether or not to output an alarm signal based on the addition average value and the determination threshold value is executed.

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