Personal dosimeter capable of identifying nuclide

Abstract

The invention discloses a personal dosimeter capable of nuclide identification, and the dosimeter comprises a scintillation detector which is composed of a scintillation crystal and SiPM and captures an energy spectrum signal of a ray; the signal amplifier receives the voltage signal output by the SiPM and preprocesses and amplifies the voltage signal; the multichannel analyzer is used for receiving the amplified signal output by the signal amplifier and realizing energy spectrum acquisition in a target energy range; and the MCU receives the signals acquired by the multichannel analyzer and performs energy spectrum analysis. According to the invention, the scintillation detector based on SiPM and scintillation crystals is used, so that the small size and high sensitivity of the personal dosimeter are realized; according to the multi-channel analyzer, the multi-channel analyzer capable of setting the energy range is realized through the ADC and the comparator, and the design of a peripheral circuit is extremely simplified; the simplified nuclide identification method is designed based on prior information, the range of a nuclide library is narrowed, and the requirements of nuclide identification in a specified application scene for the computing power of a system and the complexity of an analog circuit are further reduced.

Description

Technical Field

[0001] The invention relates to the field of radiation measurement, in particular to a personal dosimeter capable of nuclide identification. Background Art

[0002] Ionizing radiation personal dosimeters are widely used in nuclear medicine, radiology, nuclear industry, non-destructive testing and other industries to monitor the intensity of ionizing radiation received by workers in real time and to issue alarms when the radiation intensity exceeds the threshold. On the one hand, this can prevent workers from being accidentally exposed to radiation, and on the other hand, it can quantitatively measure the cumulative dose equivalent of the radiation received. However, current personal dosimeters only measure the real-time dose equivalent rate and cumulative dose equivalent of ionizing radiation, and cannot realize the nuclide identification function.

[0003] Photomultiplier tube (PMT) is a vacuum electronic device that converts weak light signals into electrical signals. Photomultiplier tubes are used in optical measuring instruments and spectral analysis instruments. It can measure extremely weak radiation power with a wavelength of 200~1200 nanometers in low-level photometry and spectroscopy. The emergence of scintillation counters has expanded the application range of photomultiplier tubes. The development of laser detection instruments is closely related to the use of photomultiplier tubes as effective receivers. The emission and image transmission of television and movies are also inseparable from photomultiplier tubes. Photomultiplier tubes are widely used in metallurgy, electronics, machinery, chemical industry, geology, medicine, nuclear industry, astronomy and space research.

[0004] At present, most personal dosimeters use Geiger counters, which are also called Geiger-Müller counters (GM tubes). They are counting instruments that specifically detect the intensity of ionizing radiation (alpha particles, beta particles, gamma rays and X-rays). The probe is made of an inflated tube or chamber. When the voltage applied to the probe reaches a certain range, each time the radiation ionizes in the tube to produce a pair of ions, it can be amplified to produce an electric pulse of the same size and recorded by the connected electronic device, thereby measuring the number of radiation per unit time. Its advantages are low cost and easy use, but its disadvantages are also obvious. Since it is a gas detector, it is relatively fragile and it is difficult to achieve a relatively high sensitivity in a small size. The personal dosimeter needs to be carried by the staff. If the size is increased to obtain a higher sensitivity, its portability will be greatly lost; at the same time, the biggest problem is that the signal output by the Geiger counter is the information of the number of rays, not the energy information of the rays, which also makes it impossible to realize the nuclide identification function through the energy information of the X-rays and gamma rays. At the same time, the energy spectrometer that can perform nuclide identification is generally large and bulky, and expensive.

[0005] The shortcomings of existing personal dosimeters include: 1. Personal dosimeters that use Geiger counters as detectors cannot achieve high detector sensitivity in a small size, making them respond slowly, lag or even fail to respond to relatively weak radiation fields, which is very unfavorable for wearers to avoid accidental exposure; 2. Personal dosimeters cannot identify nuclides. For places where unsealed radioactive nuclides are used, they cannot immediately determine the type of contaminated radiation source; 3. Energy spectrometers with radionuclide identification functions need to collect a large number of fine energy spectra, so their scintillation detectors are large in size and the peripheral circuits are relatively complex. Therefore, it is difficult to ensure overall portability and cannot be integrated into personal dosimeter products. Summary of the invention

[0006] The purpose of the present invention is to provide a personal dosimeter capable of nuclide identification, which uses a scintillation detector based on SiPM and scintillation crystal. Compared with a scintillation detector based on a photomultiplier tube, the size of the photodetector part is reduced by more than 90%, making it possible to realize a small-sized personal dosimeter.

[0007] At the same time, analog-to-digital converters and comparators are used in personal dosimeters to implement a low-channel multi-channel analyzer with an adjustable energy range to analyze the energy spectrum information of the rays captured by the scintillation detector. At the same time, in many cases, the types of nuclides that users can access are fixed and limited, and nuclides can be identified through the prior information of this known nuclide library.

[0008] The technical solution of the present invention is: A personal dosimeter capable of nuclide identification includes a scintillation detector, a signal amplifier, a multi-channel analyzer, a high-voltage power supply, a button, an MCU, a display screen, and a power supply; wherein: The scintillation detector, which consists of a scintillation crystal and a photodetector, captures the energy spectrum signal of the radiation; A signal amplifier receives the voltage signal output by the photodetector and performs pre-processing and amplification; A multi-channel analyzer receives the amplified signal output by the signal amplifier and realizes the collection of the energy spectrum in the target energy range; MCU receives the signal collected by the multi-channel analyzer and performs energy spectrum analysis.

[0009] Preferably, the photodetector is one of SiPM, photodiode and PMT.

[0010] Preferably, the multi-channel analyzer comprises a first comparator, a second comparator and an ADC; The pulse signal output by the signal amplifier is input into the first comparator and the second comparator respectively on the one hand, and is input into the ADC on the other hand. The first comparator and the second comparator are set with different thresholds corresponding to the upper energy limit EH and the lower energy limit EL respectively. The outputs of the two comparators are input into the acquisition trigger control interface of the ADC together; when the ray energy output by the signal amplifier is between the set target energy lower limit EL and the energy upper limit EH, the ADC is triggered to acquire the analog information of the pulse signal.

[0011] Preferably, the working method of the personal dosimeter comprises the steps of: (1) Determine the nuclide library of interest; (2) Query the characteristic peak of the nuclide as the target detection peak; (3) Determine the energy range of interest: evaluate the upper and lower limits of the energy range based on the energy resolution of the scintillation detector used; (4) The number of channels to be distinguished shall not be less than the number of nuclides in the nuclide library x 3; (5) Setting the comparator thresholds. The peak voltage of the pulse output by the scintillation detector is proportional to the gamma rays detected by it. The thresholds of the first comparator and the second comparator can be calculated based on the upper and lower energy limits EL and EH of interest. (6) Place the personal dosimeter around the radiation source to be measured to collect data, and the amount of data collected shall not be less than 500; (7) Energy spectrum analysis: After the energy spectrum is collected, the type of nuclide can be estimated based on the characteristic peaks and morphology of the energy spectrum.

[0012] Preferably, the scintillation crystal has an energy resolution better than 10% @ 662keV and a density greater than 5g / cm3; The light-emitting surface of the scintillation crystal and the light-sensitive surface of the photodetector have the same shape.

[0013] Preferably, a high voltage power supply is also included to provide a bias operating voltage to the SiPM, and the voltage range is 25-34V.

[0014] Preferably, it also includes buttons and a display screen respectively connected to the MCU, which are used to realize user interaction and display of data results respectively.

[0015] Preferably, the number of comparators of the multi-channel analyzer is further increased to three or more, so as to divide the energy segments into finer and more numerous segments, and more accurately collect the energy segments of characteristic peaks in the nuclide library, so as to realize the identification of a larger number of nuclides.

[0016] Preferably, the ADC and comparator of the multi-channel analyzer are formed using on-chip resources of the MCU.

[0017] Preferably, the scintillation crystal is relaxed according to the cost and actual nuclide library conditions, and inorganic scintillation crystals such as NaI, CsI, YSO, LSO, LYSO, or one of plastic scintillators and liquid scintillators are selected.

[0018] Preferably, the ADC and comparator of the multi-channel analyzer are implemented using FPGA in conjunction with the comparator.

[0019] The advantages of the present invention are: 1. The present invention uses a scintillation detector based on SiPM and scintillation crystal, which is a solid detector. Usually, in the size specifications of personal dosimeter products, its sensitivity is usually more than 20 times that of Geiger tubes. For example, the sensitivity test of J-703 Geiger tube is 0.3 CPS / uSv / h @662keV, and the sensitivity of BGO scintillation crystal (3.5*3.5*7mm3) of similar size can reach 7cps / uSv / h, making the design of small and highly sensitive personal dosimeters possible; 2. The present invention realizes a multi-channel analyzer with settable energy range through ADC and comparator, greatly simplifies the design of peripheral circuits, and makes it possible to miniaturize the nuclide identification function; 3. The present invention designs a simplified method of nuclide identification based on prior information, narrows the scope of the nuclide library, and further reduces the requirements for system computing power and analog circuit complexity for nuclide identification in specified application scenarios, making it possible to integrate nuclide identification in personal dosimeters and greatly reducing the cost of nuclide identification. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with the accompanying drawings and embodiments: Figure 1 It is a system principle block diagram of the personal dosimeter of the present invention; Figure 2 It is a schematic diagram of the Cs-137 energy spectrum; Figure 3 This is the principle block diagram of the multi-channel analyzer; Figure 4 Workflow diagram of the personal dosimeter of the present invention; Figure 5 This is a schematic diagram of the F-18 energy spectrum in the embodiment; Figure 6 This is a schematic diagram of the energy spectrum of I-131 in the embodiment; Figure 7 This is a schematic diagram of an energy spectrum diagram without a radiation source in the embodiment; Figure 8 It is a schematic diagram of the comprehensive energy spectrum of F-18 and I-131 in the embodiment. DETAILED DESCRIPTION

[0021] like Figure 1 As shown, the personal dosimeter of the present invention mainly includes a scintillation detector (composed of a scintillation crystal and a SiPM), a high-voltage power supply, a button, an MCU, a display screen, a power supply, a signal amplifier, and a multi-channel analyzer (composed of a comparator and an ADC).

[0022] Among them, the scintillation detector composed of scintillation crystal and SiPM should use scintillation crystal with high energy resolution and high density. Generally, the energy resolution is better than 10% @ 662keV and the density exceeds 5g / cm3, such as BGO, CsI, NaI, etc. On the one hand, it can have more accurate energy information, and on the other hand, it can have relatively high sensitivity. In terms of structure, due to the square photosensitive surface of SiPM, the scintillation crystal can be a cubic structure, a rectangular parallelepiped structure, or other shapes with the end faces consistent with the photosensitive surface of SiPM, such as trapezoidal and other special shapes.

[0023] For a scheme using a photoelectric device similar to a PMT, the photosensitive surface may be circular, and the light emitting surface of the scintillation crystal and the photosensitive surface of the photoelectric device may be consistent.

[0024] Usually in the size specifications of personal dosimeter products, its sensitivity is usually more than 20 times that of Geiger tubes. For example, the sensitivity test of J-703 Geiger tube is 0.3 CPS / uSv / h @662keV, and the sensitivity of BGO scintillation crystal (3.5*3.5*7mm3) of similar size can reach 7cps / uSv / h.

[0025] The high voltage power supply provides bias operating voltage to the SiPM, which is generally in the range of 25~34V.

[0026] Buttons and display screen are used to realize user interaction and display data results.

[0027] MCU refers to a single-chip microcomputer, which is the data processing center of the entire system.

[0028] The power supply is the part that provides power to the entire system.

[0029] The signal amplifier is used to receive the voltage signal output by the SiPM and perform preprocessing and amplification so that the amplitude of the pulse output by the SiPM is within the optimal operating range of the ADC, which generally refers to the range of 20% to 80% of the operating voltage range of the ADC.

[0030] The ADC and comparator form a multi-channel analyzer to achieve the acquisition of the energy spectrum in the target energy range.

[0031] The multi-channel analyzer in the present invention can realize the energy spectrum within the specified energy range. It is limited by the instrument size of the personal dosimeter (in order to ensure portability, its general size is within 60mm x 60mm x 30mm). The computing power performance of its MCU and the complexity of the analog signal processing circuit generally cannot meet the needs of energy spectrum analysis and nuclide identification with a wide energy range (referring to the energy range of rays that can be detected by scintillation crystals, which is related to the light output and size of the scintillation crystals. The larger the size, the higher the upper limit of detectable energy, the higher the light output of the scintillation crystals, and the lower the lower limit of its energy detection), and a high number of channels (such as 256, 512, and 1024 channels commonly used by multi-channel analyzers for nuclide identification).

[0032] The basic working principle of the energy spectrometer is that each nuclide has at least one characteristic energy spectrum peak, such as 662keV for Cs-137 (such as Figure 2 ), F-18 is 512keV, I-131 is 364.5keV. The spectrometer can obtain the energy spectrum of the radiation source, and then find the characteristic peaks through calculation, and then infer the type of nuclide.

[0033] Since the nuclides that users of general personal dosimeters may come into contact with are limited and known in their usage scenarios, for example, the nuclear medicine department of a hospital generally only comes into contact with F-18, I-131, Tc-99m, and I-125, and the industry uses Cs-137 and Co-60, etc., we can use this prior information to narrow the number of nuclides in the nuclide library for nuclide identification by allowing customers to specify the types of nuclides that they may come into contact with or be interested in, thereby reducing the requirements for the number of energy spectrum channels and computing power performance, and performing nuclide identification in a limited number of nuclide libraries.

[0034] The present invention realizes the energy spectrum acquisition within the target energy range through a multi-channel analyzer composed of a comparator and an ADC. The working process is as follows: Figure 3 shown.

[0035] The scintillation detector signal is amplified by the signal amplifier to the working range of the ADC. The output pulse signal enters comparator 1 and comparator 2 on the one hand, and goes to the ADC on the other hand. Comparator 1 and comparator 2 set different thresholds corresponding to the energy upper limit EH and energy lower limit EL respectively. Here, the energy upper limit is greater than the energy lower limit, so the threshold of comparator 1 is higher than the threshold of comparator 2. The outputs of the two comparators are input to the acquisition trigger control interface of the ADC together. The possible outputs of the comparators are shown in Table 1.

[0036] Table 1 Comparator combination logic table

[0037] Therefore, when the situation is 2, it can be determined that the energy of the ray is between the set target energy lower limit EL and energy upper limit EH. The ADC triggers analog-to-digital conversion when and only when the situation is 2 to collect the analog information of the pulse signal.

[0038] The workflow of the personal dosimeter of the present invention is as follows: Figure 4 As shown, the following steps are included.

[0039] (1) Determine the nuclide library of interest. For example, if the nuclear medicine department of a hospital may be exposed to F-18 and I-131, then confirm that there are two types of nuclides in the library; (2) Query the characteristic peaks of the nuclide. The nuclide database shows that the γ characteristic energy of F-18 is 511keV and that of I-131 is 364.5keV. These two peaks are the target detection peaks. (3) Define the energy range of interest. According to the result of step (2), the characteristic peaks of the two nuclides in the nuclide library are 364.5 keV and 511 keV. Generally, the upper and lower limits of the energy range can be evaluated based on the energy resolution of the scintillation detector used. For example, if the energy resolution ER = 10% @ 662 keV and the 99.7% confidence interval is plus or minus 3 sigma according to the normal distribution characteristics, then a reasonable evaluation is: The lower energy limit of interest EL = the lower energy limit of the target characteristic nuclide x 0.7; The upper energy limit of interest EH = the upper energy limit of the target characteristic nuclide x 1.3; Then, the energy range of interest is EL=364.5*0.7=255keV, EH=511*1.3=664keV.

[0040] (4) According to the experience of test results, to obtain better peak identification results, the number of channels to be distinguished should not be less than the number of nuclides in the nuclide library x3. For this scheme, the number of channels is 2x3=6; (5) Set the comparator threshold. Since the peak voltage of the pulse output by the scintillation detector is proportional to the gamma ray it detects (here we assume that the ratio k = peak voltage / energy = 2 mV), based on the upper and lower energy limits EL and EH of interest, we can calculate that the threshold of comparator 1 is 2 * 255 = 510 mV, and the threshold of comparator 2 is 2 * 664 = 1328 mV. (6) Place the device around the source to be tested to collect data. According to test experience, the amount of data collected is generally not less than 500 (7) Energy spectrum analysis: After collecting the energy spectrum, the type of nuclide can be estimated based on the characteristic peaks and morphology of the energy spectrum. For example, Figure 5-8 shown.

[0041] (8) Results display.

[0042] In the system of the present invention, the number of comparators of the multi-channel analyzer can be further increased to divide the energy segments into finer and more segments, so that the energy segments of characteristic peaks in the nuclide library can be more accurately collected. For example, when the nuclide library has 3 nuclides, 6 comparators can be used to divide the energy ranges into 3 segments of interest.

[0043] In the system of the present invention, the ADC and comparator of the multi-channel analyzer can also use the on-chip resources of the MCU, further reducing the demand for chips.

[0044] The performance requirements of the scintillation crystal of the present invention are: better than 10% @ 662keV, density exceeding 5g / cm3, which can also be relaxed according to the cost and actual nuclide library conditions, so the scintillation crystal can be selected from inorganic scintillation crystals such as NaI, CsI, YSO, LSO, LYSO, etc.; In the system of the present invention, the ADC and comparator of the multi-channel analyzer can also be implemented by using FPGA in conjunction with the comparator.

[0045] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any modifications made according to the spirit of the main technical solution of the present invention should be included in the protection scope of the present invention.

Claims

1. A personal dosimeter capable of nuclide identification, characterized in that: It includes scintillation detector, signal amplifier, multi-channel analyzer, high voltage power supply, button, MCU, display screen and power supply; among them, The scintillation detector, which consists of a scintillation crystal and a photodetector, captures the energy spectrum signal of the radiation; A signal amplifier receives the voltage signal output by the photodetector and performs pre-processing and amplification; A multi-channel analyzer receives the amplified signal output by the signal amplifier and realizes the collection of the energy spectrum in the target energy range; MCU receives the signal collected by the multi-channel analyzer and performs energy spectrum analysis.

2. The personal dosimeter capable of nuclide identification according to claim 1, characterized in that: The photodetector is one of SiPM, photodiode and PMT.

3. The personal dosimeter capable of nuclide identification according to claim 1, characterized in that: The multi-channel analyzer includes a first comparator, a second comparator and an ADC; The pulse signal output by the signal amplifier is input into the first comparator and the second comparator respectively on the one hand, and is input into the ADC on the other hand. The first comparator and the second comparator are set with different thresholds corresponding to the upper energy limit EH and the lower energy limit EL respectively. The outputs of the two comparators are input into the acquisition trigger control interface of the ADC together; when the ray energy output by the signal amplifier is between the set target energy lower limit EL and the energy upper limit EH, the ADC is triggered to acquire the analog information of the pulse signal.

4. The personal dosimeter capable of nuclide identification according to claim 3, characterized in that: The working method of the personal dosimeter comprises the steps of: (1) Determine the nuclide library of interest; (2) Query the characteristic peak of the nuclide as the target detection peak; (3) Determine the energy range of interest: evaluate the upper and lower limits of the energy range based on the energy resolution of the scintillation detector used; (4) The number of channels to be distinguished shall not be less than the number of nuclides in the nuclide library x 3; (5) Setting the comparator thresholds. The peak voltage of the pulse output by the scintillation detector is proportional to the gamma rays detected by it. The thresholds of the first comparator and the second comparator can be calculated based on the upper and lower energy limits EL and EH of interest. (6) Place the personal dosimeter around the radiation source to be measured to collect data, and the amount of data collected shall not be less than 500; (7) Energy spectrum analysis: After the energy spectrum is collected, the type of nuclide can be estimated based on the characteristic peaks and morphology of the energy spectrum.

5. The personal dosimeter capable of nuclide identification according to claim 1, characterized in that: The scintillator crystal has an energy resolution better than 10% @ 662keV and a density of more than 5g / cm3; The light-emitting surface of the scintillation crystal and the light-sensitive surface of the photodetector have the same shape.

6. The personal dosimeter capable of nuclide identification according to claim 1, characterized in that: It also includes a high-voltage power supply to provide bias operating voltage to the SiPM, with a voltage range of 25~34V.

7. The personal dosimeter capable of nuclide identification according to claim 1, characterized in that: It also includes buttons and a display screen connected to the MCU, which are used to realize user interaction and display data results respectively.

8. The personal dosimeter capable of nuclide identification according to claim 2, characterized in that: The number of comparators of the multi-channel analyzer is further increased to three or more, which divides the energy segments into finer and more numerous segments, and more accurately collects the energy segments of characteristic peaks in the nuclide library, so as to realize the identification of a larger number of nuclides.

9. The personal dosimeter capable of nuclide identification according to claim 2, characterized in that: The ADC and comparator of the multi-channel analyzer are composed of on-chip resources of the MCU.

10. The personal dosimeter capable of nuclide identification according to claim 2, characterized in that: The scintillation crystal is relaxed according to the cost and the actual nuclide library situation, and inorganic scintillation crystals NaI, CsI, YSO, LSO, LYSO, or one of plastic scintillators and liquid scintillators are selected.

11. The personal dosimeter capable of nuclide identification according to claim 2, characterized in that: The ADC and comparator of the multi-channel analyzer are implemented by using FPGA in conjunction with the comparator.

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