KR101051126B1 - Plastic Scintillator-based Radiation Detector and Radionuclide Detection Method Using the Same - Google Patents

Abstract

The present invention relates to a plastic scintillator based radiation detector and a radionuclide detection method using the same. More specifically, the energy spectrum of radiation detected through the plastic scintillator is divided into a plurality of sections according to energy levels, thereby calculating coefficient density values in each section. The present invention relates to a radiation detector and a method for detecting radionuclides using the same, which can efficiently obtain information on radioactive materials emitting radiation through relatively comparative energy level analysis.

The plastic scintillator based radiation detector according to the present invention is a plastic scintillator for converting incident radiation into visible light, and an optical multiplier pipe connected to the plastic scintillator to focus visible light generated from the plastic scintillator and convert it into an electrical signal. A plurality of scintillator detector modules configured; An electrical signal processor connected to the plurality of scintillator detector modules at the same time, summing signals received from the optical multipliers of the scintillator detector modules to remove noise and amplify the signals; An area band having a maximum coefficient density by generating an energy spectrum of incident radiation from a signal received from the electric signal processor and dividing the generated energy spectrum into a plurality of lower areas according to energy levels. And an energy analysis unit for determining a radioactive material through the calculating process.

Plastic scintillation, radiation detector, compton scattering, compton edge, energy spectrum, radionuclide detection

Description

A radiation detector based on plastic scintillator and the radionuclide-detection method using the same}

The present invention relates to a plastic scintillator based radiation detector and a radionuclide detection method using the same. More specifically, the energy spectrum of radiation detected through the plastic scintillator is divided into a plurality of sections according to energy levels, thereby calculating coefficient density values in each section. The present invention relates to a radiation detector and a method for detecting radionuclides using the same, which can efficiently obtain information on radioactive materials emitting radiation through relatively comparative energy level analysis.

The radiation detector is a device for measuring radiation dose or radiation energy, and may be classified into a gas detector, a scintillator detector, a semiconductor detector, and the like according to a material used. The scintillator detector converts incident radiation into light using excitation of the scintillator material, and converts the converted light into an electrical signal through a photomultiplier tube (PMT).

Types of scintillators used in scintillation detectors include organic scintillators and inorganic scintillators. Recently, plastic scintillators, which are one of organic scintillators, have been widely used to realize low-cost and large-area radiation detectors. This is because the use of plastic scintillator makes it possible to manufacture a large-area detector with high sensitivity of radiation even at low cost.

Since the plastic scintillator has a low density, mainly compton scattering occurs in reaction with incident radiation, rather than photoelectric absorption reaction, so that detailed information for determining energy of incident radiation can be obtained. none. In other words, the plastic scintillator is inferior in energy resolution compared to NaI, which is a scintillator material that mainly detects radiation through photoabsorption, or HPGe, which is a semiconductor detector, and thus provides only limited energy information on incident radiation.

Thus, plastic scintintillator-based radiation detectors using plastic scintillators are difficult to provide an energy spectrum with accurate energy information for incident radiation. On the other hand, these plastic scintillator based radiation detectors are generally used as gross counters for quantitatively measuring radiation, rather than for the purpose of analyzing radiation energy because of their good sensitivity to incident radiation.

1 is a graph showing energy spectra of some nuclides measured with a conventional plastic scintillation based radiation detector, showing energy spectra of plutonium (Pu), high enriched uranium (HEU), and background radiation; have.

As can be seen in FIG. 1, the spectra of Pu, HEU and background radiation all have a similar pattern in the high energy region (250 channels or more), but in the low and medium energy region, between the spectra of Pu and HEU and the spectrum of background radiation. In part there is a difference.

The energy level analysis method using a conventional plastic scintillator-based radiation detector divides the detected energy spectrum into several regions (for example, three energy regions of low, medium, and high), and the spectral pattern of radioactive material in each region. The radionuclide of the radioactive material has been distinguished by comparing with the spectral pattern of the background radiation.

However, this conventional method has two problems as follows.

The first is the difficulty of analysis. For example, in the case of HEU, the energy detection efficiency and accuracy of the HEU does not show a significant difference in the energy pattern from the background radiation, and even in some regions of the low energy region where the difference in the energy pattern is similar to that of other nuclides Pu. There is a problem that it is difficult to determine the exact nuclide because it shows the energy level. In particular, since such problems still exist in various nuclides of FIG. 2 to be described later, which are the detection targets of the present invention, there are limitations in detecting and distinguishing various radionuclides for the prevention of radioactive terrorism.

Second, it is difficult to improve the sensing area. In order to improve detector sensitivity, the detection area for incident radiation must first be large. In order to increase the detection area, a scintillator detector module consisting of a plastic scintillator, a photomultiplier tube (PMT) and an electronic circuit must be newly added to the existing system. Even if irradiated, energy spectrum with the same characteristics cannot be obtained. If you integrate spectra with different shapes from different plastic scintillators, the spectra are so distorted that you cannot analyze them to determine the radioactive material. That is, in the case of using the conventional energy level analysis method, there is a limit in increasing the overall sensitivity of the radioactive detector by simply adding a scintillator detector module to the existing system to increase the reaction cross-sectional area.

The present invention is to solve the problems of the plastic scintillator based radiation detector according to the prior art. That is, an object of the present invention is to emit radiation through energy level analysis in which the energy spectrum of the radiation detected through the plastic scintillator is divided into a plurality of sections according to energy levels, and the coefficient density values in each section are compared relatively. To provide a plastic scintillation-based radiation detector and a radionuclide detection method using the same can efficiently obtain information about the radioactive material.

In addition, another object is to easily improve the detection capability of the detector by constructing multiple plastic scintillators in parallel to increase the sensing area for incident radiation without the hassle of matching spectral channels.

The present invention as a technical concept for achieving the above object, the plastic scintillator for converting the incident radiation into visible light, and the visible light generated by the plastic scintillator connected to the plastic scintillator to focus and convert into an electrical signal A plurality of scintillator detector modules composed of photomultipliers; An electrical signal processor connected to the plurality of scintillator detector modules at the same time, summing signals received from the optical multipliers of the scintillator detector modules to remove noise and amplify the signals; An area band having a maximum coefficient density by generating an energy spectrum of incident radiation from a signal received from the electric signal processor and dividing the generated energy spectrum into a plurality of lower areas according to energy levels. It provides a plastic scintillator-based radiation detector comprising a; energy analysis unit for determining the radioactive material through the calculation process.

In addition, the present invention includes an energy spectrum generation step of generating an energy spectrum from the measurement signal of the detected radiation; An energy section dividing step of dividing an energy section of the generated energy spectrum by a predetermined number; Calculate count density for each section by summing the count values for each energy section for each of the divided energy sections and dividing the value by the energy range for each section, and calculating the energy having the maximum value among the calculated count density values. Determining a maximum coefficient density section for determining a section; Radionuclide discrimination step of discriminating the radionuclide in which the compton edge appears in the determined energy interval as a radioactive material that emits the detected radiation; Radionuclides using a plastic scintillator-based radiation detector, characterized in that it comprises a A detection method is provided.

Plastic scintillator based radiation detector and radionuclide detection method using the same according to the present invention, by performing an efficient and accurate energy level analysis using a high sensitivity plastic scintillator, radioactive material that can not be obtained in conventional plastic scintillator based radiation detector It is effective in providing information about the user quickly and accurately.

In addition, the present invention also has the effect of greatly improving the radioactive detection capability in a low-cost and simple manner by simply adding a plurality of scintillator detector modules.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Instead of the spectral pattern comparison method used in the conventional radionuclide detection method, the present invention divides an energy spectrum collected through a plastic scintillator into a plurality of lower regions according to energy levels to find an area where peak values of count values appear. By using this method, the radionuclides are distinguished by using the intrinsic properties of radioactive substances represented by the peaks of the count values due to Compton scattering of gamma rays in a specific region, and the energy spectrum shown by the radioactive materials during Compton scattering prior to the detailed description of the present invention. Let's take a look at the unique characteristics of.

Figure 2 is a graph showing the energy spectrum for the radioactive material selected as the detection target in the present invention.

When gamma rays emitted from the radioactive material enter the scintillator, the gamma rays collide with electrons of the plastic scintillator, and a scattering reaction occurs. In the radiation energy spectrum obtained through the plastic scintillator-based radiation detector, the scattering reaction results in the region A of FIG. 2. As shown in the figure, a compton edge at which the detection efficiency value peaks appears. That is, gamma rays emitted from each radioactive material enter and react with scintillators to generate the most signal near the Compton edge, which in turn generates peak values of detection efficiency or count value on the energy spectrum. As such, the energy region in which the Compton edge appears in the energy spectrum is inherent in each material depending on the type of radioactive material. The present invention uses the inherent properties of radioactive materials to divide the energy spectrum into a plurality of energy regions, and calculates an energy region band having a maximum value of count density among the divided energy regions, thereby producing a Compton edge region. From this, it is possible to determine the type of radioactive material. Here, the coefficient density is defined as a value (counts / Mev) obtained by dividing the sum of the count values of each section by the energy range of the liver section, and the section having the maximum value of the count density among the entire sections by calculating the count density for each section. This corresponds to the Compton edge region.

As described above, the radionuclide detection method according to the present invention discriminates only the band having the maximum coefficient density value on the energy spectrum instead of using the conventional method of comparing the energy spectrum with the energy spectrum of the background radiation, thereby improving the detection area. For this reason, even if a plurality of scintillator detector modules are provided in parallel, it is not necessary to exactly match the signal channels of the scintillator detector modules, even though the boundaries dividing the energy spectrum lower region of each scintillator detector module do not exactly coincide with each other. This is because there is no change in the rank of the coefficient density values for each region on the energy spectrum where the signals of the scintillator detector module are summed. Thus, when using multiple independently existing scintillator detector modules simultaneously or adding separate scintillator detector modules, no cumbersome calibration is required, which requires precision to accurately match the signal channels of each scintillator detector module. Easy system configuration is possible.

3 is a block diagram showing the configuration of a plastic scintillator based radiation detector according to an embodiment of the present invention.

As shown in FIG. 3, the plastic scintillator based radiation detector according to an embodiment of the present invention includes a plurality of scintillator detector modules 1 and 2 composed of plastic scintillators 11 and 12 and photomultipliers 21 and 22. , An electrical signal processor 30, an energy analyzer 40, and an operating system 50.

The plastic scintillators 11 and 12 convert the incident radiation into visible light, and the photomultipliers 21 and 22 are connected to the plastic scintillators 11 and 12 to display visible light generated from the plastic scintillators 11 and 12. After focusing and converting the signal into an electrical signal, the converted electrical signal is amplified and output for ease of signal processing. Here, when the thickness of the plastic scintillators 11 and 12 is small, the reaction rate with radiation is small and the energy transmitted by reaction becomes small. Therefore, in order to apply the present invention to distinguish the nuclides by using the intrinsic properties of the radioactive material exhibiting the peak of the count value due to Compton scattering of gamma rays in a specific energy region, the plastic scintillators 11 and 12 can be used in the energy spectrum comp. It should be provided in a form thick enough with respect to the direction of radiation incidence so that as many reactions as possible occur in the vicinity of the turn edge region, it is preferable to have a thickness between 2 cm and 10 cm.

In the present embodiment, a plurality of scintillator detector modules (1, 2) consisting of the plastic scintillator (11, 12) and the photo detector are connected in parallel to the electrical signal processor (30). Increase the detection area of the detector and improve the detection capability of the detector. In addition, according to the present invention, even when the plastic scintillation detector set having the above configuration is added to the existing general plastic scintillation-based radiation detector to increase the detection area for radiation, whether or not the spectral channel coincides with the existing detector and the added detector. Regardless of the accuracy, the performance of the detector can be easily improved.

The electrical signal processor 30 is connected to the optical multipliers 21 and 22 of the scintillator detector modules 1 and 2 at the same time, summing the signals received from the respective optical multipliers 21 and 22 to remove the noise and reduce the noise. Amplify the removed signal.

The energy analyzer 40 is connected to the electrical signal processor 30 to process an electrical signal received from the electrical signal processor 30 to generate an energy spectrum of radiation incident on the plastic scintillators 11 and 12, and generated The above-described analysis algorithm is applied to the energy spectrum to determine the energy level of the radioactive material, from which the nuclide of the target radioactive material is determined. Here, a detailed energy level analysis process of the energy analyzer 40 will be described in detail later.

The operating system 50 is connected to the energy analysis unit 40, receives the energy level information and radioactive material information measured by the energy analysis unit 40 and displays it to the end user, and as a result of the energy level monitoring to determine the dangerous radioactive material If so, alarms can be triggered by screen or sound, allowing immediate action.

Hereinafter, a radionuclide detection method using a plastic scintillator-based radiation detector according to an embodiment of the present invention will be described.

The plastic scintillator-based detector according to the present invention is not suitable for precise nuclide analysis due to low energy resolution unlike a detector using NaI or HPGe as a scintillator, but is very useful for radioterrorism detection equipment that needs to detect some limited radioactive substances with high sensitivity. It can be usefully applied. This is because a detector used to prepare for radioterrorism does not need to distinguish all nuclides, but only some of the substances that may be used for radioterrorism. Therefore, in the present embodiment, in selecting the radioactive material to be detected, the purpose of the detection equipment, such as the use of domestic radioactive material and radioterrorism preparedness, was considered. -235 (Uranium-235), Ir-192 (Iridium-192), Ba-133 (Barium-133), Cs-137 (Cesium-137), Du (Depleted Uranium), Nat.U (Nnatural uranium), Co -60 (Cobalt-60) was selected. These radioactive materials to be detected are divided into 5 groups according to the Compton scattering characteristics of each radioactive substance. Group 1 is Co-57 and U-235, Group 2 is Ir-192 and Ba-133, and Group 3 is Cs-. 137, Group 4 is composed of Du, Nat.U, Group 5 is Co-60, the radioactive material in the same group has a Compton edge in the same region or immediately adjacent to the radiation energy spectrum.

4 is a flow chart showing a radionuclide detection process according to an embodiment of the present invention, Figure 5 is a flow chart showing the detailed procedure of the radionuclide determination step shown in FIG.

As shown in FIG. 4, first, the detected radiation energy measurement is compared with the energy measurement of the background radiation to determine whether radiation emitted from the radioactive material is incident (S10). Here, if the following Equation 1 is satisfied, it is determined whether the incident radiation is radiation emitted from a radioactive material, not a background radiation.

Measured value ≥ N + 3σ

Where N is the average energy measurement of the background radiation, and σ is the standard deviation of the background radiation energy measurements.

If it is determined in step S10 that the normal background radiation is determined to continue the radiation measurement (S20), on the contrary, if it is determined that the radiation emitted from the radioactive material, the energy spectrum is generated from the measurement signal of the detected radiation (S30).

Thereafter, the energy sections of the generated energy spectrum are divided into a predetermined number (S40). In this embodiment, in consideration of the Compton scattering characteristics of the radioactive material to be sensed above, a total of seven energy intervals of the energy spectrum, that is, 0.02 MeV or less (section 0), 0.02 to 0.13 MeV (section 1), 0.13 to 0.3 MeV (section 2), 0.3-0.6 MeV (section 3), 0.6-0.9 MeV (section 4), 0.9-1.2 MeV (section 5) and 1.2-3.0 MeV (section 6). Sections 1 to 5 of these sections correspond to one-to-one sections corresponding to the G1 to G5 groups that classify the radioactive substances to be detected, respectively, and each group of radioactive materials has a characteristic that a Compton edge occurs in a corresponding specific energy section. Section 6 is a section corresponding to radiation emitted from a material existing in a natural state, that is, background radiation, and K-40 (potassium-40) is a representative material emitting such a background radiation. On the other hand, interval 0, which is 0.02 MeV or less, may be regarded as a signal generated by system noise (quantum noise or electrical noise) rather than a signal generated by the reaction between the radiation and the scintillator material and thus is excluded from the following spectral analysis process.

Subsequently, the energy density of each energy section is calculated for each of the divided energy sections (S50), and the energy level of the radiation incident on the scintillator is analyzed by determining an energy section having a maximum value among the calculated count densities (S50). S60).

Subsequently, the nuclide of the group corresponding to the energy section having the maximum modulus density determined through the step S60 is determined as the radioactive material that emits radiation (S70). The detailed procedure will be described with reference to FIG. same.

First, when the energy section having the maximum counting density is section 1, that is, between 0.02 and 0.13 MeV sections, the ratio of the counting density in section 1 of section 2, that is, between 0.13 and 0.3 MeV sections is calculated, The calculated count density ratio is compared with the predetermined reference value (0.8) (S71). Here, the radioactive material belonging to group 2 has a maximum counting density because the counting density of section 1 is larger than the counting density of section 2, even though the compton edge occurs in section 2, when calculating the counting density. In the case where the section is section 1, in order to clearly distinguish whether the radioactive material belongs to group 1 or group 2, the count density in section 2 and section 1 should be relatively compared through step S71.

If the comparison result in step S71 is not larger than the reference value, it is determined that the radioactive material that emits radiation is a radionuclide corresponding to group 1, that is, Co-57 or U-235 (S72), on the contrary, when the comparison value is larger than the reference value, It is determined that the nuclide corresponding to 2, that is, Ir-192 or Ba-133 (S73).

On the other hand, when the energy section having the maximum count density is the section 3 to section 6, the nuclide of the group corresponding to each section is determined as a radioactive material that emits radiation. That is, in case of section 3 (0.3 ~ 0.6 MeV), in group 3, Cs-137 (S74), in case of section 4 (0.6 ~ 0.9 MeV), in group 4, Du or Nat.U (S75), section 5 (0.9 In the case of ˜1.2 MeV), the radioactive material may be determined as Co-60 of group 5 (S76), and in the case of section 6 (1.2 to 3.0 MeV) as a material (K-40) that emits background radiation.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes are possible in the art without departing from the technical spirit of the present invention. It will be clear to those of ordinary knowledge.

1 is a graph showing energy spectra of some nuclides measured with a conventional plastic scintillator based radiation detector.

Figure 2 is a graph showing the energy spectrum for the radioactive material selected as the detection target in the present invention.

Figure 3 is a block diagram showing the configuration of a plastic scintillator based radiation detector according to an embodiment of the present invention.

Figure 4 is a flow chart showing a radionuclide detection process according to an embodiment of the present invention.

5 is a flowchart showing the detailed procedure of the nuclide determination step shown in FIG.

<Explanation of symbols for the main parts of the drawings>

1, 2: scintillation detector module 11, 12: plastic scintillator

21, 22: photomultiplier pipe 30: electrical signal processing unit

40: energy analysis unit 50: operating system

Claims (8)

A plastic scintillator based radiation detector, A plurality of scintillator detector modules comprising a plastic scintillator for converting incident radiation into visible light, and a photomultiplier tube connected to the plastic scintillator to focus visible light generated from the plastic scintillator and convert the incident light into an electrical signal; An electrical signal processor connected to the plurality of scintillator detector modules at the same time, summing signals received from the optical multipliers of the scintillator detector modules to remove noise and amplify the signals; A maximum count density by generating an energy spectrum of incident radiation from a signal received from the electrical signal processor and dividing the generated energy spectrum into a plurality of lower regions according to energy levels. It is configured to include; an energy analysis unit for determining the radioactive material through the process of calculating the area band having Obtain information about radioactive materials that emit radiation by dividing the energy spectrum of the radiation detected through the plastic scintillator into a number of sections according to energy levels and comparing the count density values in each section relatively. Plastic scintillation-based radiation detector, characterized in that configured to be. The method of claim 1, The plastic scintillator, A plastic scintillator based radiation detector for energy level determination, characterized in that it is configured to have a thickness between 2 cm and 10 cm with respect to the direction of radiation incidence. A method of detecting radionuclides using a plastic scintillator based radiation detector, Generating an energy spectrum from the measured signal of the detected radiation; An energy section dividing step of dividing an energy section of the generated energy spectrum by a predetermined number; Calculate count density for each section by summing the count values for each energy section for each of the divided energy sections and dividing the value by the energy range for each section, and calculating the energy having the maximum value among the calculated count density values. Determining a maximum coefficient density section for determining a section; A radionuclide discrimination step of discriminating a nuclide having a Compton edge in the determined energy section as a radioactive material that emits detected radiation; Consists of including, A radionuclide detection method using a plastic scintillation-based radiation detector, characterized in that the radionuclide is determined using the inherent properties of the radioactive material in which the peak of the count value due to Compton scattering of gamma rays appears in a specific energy region. The method of claim 3, Before the energy spectrum generation step, And comparing the energy measurement of the detected radiation with the energy measurement of the background radiation to determine whether the incident radiation is radiation emitted from a radioactive material or background radiation. Radionuclide detection method using. The method of claim 3, In the energy section dividing step, The energy range of the energy spectrum is 0.02 MeV or less (section 0), 0.02 to 0.13 MeV (section 1), 0.13 to 0.3 MeV (section 2), 0.3 to 0.6 MeV (section 3), 0.6 to 0.9 MeV (section 4), A radionuclide detection method using a plastic scintillator-based radiation detector characterized in that divided into 0.9 ~ 1.2 MeV (section 5) and 1.2 ~ 3.0 MeV (section 6). The method of claim 5, In the radionuclide determination step, When the energy section determined in the determining the maximum coefficient density section belongs to any one of the section 3 to section 5, The radionuclide detection method using a plastic scintillation-based radiation detector, characterized in that the radionuclide in which the Compton edge appears in the determined energy section is determined as the radioactive material that emitted the detected radiation. The method of claim 5, In the radionuclide determination step, When the energy section determined in the determining the maximum coefficient density section belongs to section 1, Calculate the ratio of the coefficient density in the interval 1 to the coefficient density in the interval 2, By comparing the calculated ratio with a predetermined reference value, when the calculated ratio is not greater than the predetermined reference value, the nuclide where the Compton edge appears in interval 1 is determined as a radioactive material that emits radiation, The radionuclide detection method using a plastic scintillation-based radiation detector, characterized in that the radionuclide is determined to emit a radionuclide in which the Compton edge appears in the interval 2 when the calculated ratio is greater than the predetermined reference value. The method of claim 5, In the radionuclide determination step, When the energy section determined in the determining the maximum coefficient density section is section 0 or section 6, A radionuclide detection method using a plastic scintillator based radiation detector, characterized in that the incident radiation is distinguished as background radiation.

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