JP6843350B2 - Radiation amount measuring device, radiation amount measuring method and radiation amount measuring system - Google Patents

Description

The present invention relates to an apparatus, method and system for measuring the amount of radiation from a radioactive substance.

Radiation dose measurement for measuring the amount of surface contamination by radioactive substances and the air dose rate generally includes portable measurement that measures the surrounding distribution in a short time using a portable measuring instrument and long-term installation at a fixed position. There are two types of measurement methods, stationary measurement, which performs specific monitoring.

The portable measurement method is used for grasping the radioactive contamination distribution and contamination level, and for monitoring for decontamination. However, in recent years, there is a technical problem of searching and identifying spots called hot spots (highly polluted spots where extremely partially remaining on the ground surface) where pollution distribution is sparsely scattered.

Further, when measuring in a short time using a portable measuring instrument, the variation can be removed by statistical processing by standing still on the measurement point and performing repeated sampling within 30 seconds to 1 minute.

In Patent Document 1, as a method of specifying the surface contamination detection range, when a radiation detector is moved along the surface of an object to be measured at a substantially constant speed by using a GM survey meter that detects beta rays, first, The slope of the approximate straight line is obtained from the radiation intensity detected at regular time intervals. Next, when the difference in inclination exceeds the positive threshold value, it is determined to be the contamination start position, and finally, when the difference in inclination exceeds the negative threshold value, it is determined to be the contamination end position.

Patent Document 2 is a simple method of predicting and calculating the final response value of a radiation amount measuring device without waiting for the passage of a time constant.

Japanese Unexamined Patent Publication No. 2008-101922 Japanese Patent No. 5071813

Radiation measurement while moving has lower detection sensitivity than static measurement. Moreover, the degree to which the sensitivity is reduced seems to be related to the magnitude of the moving speed. In addition, the amount of speed that can be moved depends on the sensitivity of the detector itself and the detection mechanism of the detector, and if the speed exceeds a certain limit, accurate detection cannot be performed due to the detection limit of the detection device.

In addition, in the case of a GM survey meter that detects beta rays, the beta rays emitted from hot spots have a weak penetrating power, and the measured value decreases due to a shield such as soil, so the slope is linear even at a speed of 50 mm / s. Even with interpolation (least squares processing), it is difficult to obtain a sufficient slope to compare in order to obtain a change, and there is little empirical comparison between the theory that derives the slope difference and the actually expected sampling result. In other words, in the actual state where pollution has penetrated into the soil, the number of counts that can be obtained is small, so even if it is applied to the theory that derives the difference in slope, an appropriate answer cannot be obtained.

The present invention has been intensively researched and completed by paying attention to such a problem, and an object of the present invention is to scan a radiation detector while moving and calculate a result equivalent to radiation dose measurement at the time of static measurement. To estimate.

In order to solve the above problems, the present invention dynamically uses a radiation detector that detects the radiation amount, a sensor that measures the speed at which the radiation detector moves, and the detected radiation amount and the measured speed. It is a radiation amount measuring device including an estimation unit for estimating a radiation amount and a determination unit for determining whether or not a radiation amount equivalent to a stationary state could be detected from a dynamic radiation amount.

According to the present invention, the radiation detector can be scanned while moving, and a result equivalent to the radiation amount measurement at the time of static measurement can be calculated and estimated.

It is a schematic block diagram of the mobile radiation amount measuring apparatus which concerns on Example 1 of this invention. It is a figure for demonstrating the situation of measuring the radiation amount using the mobile radiation amount measuring apparatus 8. It is a figure for demonstrating (a) a case where a mobile radiation amount measuring apparatus 8 is attached to a foot, and (b) a case where it is attached to a trolley. It is a schematic block diagram of a mobile radiation amount measurement system. It is a flowchart which shows an example of the operation of the mobile radiation amount measurement system 100. It is a figure for demonstrating the variation of stochastic behavior. It is a figure for demonstrating the sampling data of the radiation amount and the background radiation amount. It is a figure for demonstrating the environment of the ground surface radioactive contamination search. It is an external view of the mobile radiation amount measuring apparatus 8 and the electronic terminal 35. It is a figure for demonstrating the behavior in a plurality of scans. It is a figure for demonstrating the function model fitting. It is a figure which shows the calculated fitting parameter. It is a figure which shows the estimation by approximate interpolation.

Embodiments of the present invention will be described with reference to the drawings. In addition, the same reference numerals are given to common parts in each figure, and duplicate description is omitted.

FIG. 1 is a schematic configuration diagram of a mobile radiation amount measuring device according to a first embodiment of the present invention. The mobile radiation amount measuring device 8 includes an input / output unit including a sounding body 1, a wireless communication unit 2, and an external input unit 3, a measurement / calculation unit 4, a sensor unit including an attitude control sensor 5, and a hall sensor 6. It includes a power source 7 that supplies power to the entire device.

The mobile radiation amount measuring device 8 is, for example, a scintillation detector (radiation detector) that detects gamma rays, and data from the detection unit 12 described later is collected at regular time intervals (0.5 s depending on the specifications of the radiation detector). The measurement / calculation unit 4 samples at intervals (the time is determined at intervals of 1.0 seconds). At the same time, the measurement / calculation unit 4 measures the mobile radiation amount from the three-dimensional attitude control sensor 5 at regular time intervals (for example, a resolution of 10 ms to 100 ms is suitable for calculating the speed from the attitude control sensor 5). Sample the moving speed information of the device.

Here, the reason for measuring with gamma rays in this embodiment is that if the measurement of permeated contamination such as soil contamination is performed with beta rays, the count value decreases due to the shielding by soil.

When measuring gamma rays in a high-dose background, the dose is measured from the surroundings other than the measurement target such as soil, so the background count value and fluctuations increase compared to when measuring beta rays. .. Therefore, it is necessary to adjust the standard deviation count appropriate for the dose in order to reduce the effects of background fluctuations.

In the measurement / calculation unit 4, in order to set the reference speed for movement based on the information obtained from the external input unit 3, it is obtained from the specified movement distance and the time required (for example, the number of seconds required to move 5 m). The moving speed can be calibrated. Here, the external input unit 3 is a start / stop switch for capturing the movement of the attitude control sensor 5 and grasping the speed while moving in the vicinity of the background before starting the measurement. The speed calibration can be performed by the external input unit 3. It is also possible to measure the background at the same time.

Further, the measurement / calculation unit 4 recognizes that the user has started the measurement during the measurement, and in order to grasp the magnitude of the count rate from the radiation detector obtained by the measurement, the sounding body 1 Emits beeps with different cycles in several stages.

Further, the measurement / calculation unit 4 can accumulate the collected sampling data inside and perform numerical calculation, and converts the data obtained from the attitude control sensor 5 or the hall sensor 6 into speed data. In addition, at regular time intervals (for example, since the cycle of obtaining data from the radiation detector is the longest interval, it is adjusted to the time timing), the data processed during that time is loaded into the wireless communication unit 2 to prepare for wireless transmission. I do.

In the wireless transmission, the wireless communication unit 2 conforming to the communication standard represented by IEEE802.5.1 or IEEE802.154 is connected and used in consideration of the distance of the wireless communication to be transmitted and the surrounding environmental conditions. The amount of data transferred is count rate and speed information composed of several bytes, and is sent by the serial transfer method expressed in ASCII format.

FIG. 2 is a diagram for explaining a situation in which a radiation amount is measured by using the mobile radiation amount measuring device 8. The mobile radiation amount measuring device 8 can be held by hand, and is measured by the user 10 while holding it by hand as a handheld terminal or by moving it with reference to a height of 1 meter from the ground surface, for example, while wearing it near the waist. can do. Further, for example, when a mobile radiation amount measuring device 8 is mounted on a push cart 9 provided with wheels and moved for scanning based on a height of 1 to 10 cm from the ground surface, or when a person searches on foot, the ankle. It can be used in the case of scanning while temporarily stopping a small amount while the mobile radiation amount measuring device 8 is mounted in the vicinity. In either case, the drive power is supplied from the power supply unit 7 of FIG.

FIG. 3 is a diagram for explaining (a) a case where the mobile radiation amount measuring device 8 is mounted on a foot and (b) a case where the mobile radiation amount measuring device 8 is mounted on a trolley.

Fig. (A) When attached to the foot and measured by walking, the behavior axis 23 is moved by raising the foot or the like using the acceleration sensor 5 which is a posture control sensor built in the mobile radiation amount measuring device 8. The walking speed v can be estimated by performing arithmetic processing represented by the equation (1) based on the time interval t that swings periodically and the stride size l of one leg.

同図（ｂ）台車に搭載し、車輪による計測をする場合においては半径ｒの車輪２５に電磁石を取り付け、車輪が回転することを利用して電磁石が通過する側面にホールセンサ６を装着することで、式（２）に示す通り、車輪２５が一回転する時間間隔ｔを用いて容易に速度ｖに換算し算出することができる

In the case of mounting on a trolley (b) and measuring with wheels, an electromagnet is attached to a wheel 25 having a radius r, and a hall sensor 6 is attached to a side surface through which the electromagnet passes by utilizing the rotation of the wheel. Then, as shown in the equation (2), it can be easily converted into the speed v and calculated by using the time interval t in which the wheel 25 makes one rotation.

（本実施例の目的）
ここで、本実施例の目的は、表面汚染放射線量の検出限界を基準指標として、幾つかの数値指標を定義し、移動しながら検出器を走査し基準線量以上の線量レベルを探索して、静止計測時の線量計測と同等の結果を算出し推定することにある。

(Purpose of this embodiment)
Here, the purpose of this embodiment is to define some numerical indexes using the detection limit of the surface contaminated radiation amount as a reference index, scan the detector while moving, and search for a dose level above the reference dose. The purpose is to calculate and estimate the same result as the dose measurement during static measurement.

Specifically, it has been found from past surveys that in a place where the ground surface height is 1 m and 0.23 μSv / h can be measured at rest, it can be converted as 1 μSv / h at a ground surface height of 10 cm. In such an environment, within a constant speed range of about 50 mm / s, if the distance between sampling points is within a range of about 30 cm to 60 cm in a stationary state, and if the speed is up to about 15 cm / s, per sampling point. It is possible to sample 2-4. Moving at a slower speed will result in more sampling. In order to measure while moving the detector in this way, how many samplings are required is an important factor for improving the detection accuracy.

In addition, hotspot nuclides emit several types of radiation. Here, beta rays have a maximum range and a large shielding rate by soil. When actually measuring uneven ground surfaces while moving, gamma rays, which are less affected by soil shielding, have an advantageous effect on detection estimation.

On the other hand, when evaluating hot spots by measuring gamma rays, the radiation dose below the detection standard, which is not judged to be significant surface contamination, is probabilistic temporally and spatially at the location where surface contamination is to be detected. It is changing with fluctuations. The dose emitted by the hotspot also fluctuates in the same environment, and is the starting point of the sampling transition, which is an important technical element claimed by the prior art, due to the fluctuation of the background (or non-significant surface contamination)? , Not determined to be the cause of hot spots (or significant surface contamination). As a result, the possibility and frequency of erroneous calculation and estimation by determining the variation due to the probability fluctuation as the change in the counting rate due to the hot spot factor may increase.

In the background determination of this embodiment, the background fluctuation is statistically processed as a screening before the movement measurement, and the background level is calculated in advance. In addition, even when erroneous detection data due to external noise is obtained, erroneous judgment is prevented by taking the rate of increase / decrease from the time series data before 1 and 2 sampling as a mechanism to distinguish it from the rise due to the hot spot factor. Perform the following filtering process.

Regarding the speed measurement, the estimated value is obtained by multiplying the behavior of the sampling data under a constant speed setting (50 mm / s). In the speed measurement in this embodiment, the arithmetic processing according to the speed is performed by estimating using the conversion coefficient at rest according to the magnitude of the speed. As a method of speed measurement, for example, a sensor can be built in a mobile radiation amount measuring device to estimate the speed amount. Considering the cost of the sensor, the speed is not directly measured, but the speed can be calculated by converting it from the amount of change in acceleration and its period in the calculation unit. It is also possible to obtain the speed from a position sensor that can detect the speed from the outside, a camera image by motion flow, the number of rotations of the motor, and the like.

(Mobile radiation measurement system)
FIG. 4 is a schematic block diagram of a mobile radiation amount measurement system. The mobile radiation amount measuring system 100 includes a mobile radiation amount measuring device 8 and an electronic terminal 35. Needless to say, it may be an integrated mobile radiation amount measuring device that integrates the functions of the mobile radiation amount measuring device 8 and the electronic terminal 35.

The mobile radiation amount measuring device 8 includes an input unit 11 for setting a reference speed for movement, a detection unit 12 for detecting the radiation amount, and a sensor 13 for measuring the speed at which the radiation detector moves. It includes a measurement / calculation unit 14 that calibrates the moving speed, and a transmission unit 16 that wirelessly transmits data to the electronic terminal 35.

The electronic terminal 35 includes a receiving unit 17 that wirelessly receives data from the transmitting unit 16 and a software processing unit 110 that will be described later. The electronic terminal 35 may be, for example, a PC (personal computer) terminal capable of performing calculations for data processing at high speed, or a tablet terminal that can be operated by a finger pressure sensing type input (touch panel). In these terminals, the sampling data received by software processing is arithmetically processed to estimate the radiation amount detected from the target hot spot factor.

FIG. 5 is a flowchart showing an example of the operation of the mobile radiation amount measurement system 100. The operation of the software processing unit 110 of FIG. 4 will be described with reference to FIG.

The filter processing unit 18 filters the sampling data including the statistical variation (S110). The time-series data 32 (radiation detection data x = x1, x2, x3, ... at time t = t0, t1, t2 ...) obtained sequentially has variations like distribution 31 with stochastic fluctuations (Gauss). Called to have sex).

FIG. 6 is a diagram for explaining variations in stochastic behavior. It is known that the data in which the range of variation is within ± σ (1 standard deviation) occupies about 68%.

In the filter processing unit 18, any standard deviation of the dose other than the hot spot (that is, non-significant contamination) is set as the background information (background) 33.

FIG. 7 is a diagram for explaining the sampling data 32 of the radiation amount and the background radiation amount 33. The horizontal axis is time t, and the vertical axis is CPM (Count Per Minutes), which indicates the counted number of radiation passing through the measurement effective area of the detector portion of the radiation detector 12 per minute. In this case, for the purpose of accelerating the degree of convergence, as shown in Eq. (3), preprocessing may be performed to reduce the variation by the moving average MA extracted from the sampling data.

バックグラウンドレベルを定めるには、放射線検出器１２によって指し示す放射線量が基準とする放射線量に満たない安定した地点において、例として６０秒から１８０秒のデータを捕捉して算出するのがよい。

In order to determine the background level, it is preferable to capture and calculate data of 60 to 180 seconds as an example at a stable point where the radiation amount indicated by the radiation detector 12 is less than the reference radiation amount.

FIG. 8 is a diagram for explaining the environment for searching for radioactive contamination on the ground surface. Before the mobile radiation amount measuring device 8 searches for the ground surface radioactive contaminant 34, it is preferable to scan a stable point below the reference radiation amount described above, and capture and calculate the data.

FIG. 9 is an external view of the mobile radiation amount measuring device 8 and the electronic terminal 35. The mobile radiation amount measuring device 8 scans a stable point less than the reference radiation amount in advance and transfers the data to the electronic terminal 35.

FIG. 10 is a diagram for explaining the behavior in a plurality of scans. These are three types of sampling data (A, B, C) and background (BG) data at the time of 8.85 cm / s scanning. All of A, B, and C peak at point 42, and it can be seen that the ground surface radioactive contaminant 34 is located here. However, as in point 41, only C may reach its peak, and there is a possibility of erroneously diagnosing that point 41 also contains contaminants.

Further, as a mechanism for removing abnormal values inside the detector and external burst noise due to cosmic rays, the filter processing unit 18 takes a difference of 2 sampling seconds delay from the time series data obtained sequentially as shown in the equation (4). It may be possible to determine whether the detection started due to a hotspot factor depending on whether the minimum value has a trend.

次に、関数処理部１９は、式（５）に示す通り、複数のフィッティングパラメータβ４５を持つ関数モデルにサンプリングデータを入れた関数値を求める（Ｓ１２０）

Next, as shown in Eq. (5), the function processing unit 19 obtains a function value obtained by putting sampling data into a function model having a plurality of fitting parameters β45 (S120).

本実施例による放射線量の算出では、先述により得られたサンプリングデータおよび速度計測データを入力データとして曲線あてはめ（関数フィッティング）法を用いた動的放射線量のモデル推定を行う。関数は式（５）のガウス関数モデルを用いる。

In the calculation of the radiation amount according to this embodiment, the model estimation of the dynamic radiation amount using the curve fitting (function fitting) method is performed using the sampling data and the velocity measurement data obtained in the above as input data. The function uses the Gaussian function model of Eq. (5).

The count of radiation emitted by nuclide decay is subject to statistical fluctuations. Also, when measuring radiation, it is possible to approximate the Gaussian function by finding an appropriate parameter coefficient. Specifically, as will be described later, an operation is performed to estimate the coefficient by performing an iterative operation such that the sum of squares of the differences between the plurality of sampled values and the equation is used as the objective function to obtain the minimum value (nonlinear least squares method).

At this time, A is the peak level of the radiation amount measurement during movement, B is the background level, and μ is the time to reach the peak according to the velocity. σ indicates the half width of the function centered on the peak. The advantage of fitting is that the variability that the monitoring data originally contains stochastically can be smoothed by the approximate curve of the function model itself.

As shown in the equation (6), the initial value of the first parameter needs to be a value close to the estimated value. This is because the objective function r shown in Eq. (7) converges to the optimum solution in the periphery by repeating the iterative operation.

最小二乗処理部２０では、目的関数を最小二乗処理によって式（８）の解としてS(β)を最小にするβを求めることと同値となる（Ｓ１３０）

In the least squares processing unit 20, the objective function is the solution of the equation (8) by the least squares processing, and the value is equivalent to finding β that minimizes S (β) (S130).

図１１は、関数モデルフィッティングを説明するための図である。ホットスポット要因による線量を示す時系列データ４３からＳ１３０までの処理を施すことによってフィッティング関数４４を得ることができる。

FIG. 11 is a diagram for explaining the function model fitting. The fitting function 44 can be obtained by performing the processing from the time series data 43 to S130 indicating the dose due to the hot spot factor.

FIG. 12 is a diagram showing the calculated fitting parameters. In this way, the dynamic dose estimation unit 21 determines the fitting parameter 45 and estimates the detected dose level during movement, that is, the dynamic radiation amount (S140).

Finally, the determination unit 22 converts the detected dose level at the moving speed into the detected dose level at rest, and determines whether the radiation amount corresponding to the rest can be detected (S150). Approximate interpolation is performed using a conversion table from the reduction ratio of the detection level with respect to the movement speed obtained in advance in the preliminary experiment, and this is calculated.

FIG. 13 is a diagram showing estimation by approximate interpolation. 46 indicates approximate interpolation. In the conversion table, the radiation dose coefficient can be prepared in advance for each velocity sample in a preliminary experiment. Therefore, after the dose level during movement was estimated by scanning, the conversion table was converted from the conversion table showing the reduction rate in the moving velocity at rest. It can be estimated as a dose level.

In the process of calculating the movement speed described above, the parameters of the uniaxial direction component in which the movement direction travels straight is currently extracted, but the user who uses the mobile radiation dose measuring device sets the target area on a flat ground, etc. When searching in a plane, it is possible to simultaneously estimate and record the direction and distance of movement in two dimensions of the xy axis. In addition, when searching for a slope called a satoyama in a mountainous area, it is possible to estimate and record the direction and position when moving in a three-dimensional space including the z-axis indicating the height direction in addition to the xy axis. Of course.

(effect)
According to this embodiment, the background level and the detection level due to the hot spot factor can be separated. This makes it possible to clarify the position of the start of contamination, and by making an estimation that is not sensitive to variations using the fitting function without handling sampling data with variations as it is, erroneous judgment due to variations can be made. I'm preventing it.

Further, when the scanning and searching of the radiation amount while walking realized by this embodiment are taken into consideration, it corresponds to the case where the speed is so slow that walking becomes difficult and the speed amount differs depending on the environmental conditions around walking. be able to.

Further, according to this embodiment, since the function model has non-linearity premised on the curved shape, it is possible to perform optimization calculation processing by fitting for the purpose of approaching and approximating the locus. ..

Furthermore, for this fitting, the sampling points of the entire target section are used, and the non-linear least squares method that minimizes the sum of squares of the differences is used for the purpose of canceling the stochastic variation over the entire section, so that it is non-linear. Arithmetic processing can be performed as it is.

Although the examples (including modified examples) of the present invention have been described above, two or more of these examples may be combined and implemented. Alternatively, one of these examples may be partially implemented. Furthermore, among these, two or more examples may be partially combined and carried out.

For example, the present invention can be applied not only when searching for flat land but also for sloping land such as satoyama when a mobile radiation amount measuring device is attached to the foot. In addition, the measurement by walking can be performed by attaching a mobile radiation dose measuring device not only to one foot but also to both feet, so that the same target range can be measured in the same time period by doubling the time, so that the counting is increased and the accuracy is improved. High measurement is possible.

The present invention is not limited to the description of the examples of the above invention. Various modifications are also included in the present invention as long as those skilled in the art can easily conceive without departing from the description of the scope of claims. For example, by using the attitude control sensor used for speed calculation as a control parameter for three axes, the conventional technology only supports movement detection for the linear axis (one axis). , Plane axes (2 axes), and even spatial axes (3 axes) including tilt can be scanned and analysis of mobile radiation search detection possible.

1 Sounding body 2 Wireless communication unit 3 External input unit 4 Measurement / calculation unit 5 Attitude control sensor 6 Hall sensor 7 Power supply 8 Mobile radiation amount measurement device 11 Input unit 12 Detection unit 13 Sensor unit 14 Measurement / calculation unit 16 Transmission unit 17 Receiver 18 Filter processing unit 19 Function processing unit 20 Minimum square processing unit 21 Dynamic dose estimation unit 22 Judgment unit 100 Mobile radiation dose measurement system

Claims (5)

A radiation detector that detects the amount of radiation and
A sensor that measures the speed at which the radiation detector moves, and
An estimation unit that estimates a dynamic radiation amount model using the function fitting method with the radiation amount and the velocity as inputs, and an estimation unit.
A determination unit for determining whether or not a radiation amount equivalent to a stationary state could be detected from the dynamic radiation amount model,
A radiation dose measuring device equipped with. Comprising a calculation unit for calculating a background radiation dose is an average radiation dose point other than hot spots scattered at a high concentration of contamination with radioactive materials,
Before moving the radiation detector, the calculation unit uses the radiation amount detected by the radiation detector for a predetermined time at a stable point where the radiation amount detected by the radiation detector does not meet the threshold value. The radiation amount measuring device according to claim 1, wherein the background radiation amount is calculated. While the radiation detector is moving, the calculation unit takes a difference of 2 sampling seconds delay from the time series data of the radiation amount detected by the radiation detector, and determines whether the minimum value has a trend. The radiation amount measuring device according to claim 2, wherein it is determined whether or not the detection of the radiation amount from the radioactive substance has started. It is a radiation amount measurement method that uses a radiation detector to detect the radiation amount.
Measure the speed at which the radiation detector moves and
Using the radiation amount and the velocity as inputs, a dynamic radiation amount model using the function fitting method was estimated.
A radiation amount measuring method for determining whether or not a radiation amount equivalent to that at rest can be detected from the dynamic radiation amount model. It is a radiation amount measurement system equipped with a radiation amount measurement device and an electronic terminal.
The radiation amount measuring device is
A radiation detector that detects the amount of radiation and
A sensor that measures the speed at which the radiation detector moves, and
A transmitter that wirelessly transmits the radiation amount and the speed to the electronic terminal,
Have,
The electronic terminal is
A receiving unit that wirelessly receives the radiation amount and the speed from the radiation amount measuring device, and
An estimation unit that estimates a dynamic radiation amount model using the function fitting method with the radiation amount and the velocity as inputs, and an estimation unit.
A determination unit for determining whether or not a radiation amount equivalent to a stationary state could be detected from the dynamic radiation amount model,
Radiation metering system with.

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