JP3310030B2 - Radiation monitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation monitor for detecting radioactive contamination of articles, clothes, and other solid objects used in a nuclear facility or the like. The present invention relates to a radiation monitor applicable to an apparatus for measuring radioactivity while transporting a measurement object on a conveyor.

[0002]

2. Description of the Related Art FIG. 6 shows a conventional article discharge monitor. Reference numeral 1 shown in the figure is a conveyor. The conveyor 1 is provided with a motor 2 for driving the conveyor. The radiation detector 3 faces the conveyor surface.
And an object detection sensor 4 are provided. The outputs of the radiation detector 3 and the object detection sensor 4 are input to the data processing device 5, respectively.

[0005] The article carry-out monitor operates according to the flowchart shown in FIG.

That is, the data processing device 5 counts a pulse signal input from the radiation detector 3 based on the output of the measurement object detection sensor 4 when the object M is not in the effective detector L of the radiation detector 3. To measure the background BG. Then, when the device under test M placed on the conveyor 1 driven at a fixed speed V set in advance by the motor 2 comes to the validity detection unit L, it counts for a preset time,
The count value, the count time T and the background BG
Then, the contamination of the object M is determined. The result of the determination is output to a display device (not shown) or the like.

[0005] In the conventional radiation monitor including the above-mentioned article discharge monitor, the conveyor speed and the counting time are fixed values set in advance. This fixed value is determined as follows.

First, the radiation monitor has a contamination control level (range) determined according to the specifications. In order to maintain a certain statistical error, only radiation from the radiation source of a predetermined measurement object M is counted. Count value (hereinafter referred to as "true count value")
Must be measured within the above contamination control level.
In the present specification, the contamination management level refers to a value obtained by multiplying the detection efficiency of the radiation detector by a statistical error.

On the other hand, since the count value actually counted by the data processing unit 5 (hereinafter referred to as “apparent count value”) includes the background, the background is removed from the apparent count value. It is necessary to put the counted value within the range of the pollution control level. However, since the background fluctuates, even if the apparent count value is within the range of the contamination control level, the true count value may not be within the range of the contamination control level.

Therefore, the conventional radiation monitor takes into account the expected upper limit of the background and sets the contamination count time T so that the true count value always falls within the range of the contamination control level.
Was set. That is, the background is high,
Even if the apparent count value is high, a sufficiently long contamination count time T is set so that the actual statistical error does not increase. Also, the conveyor speed has been set to a low speed corresponding to such a long contamination counting time T.

[0009]

As described above, in the conventional radiation monitor, the contamination counting time T is set in accordance with the expected upper limit of the background, so that the background before the background reaches the expected upper limit. In the state (1), the contamination counting time T becomes unnecessarily long, which causes a reduction in processing capacity.

[0010]

In order to achieve the above object, the present invention provides an object to be measured placed on a conveyor, conveyed, and emitted from the object to be measured by a radiation detector arranged opposite to the conveyor. In a radiation monitor that counts radiation for a predetermined time and determines a contamination state of the object from the count value and the contamination counting time , a background measurement unit that measures a background level at an installation location of the radiation detector, From the measured value measured by the background measuring means and the predetermined contamination control level, the conveyor speed is adjusted according to the contamination counting time that brings the true count value not including the background into the range of the contamination control level. Speed control means for controlling, and a short time for counting the pulse signal output from the radiation detector for a short time
A counting unit; and a high-speed measurement determining unit that outputs a high-speed transport command to the speed control unit when the short-time count value is greater than a predetermined count value .

[0011]

According to the radiation monitor of the action described above of the present invention configured as the measured value measured by the background measurement means are inputted to the counting time determining means, the counting time determined hand
Contamination meter from the background measurement and the contamination control level stage add true count value in the range of the pollution control level
Several hours are required. The contamination counting time is input to the speed control means, and the speed of the conveyor is controlled according to the contamination counting time . Accordingly, the conveyor speed is appropriately updated according to the increase and decrease of the background. Further, the pulse signal output from the radiation detector is counted for a short time by the short time counting unit, and the short time counting value is input to the high speed measurement determining unit. When the short time counting value is larger than the predetermined counting value, The high-speed measurement determining unit outputs a high-speed transport command to the speed control unit. Therefore, when the count value obtained by the short-time counting before the main measurement is larger than the predetermined value and the radiation level is high, the conveyor speed can be increased, and the measurement time can be shortened.

[0012]

According to the radiation monitor of the present invention configured as described above, the measurement value measured by the background measurement means is input to the counting time determination means, and the background measurement value and the contamination are measured by the counting time determination means. From the control level, a contamination counting time for bringing a true count value into the range of the contamination control level is obtained. The contamination counting time is input to the speed control means, and the speed of the conveyor is controlled according to the contamination counting time. Accordingly, the conveyor speed is appropriately updated according to the increase and decrease of the background.

[0013]

Embodiments of the present invention will be described below.

FIG. 1 shows a schematic configuration of an article unloading monitor according to an embodiment of the present invention, and FIG. 2 shows functional blocks of main parts of the article unloading monitor.

The article unloading monitor according to the present embodiment is provided with an object M to be measured.
Conveyor 1, a motor 2 for driving the conveyor 1, a radiation detector 3 disposed opposite the conveyor 1, a measurement object detection sensor 4, a data processing unit 10 having an automatic setting function of a contamination counting time, and a motor 2 A speed control unit 11 for controlling the rotation speed is provided.

The data processing unit 10 includes a count value calculation unit 12 for calculating a true count value, a contamination determination unit 13 for determining a contamination from the true count value obtained by the count value calculation unit 12, and a BG for counting the background. The counting unit 14 includes a counting time determination unit 15 that calculates an optimal contamination counting time from a background count value (hereinafter, referred to as a “BG count value”) obtained by the BG counting unit 14.

The count value calculator 12 counts the pulse signal input from the radiation detector 3 over the contamination count time set by the count time determiner 15 to obtain an apparent count value.
The operation is performed so as to obtain the true count value by dividing the apparent count value by the BG count value taken in from the BG counting unit 14.

The BG counting unit 14 counts a pulse signal input from the radiation detector 3 when the input signal from the object detection sensor 4 indicates that there is no portion to be measured M in the detection effective portion on the conveyor. The BG count value is always measured.

The count value calculating section 12 and the BG counting section 14
Means that counting is performed using the same counter in a time-division manner.

The counting time determining section 15 has a function of constantly changing the contamination counting time of the counting value calculating section 12 to an optimum time according to the change of the BG value.

Here, the principle of determining the optimum contamination counting time t in the counting time determination unit 15 will be described.

When radiation is counted, a statistical error occurs. This statistical error is the minimum detectable level. When the system is configured so that the minimum detectable level matches the pollution control level, the following relational expression holds.

Contamination control level = detection efficiency × statistical error A = a × K / 2 [K / t + {(K / t) ² +4 NB (1 / t + 1 / Tb)} ^1/2 ] (1) where t Is the contamination count time, A is the contamination management level, a is the detection efficiency, K is the reliability, nb is the BG count rate, and Tb is the BG count time.

When the above equation is solved for the contamination counting time t, the following is obtained.

T = (4nb−4A / a) / {(2A / aK) ² −4nb / Tb} (2) Each symbol A, a, K, nb, Tb in the above equation can be treated as a constant. By taking the GB count value from the GB counting unit 14 and performing the calculation of the above equation (2), the minimum contamination count time t within a range not exceeding the contamination management level is obtained.

Each time the BG count value input from the BG count unit 14 changes, the count time determination unit 15 determines the contamination count time t, and outputs it to the count value calculation unit 12 and the speed control unit 11. are doing.

The speed controller 11 determines the transport speed V of the conveyor 1 from the following equation, where L is the effective measurement dimension of the radiation detector 3 and V is the transport speed of the conveyor 1.

V = L / t (3) The motor 2 is controlled so that the conveyor speed of the conveyor 1 becomes V calculated.

The present embodiment configured as described above is similar to that of FIG.
It operates according to the flowchart shown in FIG. That is, the outputs of the radiation detector 3 and the measurement unit detection sensor 4 are input to the BG counting unit 14 and the count value calculation unit 12, respectively.

The BG counting section 14 counts the pulse signal from the radiation detector 3 for a predetermined time Tb when it determines from the input signal from the object sensor 4 that there is no measured section M in the detection effective section on the conveyor. The BG count value is measured using
The G count value is output to the count value calculation unit 12 and the count time determination unit 15.

When the BG value is input from the BG counting unit 14, the counting time determining unit 15 determines the minimum contamination time among the counting times that can put the true count value within the range of the contamination management level based on the above equation (2). The counting time t is calculated. The contamination count time t obtained here is calculated by the count value calculation unit 12 and the speed control unit 1.
1 is output.

The speed control unit 11 includes a counting time determination unit 15
When the contamination counting time t is input from the above, the transport speed V of the conveyor 1 is obtained based on the above equation (3), and the motor 2 is controlled to adjust the transport speed V of the conveyor 1.

As the background fluctuates,
The above-described operations are sequentially performed, and the conveyor 1 is controlled at a speed corresponding to the minimum contamination counting time t that always keeps the true count value within the range of the contamination management level.

On the other hand, when the count value calculating section 12 determines that the object M has come to the detection valid section of the radiation detector 3 based on the output from the measured object detection sensor 4, the counting time determining section 1
5 and the radiation detector 3 over the contamination counting time t set.
And counts the pulse signals from the CPU to obtain an apparent count value.
When the contamination count time t has elapsed, a true count value is obtained from the BG count value input from the BG count unit 14, the contamination count time t, and the apparent count value, and the true count value is sent to the contamination determination unit 13. Output.

The contamination determination section 13 compares the true count value from the count value calculation section 12 with a predetermined threshold value to determine the presence or absence of contamination of the measured object M.

As described above, according to the present embodiment, the minimum contamination counting time t that allows the true count value to fall within the range of the contamination control level in response to the fluctuation of the background is determined, and the conveyor 1 is contaminated with this contamination count. Since the speed is controlled in accordance with the counting time t, even when the background level rises more than expected, the true count value can be within the range of the contamination control level, and the normal radioactive contamination can be achieved. Maintain control. In addition, since the contamination measurement is performed in the minimum contamination counting time t among the counting times in which the true count value can be included in the range of the contamination control level in response to the fluctuation of the background level, the contamination measurement is performed in comparison with the conventional apparatus. Thus, the processing amount per unit time can be reliably increased, and the processing capacity can be improved.

When the radioactivity level of the device under test M is high, high accuracy can be obtained even by counting for a short time. Therefore, when the device under test M enters the detection effective portion, a short time counting is performed, and when the counted value is equal to or more than a predetermined value, the speed control based on the BG count value described above is prohibited, and the high speed measurement is performed. It can also be configured to be implemented.

FIG. 4 shows a functional block of a radiation monitor to which such a high-speed measurement function is added. The operation of the radiation monitor according to the functional blocks of FIG. 4 is shown in the flowchart of FIG.

The pulse signal output from the radiation detector 3 is input to the short time counting section 20, and when the device under test M enters the detection effective section, the pulse signal is counted for a short time (Δt). Then, the high-speed measurement deciding section 21 makes the short-time counting section 2
The device under test M is determined from the short-time count value of 0. When the radioactivity level of the DUT is high enough that the predetermined accuracy can be maintained even if the measurement time is shortened,
A speed command is issued directly to the speed controller 11 to carry out high-speed conveyance.

The count value calculating section 12 performs a contamination measurement on the object M conveyed at a high speed.

Further, the contamination counting time t does not necessarily need to be obtained by using the above equation (2), and the contamination counting time may be determined by a method similar to the equation (1). In the above embodiment, when the background level rises abnormally, the contamination counting time becomes longer. However, an alarm may be output even when the background level is abnormally high.

A value obtained by giving a predetermined margin to the contamination management level A (for example, a value slightly smaller than A) may be used.

The present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0044]

As described above in detail, according to the present invention, a radiation monitor capable of automatically setting the contamination counting time to the required minimum time in accordance with the background fluctuation and improving the processing capacity can be achieved. Can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic view of a radiation monitor according to one embodiment of the present invention.

FIG. 2 is a functional block diagram of a main part of the embodiment shown in FIG.

FIG. 3 is a flowchart showing the operation of the embodiment shown in FIG.

FIG. 4 is a functional block diagram of a modification of the embodiment shown in FIG. 1;

FIG. 5 is a flowchart showing the operation of the modification shown in FIG.

FIG. 6 is a schematic diagram of a conventional article carry-out monitor.

FIG. 7 is a flowchart showing an operation of the article carrying-out monitor shown in FIG. 6;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Conveyor, 2 ... Motor, 3 ... Radiation detector, 10 ...
Data processing device, 11: speed control unit, 12: count value calculation unit, 13: contamination determination unit, 14: BG counting unit, 15: counting time determination unit.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01T 1/17 G01T 1/167

Claims (1)

(57) [Claims] An object to be measured is conveyed on a conveyor, radiation emitted from the object is counted for a predetermined time by a radiation detector arranged opposite to the conveyor, and the radiation value is counted from the count value and the contamination count time. In the radiation monitor that determines the contamination state of the object to be measured, a background measurement unit that measures a background level at an installation location of the radiation detector, and a measurement value measured by the background measurement unit and a predetermined value are set in advance. Speed control means for controlling the speed of the conveyor in accordance with a contamination count time which brings a true count value not including the background from the contamination control level into the range of the contamination control level, and output from the radiation detector. A short-time counting unit that counts pulse signals for a short time and this short-time counter
A radiation monitor comprising: a high-speed measurement determining unit that outputs a high-speed transport command to the speed control unit when a numerical value is larger than a predetermined count value .