KR20160109696A - Apparatus and method for determining source depth and radioactivity in medium - Google Patents

Abstract

The present invention relates to an apparatus and a method of simply determining a source depth and radioactivity in a medium without relying on a radiation detector on a screen realized in excel visual basic application (VBA). The method of determining a source depth and radioactivity in a medium comprises: a step of calculating a theoretical radiation fluence rate, and a radiation count rate measured with respect to a source in an actual medium at two radiation detector heights; a step of determining a depth where the radiation fluence rate is identical to the radiation count rate by changing the depth of the source in the medium; and a step of determining the radioactivity of the source in the medium by correcting a density of the radiation fluence measured in a determined depth of the source in the medium.

Description

[0001] APPARATUS AND METHOD FOR DETERMINING SOURCE DEPTH AND RADIOACTIVITY IN MEDIUM [0002]

The present invention relates to a radioactivity determining apparatus and method that can easily determine the depth and radioactivity of a nuclide in a medium without depending on a radiation detector.

For dismantling or decontamination of nuclear facilities, it is necessary to find the depth of the maximum radioactivity concentration in the medium in which radioactive contamination is present, or to determine the depth of the actually embedded radioisotope (RI) in the medium.

Spectroscopic analysis using a mobile radiation detector is used for this purpose. A method using a specific algorithm (Health Physics, vol. 84 (5), p. 632-636) developed by Al-Ghamdi et al. However, this method can only detect the depth of the radioactive material buried in the medium, but it does not provide information about the radioactivity value of the radioactive material at the found depth.

Therefore, in order to determine the radioactivity, another in-situ program should be used, the program is entirely dependent on imports, and due to the nature of on-site analytical programs provided by major majors, Is required.

Figure 1 shows an arrangement of radionuclides and a radiation detector.

Referring to FIG. 1, a simple method (algorithm) for finding the depth of the radionuclide (or source) S buried in the medium 100 can be represented by Equation (1). The method is described in detail in Al-Ghamdi's paper and is now widely used in on-site analysis.

[Equation 1]

Where C ₁ (E) and C ₂ (E) are the height h ₁ of the radiation detector 200 And the counting rate (cps) of the radiation E at energy h ₂ , where x is the depth in the media.

By the way, the detector height (h ₁ And h ₂ mean the distance to the effective center d of the radiation detection area, not the height to the incident surface of the radiation detector 200, as shown in Fig. That is, the distance from the incidence plane to the effective center d is different for each radiation detector used.

Therefore, in case of using the above method, it is necessary to experimentally determine the effective center value of the used radiation detector. In addition, since the position information on the right side in Equation 1 is a ratio of the second order, even if the effective center distance of the detector 200 is small, its dependency is large, which depends on the detector used (To be influenced).

In order to measure (determine) the radioactivity of the radionuclide (S) present at the measured depth (x), an expensive modeling program equipped with theoretical simulation function is required. FIG. 2 shows an ISOCS (in-situ object counting system) modeling program of Canberra equipped with a simulation function.

However, the modeling program as described above is not only expensive, but also requires expert knowledge for operating the program in order to obtain accurate measurement values, which inevitably leads to time and cost disadvantages.

It is an object of the present invention to provide an apparatus and method for determining the depth and radioactivity of a radionuclide in a medium that can measure the depth and radioactivity of the radionuclide in the medium without depending on the radiation detector.

It is another object of the present invention to provide an apparatus and method for determining the depth and radioactivity of a radionuclide in a medium, which can be simultaneously implemented in a single program to measure the depth and radioactivity of the radionuclide in the medium.

It is another object of the present invention to provide an apparatus and method for determining the depth and radioactivity of a radionuclide in a medium, which can be easily utilized by anyone who implements all procedures for calculating the radioactivity and the depth in the medium of the radionuclide on an Excel program basis.

In order to achieve the above object, a method of determining the depth and radioactivity of a radionuclide in a medium according to an embodiment of the present invention is characterized in that a ratio of a theoretical radionuclide ratio to a radionuclide ratio Calculating; Varying the depth of the nuclide in the medium to determine the depth at which the radiation fluence ratio and the radiation rate ratio are equal; And determining the radioactivity of the nuclide in the medium by correcting the density of the measured radiation fluences at the determined depth of the nuclide in the medium.

Calculating the rate ratio comprises: selecting the energy of the radionuclide and the height of the radiation detector; Calculating radiation fluences along a depth of the radionuclide in the medium at the selected two radiation detector heights; Calculating a radiation count rate by inputting a count value and a measurement time of a gamma ray emitted from a radionuclide at the height of the two radiation detectors; And calculating the radiation fluence ratio and the radiation count ratio at the two radiation detector heights.

The step of determining the depth of the nuclide in the medium is implemented by an Excel VBA (visual basic application), and the depth of the nuclide is changed by the scroll bar displayed in association with the depth value of the nuclide.

Determining the radioactivity of the nuclide comprises calculating radiation fluence at each detector height according to the determined depth of the radionuclide; Calculating a response function value of the detector with respect to the energy of the radionuclide; Correcting the density of the calculated fluence to the density of the actual medium; Multiplying the density-corrected fluence by the calculated response function value to calculate a calibration value; And determining the radioactivity of the radionuclide using the calculated radiation count value at each detector height, the calculated calibration value, and the gamma radiation rate of the radionuclide in the medium.

The step of determining the radioactivity of the nuclide is implemented as an Excel VBA (visual basic application).

According to an aspect of the present invention, there is provided an apparatus for determining the depth and radioactivity of a nuclide in a medium, comprising: a radiation detector for measuring radiation of a nuclide in the medium; And the ratio of the actual radiation flux ratio of the radionuclide in the medium to the theoretical radiation fluence ratio at different heights of the radiation detector and the depth of the radionuclide having the same ratio of the radiation fluence ratio to the radiation ratio, And a control device for determining the radioactivity of the nuclide at the depth of the determined nuclide.

The method of determining the depth and radioactivity of a nuclide in a medium according to an embodiment of the present invention is to determine the depth of the maximum radioactive concentration in a medium in which radioactive contamination exists for decomposition or decontamination of a nuclear power facility, It is possible to easily find the depth of the element itself.

The method of determining the depth and radioactivity of a radionuclide in a medium according to an embodiment of the present invention is a database of theoretical calculation results of a simple radiation fluence without the aid of an expensive field analysis program which is totally dependent on importation. Can be accurately calculated.

The method of determining the depth and radioactivity of the radionuclide in the medium according to the embodiment of the present invention has an effect of easily detecting the depth of the radionuclide only by the counting rate of the altitude regardless of the type of the detector used.

The depth and radioactivity determination method of the nuclide in the medium according to the embodiment of the present invention can realize all the procedures for calculating the depth of the radionuclide and calculating the radioactivity in the Excel program base so that anyone can easily utilize it without the expertise in the calculation of radioactivity and program operation There are advantages to be able to.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows an example of a radionuclide and detector arrangement.
FIG. 2 is a diagram illustrating an ISOCS modeling program. FIG.
Figure 3 is a graph showing radiation fluence measured according to the nuclide depth in the medium at the height of the radiation detector.
4 is a flowchart illustrating a method of determining the depth and radioactivity of a nuclide according to an embodiment of the present invention.
5 and 6 show an example of a program screen in which the step of determining the depth of a nuclide is implemented by an Excel VBA (visual basic application).
FIG. 7 shows an example of a program screen in which the step of determining the radioactivity of a nuclide is implemented with Excel VBA.
8 is an embodiment showing a density correction method of radiation fluence.

In the present specification, the same or similar elements are denoted by the same reference numerals regardless of the reference numerals, and redundant explanations thereof will be omitted. The terms "algorithm", "program" and "method" used in the following description are to be given or mixed only in consideration of ease of specification, and they do not have their own meaning or role.

 The objects, features and advantages of the present invention will become more apparent from the following detailed description taken in connection with the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. In addition, it should be noted that the attached drawings are only for easy understanding of the embodiments disclosed in the present specification, and should not be construed as limiting the technical idea disclosed in the present specification by the attached drawings.

In the past, the depth and radioactivity of radionuclides in the medium were determined by using a different program, ie, a detector, to find the depth of the radionuclide in the medium (algorithm) and to determine the radioactivity of the radionuclide. As a result, it took a lot of time and money to operate each program.

Therefore, the present invention proposes a method for determining the depth and radioactivity in a medium of a nuclide using a single program without depending on a detector.

The present invention employs the arrangement of the radionuclide and the radiation detector shown in FIG. 1, and a controller is connected to the radiation detector to determine the depth and the radioactivity of the radionuclide. The control device may include a display unit and an input unit for user input. For example, the control device may be a PC.

The present invention is not limited to this, and the control device may be provided in the radiation detector. In this case, the display unit is implemented so that touch input is possible.

All procedures for determining the depth and activity of the radionuclide are implemented on an Excel program base and displayed on the screen of the controller. The operator obtains the depth and the radioactivity of the radionuclide on the screen implemented with Excel using the calculated radiation rate through the radiation detector and the theoretically calculated fluence.

In the present invention, a method (algorithm) for finding the depth in the medium of a radionuclide can be expressed by the following equation (2). The above method is based on the theory that, when there is a radionuclide at a certain depth in the medium, theoretically calculated ratio of the radiation fluences (number of radiation per unit area) at two detector heights to the counting rate measured by the actual radiation detector is in principle the same depart.

&Quot; (2) "

Here, C _i (E) and C _j (E) represent the counting rate (cps) of the radiation E at the height i and j of the radiation detector, and F _i (E) and F _j Which is the energy (E) at the height.

Therefore, when the equations (1) and (2) are compared, the right of the fluence ratio in the equation (2) is the ratio to the first order, so that the dependence of the distance on the second order of the distance of the formula Information about the effective center of the detector becomes unnecessary.

The theoretical radiation fluence is easily calculated by the Monte Carlo method. For example, FIG. 3 discloses radiation fluences at depth and detector height in the media for Cs-137 662 keV gamma rays calculated using MCNP codes.

As shown in Fig. 3, when the detector heights (i, j) are respectively determined, the fluence values (F _i , F _j ) according to the depth in the medium of the radionuclide at the corresponding heights are calculated from the graphs As shown in Fig.

&Quot; (3) "

&Quot; (4) "

Here, a, b, c, d, e, f, g and h mean constants based on fitting results, and x means depth of nuclides in the medium. And, the scale of the F values is the natural log (log 10) scale.

Therefore, the ratio (F _i / F _j ) of the two fluences is checked while changing the depth in the medium of the nuclide, and the two fluence ratios (F _i / F _j ) (C _i / C _j ), the corresponding depth is the depth (x) in the medium of the radionuclide.

The present invention can simultaneously determine the depth and radioactivity of a nuclide in a medium in a program screen implemented with an Excel VBA (visual basic application).

FIG. 4 is a flowchart illustrating a method of determining the depth and radioactivity of a nuclide according to an embodiment of the present invention. FIGS. 5 and 6 are flowcharts illustrating steps of determining a depth of a nuclide using an Excel VBA (visual basic application) Yes.

Determination of the depth of nuclides in the medium

4 and 5, first, the energy of the nuclide and the height of the radiation detector are selected (S100), the theoretical radiation fluence at the height is calculated, the measurement time and the count value are input, The radiation count rate is measured (S110).

The steps S100 and S110 may be performed through blocks (or areas) 1 and 2 (50 and 51) of the screen in FIG.

That is, the operator first selects energy (keV) and detector heights (h1-h3) of the radionuclide using a combo box in block 1 (50) (photon energy & geometry). In this case, the height h of the detector can be measured at two points and compared once, but it is preferable to obtain three comparison data by measuring at three points (h1 to h3) for accurate determination (F3 / F2, F3 / F1, F2 / F1).

If the energy (keV) of the radionuclide and the detector heights (h1-h3) are selected, the controller displays in the graph at the bottom of the screen a plot of the radionuclide heights (h1, h2, h3) Radiation fluences (F1, F2, F3) are diagrammed and displayed, which can utilize the fitting results of FIG.

The block 2 51 is a part indicating the measurement results of the radiation detectors D1 to D3 and is a part of the radiation emitted from the corresponding radionuclide at the detector heights h1 to h3 measured by the radiation detectors D1 to D3. (Counts) of the gamma ray and the measurement time (s) are input respectively. When the count value (counts) and the measurement time (s) of the gamma ray are input and the cps_calculator button is clicked, the control unit calculates the counting rate.

Then, the control unit calculates the fluence ratio between the height of the two detectors according to the depth of the nuclide using equations (3) and (4), displays them on the fluence column, calculates the ratio of counting rate based on the counting rate obtained in step (Step S120). In addition, the above table also shows the ratio of the counting rate to the fluence (cps / fluence).

(Cps & fluence ratio) in the counting rate (cps) column, a counting ratio ratio in h3 and h2 at a predetermined nuclide depth (eg, 0.1 cm), h3 And the ratio of counting rate at h1 and the ratio of counting rate at h2 and h1 are calculated and displayed.

Therefore, when the operator changes the depth of the nuclide, the controller determines the depth of the radionuclide in the medium by the depth at which the ratio of the radiological fluence and the ratio coincides with each other (S130). 5, when the operator moves the scroll bar 60 indicating the depth of the nuclide in the soil (d), the fluence ratio F _i / F _j and the counting ratio C _j / C _i ), that is, the exact depth (d) of the nuclide in the soil.

The depth d of the radionuclide is displayed in the area 61 of the block 3 every time the scroll bar 60 is moved and the fluence ratio at the detector height by the radionuclide emitted at the displayed depth d, 3 < / RTI >

Therefore, as shown in Fig. 6, the movement of the scroll bar 60 causes the values of the counting rate column and the fluence column at block 3 to become equal, resulting in a point at which the right cps / fluence column values become almost 1 (D) of the radionuclide. That is, the depth displayed in the region 61 when the cps / fluence column values become almost 1 by the movement of the scroll bar 60 is the exact depth d of the radionuclide. For example, the depth (d) of the radionuclide (Cs-137) is 36.8 cm, which is almost identical to the actual depth of the source (37 cm).

Therefore, since the present invention determines the ratio of the two radiation fluences to determine the depth of the nuclide in the medium, this value is independent of the density because the density term of the medium is canceled. Therefore, the fluence ratio may be obtained for one arbitrarily designated medium density.

Thereafter, the controller may determine the radioactivity using the radiation crystallization formula at the depth of the determined nuclide (S150).

An advantage of the method according to the present invention is that the depth of the nuclide in the medium is determined by using radioactive fluences, and knowing the fluence at that depth provides information that can determine the radioactivity of the radionuclide. That is, the radioactivity from the fluence value can be directly determined using the following equation (5) without the need for a program for another expensive radioactivity calculation. Equation (5) is obtained from H.L. The method proposed by Beck et al. Is detailed in HASL-258.

&Quot; (5) "

Here, φ / γ is the fluence at the detector height per radiation emitted from the radionuclide in the medium, the depth (d) calculated in FIG. 6 and the fluence at the detector height can be found in the graph in FIG. N ₀ / φ can be calculated theoretically using the MCNP code or the like as a reaction function of the detector for radiation incident parallel to the detector axis. N / N ₀ is the correction term for the angle of the fluence incident on the actual detector. It is close to 1 when the radionuclide in the medium is dotted line. Even if it is a source of sufficiently large area, it is possible to use a collimator As shown in Fig. 1, when the shield is closed, the angular correction term of the fluence entering the detector becomes close to 1 as well. And N / γ is the theoretical calibration function, which means the counting rate at the detector height per unit gamma ray emitted from the radionuclide in the medium.

Determination of radioactivity of nuclides in medium

FIG. 7 is an example of a program screen in which the radioactivity of a nuclide is determined by an Excel VBA, and FIG. 8 is an embodiment showing a density correction method of radiation fluence.

Referring to FIG. 7, when the fluence calculator button is clicked in block 1 (fluence from the embedded source), the controller calculates the detector height h1 (d) according to the depth (d) to h3 are calculated in the fluence graph of FIG. 6 and displayed in the table of block 1 (70). In this case, the angular correction term (N / N0) of the fluence may be calculated separately, but it may be set to 1 when it is assumed to be a dotted circle or when the detector is shielded by a collimator.

In Block 2 (71) (detector response for incident photon fluence), select the radiation detector (eg, HPGe) used for the actual measurement with the option button and press the response_calculator button, The detector response function N ₀ / φ value (eg, 8.9178) is displayed. It utilizes a database of results computed with MCNP and can be found in the detector response graph on the right side of the screen. For this purpose, a database should be preceded by a detector.

If the above two processes are performed, the theoretical calibration function (N / γ) can be directly obtained by using the equation (5), but the fluence values calculated in the block 1 70 can be obtained when the density of the medium is 1.6 g / Value, it should be converted into the fluence value for the actual medium density. Therefore, H.L. Equation 5 proposed by Beck et al. Should be transformed into Equation 6 below.

&Quot; (6) "

Here, f (ρ) / f (1.6) is the fluence per unit radiance calculated at the medium density of 1.6 g / cm 3 and the fluence per unit radiance f (ρ) = φ (ρ) f (1.6) =? (1.6) /?

The values of f (rho) / f (1.6) can be found by theoretical calculations and FIG. 9 shows the ratio of fluences emitted from various depths in the medium to the 662 keV gamma ray of Cs-137.

Accordingly, when the depth of the nuclide in the medium is determined using the scroll bar 60 of FIG. 6, the depth of the nuclide corresponding to the depth is selected to fit the values of f (?) / F (1.6) Can be used. At this time, the fitting result can be expressed by Equation (7).

&Quot; (7) "

Here, a and b are constants based on fitting results, and the y-axis, f (ρ) / f (1.6), can be expressed as a first order of density when expressed as a log10 scale.

Therefore, in order to correct the density accurately for the fluence, the density value (eg, 1 g / cm ³ ) of the actual medium is input first in block 3 72 (calibration factor for the embedded source) Use the box to select a reference source depth (eg, 35 cm) similar to the depth of the source found previously (36.8 cm). Then, the values of f (ρ) / f (1.6) according to the density of the medium at the corresponding depth are plotted on the right graph, and the values for the density entered are calculated and displayed.

The value of f (rho) / f (1.6) in block 3 (72) is also user input. That is, if the comparison depth is 37 cm, an average of f (?) / F (1.6) values at 35 cm and 40 cm may be used.

)이 검출기 높이에 따라 블록 3 내(73)의 표에 표시된다. Then, when the CF_calculator button in the block 3 (72) is pressed, the fluence correction value (eg, 4.9877) for the actual density and the calculation result of the equation (6)

) Is displayed in the table in block 3 according to the height of the detector.

Finally, the radioactivity value of the radionuclide at any depth in the medium is calculated by block 4 (73) of FIG. First, when the counting rate calculator button of the block 2 51 is pressed on the screen for finding the depth of the nuclides in FIG. 5, the radiation count rate (cps) measured at the height of the detector is displayed in block 4 (73) of FIG.

Therefore, the radioactivity value is determined by the following equation (8) using the counting rate value measured at each detector height, the calibration value calculated in block 3 (72), and the gamma ray emission rate (Y) of the radionuclide in the medium.

&Quot; (8) "

Here, N (cps) is the value of the radiation count rate measured at the detector height, CF (cps / gamma) is the calibration value calculated in block 3 (72) of FIG. 7, and Y is the gamma radiation rate of the radionuclide in the medium .

In the present invention, for convenience of description, a method of determining the depth and radioactivity of a nuclide in a medium by dividing program screens implemented in Excel VBA has been described, but in reality, both control screens operate on the same page of Excel.

As described above, It is possible to find the depth of the maximum radioactivity concentration in the medium in which radioactive contamination exists or to simply find the depth of the actually buried unknown radioactive isotope itself in the medium for disassembly or decontamination of the nuclear facility.

The present invention can accurately calculate the radioactivity of the radionuclide in the medium to a database (DB) of the theoretical calculation results of simple radiation fluences, without the aid of expensive in-situ programs that are entirely dependent on imports .

Further, the present invention can easily find the depth of the radionuclide only by the counting rate of each altitude regardless of the type of detector used.

In addition, the present invention implements all procedures for finding depth and calculating radioactivity on an Excel program basis, so that anyone can easily utilize the procedure without any expertise in radiation calculation and program operation.

The present invention described above can be embodied as computer-readable codes on a medium on which a program is recorded. The computer readable medium includes all kinds of recording devices in which data that can be read by a computer system is stored. Examples of the computer readable medium include a hard disk drive (HDD), a solid state disk (SSD), a silicon disk drive (SDD), a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, , And may also be implemented in the form of a carrier wave (e.g., transmission over the Internet). Also, the computer may include a control unit 180 of the terminal. Accordingly, the above description should not be construed in a limiting sense in all respects and should be considered illustrative. The scope of the present invention should be determined by rational interpretation of the appended claims, and all changes within the scope of equivalents of the present invention are included in the scope of the present invention.

100: medium 200: radiation detector
50 to 53, 70 to 73: block (area) 60: scroll bar
61: Nuclide depth display area

Claims (17)

Calculating a theoretical radiation fluence ratio at the height of the two radiation detectors and a ratio of the radiation count ratio measured for the intracellular nuclides;
Determining the depth at which the radiation fluence ratio and the radiation rate ratio are equal to the depth of the nuclide by varying the depth of the nuclide in the medium; And
And determining the radioactivity of the radionuclide in the medium by correcting the density of the radiation fluences measured at the depth of the determined radionuclide. The method of claim 1, wherein the radiation fluence comprises
Lt; RTI ID = 0.0 > MCNP < / RTI > code. The method of claim 1, wherein the radiation fluence comprises
Wherein the density of the medium is corrected to the density of the actual medium once the depth of the radionuclide in the medium is determined, with the fluence calculated at the density of the medium of 1.6 g / cm < ³ >. 2. The method of claim 1, wherein calculating the rate ratio further comprises:
Selecting the energy of the radionuclide and the height of the radiation detector;
Calculating radiation fluences along a depth of the radionuclide in the medium at the selected two radiation detector heights;
Calculating a radiation count rate by inputting a count value and a measurement time of a gamma ray emitted from the radionuclide at the height of the two radiation detectors; And
Calculating a ratio of the radiation fluence ratio and the radiation count ratio at the height of the two radiation detectors. 5. The method of claim 4, wherein determining the depth of the nuclide in the medium
It is implemented as an Excel VBA (visual basic application)
Wherein the depth of the nuclide is changed by a scroll bar displayed in association with a depth value of the nuclide. The method of claim 1, wherein determining the radioactivity of the nuclide comprises:
Calculating radiation fluences at each detector height according to the depth of the determined radionuclide;
Calculating a response function value of the detector with respect to the energy of the radionuclide;
Correcting the density of the calculated fluence to the density of the actual medium;
Multiplying the density-corrected fluence by the calculated response function value to calculate a calibration value; And
Determining the radioactivity of the radionuclide using the calculated radiation count values at the respective detector heights, the calculated calibration values, and the gamma ray emission rates of the radionuclides in the medium. 7. The method of claim 6, wherein determining the radioactivity of the nuclide comprises:
Characterized in that it is implemented as an Excel VBA (visual basic application). 7. The method of claim 6, wherein the radioactivity of the nuclide is
Is determined by the following equation.

Where N (cps) is the radiation count value measured at the detector height, CF (cps / y) is the radiation fluence corrected at the density of the actual medium, and Y is the gamma radiation release rate of the radionuclide in the medium. A radiation detector for measuring the radiation fluence of the nuclides in the medium; And
We calculated the ratio of the radionuclides of the radionuclides in the medium to the theoretical radionuclide ratios at different heights of the radiation detectors and calculated the depth of the radionuclides with the same ratio of radionuclide to radiation ratio, And determining a radioactivity of the radionuclide at the depth of the determined radionuclide. 10. The apparatus according to claim 9, wherein the control device
Characterized in that the radiation fluence is theoretically calculated using an MCNP code. 10. The apparatus according to claim 9, wherein the control device
The energy of the radionuclide and the height of the radiation detector are selected,
Calculating radiation fluences along a predetermined depth of the radionuclide in the medium at the selected two radiation detector heights,
The coefficient of the gamma ray emitted from the radionuclide at the height of the two radiation detectors and the measurement time are input to measure the radiation count rate,
And calculating the radiation fluence ratio and the radiation count ratio at the two radiation detector heights. 12. The apparatus of claim 11, wherein the control device
Wherein the nuclide depth determination screen implemented by an Excel VBA (visual basic application) is displayed, and the depth of the nuclide is varied by a scroll bar displayed in association with a depth value of the nuclide. 10. The apparatus according to claim 9, wherein the control device
Calculating the radiation fluence at each detector height according to the depth of the determined radionuclide,
Calculating a response function value of the detector with respect to the energy of the radionuclide,
Correcting the density of the calculated fluences to the density of the actual medium,
Multiplying the density-corrected fluence by the calculated response function value to calculate a calibration value,
Wherein the radioactivity of the radionuclide is determined using the values of the radiation count rate measured at each detector height, the calculated calibration value, and the gamma radiation rate of the radionuclide in the medium. 14. The apparatus of claim 13, wherein the control device
Characterized in that a radioactivity determination screen implemented by an Excel VBA (visual basic application) is displayed. 14. The apparatus of claim 13, wherein the control device
Wherein the radioactivity of the nuclide is determined by the following equation.

Where N (cps) is the radiation count value measured at the detector height, CF (cps / y) is the radiation fluence corrected at the density of the actual medium, and Y is the gamma radiation release rate of the radionuclide in the medium. Calculating the ratio of the radiation dose rate measured at the height of the two radiation detectors to the theoretical radiation fluence ratio and the radionuclide in the actual medium; Varying the depth of the nuclide in the medium to determine the depth at which the radiation fluence ratio and the radiation rate ratio are equal; And determining the radioactivity of the radionuclide in the medium by correcting the density of the radiation fluences measured at the determined depth of the radionuclide in the medium. Calculating the ratio of the radiation dose rate measured at the height of the two radiation detectors to the theoretical radiation fluence ratio and the radionuclide in the actual medium; Varying the depth of the nuclide in the medium to determine the depth at which the radiation fluence ratio and the radiation rate ratio are equal; And determining the radioactivity of the radionuclide in the medium by correcting the density of the measured radiation fluences at the determined depth of the radionuclide in the medium.

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