Method for correcting gamma ray spectrum of nai(TL) detector

Abstract

The present invention relates to a method for correcting a channel shift of a gamma ray spectrum measured by a NaI(Tl) detector, the method comprising the steps of: acquiring a gamma ray spectrum of a reference source; setting, as a reference channel, a position of a peak channel in the gamma ray spectrum of the reference source; acquiring a gamma ray spectrum of a quality control (QC) source; calculating the amount of channel shift by calculating the difference between the reference channel and a peak channel in the gamma ray spectrum of the QC source; and correcting the gamma ray spectrum of the QC source on the basis of the calculated amount.

Description

Correction method for the gamma-ray spectrum of an NAI(TL) detector

[0001] The present invention relates to a method for correcting the gamma ray spectrum of a NaI(Tl) detector.

[0002] The NaI(Tl) detector is a detector widely used for gamma ray measurement and consists of a crystal NaI(Tl) element, a photomultiplier tube, and a preamplifier.

[0003] When gamma rays interact with the NaI(Tl) element, light is generated, and the amount of this light is proportional to the energy of the incident gamma rays. The generated light is converted into an electrical signal by a photomultiplier tube, amplified, and output in the form of pulses that can be analyzed by a multi-channel pulse height analyzer (MCA). The MCA generates a gamma ray spectrum by analyzing the height of the pulses, which allows for the analysis of the type and amount of radioactive isotopes.

[0004] However, NaI(Tl) detectors have the disadvantage of being sensitive to changes in ambient temperature. As the amount of light emitted from the NaI(Tl) element changes when the temperature changes, the pulse height changes even for gamma rays of the same energy. This causes a channel shift in the spectrum appearing in the MCA, which consequently lowers the accuracy of radionuclide analysis.

[0005] Therefore, a technology is required to minimize the influence of temperature changes and improve the accuracy of radionuclide analysis in gamma-ray spectrum analysis using NaI(Tl) detectors.

[0006] The object of the present invention is to provide a method for correcting the gamma ray spectrum of a NaI(Tl) detector.

[0007] The present invention relates to a method for correcting channel shift of a gamma ray spectrum measured in a NaI(Tl) detector, comprising: acquiring a gamma ray spectrum of a reference source; setting a peak channel position in the gamma ray spectrum of the reference source as a reference channel; acquiring a gamma ray spectrum of a quality control (QC) source; calculating a channel shift amount by calculating the difference between the peak channel in the gamma ray spectrum of the QC source and the reference channel; and correcting the gamma ray spectrum of the QC source based on the calculated value.

[0008] The step of acquiring the gamma ray spectra of the reference source and the QC source may include: bringing the reference source and the QC source close to a NaI(Tl) detector; amplifying the signal output from the NaI(Tl) detector; converting the amplified signal into a digital signal using a multi-channel analyzer (MCA); and generating a gamma ray spectrum using the digital signal.

[0009] The step of acquiring the gamma ray spectrum of the reference source further includes the step of retrieving the gamma ray spectrum of the reference source that was previously stored, and the gamma ray spectrum of the reference source may be the average value of the gamma ray spectra measured over a certain period of time.

[0010] The step of setting the reference channel above may set the channel having the maximum count value in the gamma ray spectrum of the reference source and / or the channel corresponding to the center value in the peak region as the reference channel.

[0011] The step of obtaining the above-mentioned output value may include: calculating the Jensen-Shannon Divergence (JSD) between the gamma ray spectrum of the QC source and the gamma ray spectrum of the reference source within a preset range centered on the reference channel; assigning weights by multiplying the JSD value for each channel by a channel shift amount; and determining the channel shift amount at which the weight has a minimum value as the channel shift amount.

[0012] The step of calculating the above Jensen-Shannon Divergence (JSD) can use the following [Equation 1].

[0013] [Mathematical Formula 1]

[0014]

[0015]

[0016]

[0017]

[0018] Here, P is the reference line 137 Cs is the channel-specific normalized count in the 300–400 channel range, and Q is the channel-specific normalized count in the 300–400 channel range of the QC source. Here, P, Q, and M are column vectors, each with 100 elements.

[0019] The step of correcting the gamma ray spectrum of the above QC source can shift the gamma ray spectrum of the above QC source by the channel shift amount.

[0020] The above standard crew member 137 It can include Cs.

[0021] The above QC crew member 137 Cs and 60 It may include at least one of Co.

[0022] The above method can be used for quality control of internal exposure dose measurement equipment in nuclear power plants.

[0023] According to the present invention, a method for correcting the gamma ray spectrum of a NaI(Tl) detector is provided.

[0024] FIG. 1 is a flowchart illustrating a method for correcting the gamma ray spectrum of a NaI(Tl) detector according to an embodiment of the present invention, and

[0025] FIG. 2 shows the gamma ray spectrum of a reference source measured by a NaI(Tl) detector according to an embodiment of the present invention, and

[0026] FIG. 3 shows the peak channels of the gamma ray spectra of a reference source and a quality control source measured by a NaI(Tl) detector according to an embodiment of the present invention, and

[0027] FIG. 4 shows the JSD value between the peak channels of the gamma ray spectra of a reference source and a quality control source measured by a NaI(Tl) detector according to an embodiment of the present invention, and

[0028] Figure 5 shows the result value according to the correction of the gamma ray spectrum of a quality control source according to an embodiment of the present invention.

[0029] The present invention will be described in more detail below with reference to the drawings.

[0030] The attached drawings are merely examples illustrated to further explain the technical concept of the present invention, and therefore the concept of the present invention is not limited to the attached drawings. Additionally, the sizes and spacing, etc., in the attached drawings may be exaggerated from reality to explain the relationships between the components.

[0031] With reference to FIGS. 1 to 5, a method for correcting the gamma ray spectrum of a NaI(Tl) detector according to an embodiment of the present invention (hereinafter referred to as the “correction method”) will be described.

[0032] FIG. 1 is a flowchart showing a method for correcting the gamma ray spectrum of a NaI(Tl) detector according to an embodiment of the present invention, FIG. 2 shows the gamma ray spectrum of a reference source measured by a NaI(Tl) detector according to an embodiment of the present invention, FIG. 3 shows the peak channels of the gamma ray spectra of a reference source and a quality control source measured by a NaI(Tl) detector according to an embodiment of the present invention, FIG. 4 shows the JSD values ​​between the peak channels of the gamma ray spectra of a reference source and a quality control source measured by a NaI(Tl) detector according to an embodiment of the present invention, and FIG. 5 shows the result values ​​according to the correction of the gamma ray spectrum of a quality control source according to an embodiment of the present invention.

[0033] A correction method according to one embodiment of the present invention includes, as illustrated in FIG. 1, a step of acquiring a gamma ray spectrum of a reference source (S100), a step of setting a peak channel position in the gamma ray spectrum of the reference source as a reference channel (S200), a step of acquiring a gamma ray spectrum of a quality control (QC) source (S300), a step of calculating a channel shift amount by calculating the difference between the peak channel and the reference channel in the gamma ray spectrum of the QC source (S400), and a step of correcting the gamma ray spectrum of the QC source based on the calculated value (S500).

[0034] First, the standard crew ( 137 The gamma ray spectrum of Cs) is obtained. (S100) As a reference source, 137 It uses Cs, which emits a single-energy gamma ray of 662 keV.

[0035] In step S100, the reference source can acquire the gamma ray spectrum of the 137Cs source using a NaI(Tl) detector.

[0036] A specific method for obtaining the gamma-ray spectrum of a reference source involves bringing the reference source close to a NaI(Tl) detector, amplifying the signal output from the NaI(Tl) detector, converting the amplified signal into a digital signal using a multi-channel analyzer (MCA), and then generating the gamma-ray spectrum of the reference source using the digital signal.

[0037] Here, the average value of the gamma ray spectrum measured over a certain period of time may be used to ensure the stability of the measurement environment. Additionally, step S100 may retrieve the gamma ray spectrum of a reference source that has been measured and stored in advance.

[0038] Next, referring to FIG. 2, the peak channel position in the gamma ray spectrum of the reference source is set as the reference channel. (S200)

[0039] In the S200 stage, acquired 137 The channel with the maximum count value in the Cs gamma ray spectrum and / or the channel corresponding to the center value in the peak region is set as the reference channel.

[0040] Subsequently, the gamma ray spectrum of the quality control (QC) source is obtained. (S300) Here, the QC source is 137 Cs Department 60 Use a mixed source containing Co. 60 Co emits two energies of gamma rays: 1173 keV and 1332 keV.

[0041] In the S300 step, the specific method for acquiring the gamma-ray spectrum of the QC source is the same as acquiring the gamma-ray spectrum of the reference source; after bringing the QC source close to the NaI(Tl) detector, the signal output from the NaI(Tl) detector is amplified, the amplified signal is converted into a digital signal using a multi-channel analyzer (MCA), and then the gamma-ray spectrum of the QC source is generated using the digital signal.

[0042] Next, the channel shift amount is calculated by calculating the difference between the peak channel and the reference channel in the gamma ray spectrum of the QC source. (S400)

[0043] In the S400 stage, in the gamma ray spectrum of the QC source 137 The channel shift amount is calculated by determining the difference between the channel corresponding to the Cs peak and the reference channel.

[0044] 137 The Cs peak channel can use the channel with the maximum count value or the channel corresponding to the center value in the peak region.

[0045] The step of obtaining the output value in the S400 step is performed by calculating the Jensen-Shannon Divergence (JSD) between the gamma ray spectrum of the QC source and the gamma ray spectrum of the reference source within a preset range centered on the reference channel.

[0046] Here, the JSD calculation uses the following mathematical formula 1.

[0047] [Mathematical Formula 1]

[0048]

[0049]

[0050]

[0051]

[0052] Here, P is the reference line 137 Cs is the channel-specific normalized count in the 300–400 channel range, and Q is the channel-specific normalized count in the 300–400 channel range of the QC source. Here, P, Q, and M are column vectors, each with 100 elements.

[0053] As shown in Figure 4, the JSD value obtained through calculation is positive even when the channel is shifted left or right, so the direction of the channel shift cannot be determined. Accordingly, a weight is assigned by multiplying the JSD value for each channel by the channel shift amount, and the channel shift amount having the minimum weight is determined as the final channel shift amount.

[0054] Next, the gamma ray spectrum of the QC source is corrected based on the calculated value. (S500)

[0055] Step S500 shifts the entire gamma ray spectrum of the QC source by the calculated channel shift amount. At this time, as shown in Fig. 5, since the value becomes negative when the channel is shifted to the left and positive when it is shifted to the right, the sign and magnitude of the channel shift (left or right) can be determined by multiplying the JSD value by the degree of channel shift (Δchannel). Here, the degree of channel shift (Δchannel) represents the degree to which the channel is shifted to the left or right.

[0056] The gamma-ray spectrum correction method for a NaI(Tl) detector according to one embodiment of the present invention can effectively correct the shift in the position of the gamma-ray spectrum peaks of the NaI(Tl) detector caused by various factors such as temperature changes, voltage fluctuations, and the passage of time. Furthermore, the accuracy of the correction is improved by calculating an accurate channel shift amount using JSD. Additionally, it enables accurate radiation measurement using the NaI(Tl) detector in various fields, such as internal exposure dose measurement equipment for nuclear power plants.

[0057] Although the present invention has been described with reference to an embodiment illustrated in the accompanying drawings, this is merely illustrative, and those skilled in the art will understand that various modifications can be made to the present invention. Accordingly, the technical scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method for correcting channel shift of a gamma-ray spectrum measured in a NaI(Tl) detector, Step of acquiring the gamma ray spectrum of a reference source; A step of setting the peak channel position in the gamma ray spectrum of the above reference source as the reference channel; Step of acquiring the gamma ray spectrum of a quality control (QC) source; A step of calculating the difference between the peak channel and the reference channel in the gamma ray spectrum of the above QC source to calculate the channel shift amount; and A method for correcting a gamma ray spectrum comprising the step of correcting the gamma ray spectrum of the QC source based on the above calculated value.

2. In Paragraph 1, The step of acquiring the gamma ray spectra of the above reference source and the above QC source is, A step of bringing the above reference source and QC source close to a NaI(Tl) detector; A step of amplifying the signal output from the above NaI(Tl) detector; A step of converting the amplified signal into a digital signal using a multi-channel analyzer (MCA); and A method for correcting a gamma ray spectrum comprising the step of generating a gamma ray spectrum using the above digital signal.

3. In Paragraph 2, The step of acquiring the gamma ray spectrum of the above-mentioned reference source is, It further includes a step of loading the gamma ray spectrum of a pre-stored reference source, A method for correcting the gamma ray spectrum, wherein the gamma ray spectrum of the above reference source is the average value of the gamma ray spectrum measured over a certain period of time.

4. In Paragraph 1, The step of setting the above reference channel is, A method for correcting a gamma ray spectrum, wherein a channel having a maximum count value in the gamma ray spectrum of the above reference source and / or a channel corresponding to a center value in the peak region is set as the reference channel.

5. In Paragraph 1, The step of obtaining the above-mentioned output value is, A step of calculating the Jensen-Shannon Divergence (JSD) between the gamma ray spectrum of the QC source and the gamma ray spectrum of the reference source within a preset range centered on the reference channel; A step of assigning weights by multiplying the JSD value for each channel by the channel shift amount; and A method for correcting a gamma ray spectrum comprising the step of determining the channel shift amount having the minimum value of the above weight as the channel shift amount.

6. In Paragraph 5, The step of calculating the above Jensen-Shannon Divergence (JSD) is a method for correcting a gamma ray spectrum using the following [Equation 1]. [Mathematical Formula 1] Here, P is the reference line 137 Cs is the channel-specific normalized count in the 300–400 channel range, and Q is the channel-specific normalized count in the 300–400 channel range of the QC source. Here, P, Q, and M are column vectors, each with 100 elements.

7. In Paragraph 1, The step of correcting the gamma ray spectrum of the above QC source is, A method for correcting a gamma ray spectrum that shifts the gamma ray spectrum of the QC source by the channel shift amount.

8. In Paragraph 1, The above standard crew member 137 A method for correcting a gamma ray spectrum containing Cs.

9. In Paragraph 1, The above QC crew member 137 Cs and 60 A method for correcting a gamma ray spectrum of a mixed source containing at least one of Co.

10. In Paragraph 1, The above method is a method for correcting gamma ray spectra used for quality control of internal exposure dose measuring equipment in nuclear power plants.

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