JP6443876B2 - Radioactivity concentration measuring device - Google Patents

Description

  The present invention relates to a radioactivity concentration measuring apparatus that measures the radioactivity concentration of an object to be measured containing a radioactive substance.

  Conventionally, a radiation measurement system described in Patent Document 1 is known as a technique in the field of measuring a radiation dose. This system includes a fixing mechanism that holds the position of the radiation dosimeter in a storage container that stores a measurement sample. According to this fixing mechanism, since the radiation dosimeter is fixed at the same position with respect to the container in the background measurement and the main measurement, the background radiation dose superimposed on the measurement value of the main measurement and the background measurement The obtained measurement value can be made the same. Therefore, the net value of the measurement sample can be accurately measured by subtracting the measurement value of the background measurement from the measurement value of the main measurement.

JP 2013-36957 A

  By the way, depending on the measurement environment of the radioactivity concentration, the background radioactivity concentration may change with time. When the background radioactivity concentration changes with time, the background radioactivity concentration superimposed on the measurement value of this measurement is different from the radioactivity concentration in the background measurement. Then, even if the radioactivity concentration value in the background measurement is subtracted from the measured value, it is difficult to say that appropriate background correction has been performed. Therefore, it is difficult to obtain a reliable radioactivity concentration in an environment where the background radioactivity concentration changes with time.

  Then, an object of this invention is to provide the radioactive concentration measuring device which can obtain the reliable radioactive concentration of a to-be-measured object.

  In one embodiment of the present invention, in a radioactivity concentration measuring device for obtaining a radioactivity concentration of a measurement object containing a radioactive substance, a measurement object measurement unit for obtaining a measurement detection value indicating the radioactivity concentration of the measurement object, A first reference measurement unit that obtains a first reference detection value indicating a first radioactive concentration in a first radiation source unit having a known radioactive concentration, and a second radiation having a known radioactive concentration A second reference measurement unit for obtaining a second reference detection value indicating a second radioactive concentration in the source unit; a first radioactive concentration; a second radioactive concentration; a first reference detection value; And a processing unit that calculates a conversion function using the reference detection value of 2, and calculates a radioactivity concentration of the measurement object using the conversion function and the measurement detection value, the first radiation source unit, The second radiation source unit is disposed close to the object to be measured, and the first reference detection value and the second reference detection value are: Is acquired at the same timing as the detection value measured, the value of the first activity concentration is different from the value of the second activity concentration.

  According to this configuration, combination data of the first radioactivity concentration and the first reference detection value is obtained from the first reference measurement unit. Further, combination data of the second radioactivity concentration and the second reference detection value is obtained from the second reference measurement unit. Then, by using these data, the processing unit calculates a conversion function indicating the relationship between the radioactive concentration and the detection value. And the radioactivity density | concentration of a to-be-measured object can be obtained by applying a measurement detection value to this conversion function. Here, since the first and second radiation source units are arranged in the vicinity of the measurement object, the first radiation source unit, the second radiation source unit, and the measurement object have substantially the same background. It will be placed in a radioactive concentration environment. Then, the influence of the background radioactivity concentration is corrected by the radioactivity concentration of the measurement object using the conversion function. Furthermore, since the first and second reference detection values are acquired at the same timing as the measurement detection value of the measurement object, correction according to the background radioactivity concentration at the time of measurement of the radioactivity concentration becomes possible. Therefore, even in a measurement environment where the background radioactivity concentration changes with time, a reliable radioactivity concentration of the measurement object can be obtained.

  The measurement object measurement unit includes a measurement object sensor that contacts the measurement object and measures a measurement detection value, and the first reference measurement unit contacts the first radiation source unit and is first. A second reference measurement unit that measures the second reference detection value in contact with the second radiation source unit. It is good also as having a sensor. According to this configuration, the measurement detection value and the first and second reference detection values can be easily measured.

  The measurement object measurement unit further includes a measurement object shield that covers a region of the measurement object that is in contact with the measurement object sensor, and the first reference measurement unit is in contact with the first reference sensor. A first reference shield that covers the region of the first radiation source unit is further included, and the second reference measurement unit covers the region of the second radiation source unit that is in contact with the second reference sensor. It may be further provided with a second reference shield. According to this configuration, the S / N ratio of the measurement detection value output from the measurement object sensor can be improved. In addition, the S / N ratio of the first and second reference detection values output from the first and second reference sensors can be improved.

  The first radiation source unit and the second radiation source unit may include radiation source bodies having different densities. According to this configuration, it is not necessary to correct the influence of the density difference between the measurement object and the first and second radiation source units by calculation, and the radioactivity concentration of the measurement object can be measured with higher accuracy. .

  ADVANTAGE OF THE INVENTION According to this invention, the radioactive concentration measuring apparatus which can obtain the reliable radioactive concentration of a to-be-measured object is provided.

FIG. 1 is a schematic diagram of a radioactivity concentration measuring apparatus according to an embodiment of the present invention. FIG. 2 is a functional block diagram of the radioactive concentration measuring apparatus. FIGS. 3A, 3B, and 3C are views showing an environment in which the radioactivity concentration measurement is performed by the radioactivity concentration measurement apparatus. FIG. 4 is a graph showing the relationship between the detection value output from the radioactivity concentration measurement unit and the radioactivity concentration.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  The radioactivity concentration measuring apparatus is an apparatus for measuring the radioactivity concentration of an object to be measured containing a radioactive substance contained in a flexible container bag (hereinafter also simply referred to as “bag”). This radioactivity concentration measuring apparatus measures the radioactivity concentration of a measurement object in the state accommodated in the bag, without opening a bag and taking out a measurement object. As shown in FIG. 1, the radioactivity concentration measurement apparatus 1 includes a measurement object measurement unit 2, reference measurement units 3 and 4, and a processing unit 6. The measurement object measurement unit 2 and the reference measurement units 3 and 4 are connected to the processing unit 6, and the measurement detection value is output to the processing unit 6 and the first and second reference detection values are output to the processing unit 6. Is output. The processing unit 6 calculates the radioactivity concentration of the measurement object 7 using data such as the measurement detection value and the reference detection value.

The measurement object 7 is accommodated in a bag 8 having a volume of about 1 m ³ , for example. The measurement object 7 includes soil containing radioactive material, sludge, vegetation, and the like. The bag 8 preferably has a larger volume than an effective detection area 9 described later. When it is larger than the effective detection area 9, the radioactivity concentration measuring apparatus 1 can measure the radioactivity concentration regardless of the shape, size, and weight of the measurement object 7.

  The measurement object measurement unit 2 includes a radioactivity concentration sensor (measurement object sensor) 11 and a simple shield (measurement object shield) 12. The radioactivity concentration sensor 11 is for contacting the bag 8 and measuring the radioactivity concentration of the measurement object 7 existing in the effective detection region 9 near the contact portion. The radioactivity concentration sensor 11 includes, for example, a device having a scintillator that absorbs radiation energy and generates fluorescence, and a photoelectric conversion unit that converts light generated by the scintillator into an electrical signal. As the scintillator, for example, NaI (Tl) scintillator or CsI (Tl) scintillator is used. From such a radioactive concentration sensor 11, a value (CPS) obtained by counting light generated by the scintillator is output as a measurement detection value.

  The radioactivity concentration sensor 11 is covered with a simple shield 12. The simple shield 12 is for ensuring the S / N ratio rather than canceling the background radioactivity concentration. More specifically, in the radioactivity concentration sensor 11, the measurement surface 11a is brought into contact with the bag 8, and the portion other than the measurement surface 11a is covered with the simple shield 12. That is, the effective detection area 9 in the vicinity of the radioactivity concentration sensor 11 is covered with the simple shield 12. For such a simple shield 12, for example, a member made of a metal having an ability to block radiation such as iron or lead is used.

  The measurement object measuring unit 2 includes a weight scale 13 for measuring the weight of the measurement object 7. From the weigh scale 13, the weight value of the measurement object 7 is output to the processing unit 6.

  The reference measurement unit (first reference measurement unit) 3 includes a reference radiation source body (first radiation source unit) 3a, a radioactivity concentration sensor (first reference sensor) 11, and a simple shield ( First reference shield) 12. The reference measurement unit (second reference measurement unit) 4 includes a reference radiation source body (second radiation source unit) 4a, a radioactivity concentration sensor (second reference sensor) 11, and simple shielding. And a body (second reference shielding body) 12. That is, the reference measurement units 3 and 4 are different from the measurement object measurement unit 2 in that the reference measurement source units 3 and 4 have the reference radiation source bodies 3a and 4a. A value (CPS) obtained by counting the light generated by the scintillator is output from the radioactivity concentration sensor 11 of the reference measurement unit 3 to the processing unit 6 as a first reference detection value. A value (CPS) obtained by counting the light generated by the scintillator is output from the radioactivity concentration sensor 11 of the reference measurement unit 4 to the processing unit 6 as a second reference detection value.

  The reference radiation source bodies 3a and 4a are arranged in close proximity to the measurement object 7. This close arrangement means that the measurement object 7 and the reference radiation source bodies 3a and 4a are arranged in an environment having an equivalent background radiation concentration. Further, the reference radiation source bodies 3a and 4a have different known radioactivity concentrations. For example, the reference radiation source body 3a is not contaminated, that is, has a radioactive concentration of 0 Bq / kg. On the other hand, the reference radiation source body 4a has a radioactivity concentration of 8000 Bq / kg. Further, the reference radiation source bodies 3 a and 4 a are made of a material having a density substantially equal to that of the measurement object 7. For example, sand is used as the reference radiation source bodies 3a and 4a.

  Here, the radioactivity concentration sensor 11 in the measurement object measuring unit 2 has the same configuration and characteristics as the radioactivity concentration sensor 11 in the reference measurement units 3 and 4, and can be exchanged with each other. is there. By replacing these radioactivity concentration sensors 11 periodically, it becomes possible to determine whether the radioactivity concentration sensor 11 has failed or deteriorated. More specifically, according to the radioactivity concentration sensor 11 which is originally corrected and has the same characteristics, even if each is replaced, the detected value should show only a difference of an allowable error. Therefore, when a difference in detected values that exceeds an allowable error appears, it can be seen that a failure has occurred in any of the three radioactive concentration sensors 11. As described above, since the deterioration tendency of the radioactivity concentration sensor 11, abnormality determination, and failure determination can be made depending on the degree of deviation from the tolerance of the detected value, the aging degradation or failure of the scintillator in the radioactivity concentration sensor 11 is possible. Inappropriate measurement due to can be eliminated.

  As shown in FIG. 2, the processing unit 6 includes, as functional components, a measurement detection value input unit 14, a reference detection value input unit 16, a reference radioactivity concentration input unit 17, and a conversion function calculation unit 18. And a measurement value calculation unit 19. The processing unit 6 also includes an input device 21 for inputting data other than the measurement detection value and the reference detection value (for example, the radioactivity concentration of the reference radiation source bodies 3a and 4a), and an output device 22 for displaying the calculation result. Is further provided. The processing unit 6 can cause the computer to function as the processing unit 6 of the present embodiment by executing the processing program in the computer. Hereinafter, the function of each component will be described.

  The measurement detection value input unit 14 is connected to the radioactivity concentration sensor 11 in the measurement object measurement unit 2, and the measurement detection value is input from the radioactivity concentration sensor 11. Then, the measurement detection value input unit 14 outputs the measurement detection value to the measurement value calculation unit 19. The reference detection value input unit 16 is connected to the radioactivity concentration sensors 11 of the reference measurement units 3 and 4, and the first reference detection value and the second reference detection value are input from the respective radioactivity concentration sensors 11. The Then, the reference detection value input unit 16 outputs the first and second reference detection values to the conversion function calculation unit 18. The reference radioactivity concentration input unit 17 is connected to the input device 21, and the known first radioactivity concentration of the reference radiation source body 3a and the known second activity concentration of the reference radiation source body 4a Is entered. Then, the reference radioactivity concentration input unit 17 outputs the first radioactivity concentration and the second radioactivity concentration to the conversion function calculation unit 18.

The conversion function calculation unit 18 includes the first reference detection value and the second reference detection value input from the reference detection value input unit 16, the first radioactive concentration and the second radiation input from the input device 21. The conversion function is calculated using the active density. More specifically, a coefficient indicating the conversion function is calculated. If the conversion function is a linear function, for example, the conversion function is expressed by the following equation (1).
BS = a × CS + b (1)
However, a = (B2-B1) / (C2-C1), b = B1- (B2-B1) / (C2-C1) × C1. Further, CS is a measurement detection value of the measurement object 7, C1 is a first reference detection value of the reference radiation source body 3a, B1 is a first radioactive concentration of the reference radiation source body 3a, C2 is the second reference detection value of the reference radiation source body 4a, and B2 is the second radioactive concentration of the reference radiation source body 4a.

  The measurement value calculation unit 19 inputs the measurement detection value CS input from the measurement detection value input unit 14 into the above equation (1), and calculates the radioactivity concentration BS of the measurement object 7. Then, the calculated radioactivity concentration BS of the measured object 7 is output to the output device 22.

  Next, the process of measuring the radioactivity concentration of the measurement object 7 accommodated in the bag 8 using the radioactivity concentration measurement device 1 will be specifically described. In addition, the numerical value shown below is illustrated for convenience of explanation.

  As shown in FIGS. 3A to 3C, the bag 8 a is carried from the storage area 23 and placed on the track 24, and the radioactivity of the measurement object 7 in the bag 8 a placed on the track 24. The concentration BS is measured. Here, it is assumed that the radioactivity concentration B1 of the reference radiation source body 3a is not contaminated, that is, 0 Bq / kg, and the radioactivity concentration B2 of the reference radiation source body 4a is 8000 Bq / kg.

First, as shown in FIG. 3A, the bag 8a is placed on the track 24, and the measurement detection value CS is acquired. At this time, there are five bags 8b to 8f in the storage area 23. These bags 8b to 8f can be background radiation sources in the measurement of the measurement detection value CS of the bag 8a. The reference radiation source body 4a is also a radioactive substance. For this reason, the reference radiation source body 4a can also be a background radiation source in the measurement of the measurement detection value CS of the bag 8a. Therefore, in order to suppress the influence on the measurement of the bag 8a, it is preferable to provide a shielding wall between the bag 8a and the reference radiation source body 4a. In addition, when the reference radiation source body 3a is also a radioactive substance, it is preferable to provide a shielding wall between the bag 8a and the reference radiation source body 3a. As a result of measurement in the state of FIG. 3A, for example, the following numerical values are obtained.
Measurement detection value CS of measurement object 7: 11000 [CPS]
Reference detection value C1: 2000 [CPS] of the reference radiation source 3a
Radioactivity concentration B1: 0 [Bq / kg] of the reference radiation source 3a
Reference detection value C2 of the reference radiation source body 4a: 10000 [CPS]
Radioactivity concentration B2 of reference radiation source body 4a: 8000 [Bq / kg]

Substituting the radioactivity concentrations B1 and B2 and the reference detection values C1 and C2 into the above equation (1), the following equation (2) is obtained. This equation (2) corresponds to the graph G1 in FIG. Here, on the graph G1, a point P1 indicates measurement data (C1, B1 = 2000, 0) of the reference radiation source body 3a. Point P2 indicates measurement data (C2, B2 = 10000, 8000) of the reference radiation source body 4a.
BS = CS-2000 (2)
When the measurement detection value CS (= 11000) of the measurement object 7 is substituted into the above equation (2), it can be seen that the radioactive concentration BS of the measurement object 7 accommodated in the bag 8a is 9000 Bq / kg.

Next, as shown in FIG. 3B, the bag 8d is placed on the track 24, and the measurement detection value CS is acquired. At this time, the storage area 23 includes two bags 8e and 8f. These bags 8e and 8f can be a background radiation source in the measurement of the measurement detection value CS of the bag 8d. However, since the number of bags 8e and 8f is smaller than the situation shown in part (a) of FIG. 3, the background radioactivity concentration is expected to change. Specifically, the background radioactivity concentration is expected to tend to decrease. As a result of measurement in the state of FIG. 3B, for example, the following numerical values are obtained.
Measured detection value CS of measurement object 7: 10000 [CPS]
Reference detection value C1: 1000 [CPS] of the reference radiation source 3a
Radioactivity concentration B1: 0 [Bq / kg] of the reference radiation source 3a
Reference detection value C2 of the reference radiation source body 4a: 9000 [CPS]
Radioactivity concentration B2 of reference radiation source body 4a: 8000 [Bq / kg]

Substituting the radioactive concentrations B1 and B2 and the reference detection values C1 and C2 into the above equation (1), the following equation (3) is obtained. This equation (3) corresponds to the graph G2 in FIG. Here, on the graph G2, a point P3 indicates measurement data (C1, B1 = 1000, 0) of the reference radiation source body 3a. A point P4 indicates measurement data (C2, B2 = 9000, 8000) of the reference radiation source body 4a.
BS = CS-1000 (3)
When the measured detection value CS (= 10000) of the measurement object 7 is substituted into the above equation (3), it can be seen that the radioactive concentration BS of the measurement object 7 accommodated in the bag 8d is 9000 Bq / kg.

Next, as shown in part (c) of FIG. 3, the bag 8 f is placed on the track 24 and the measurement detection value CS is acquired. At this time, there is no bag in the storage area 23. Therefore, it is expected that the background radioactivity concentration tends to be smaller than those in FIGS. 3 (a) and 3 (b). Assume that the following numerical values are obtained as a result of measurement in the state shown in FIG.
Measurement detection value CS of measurement object 7: 9000 [CPS]
Reference detection value C1: 0 [CPS] of the reference radiation source 3a
Radioactivity concentration B1: 0 [Bq / kg] of the reference radiation source 3a
Reference detection value C2 of the reference radiation source body 4a: 8000 [CPS]
Radioactivity concentration B2 of reference radiation source body 4a: 8000 [Bq / kg]

Substituting the radioactive concentrations B1 and B2 and the reference detection values C1 and C2 into the above equation (1), the following equation (4) is obtained. This equation (4) corresponds to the graph G3 in FIG. Here, on the graph G3, a point P5 indicates measurement data (C1, B1 = 0, 0) of the reference radiation source body 3a. A point P6 indicates measurement data (C2, B2 = 8000, 8000) of the reference radiation source body 4a.
BS = CS (4)
When the measurement detection value CS (= 9000) of the measurement object 7 is substituted into the above equation (4), it can be seen that the radioactivity concentration BS of the measurement object 7 accommodated in the bag 8f is 9000 Bq / kg.

  Here, referring to the graphs G1, G2, and G3 shown in FIG. 4, every time the measurement environment is different, different tendencies are shown. More specifically, the X intercepts of the respective graphs G1, G2, and G3 change. This X intercept is a measurement detection value CS output from the radioactivity concentration sensor 11 when a measurement object having a radioactivity concentration BS of zero is measured. That is, it corresponds to the background radioactivity concentration. Then, the largest background radioactivity concentration is measured when a large number of bags 8b to 8f are present in the storage area 23 (see FIG. 3A), and there are bags in the storage area 23. It can be seen that the lowest background radioactivity concentration was measured when the state was not (see (c) of FIG. 3). Therefore, the radioactivity concentration measuring apparatus 1 can obtain a reliable radioactivity concentration value even in an environment where the background radioactivity concentration changes for each measurement.

  According to the radioactivity concentration measurement apparatus 1, combination data of the radioactivity concentration B1 and the reference detection value C1 is obtained from the reference measurement unit 3. Further, combination data of the radioactivity concentration B2 and the reference detection value C2 is obtained from the reference measurement unit 4. Then, by using these data, the processing unit 6 calculates a conversion function (see the above formulas (1) to (4)) indicating the relationship between the radioactive concentration BS and the measured detection value CS. Then, by applying the measurement detection value CS to this conversion function, the radioactivity concentration BS of the measurement object 7 can be obtained.

  Here, since the reference radiation source bodies 3a and 4a are arranged in the vicinity of the object 7 to be measured, the reference radiation source bodies 3a and 4a and the object 7 to be measured are in an environment having substantially the same background radioactivity concentration. Will be placed. Since the radioactivity concentration BS of the measurement object 7 is calculated using the conversion function, the influence of the background radioactivity concentration is corrected. Furthermore, since the reference detection values C1 and C2 are acquired at the same timing as the measurement detection value CS of the measurement object 7, correction according to the background radioactivity concentration at the time of measurement of the radioactivity concentration BS becomes possible. Accordingly, a reliable radioactivity concentration BS of the measurement object 7 can be obtained even in a measurement environment where the background radioactivity concentration changes with time.

  Further, the measurement object measurement unit 2 has a radioactivity concentration sensor 11 that contacts the measurement object 7 and measures the measurement detection value CS, and the reference measurement unit 3 contacts the reference radiation source 3a. The reference measurement value C1 is measured, and the reference measurement unit 4 has a radioactivity concentration sensor 11 that measures the reference detection value C2 in contact with the reference radiation source 4a. . According to this configuration, the measurement detection value CS and the reference detection values C1 and C2 can be easily measured.

  The measurement object measurement unit 2 and the reference measurement units 3 and 4 further include a simple shield 12. According to this configuration, the S / N ratio of the measurement detection value CS and the reference detection values C1 and C2 output from the radioactivity concentration sensor 11 can be improved.

  The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.

  For example, the radioactivity concentration measuring apparatus 1 includes two or more reference measurement units such as a third reference measurement unit and a fourth reference measurement unit in addition to the first and second reference measurement units. May be provided. According to such a configuration, a plurality of combination data of the radioactivity concentration and the reference detection value is obtained corresponding to the number of reference measurement units. For this reason, the conversion function can be a high-order function such as a quadratic function or a cubic function, or an approximate function using a plurality of data. Therefore, it is possible to improve the conversion accuracy for converting the measured detection value to the radioactive concentration.

  In order to improve the measurement accuracy of the radioactivity concentration of the object 7 to be measured, the first radiation source unit and the second radiation source unit include radiation source bodies having different densities and obtain a reference detection value. Depending on the density of the measurement object 7, a reference radiation source having a substantially equivalent density may be selected as appropriate. For example, when the measurement object 7 is soil, a reference radiation source having a density equivalent to that of the soil may be selected. In addition, when the measurement object 7 is a plant, a reference radiation source having a density equivalent to that of the plant may be selected.

DESCRIPTION OF SYMBOLS 1 ... Radioactivity concentration measuring device, 2 ... Measurement part for to-be-measured object, 3 ... Reference | standard measurement part (1st reference | standard measurement part), 3a ... Reference | standard radiation source body (1st radiation source part), 4 ... Reference measurement unit (second reference measurement unit), 4a ... reference radiation source body (second radiation source unit), 6 ... processing unit, 7 ... measurement object, 8, 8a to 8b ... bag, 9 ... Effective detection area, 11 ... Radioactivity concentration sensor (measurement object sensor, first reference sensor, second reference sensor), 11a ... measurement surface, 12 ... simple shield (measurement object shield, first 14 ... measurement detection value input unit, 16 ... reference detection value input unit, 17 ... reference activity concentration input unit, 18 ... conversion function calculation unit, 19 ... measurement Value calculation unit, 21 ... input device, 22 ... output device, 23 ... storage area, 24 ... truck, B1, B2, BS ... radioactivity concentration, C , C2 ... reference detection value, CS ... measurement detection value.

Claims (3)

In the radioactivity concentration measurement device that obtains the radioactivity concentration of the object to be measured including radioactive substances,
A measurement unit for a measurement object for obtaining a measurement detection value indicating the radioactivity concentration of the measurement object;
A first reference measurement unit for obtaining a first reference detection value indicating the first radioactive concentration in the first radiation source unit having a known radioactive concentration;
A second reference measurement unit for obtaining a second reference detection value indicating the second radioactive concentration in the second radiation source unit having a known radioactive concentration;
A conversion function is calculated using the first radioactivity concentration, the second radioactivity concentration, the first reference detection value, and the second reference detection value, and the conversion function, the measurement detection value, A processing unit that calculates the radioactivity concentration of the object to be measured using
The first radiation source unit and the second radiation source unit are arranged close to the object to be measured,
The first reference detection value and the second reference detection value are acquired at the same timing as the measurement detection value,
The radioactivity concentration measuring device, wherein the value of the first radioactivity concentration is different from the value of the second radioactivity concentration. The measurement object measurement unit has a measurement object sensor that contacts the measurement object and measures the measurement detection value.
The first reference measurement unit includes a first reference sensor that contacts the first radiation source unit and measures the first reference detection value.
2. The radioactivity concentration measurement according to claim 1, wherein the second reference measurement unit includes a second reference sensor that contacts the second radiation source unit and measures the second reference detection value. apparatus. The measurement object measurement unit further includes a measurement object shield that covers an area of the measurement object that is in contact with the measurement object sensor,
The first reference measurement unit further includes a first reference shield that covers a region of the first radiation source unit that is in contact with the first reference sensor.
3. The radioactivity according to claim 2, wherein the second reference measurement unit further includes a second reference shield that covers an area of the second radiation source unit that is in contact with the second reference sensor. Concentration measuring device.

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