Method for underwater online rapid analysis of seawater environment nuclear pollution
By suspending a sodium iodide gamma spectrometer in seawater and using the exponential decay fitting method to remove noise signals, the problem of long detection time and poor resolution of 137Cs in seawater environment was solved, and rapid and accurate 137Cs detection was achieved, significantly improving Seawater environmental radioactivity monitoring capabilities.
Patent Information
- Application Number
- CN202411835120.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-13
- Publication Date
- 2025-01-21
AI Technical Summary
The detection method of 137Cs in the existing seawater environment takes 3-5 days and cannot meet the needs of emergency monitoring of marine nuclear leakage accidents. Moreover, the resolution of the sodium iodide detector is poor, making it difficult to accurately identify the signal of 137Cs.
At room temperature of 25°C, use an iron stand to support the sodium iodide gamma spectrometer and hang it in 40 L of 137Cs-free seawater sample. All the instrument probes are immersed in seawater. Tests are conducted by adding 137Cs of different activities to the seawater sample. , using the exponential decay fitting method to remove the noise signals of seawater and the instrument itself, determine the γ-ray energy peak range of 137Cs, and calculate its detection limit.
The detection limit of 137Cs in 40 L of seawater was reduced to 60 mBq/L within 24 hours. The detection limit of 137Cs in surface seawater tested on site was 6.08 mBq/L, which was much lower than the previous results, significantly improving the radioactivity of seawater environment. Monitoring capabilities.
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Abstract
Description
Technical Field
[0001] The invention relates to a method for rapidly analyzing nuclear pollution in a seawater environment, in particular to a method for rapidly detecting key nuclides in a marine nuclear safety emergency system. Background Art
[0002] The nuclear power industry occupies an increasingly important position in the global energy landscape. However, most nuclear power plants are built in coastal areas, and the development of the nuclear power industry will inevitably bring huge risks to the marine nuclear radiation ecological environment. How to quickly and effectively monitor the marine environment is the future development direction of nuclear radiation monitoring and emergency prevention.
[0003] radioactivity 137 Cs is a representative nuclide for detecting nuclear contamination at home and abroad, and is also a decisive nuclide for rapid evaluation of nuclear contamination levels. 137 Cs exists mainly in ionic form in seawater and is easily absorbed and enriched by marine organisms. 137 Traditional methods for enriching Cs mainly include co-precipitation and adsorption. Among them, the ammonium phosphomolybdate co-precipitation method is complicated and time-consuming; the copper ferrocyanide adsorption method is convenient to operate, but the preparation of enrichment materials is time-consuming and the adsorption capacity is low. 137 The analysis method of Cs basically takes 3-5 days, and the existing analysis technology can hardly meet the needs of emergency monitoring of marine nuclear leakage accidents.
[0004] Compared with indoor experimental analysis technology, the use of underwater gamma spectrometers for on-site monitoring and analysis has many advantages: (1) real-time and continuous monitoring (buoy system); (2) rapid measurement of the scope of the contamination diffusion zone (towed body). HPGe detectors have high resolution, but they are large in size and weight, and require liquid nitrogen refrigeration, which makes them less portable. Therefore, most underwater gamma spectrometers use sodium iodide detectors, mainly because they are light and easy to carry, have high detection efficiency, and are low in price. However, in general marine nuclear pollution situations, sodium iodide detectors cannot obtain specific levels of contamination due to their poor resolution. This is mainly because the signals detected by sodium iodide detectors are usually the natural background of radioactive gamma nuclides in seawater or seabed sediments, which are difficult to identify. 137 Therefore, without considering the response of the natural γ-nuclides background in the seawater environment to the detector, the key representative nuclides 137 The detection limit of Cs will be higher. Summary of the invention
[0005] The purpose of the present invention is to provide a method for rapid online underwater analysis of nuclear contamination in seawater environment, so as to solve the problem of nuclear contamination in seawater after nuclear accidents. 137The problem of rapid and efficient detection of Cs is solved, and the shortcomings of existing technologies in background signals and detection limits are overcome to achieve the purpose of rapid analysis of the degree of nuclear contamination in the seawater environment.
[0006] The specific technical solution for achieving the purpose of the present invention is: A method for rapid online analysis of nuclear contamination in seawater environment is provided. The method comprises the following steps: at room temperature of 25°C, a sodium iodide gamma spectrometer (Φ75×75 mm, with an energy resolution of 7% for 1332 keV gamma rays) is supported by an iron stand and suspended on a 40 L airless 137 In the Cs seawater sample (salinity 35), the instrument probe was completely immersed in the seawater, 30 cm from the bottom of the bucket, and the average background spectrum was obtained at different times. The average background spectrum count rate was fitted with an exponential decay in the [620,800] keV energy range. 137 Cs was artificially added to seawater samples at 20 Bq, 40 Bq, and 60 Bq 137 Cs, after testing for 24 hours, the counting rate was deducted from the fitted average background counting rate to obtain the net counting rate. 137 The gamma ray energy peak range of Cs is in the [640,700] keV range. 20 Bq, 40 Bq, 60 Bq will be added artificially 137 The net counting rates of Cs seawater samples in the [640,700] keV energy range were added to obtain the total net counting rate. The total net counting rate was added to the artificially added 137 The Cs activity was fitted and predicted by exponential decay. 137 When the Cs activity is 2.4 Bq, the total net count rate of the sodium iodide gamma spectrometer in the [640,700]keV energy peak range is 0, that is, 137 The detection limit of Cs can be reduced to 60 mBq / L (testing for 24 h).
[0007] Compared with the prior art, the present invention has the following beneficial effects: The method of the present invention is simple to operate and easy to implement. Through indoor simulation experiments, the average background spectrum count rate is exponentially decayed in the [620,800] keV energy range. This method can greatly reduce the noise fluctuations contributed by seawater and the instrument itself, and remove the response of the natural gamma nuclide background in the seawater environment on the sodium iodide detector. The sodium iodide gamma spectrometer was used to analyze the gamma nuclide in 40 L of seawater. 137 The detection limit of Cs can be reduced to 60 mBq / L (testing for 24 h). This method was applied to the on-board field test of surface seawater and the Cs 137 Cs The detection limit is 6.08 mBq / L (tested for 17.6 h), which is much lower than the previous result of 580 mBq / L (6 m underwater, tested for 6 h). In short, the present invention helps to improve the existing seawater environment radioactivity monitoring capabilities and provide technical support for marine radioactivity emergency and early warning monitoring management. BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Figure 1 The background spectra of the sodium iodide gamma spectrometer under different conditions (tested for 24 h) of the present invention; Figure 2 The present invention uses sodium iodide gamma spectrometer to analyze 137 Schematic diagram of the geometric concept of Cs seawater sample (40 L, salinity 35); Figure 3 The present invention uses sodium iodide gamma spectrometer to test the no 137 Energy versus count rate diagram of Cs seawater sample (40 L, salinity 35) (AVE is the average count rate); Figure 4 The present invention uses sodium iodide gamma spectrometer to analyze artificial addition 137 Energy versus count rate of Cs (20 Bq, 40 Bq, 60 Bq) seawater sample (40 L, salinity 35); Figure 5 The present invention uses a sodium iodide spectrometer to analyze the artificial addition after deducting the fitting background method. 137 The relationship between the energy and net count rate of Cs (0 Bq(a), 20 Bq(b), 40 Bq(c), 60 Bq(d)) in seawater sample (40 L, salinity 35); Figure 6 Sodium iodide spectrometer analysis of the present invention 137 Fitting relationship between Cs different activity seawater samples (40L, salinity 35) and net counting rate in the energy range [640,700]keV; Figure 7 This is the spectrum of the sodium iodide spectrometer field test of the present invention at the S1 station (34°44.331N, 119°31.763E) in the coastal waters of Lianyungang; Figure 8 The S1 station in the coastal waters of Lianyungang for the field test of the sodium iodide spectrometer of the present invention 137 Fitting curve of Cs detection limit and test time. DETAILED DESCRIPTION
[0009] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments: ① Compare the background under different conditions The main sources of background counts measured by the gamma spectrometer include: (1) natural radioactivity in environmental samples, mainly 238 U. 232 The daughters of Th decay and 40 K; (2) cosmic rays; (3) shielding materials, the detector itself and the surrounding air; (4) electronic noise. A sodium iodide gamma spectrometer (model: NJJY-WhaIe-DET-3N, sodium iodide (Tl) scintillator crystal Φ75×75 mm, operating voltage 680-750 V, energy resolution of 7% for 1332 keV gamma rays) was used to test the 24-hour background spectrum under different conditions: (1) directly exposed to air; (2) the seawater sample was placed in a 2 L Marlin cup and placed on the sodium iodide gamma spectrometer for testing; (3) the sodium iodide gamma spectrometer was placed in 40 L of seawater for testing; (4) the sodium iodide gamma spectrometer was used to test the surface seawater (3m underwater) on board. The results showed that the main radionuclides in seawater are 40 K and 214 Bi, the background signal decreases in turn under the four test conditions, especially when the instrument is carried on board for field testing, the background is the lowest. Since the main components of seawater are H and O elements with low atomic numbers, the interaction between the gamma rays of radionuclides and seawater mainly occurs through the Compton effect. Seawater can act as a natural shield, which can greatly reduce the background signal (see Figure 1 , background spectra under different conditions).
[0010] ② Background spectra at different test times In order to better study how to reduce the detection limit of artificial key nuclides, we chose to use 137 Cs seawater samples were used for indoor simulation experiments. At room temperature of 25 °C, a sodium iodide gamma spectrometer was suspended on a 40 L airless 137 In the Cs seawater sample (salinity 35), the instrument neither touches the wall nor the bottom of the bucket, and ensures that the sodium iodide probe is completely immersed in the seawater (see Figure 2 , Schematic diagram of the geometric concept of the experimental device), and the distance from the bottom of the bucket is 30 cm. By testing different time periods (1 h, 3 h, 12 h, 24 h, 32 h), it was found that as the test time was extended to 24 h, the counting rate tended to stabilize (see Figure 3 , the relationship between energy and counting rate at different measurement times), the average counting rate is used for calculation in the subsequent background subtraction to minimize the fluctuation of the background signal.
[0011] ③Artificial addition 137 Cs seawater sample Through to nothing 137 Cs was artificially added to seawater samples at 20 Bq, 40 Bq, and 60 Bq 137Cs, the spectrum will be obtained after 24 hours of testing. After deducting the average count rate from the count rate in the energy range of [620,800] keV in the spectrum, the net count rate is found to be due to the fluctuation of background counts. 137 The signal of Cs did not appear in the artificially added seawater sample of 20 Bq, but it did not appear in the artificially added seawater sample of 40 Bq. 137 Cs was not obvious in seawater samples, only when 60 Bq 137 Cs seawater samples can clearly show 137 Cs signal (see Figure 4 , artificially added 137 Cs sample energy versus count rate).
[0012] ④ Background count rate fitting Since seawater and the instrument itself contribute a considerable portion of the counting rate, it is necessary to deduct 40 L of 0 Bq with a salinity of 35 137 The counting rate contributed by Cs seawater and sodium iodide gamma spectrometer itself. In order to further reduce the fluctuation of background counting rate during the test, no artificial addition 137 The background average count rate of Cs seawater samples was fitted with exponential decay in the energy range of [620,800] keV (R 2 =0.99) (see Figure 5 a, sodium iodide spectrometer analysis of artificial addition 137 The relationship between energy and net count rate for Cs 0 Bq seawater sample). The fitted trend line can be used to calculate the relationship between energy and net count rate for 40 L 0 Bq 137 Background count rates contributed by Cs seawater and sodium iodide gamma spectrometer itself.
[0013] ⑤Confirmation 137 Cs energy range 40 L artificially added 20 Bq 137 The count rate of the Cs (salinity 35) seawater sample in the [620,800] keV energy range is subtracted from Figure 5 The background is fitted in a to obtain the net count rate result Figure 5 b (Sodium iodide spectrometer analysis of artificial addition 137 The relationship between energy and net count rate for Cs 20 Bq seawater sample). Similarly, we can get 40 Bq 137 Cs and 60 Bq 137 The relationship between the energy and net count rate of Cs seawater samples is shown in Figure 5 c (sodium iodide spectrometer analysis of artificial addition 137 Cs 40 Bq seawater sample energy versus net count rate) and Figure 5 d (sodium iodide spectrometer analysis of artificial addition 137 The relationship between energy and net count rate for Cs 60 Bq seawater sample. Figure 4 It was found that after deducting the fitted background count rate method, 20 Bq and 40 Bq 137 Cs seawater samples can also be seen 137 Signal of Cs, 60 Bq 137 The spectrum of Cs seawater sample is more obvious, so 137 The energy peak range of Cs is set in the [640,700] keV interval.
[0014] ⑥ Calculation 137 Detection limit of Cs The formula (1) is used to calculate the concentration of sodium iodide gamma spectrometer in 40 L of seawater. 137 The detection efficiency of Cs is 1.52×10 -2 .
[0015] (1) in, for 137 Cs detection efficiency; n is the net count rate in the [640,700] keV energy range; The branch ratio is 85.1%; A is artificially added 137 Cs activity (unit: Bq).
[0016] Will Figure 5 The total net count rate obtained by adding the net count rates in the [640,700] keV energy interval in b, 5c, and 5d is different from the artificially added 137 The activity of Cs was fitted and predicted by exponential decay curve. 137 When the Cs activity is 2.4 Bq, the total net count rate of the sodium iodide gamma spectrometer in the [640,700]keV energy peak interval is 0, so the obtained sodium iodide gamma spectrometer is 137 The minimum detection limit of Cs is 2.4 Bq ( Figure 6 ,analyze 137 The fitting relationship between the net counting rate of Cs in the energy range [640,700]keV and the seawater samples with different activities. In summary, by using the exponential decay fitting method to deduct the background contribution of natural radionuclides in seawater at [640,700]keV, the Cs in 40 L seawater 137 The detection limit of Cs can be reduced to 60 mBq / L (testing for 24 h).
[0017] ⑦ On-site test of sodium iodide spectrometer 137 Cs In January 2024, a field survey was conducted in the coastal waters of Lianyungang. At the S1 station (temperature 5.68 °C, salinity 29.22), a sodium iodide gamma spectrometer was placed 3 m underwater for field testing. The measured seawater field spectrum is shown in Figure 7 (Spectrum of the field test at the S1 station in the coastal waters of Lianyungang (34°44.331N, 119°31.763E)). Calculated by formula 2, we get 137 The detection limit of Cs was 6.08 mBq / L (testing time 17.6 h).
[0018] (2) Wherein, B is the sum of background counts obtained by fitting in the [640,700] keV energy interval; for 137 The Cs detection efficiency was calculated by Monte Carlo method and was 2.05×10 -4 ; Due to the strong shielding effect of seawater, only 0.1% of the 661 keV γ-rays that pass through the 80 cm water layer do not interact with the seawater. Therefore, the water layer radius is selected as 80 cm when testing seawater in situ. V is the effective volume of seawater, 2143 L. The branch ratio is 85.1%, and T is the test time 63360 s. In addition, by using different test times, we can calculate 137 The detection limits of Cs are 22.0 mBq / L (1.4 h) and 16.5 mBq / L (3.7 h), respectively. 137 The formula of Cs detection limit and test time: (See Figure 8 , on-site testing of the S1 station in the coastal waters of Lianyungang 137 The result is much lower than that proposed by Zeng Zhi et al. (Development and preliminary test results of seawater radioactivity monitoring device, Radiation Protection. 2013, 33(1):46-53.) to use sodium iodide detector to test the radioactivity in seawater in situ. 137 The minimum detectable activity of Cs is 580 mBq / L (6 m underwater, 6 h test).
[0019] The above are only preferred feasible embodiments of the present invention, and the protection scope of the present invention is not limited thereto. Various modifications or applications made according to the above embodiments are within the protection scope of this technical solution.
Claims
1. A method for rapid online underwater analysis of nuclear contamination in seawater environment, characterized in that: The method comprises the following specific steps: (1) Background spectrum acquisition: At room temperature of 25°C, a sodium iodide gamma spectrometer was suspended on an iron stand containing 137 In a seawater sample container with a salinity of 35 and a concentration of Cs, the probe of the sodium iodide gamma spectrometer was completely immersed in the seawater, with the sodium iodide gamma spectrometer 30 cm away from the bottom of the container, and the average background count rate spectrum was obtained at different test times; (2) Average background count rate fitting: The average count rate of the background spectrum is fitted with an exponential decay in the [620,800] keV energy range; (3) Preparation of artificial additives 137 Cs seawater sample: 137 Cs was artificially added to seawater samples at 20 Bq, 40 Bq, and 60 Bq 137 Cs, after testing for 24 hours, the average background count rate calculated by fitting is deducted to obtain the net count rate spectrum, confirming 137 The energy peak of Cs gamma rays is in the [640,700] keV range; (4) 137 Detection limit of Cs: artificially add 20 Bq, 40 Bq, 60 Bq 137 The net counting rates of Cs seawater samples in the [640,700] keV energy range were added to obtain the total counting rate; the total counting rate and the artificially added 137 The Cs activity was fitted with an exponential decay and predicted. 137 When the Cs activity is 2.4 Bq, the total net count rate of the sodium iodide gamma spectrometer at the [640,700]keV energy peak is 0, that is, the analysis method of deducting the background by fitting is tested for 24 hours, and the 137 The detection limit of Cs was reduced to 60 mBq / L.