JPH0812248B2 - Radiation monitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a radiation monitor apparatus for transporting an object to be inspected.

(Prior Art) One of radiation monitoring devices for determining whether or not an article is radioactively contaminated is an article transport type apparatus. This device places an article to be inspected on a roller conveyor and conveys it from one direction at a constant speed, and measures the radioactivity concentration within a predetermined range on the conveyance line on which this article is conveyed by a radioactivity concentration measuring instrument. The presence or absence of radioactive contamination is determined based on this measured value. In this apparatus, the processing amount of the inspection object per unit time is determined by the article conveying speed of the roller conveyor, and it can be said that the higher the processing amount, the higher the performance. The article conveying speed of the roller conveyor is determined by the detection limit concentration P [μ of the radioactive concentration measuring instrument.
c / cm ² ]. The simple formula of the detection limit concentration P is the following formula (1).

P = n _S × η (1) where n _S is the detection limit count rate [count / sec = cp
s] and η are the detection efficiencies of the radioactivity concentration measuring instrument [μc / cm ² cp
s ^-1 ]. The above n _S is expressed by the following equation (2).

n _S = N _S / t (2) where N _S is the 3σ value (σ: standard deviation) in the normal distribution, and t is the measurement time. Then, if the background count rate of the above N _S is nb [cps], Is represented by That is, the detection limit concentration P [μc / cm ² ]
Is a value detected with a reliability of 3σ with respect to the statistical fluctuation of the background count value, and the measurement time t that satisfies this value is determined by the equations (2) and (3). Therefore, if the length of the roller conveyor in the article conveying direction V [cm / sec] in the article conveying direction within the predetermined range measured by the radioactivity concentration measuring device is 1 [cm], it is determined by the following equation (4). To be done.

V = l / t (4) As an actual operation, an article as an object to be inspected is transported by a roller conveyor at a constant speed V from one direction, and the radioactivity concentration when it goes out of a predetermined range on the transportation line. If the value measured by the measuring instrument is the detection limit concentration P, that is, 3σ or more in the statistical fluctuation of the radioactive concentration count value with respect to the background, it is determined to be abnormal, the article is returned to the entrance side, and an alarm is emitted with a buzzer or lamp to emit the radiation. It is supposed to inform that there is no pollution.

(Problems to be Solved by the Invention) As described above, in the conventional device of this type, the determination level of the radioactivity concentration measuring device is set as the 3σ value in the statistical fluctuation of the background count value to determine the reliability of the determination of radioactive contamination. Was ensured, which determined the measurement time and the article transport speed of the roller conveyor.
Therefore, increasing the article conveying speed to improve the throughput leads to a decrease in reliability and is difficult to carry out.

Therefore, the present invention is intended to provide a radiation monitor device capable of increasing the article conveyance speed and improving the throughput without lowering the reliability of radioactive contamination determination.

[Structure of the Invention] (Means and Actions for Solving Problems) The present invention relates to a conveying means for reciprocatingly conveying an object to be inspected, and an object to be inspected in one direction by the conveying means. The radioactivity concentration measuring means for measuring the radioactivity concentration within a predetermined range and the radioactivity concentration measurement value by this measuring means are the first
And a re-conveying means for reversing the conveying direction of the object to be inspected by the conveying means, and radioactivity within the predetermined range when the inspected object is conveyed in the opposite direction by the re-conveying means. The radioactivity concentration re-measurement means for re-measuring the concentration, the measurement value addition means for adding the measurement value obtained by this re-measurement means and the predetermined value obtained by the measurement means, and the calculation value by this addition means And a warning means for warning that the object to be inspected is radioactively contaminated when the measured value is larger than the second set value which is larger than the first set value, and the object to be inspected is conveyed by the conveying means. If the measured value of the radioactivity concentration measured by the radioactivity concentration measurement means is increased in speed, it is determined that there is no radioactive contamination without re-determination based on the highly reliable second set value. To increase the processing amount A.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 and FIG. 2 are a side view and a top view showing the external configuration of the radiation monitoring apparatus in this embodiment. As shown in both figures, a roller conveyor 2 in which a plurality of rollers are arranged is provided on the apparatus main body 1, and a tray 4 on which an article 3 as an inspection object is placed is placed on the conveyor 2 in the A direction and the B direction. Move back and forth freely. The tray 4 has a net-like shape so that the radiation such as β rays emitted from the article 3 is prevented as much as possible. And as a radioactivity concentration measuring device for measuring the radioactivity concentration of the article 3,
A pair of plastic scintillation detectors (hereinafter abbreviated as plasticine) 5 and 6 are provided in the vertical direction with the roller conveyor 2 interposed therebetween, and the radioactivity concentration in the region formed between the plasticine 5 and 6 is measured. taking measurement. Further, an inlet sensor 7 and an outlet sensor 8 for detecting passage of the article 3 are provided on the inlet side and the outlet side of the region between the plasticins 5 and 6 when viewed from the direction A in the figure.

FIG. 3 is a control block diagram of the apparatus of this embodiment. The arithmetic control unit 11 including an arithmetic circuit, a program control circuit, etc., includes a pulse counter 12, an entrance sensor 7, an exit sensor 8, a start switch for counting pulse signals output from the plasticins 5 and 6 in response to radiation detection. An output device controller 17 for controlling the operation unit 14 provided with key switches such as 13, a buzzer 15 and an LED 16 for displaying "OK" indicating no radioactive contamination or "NG" indicating radioactive contamination, the roller conveyor A motor drive circuit 19 for controlling a motor 18 for driving the motor 2 and an alarm setting memory 20 are connected. The alarm setting memory 20 stores a 2σ value in the statistical fluctuation of the background count value with respect to the article transport speed twice that of the conventional apparatus and a 3σ value in the statistical fluctuation of the background count value with respect to the article transport speed of the conventional apparatus. They are set as alarm setting values AL1 and AL2, respectively. Further, the motor drive circuit 19 controls the motor 18 so that the article conveying speed of the roller conveyor 2 becomes twice as fast as that of the conventional apparatus.

Thus, the arithmetic control unit 11 is configured to operate according to the flowchart of FIG. That is, when the start switch 13 in the operation unit 14 is turned on with the article 3 as the inspection object placed on the tray 4,
The motor drive circuit 19 is controlled to drive the motor 18 in the normal direction.
Then, the roller conveyor 2 rotates, the article 3 moves in the direction A together with the tray 4, and the entrance sensor 7 detects the entry of the plastics 5 and 6 into the area. Therefore, the arithmetic control unit 11 responds to the ON signal of the entrance sensor 7 by the pulse counter.
12 is started, and the counting of the pulse signals output from the plastics 5 and 6 is started. Then, the article 3 on the roller conveyor 2
Moves in the direction of A and moves out of the area of plasticins 5 and 6. Therefore, the arithmetic control unit 11 turns the output of the outlet sensor 8 from ON to OFF.
It is determined that the article 3 which has been detected to have changed to the state from the areas of the plastics 5 and 6 has come off to the exit side, and the motor 18 is stopped and the counting operation by the pulse counter 12 is interrupted. Then, the count value n1 of the pulse counter 12 is read, and this n1 is the set value AL set in the alarm setting memory 20.
Determine if it is greater than 1. Then, if n1 is equal to or less than AL1, it is determined that there is no radioactive contamination, and "OK" is displayed by the LED 16, and the process ends.

On the other hand, if n1 is larger than AL1, the motor 18
Is reversely driven and the counting operation by the pulse counter 12 is restarted. Then, the article 3 moves in the B direction due to the reversal of the roller conveyor 2 and reenters the area of the plastics 5 and 6, and the pulse counter 12 adds the current count value to the previous count value n1. And the entrance sensor 7 is ON
Detecting the change from OFF to OFF, the article 3 is plastic
It is determined that the motor 18 is deviated from the area of (1) to the entrance side, and the motor 18 is stopped and the counting operation by the pulse counter 12 is stopped. Then, the count value n2 of the pulse counter 12 is read, and it is determined whether or not this n2 is larger than the set value AL2 set in the alarm setting memory 20. And n1 is A
If it is L2 or more, it is judged that there is radioactive contamination, the buzzer 15 is sounded, and "NG" is displayed by the LED 16, and an alarm is given and the process ends.

On the other hand, if the count value n2 is less than or equal to the alarm setting value AL2,
When it is judged that there is no radioactive contamination, "OK" is displayed by the LED 16, and the motor 18 is driven in the forward direction to convey the article 3 in the A direction,
The motor 18 is stopped by judging from the output change of the outlet sensor 8 that the article has come off the area of the plasticine 5 and 6 to the outlet side,
This process ends.

As described above, in the present embodiment, the conveyance speed of the article 3 is set to be twice as fast as that of the conventional apparatus, the direction A is fed to measure the radioactivity concentration, and the background count value for the speed is compared with the measured value. The presence or absence of radioactive contamination is determined by the 2σ value in the statistical fluctuation of. If it is determined that there is no radioactive contamination, the article 3 is moving to the exit side,
The measurement ends as it is. On the other hand, when it is determined that radioactive contamination is present, the article 3 is fed in the B direction to re-measure the radioactivity concentration, and this re-measured value is added to the measured value in the A-direction feed, and this addition is performed. The presence or absence of radioactive contamination is determined by the 3σ value in the statistical fluctuation of the background count value with respect to the speed of the conventional device with respect to the measured value.
When it is determined that there is radioactive contamination, the article 3 has been returned to the entrance side, so the buzzer 15 and the LED 16 issue an alarm and the measurement ends. On the other hand, when it is determined that there is no radioactive contamination, the article 3 is conveyed again to the exit side, and the process ends.

That is, in the present embodiment, the final judgment on the radioactive contamination is made by the measurement by the feed in the B direction, and this judgment is made by the 3σ value in the statistical fluctuation of the background count value with respect to the speed of the conventional apparatus, and therefore it is the same as the conventional one. Confidence is obtained.

In addition, if it is determined that there is no radioactive contamination by the determination in the direction A feed, the rough determination is performed on the precondition that it is determined that there is no radioactive contamination even in the determination of the 3σ value in the conventional apparatus. . In order to satisfy this precondition, it is required that the detection probability in the A-direction feed of this embodiment when the measured value equal to the 3σ value in the conventional device actually exists is equal to or higher than the detection probability of the conventional device. .

Now, the measurement time by the conventional speed is set to 20 seconds, and the population mean of the radioactive concentration count rate against the background is 10 [cps]
And At this time, the detection limit count rate corresponding to the 3σ value is calculated by the equation (2). Becomes Therefore, the rate conversion value of the 3σ value is 10 + 3.0 = 13.0 [cps].

On the other hand, when the speed is twice as fast as the conventional speed, that is, when the measurement time is 10 seconds, the detection limit count rate corresponding to the 2σ value is calculated by the equation (2). Becomes Therefore, the rate conversion value of the 2σ value is 10 + 2.83 = 12.83 [cps].

Therefore, the 10-second 2σ value converted rate is 20
Since it is smaller than the 3σ rate converted value of the second counting, the radioactivity concentration at the same level as the 3σ rate converted value of the 20 second counting is detected with a higher probability by the 2σ value of the 10 second counting. become. Therefore, the above-mentioned prerequisite is satisfied, and 2σ
The reliability of the determination based on the value that there is no radioactive contamination is comparable to the conventional determination using the 3σ value.

On the other hand, when it is determined that there is radioactive contamination in the 2σ value determination by feeding in the A direction of the present embodiment, the probability that this determination is incorrect is about 2.3 times higher than that in the 3σ value determination. That is,
One out of every 40 measurements made an erroneous determination. At this time, the B-direction feed was carried out, and it was judged that there was no radioactivity concentration with the same reliability as the conventional equipment, and the A-direction feed was performed again. Will be transported to the side. Therefore, about 5% of the entire operation is a wasteful operation due to an erroneous determination.

However, since the article conveying speed is twice as fast as the conventional one, the total processing amount is increased by 1.9 times as compared with the conventional apparatus by the following equation (5).

2 × (1-0.05) = 1.9 (5) As described above, according to the present embodiment, the processing amount can be improved by about 1.9 times as compared with the conventional device without lowering the reliability. . Actually, most of the inspected objects do not have radioactive contamination, and the 1.9 times improvement in throughput can be expected almost as it is. Further, since the determination of the presence of radioactive contamination is made in a state where the article 3 has returned to the entrance side, it is not necessary to return the article with radioactive contamination to the entrance side as in the conventional case, and in this respect also, the throughput can be improved. obtain.

The present invention is not limited to the above embodiment. For example, the article conveyance speed may be twice as fast as that in the present embodiment, the detection limit concentration at the first measurement may be 1σ value in the statistical fluctuation of the radiation concentration count value with respect to the background, and there may be no radioactive contamination. For example, if this point is the final judgment, if there is radioactive contamination, the second measurement is carried out to judge by the 2σ value. If there is no radioactive contamination, this point is the final judgment and if there is radioactive contamination, If the third measurement is further performed to make the final determination based on the 3σ value, the processing amount can be further improved. Further, in this case, when the article 3 is stopped in the area of the plasticins 5 and 6 and the second and third measurements are performed, the radioactive contamination in the second measurement is not detected and when the third measurement is not performed. Since the feed amount of the article is reduced when the product is present, the throughput can be further improved. However, control of the roller conveyor 2 may be complicated in order to realize these methods. In addition, it goes without saying that various modifications can be made without departing from the scope of the present invention.

[Effects of the Invention] As described in detail above, according to the present invention, it is possible to provide a radiation monitor device capable of increasing the article conveyance speed and improving the throughput without lowering the reliability of radioactive contamination determination. .

[Brief description of drawings]

1 to 4 are views showing an embodiment of the present invention. FIGS. 1 and 2 are side and top views showing an external configuration of a radiation monitor apparatus, and FIG. 3 is a view showing the apparatus. The control block diagram, FIG. 4 is a flow chart showing the operation of the arithmetic control unit. 2 ... Roller conveyor, 3 ... Goods, 5,6 ... Plasin, 11 ... Arithmetic control unit, 15 ... Buzzer, 16 ... LED, 18
…… Motor, 20 …… Alarm setting value memory.

Claims (1)

[Claims] 1. Conveying means for reciprocating an object to be inspected, and radioactivity concentration measuring means for measuring the radioactivity concentration within a predetermined range when the object is conveyed in one direction by the conveying means. , The first measured value of radioactivity concentration by this measuring means
Is greater than the set value of the re-conveying means for reversing the conveying direction of the object to be inspected by the conveying means, and the radioactivity within the predetermined range when the object to be inspected is conveyed in the opposite direction by the re-conveying means. The radioactivity concentration re-measurement means for re-measuring the concentration, the measurement value addition means for adding the measurement value obtained by this re-measurement means and the measurement value obtained by the measurement means, and the calculation value by this addition means A radiation monitor device, comprising: a warning unit that warns that the inspected object is radioactively contaminated when the measured value is larger than the second set value which is larger than the first set value. .