JP4485612B2 - Radiation measurement equipment - Google Patents

Description

この場合、ｅ^-λ^/kを求め、その後、以下の計算を順次実行してもよい。
【００３３】
【数２】

上記の演算によれば、各項の値が安定するため、桁溢れといった問題を未然に回避することが可能である。このような演算を利用してあらかじめ各確率の値を記憶しておいて、各時刻で測定されたｋに基づいてＰ（ｋ）を読み出すようにしてもよい。また、あらかじめ各確率を取るｋを逆算しておいて、ｋの値から直接的に確率を求めるようにしてもよい。さらに、取りうる全ての組み合わせについてテーブルを構成し、それをＲＯＭなどに格納してもよい。
【００３４】
図１に示した実施形態によって、例えばフロア上に生じた放射性汚染を特定する場合、まず電源投入後において基準平均値が求められ、その後検出器１０をフロア面に対して近接させつつゆっくりと様々な方向へ移動させる。この場合、汚染が生じていれば、表示部３８に表示される確率が大きく変動するため、それをもって汚染箇所を特定可能である。この場合において、検出器１０のスキャニング速度との関係から確率演算の応答性を適宜設定すればよい。例えば、平均期間Ｔや積算期間ｔを適宜設定する。
【００３５】
【発明の効果】
以上説明したように、本発明によれば、バックグラウンド放射線による計数値の統計的な変動の中で、汚染による異常計数値を簡単にかつ精度良く特定できる。また、本発明によれば、測定結果の計数値の異常が、汚染等の放射線によるものであるか装置故障によるものであるかを弁別し、測定結果の信用性を高めることができる。
【図面の簡単な説明】
【図１】 本発明に係る放射線測定装置の好適な実施形態を示すブロック図である。
【図２】 各時刻で取得される計数値を表す図である。
【図３】 解析部における判定条件を示す図である。
【図４】 ポアソン分布を示す概念図である。
【符号の説明】
１０ 検出器、１４ Ａ／Ｄ変換器、１６ 演算処理部、１８ メモリ、２０基準平均値演算部、２２ 平均期間設定部、２８ メモリ、３０ 積算部、３２ 確率演算部、３４ 解析部、３６ 表示処理部、３８ 表示部。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a radiation measuring apparatus, and more particularly to an apparatus capable of providing a new index value representing a radiation abnormality.
[0002]
[Prior art]
Various apparatuses are known as radiation measuring apparatuses. For example, a radiation measurement device for measuring surface contamination is also called a surface contamination meter, and the radioactive material on the floor and the radiation material on the body surface are measured using such a device. When determining the presence or absence of contamination on the floor, the portable detector for detecting radiation is moved horizontally in parallel with the floor surface while being brought close to the floor surface. During such movement, if the radiation dose (count value) is monitored, the presence or absence of contaminants and their location can be identified.
[0003]
[Problems to be solved by the invention]
However, the number of background radiation incident on the detector changes every moment, especially when the amount of contamination is small, and it is difficult to identify the contamination peak among the fluctuations in the count value, and knowledge and experience are required. It is.
[0004]
In addition, radiation measuring devices are generally equipped with a circuit that smoothes the count value in the time axis direction, and if the time constant is set appropriately, an efficient contamination search is possible. However, setting the time constant is also experienced. The place by is big. If the time constant is set too long, the influence of the background fluctuation can be reduced, but the response of the measurement deteriorates, and it becomes difficult to identify the contaminated part. On the other hand, if the time constant is set too short, the responsiveness increases, and as a result, the count value fluctuates greatly and the contamination peak may be overlooked.
[0005]
The present invention has been made in view of the above-described conventional problems, and an object thereof is to make it possible to easily and accurately identify an abnormal count value due to contamination among statistical fluctuations of a count value due to background radiation. There is.
[0006]
Another object of the present invention is to discriminate whether an abnormality in a count value of a measurement result is due to radiation such as contamination or a device failure, and to improve the reliability of the measurement result.
[0007]
[Means for Solving the Problems]
(1) The present invention represents a count value occurrence probability using a detection unit for detecting radiation, a reference average value calculating means for calculating a reference average value by averaging the radiation count values, and the reference average value. A probability calculating means for defining a predetermined probability function and calculating a probability for each count value sequentially measured according to the probability function, and a probability representing the degree of contamination as the calculated probability or a value corresponding thereto. seen including output means for outputting information to a user, a prior surface contamination measurement, the reference average value is obtained by standard background measurements, when surface contamination measurements, the relative surface to perform certain contamination It is characterized in that it is possible to specify a contamination location by the probability information output from the output means at the time of the surface contamination measurement while the detection portion is moved close to it .
[0008]
According to the above configuration, the probability function is defined using the reference average value, and the probability can be calculated by giving the count value to the probability function. The probability represents the possibility that the count value is generated, and the degree of normality or abnormality can be determined depending on the magnitude of the probability.
[0009]
Preferably, the predetermined probability function is a function corresponding to a Poisson distribution, and a center of the Poisson distribution is determined by the reference average value. Although it is well known that the radiation count value per unit time follows a Poisson distribution, on the premise of this fact, the probability of following the Poisson distribution is calculated for each count value. The center of the Poisson distribution is defined by the reference mean value.
[0010]
For example, as shown in FIG. 4, a Poisson distribution is defined by a certain reference average value λ, and a probability P (k) is determined for each count value k. Here, if k is larger than the reference average value λ and the value of the probability P (k) by k is small, there is a high possibility that k is a value according to another Poisson distribution, specifically due to contamination. There is a high possibility that the average value λ ′ is a value according to the Poisson distribution P ′ (k). For this reason, if the probability P (k) of the count value k is expressed by any method, the presence probability of contamination can be expressed to the measurer.
[0011]
Preferably, the reference average value is obtained by standard background measurements. Alternatively, the reference average value is acquired at the start of measurement. Alternatively, the reference average value is acquired at a predetermined timing during measurement. The reference average value is desirably acquired in a standard environment in which no contamination occurs (for example, when the power is turned on), and may be updated as necessary.
[0012]
Preferably, it includes means for variably setting an average period for obtaining the reference average value according to measurement conditions. According to this configuration, the average period can be adjusted according to the size of the background. As a result, the probability calculation accuracy can be increased.
[0013]
Preferably, the count value is an integrated value within a predetermined integration period, and includes means for variably setting the integration period according to measurement conditions. The count value used for the probability calculation may be the count value (count rate) obtained for each unit time itself, or an integrated value integrated over a plurality of unit times or an average value thereof may be used. Good. In particular, if the integration period can be variably set, the responsiveness can be improved and the calculation accuracy can be improved. Preferably, the output means outputs an abnormality probability or a normal probability.
[0014]
(2) The present invention represents a count value occurrence probability using a detection unit for detecting radiation, a reference average value calculating means for calculating a reference average value by averaging the radiation count values, and the reference average value. It defines the predetermined probability function, according to the probability function, seen including a probability calculation means for calculating a probability for each count value, and a abnormality analysis means for performing abnormality analysis in accordance with the computed probability of being measured sequentially, Furthermore, the following configuration is included .
[0015]
Preferably, the abnormality analysis means includes a comparator that compares the reference average value and the respective count values, an analyzer that performs an abnormality analysis based on a comparison result of the comparator, and the calculated probability. And including.
[0016]
Preferably, the analyzer determines a device failure when the count value is lower than the reference average value and the calculated probability is equal to or less than a failure determination value.
[0017]
Preferably, the analyzer determines contamination by radioactive material when the count value is higher than the reference average value and the calculated probability is equal to or less than a contamination determination value.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.
[0020]
FIG. 1 shows a preferred embodiment of a radiation measuring apparatus according to the present invention, and FIG. 1 is a block diagram showing the overall configuration thereof.
[0021]
In FIG. 1, a detector 10 is a device that detects radiation (for example, γ-rays). Of course, other types of detectors may be used, and the present invention can also be applied to detection of radiation other than gamma rays. The detector 10 is connected to the apparatus main body by, for example, a cable and may be portable.
[0022]
The signal processing circuit 12 is a circuit that performs predetermined signal processing on the detection signal output from the detector 10. For example, the signal processing circuit includes an amplifier. Moreover, you may provide circuits, such as a wave height discriminator and a counter, as needed. The A / D converter 14 is a circuit that converts the detection signal output from the signal processing circuit 12 into a digital signal. In FIG. 1, data output from the A / D converter 14 is represented by n, and this n corresponds to a count value (count rate) per unit time.
[0023]
The memory 18 sequentially stores the count value n at each time. The memory 18 preferably has a structure such as a ring buffer, and stores each past count value within a certain period from the latest count value. For example, a series of data as shown in FIG. 2 is stored in the memory 18.
[0024]
Here, the data shown in FIG. 2 will be described. The memory 18 stores a count value n for each time. Here, Δt represents a unit measurement time, for example, Δt is 1 second. T represents an average period for acquiring the reference average value. For example, the average period T is 1 minute. Within the average period T, the reference average value λ is acquired as described later. t represents an accumulation period, and represents a period for accumulating one or more past count values including the current count value for which the probability is obtained. For example, the integration period t is 3Δt.
[0025]
Returning to FIG. 1, the reference average value calculation unit 20 integrates each count value n within the average period set by the average period setting unit 22 and averages the result by dividing the value by (T / t). Means. Here, the average period T is set by the user through the input unit 26. That is, the average period T can be variably set. The reset circuit 24 is a circuit that generates a trigger for setting an average period again at a predetermined timing and capturing a reference average value. For example, the reference average value is captured at the power-on value of the apparatus, or the reference average value is captured when the user explicitly inputs. In any case, it is desirable to capture the reference average value in a state where no contamination occurs, that is, in a standard state. The memory 28 stores the calculated reference average value λ.
[0026]
As shown in FIG. 2, the integration unit 30 is a circuit that calculates the count value k as an integration value by integrating the count value n within the integration period t. The count value k may be an average value within the integration period. In that case, the integrated value in the average period T is divided by (T / Δt) to calculate the reference average value λ. That is, it is necessary to match the time units of λ and k. The probability calculation unit 32 is a circuit that calculates a probability P (k) that the count value k is generated by substituting the count value k into a probability function (Poisson distribution) specified by the reference average value λ. FIG. 2 shows the relationship between each count value k and the probability P (k). Incidentally, the integration period t in the integration unit 30 can be variably set by the input unit 26.
[0027]
The display processing unit 36 is a circuit that performs predetermined processing on the obtained probability P (k) and outputs a value obtained by the processing to the display unit 38. In this case, for example, the probability P (k) is displayed on the display unit 38 as it is, or P (k) × 100 (%) is displayed. Alternatively, P (k) / P (λ) may be displayed that represents a ratio in which the count value k is not displaced from the reference average value λ. Alternatively, {1-P (k)} × 100 (%) may be displayed as the abnormality probability. Alternatively, 1-P (k) / P (λ) representing the displacement ratio of the count value k from the reference average value λ may be displayed.
[0028]
The analysis unit 34 is a circuit for analyzing the current state from the magnitude of the count value k and the magnitude of the probability P (k) based on, for example, a determination criterion as shown in FIG. For example, when the probability is larger than a predetermined value, it is determined as normal, and when it is smaller than that, it is determined that there is a possibility of abnormality. Further, when the count value is larger than the reference average value and the probability P (k) is small, it is determined that the possibility of contamination is high. Furthermore, when the count value k is smaller than the reference average value λ and the probability P (k) is smaller than a certain value, it is determined that there is a possibility of a failure because a device failure or the like is considered. As a possibility other than the failure, for example, a case where the apparatus exists in a shield room can be considered.
[0029]
Instead of displaying on the display unit 38, the measurement result may be expressed by, for example, lamp display of each color. A predetermined sound may be generated by a speaker or the like. Further, an existing radiation measurement device may be combined with the device shown in FIG. 1, and in that case, for example, a value obtained by further weighting the probability with respect to a generally obtained count rate or dose rate is displayed. You may make it do.
[0030]
When it is a heavy burden to calculate the probability at each time in the probability calculation unit 32, for example, when the reference average value λ is determined, each probability P (k) within a possible range is calculated in advance. Alternatively, when the measurement is actually performed, the probability value already calculated from the measurement value k may be determined.
[0031]
Incidentally, in the case of calculating the probability, if λ or k becomes large to some extent, e ⁻ λ, λ ^k , k! It can be considered that each overflows digits. Therefore, it is desirable to calculate P (k) in advance for each k in the possible range when λ is determined. For example, the probability may be calculated within the following range.
[0032]
[Expression 1]

In this case, e ⁻ λ ^{/ k} may be obtained, and then the following calculations may be executed sequentially.
[0033]
[Expression 2]

According to the above calculation, since the value of each term is stable, it is possible to avoid a problem such as overflow. The value of each probability may be stored in advance using such an operation, and P (k) may be read based on k measured at each time. Alternatively, k that takes each probability may be calculated in advance, and the probability may be obtained directly from the value of k. Further, a table may be configured for all possible combinations and stored in a ROM or the like.
[0034]
When the radioactive contamination generated on the floor, for example, is specified by the embodiment shown in FIG. 1, first, a reference average value is obtained after the power is turned on, and thereafter, the detector 10 is gradually changed while being brought close to the floor surface. Move in any direction. In this case, if contamination has occurred, the probability of being displayed on the display unit 38 varies greatly, so that the contaminated portion can be identified. In this case, the responsiveness of the probability calculation may be set as appropriate based on the relationship with the scanning speed of the detector 10. For example, the average period T and the integration period t are set as appropriate.
[0035]
【The invention's effect】
As described above, according to the present invention, it is possible to easily and accurately specify an abnormal count value due to contamination in a statistical variation of a count value due to background radiation. In addition, according to the present invention, it is possible to discriminate whether the abnormality in the count value of the measurement result is due to radiation such as contamination or the failure of the apparatus, thereby improving the reliability of the measurement result.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a preferred embodiment of a radiation measuring apparatus according to the present invention.
FIG. 2 is a diagram illustrating a count value acquired at each time.
FIG. 3 is a diagram illustrating determination conditions in an analysis unit.
FIG. 4 is a conceptual diagram showing a Poisson distribution.
[Explanation of symbols]
10 detectors, 14 A / D converters, 16 calculation processing units, 18 memories, 20 reference average value calculation units, 22 average period setting units, 28 memories, 30 integration units, 32 probability calculation units, 34 analysis units, 36 displays Processing unit, 38 display unit.

Claims (5)

A portable radiation measurement device,
A detector for detecting radiation;
A reference average value calculating means for averaging the count value of the radiation and calculating the reference average value;
Probability of calculating a probability for each count value measured sequentially according to the probability function by defining a predetermined probability function representing the probability of occurrence of a count value in a state where no contamination has occurred using the reference average value Computing means;
Output means for outputting probability information representing the degree of contamination to the user as the calculated probability or a value corresponding thereto;
Including
Before the surface contamination measurement, the reference average value is obtained by standard background measurement,
At the time of surface contamination measurement, it is moved while bringing the detection unit close to the surface on which the contamination is specified,
At the time of the surface contamination measurement, it is possible to identify the contamination location by the probability information output from the output means,
A radiation measuring apparatus characterized by that. The apparatus of claim 1.
The predetermined probability function is a function corresponding to a Poisson distribution,
The radiation measuring apparatus characterized in that the center of the Poisson distribution is determined by the reference average value. The apparatus of claim 1.
A radiation measurement apparatus comprising: means for variably setting an average period for obtaining the reference average value according to measurement conditions. The apparatus of claim 1.
The count value is an integrated value within a predetermined integration period, and includes a means for variably setting the integration period according to measurement conditions. A portable radiation measurement device,
A detector for detecting radiation;
A reference average value calculating means for averaging the count value of the radiation and calculating the reference average value;
Probability of calculating a probability for each count value measured sequentially according to the probability function by defining a predetermined probability function representing the probability of occurrence of a count value in a state where no contamination has occurred using the reference average value Computing means;
An anomaly analysis means for performing an anomaly analysis according to the calculated probability;
Including
Before the surface contamination measurement, the reference average value is obtained by standard background measurement,
At the time of surface contamination measurement, it is moved while bringing the detection unit close to the surface on which the contamination is specified, and the abnormality analysis is performed at that time,
The abnormality analysis means includes
A comparator for comparing the reference average value and the respective count values;
An analyzer that performs an abnormality analysis based on the comparison result of the comparator and the calculated probability;
Including
The analyzer determines a device failure when the count value is lower than the reference average value and the calculated probability is equal to or less than a failure determination value, and the analyzer determines the reference average value. If the count value is higher than the value and the calculated probability is less than or equal to the contamination determination value, determine contamination by radioactive material,
A radiation measuring apparatus characterized by that.

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