Nuclear field nondestructive gamma measurement device and measurement method based on NaI detector

Abstract

The invention relates to a nuclear field lossless gamma measurement device and method based on a NaI detector, and the method comprises the steps: measuring and recording a background signal reference value in a shielding box, obtaining a net signal through a background deduction algorithm after a sample is measured, and achieving the precise processing of spectrum data through multiple times of smooth and optimized energy resolution calculation. According to the method, destructive sampling or chemical treatment on the sample is not needed, secondary waste is avoided by directly measuring the gamma-ray signal, and the method has the advantage of environmental protection. The method is particularly suitable for rapid nondestructive detection of samples such as nuclear power station worker work shoes, the control releasing precision is high, and the detection level of 1e-2Bq / g can be achieved within 2 minutes. The method is simple and convenient in measurement process, flexible in operation and suitable for being used in laboratories and on-site multiple scenes.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear measurement, and in particular to a non-destructive gamma measurement device and a measurement method in the nuclear field based on a NaI detector. Background Art

[0002] Gamma ray measurement technology is widely used in the fields of nuclear energy, environmental monitoring and radiation protection. Traditional methods mainly include scintillation detector method, high purity germanium detector method and Geiger-Muller counter method. These technologies have certain advantages in the detection of radioactive nuclides, but they also have limitations.

[0003] The scintillation detector method uses the flash effect of NaI (Tl) crystals to measure gamma rays. It has high sensitivity and a wide range of applications, but its energy resolution is low and it is difficult to accurately distinguish the characteristic energy of nuclides. Although high-purity germanium detectors have extremely high energy resolution, the equipment is complex, expensive, and needs to operate under low temperature conditions, which is not suitable for rapid on-site screening. The Geiger-Mueller counter is simple to operate and is suitable for high-intensity radiation source detection, but because of its extremely low energy resolution, it is not suitable for gamma spectrum analysis.

[0004] For radionuclides in low-level contamination scenarios (such as on the shoes of nuclear power plant workers), 60 Co<0.1Bq), these traditional methods all face limitations. For example, handheld radiation detectors are not sensitive enough when measuring low activity, and HPGe spectrometers need to be tested by on-site sampling and transportation, which is a complicated and time-consuming process. In addition, the limited sensitivity of existing detection equipment may lead to reduced detection accuracy and efficiency, making it difficult to meet the needs of rapid screening in nuclear power plants. Therefore, a new technology that is efficient, sensitive, portable and has high-precision gamma-ray measurement is urgently needed to meet the challenges of low-activity nuclear contamination detection.

[0005] In view of the above problems, the present invention is proposed. Summary of the invention

[0006] The invention discloses a nuclear field nondestructive gamma measurement device and a measurement method based on a NaI detector, aiming to solve the technical problems existing in the prior art.

[0007] According to the present invention, a non-destructive gamma measurement method in the nuclear field based on a NaI detector is provided, comprising:

[0008] Without placing the sample to be measured, place the NaI detector in the shielding box, and measure and record the background signal reference value;

[0009] Placing a sample to be measured in a measurement area of ​​a NaI detector, and measuring and recording a first measurement result of the sample;

[0010] The background signal is subtracted from the first measurement result and the background signal reference value to obtain the second measurement result, using the following formula:

[0011]

[0012] in:

[0013] P smooth (E) is the spectrum after smoothing;

[0014] N is the window size;

[0015] i is the index in the window;

[0016] P measured (E) = P signal (E)+P backgruond (E)

[0017] in:

[0018] P measured (E) is the measured total spectrum;

[0019] P signal (E) is the signal spectrum of the target source;

[0020] P backgruond (E) is the background spectrum;

[0021] The second measurement result is processed to obtain the final third measurement result using the following formula:

[0022]

[0023] in:

[0024] P(E) is the count rate at energy E (spectral data);

[0025] A is the height of the peak (maximum count), indicating the intensity of the signal;

[0026] E0 is the central energy of the peak (corresponding to the characteristic gamma energy of the nuclide);

[0027] σ is the peak width and is related to the energy resolution of the NaI detector.

[0028] As a preferred technical solution, before measuring and recording the first measurement result of the sample, the detection limit and detection time parameters of the NaI detector are obtained by calculation, and the NaI detector is set according to the parameters. The calculation formula is as follows:

[0029]

[0030] in:

[0031] Lmin is the minimum detection limit;

[0032] K is a constant that depends on the sensitivity of the detector;

[0033] B is the background noise;

[0034] t is the detection time;

[0035] N signal and N background are the counts of signal and background, respectively.

[0036] As a preferred technical solution, the detection time t is based on 60 The control accuracy of the work shoes of the nuclear power plant workers of Co is determined.

[0037] As a preferred technical solution, the control accuracy is to reach the level of 1e-2Bq / g in 2 minutes of measurement.

[0038] As a preferred technical solution, the shielding box is provided with a shielding box body, a through hole is opened on the side wall of the shielding box body, and the top of the NaI detector is configured as a cylinder, which contacts the outside of the shielding box through the through hole.

[0039] As a preferred technical solution, the nuclear electronics part of the NaI detector is provided with a main amplifier circuit.

[0040] As a preferred technical solution, the main amplifier circuit includes a voltage amplifier, a first connector and a second connector. The voltage amplifier is provided with an operational amplifier U19, a feedback resistor R74 and an input resistor R68 for signal amplification; the first connector and the second connector are used to transmit the amplified signal to the outside.

[0041] As a preferred technical solution, the input resistor R68 is connected to the reverse input terminal of the operational amplifier U19, and the forward input terminal of the operational amplifier U19 is grounded.

[0042] As a preferred technical solution, the size of the shielding box is 200mm×400mm×75mm.

[0043] As a preferred technical solution, a lead plate is provided inside the shielding box, and the thickness of the lead plate is 4-7 mm.

[0044] The technical solution adopted by the present invention can achieve at least one of the following beneficial effects:

[0045] 1. The present invention significantly improves the detection efficiency by using a design combining a NaI detector and a shielding box. Through background subtraction algorithm and multiple smoothing processes, accurate γ spectrum data can be quickly obtained, thereby effectively reducing the minimum detection limit (L_min), meeting the requirements of nuclear power plant workers' work shoes control accuracy, and achieving a dual improvement in measurement efficiency and accuracy. In addition, the optimized energy resolution formula can accurately identify the characteristic γ energy peak, improving the ability to distinguish radioactive nuclides.

[0046] 2. The measurement method of the present invention does not require destructive sampling and sample preparation of the sample, and directly measures the gamma rays through the NaI detector, avoiding physical damage or chemical treatment of the sample. At the same time, no other reagents or auxiliary materials are needed, and the measurement process does not generate secondary waste, which has strong environmental protection properties. This non-destructive measurement method greatly simplifies the process and is suitable for rapid detection of various radioactive wastes, especially for rapid screening on-site in nuclear power plants.

[0047] 3. The present invention adopts a miniaturized design, equipped with a compact shielding box and an efficient shielding structure with a built-in lead plate, with a size of 200mm×400mm×75mm, which is easy to carry and transport. At the same time, through a simplified operation process, the measurement task can be completed by simply placing the sample in the shielding box, connecting the host computer and starting the measurement, which significantly reduces the complexity of the operation. This design is particularly suitable for use in laboratories, on-site or other confined spaces, providing flexibility and convenience. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments, which constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions explain the present invention and do not constitute improper limitations on the present invention. In the drawings:

[0049] Figure 1 It is a schematic diagram of the three-dimensional structure of a non-destructive γ measurement device in the nuclear field based on a NaI detector of the present invention;

[0050] Figure 2 Schematic diagram of the main amplifier circuit of the NaI detector of the present invention;

[0051] Figure 3 This is a diagram of the detection efficiency results of simulating the nuclear electronics part of the NaI detector using the Geant4 software of the present invention.

[0052] Description of reference numerals:

[0053] 1. Shielding box; 11. Shielding cover; 12. Shielding box body; 2. NaI detector; 3. Main amplifier circuit; 31. Voltage amplifier; 32. First connector; 33. Second connector. DETAILED DESCRIPTION

[0054] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. In the description of the present invention, it should be noted that the term "or" is usually used in the sense of including "and / or", unless the content clearly indicates otherwise.

[0055] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or a magnetic connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be internal communication between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. In addition, in the description of this application, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0056] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] In order to solve the problems existing in the prior art, the embodiment of the present invention provides a non-destructive γ measurement device in the nuclear field based on NaI detector, and in particular relates to an application scenario of full material measurement of radioactive materials in work shoes worn by nuclear power plant workers, such as Figure 1 As shown, it includes a shielding box 1 and a NaI detector 2. The shielding box 1 is used to provide radiation shielding, reduce the interference of scattered gamma rays in the environment, and ensure that the measured gamma ray signal is accurate and reliable; the NaI detector 2 is used to detect gamma rays, and realizes quantitative measurement of radiation intensity by converting the ray signal into an electrical signal. The shielding box 1 is provided with a shielding cover 11 and a shielding box body 12. When measuring, the shielding cover 11 is opened, and the NaI detector 2 is placed in the shielding box body 12. In order to meet the external connection needs of the NaI detector 2, the side wall of the shielding box body 12 is provided with a through hole for the cylindrical top of the NaI detector 2 to extend. In order to match the size requirements of the work shoes worn by nuclear power plant workers, preferably, the shielding box 1 is set to 200mm×400mm×75mm. Further preferably, in order to increase the radiation shielding effect, a lead plate is provided inside the shielding box 1, and the thickness of the lead plate is 4-7mm.

[0058] In some preferred embodiments, the nuclear electronics part of the NaI detector 2 includes a voltage divider, a high voltage generating circuit, a preamplifier circuit, a pole-zero phase cancellation circuit, a main amplifier circuit 3 and an FPGA digital circuit, and the whole process from gamma-ray signal detection to digital signal processing is integrated through integration. The voltage divider and the high voltage generating circuit ensure the stable operation of the NaI detector 2, the preamplifier and the pole-zero phase cancellation circuit improve the accuracy and signal-to-noise ratio of the signal, the main amplifier strengthens the signal amplitude to adapt to subsequent processing, and the FPGA digital circuit realizes efficient data acquisition and processing, improves the real-time performance, reliability and integration of the NaI detector 2, and significantly optimizes the measurement performance.

[0059] In some preferred embodiments, the main amplifier circuit 3 includes a voltage amplifier 31, a first connector 32 and a second connector 33, such as Figure 2 As shown, the voltage amplifier 31 is provided with an operational amplifier U19, and a structure with a fixed gain of 8 times is formed by a feedback resistor R74 and an input resistor R68. The input signal is connected to the reverse input terminal of the operational amplifier U19 through the input resistor R68, and the positive input terminal of the operational amplifier U19 is grounded. The feedback resistor R74 adopts a high-precision resistor, and the output terminal of the operational amplifier U19 is connected to the load matching resistor R69 to ensure output impedance matching and avoid signal reflection. The main amplifier circuit 3 is powered by a ±5V dual power supply, and the power supply decoupling capacitors C136 and C138 are used to filter out power supply noise. The final amplified signal is output through the AMP_OUT port and transmitted to other places or the outside through the first connector 32 or the second connector 33. The first connector 32 adopts a 2-pin connector for transmitting the amplified signal to the outside; the second connector 33 adopts an SMA connector for connecting to an external device or a test device to transmit the amplified signal to the outside.

[0060] In some preferred embodiments, the nuclear electronics part of the NaI detector 2 uses LTspice software to simulate part of the circuit, and uses Geant4 software to simulate important parameters such as detection efficiency, such as Figure 3 As shown, the detection efficiency results of the simulation of the nuclear electronics part of the NaI detector 2 of the embodiment of the present invention by the Geant4 software are used to optimize the nuclear electronics part of the NaI detector 2.

[0061] The present invention also provides a measurement method based on the above-mentioned nuclear field non-destructive γ measurement device, comprising:

[0062] S1: Perform background measurement;

[0063] S11: placing the NaI detector 2 in the shielding box 1, with no sample to be measured placed in the shielding box 1, and ensuring that there is no interference from any radioactive material around;

[0064] S12: Turn on the power of the NaI detector 2 and perform initialization settings;

[0065] S13: without placing the sample to be measured, measure and record the measurement time and environmental conditions, including temperature, humidity, etc., for later correction of the detection data;

[0066] S14: After the measurement is completed, the NaI detector 2 is turned off, and the obtained background signal reference value is recorded;

[0067] S2: perform sample measurement;

[0068] S21: placing the sample to be measured in the measurement area of ​​the NaI detector 2 and placing them together in the shielding box 1, adjusting the position and distance between the sample to be measured and the NaI detector 2 to ensure that the detection efficiency of each measurement is roughly the same;

[0069] S22: Set the measurement time and parameters according to the experimental requirements and sample properties; 60 Taking the work shoes of the nuclear power plant workers of Co as an example, the level of 1e-2Bq / g can be reached after measuring for 2 minutes. This accuracy is sufficient to de-control the work shoes. At this time, the detection limit and detection time of NaI detector 2 can be calculated by the following formulas:

[0070]

[0071] in:

[0072] L min is the minimum detection limit

[0073] K is a constant that depends on the sensitivity of the detector.

[0074] B is the background noise

[0075] t is the detection time

[0076] N signal and N background are the counts of signal and background, respectively.

[0077] S23: measuring the sample to be measured, and recording relevant data such as measurement time, sample information, and environmental conditions;

[0078] S24: After the measurement is completed, the NaI detector 2 is turned off and the first measurement result is recorded;

[0079] S3: Processing the above data to obtain a corrected third measurement result;

[0080] S31: Based on the background signal reference value in steps S1 and S2 and the first measurement result of the sample, background subtraction is performed on the first measurement result of the sample to obtain a pure sample signal, i.e., a second measurement result. The background subtraction adopts the following formula:

[0081]

[0082] Among them, P smooth (E) is the smoothed spectrum, N is the window size, and i is the index in the window.

[0083] P measured (E) = P signal (E)+P backgruond (E)

[0084] Among them, P measured (E) is the measured total spectrum, P signal (E) is the signal spectrum of the target source, P backgruond (E) is the background spectrum.

[0085] S32: Data analysis and processing of the sample signal after background subtraction, including steps such as nuclide peak identification fitting and net count calculation, the algorithm is as follows:

[0086]

[0087] in:

[0088] P(E) is the count rate at energy E (spectral data).

[0089] A is the height of the peak (maximum counts), indicating the intensity of the signal.

[0090] E0 is the central energy of the peak (corresponding to the characteristic gamma energy of the nuclide).

[0091] σ is the peak width, which is related to the energy resolution of the detector

[0092] S33: Based on the above data processing results, a chart is drawn and data is compared to obtain a final third measurement result.

[0093] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A non-destructive gamma measurement method in the nuclear field based on NaI detector, characterized in that: include: Without placing the sample to be measured, place the NaI detector in the shielding box, and measure and record the background signal reference value; Placing the sample to be measured in the measurement area of ​​the NaI detector, measuring and recording a first measurement result of the sample; The background signal is subtracted from the first measurement result and the background signal reference value to obtain a second measurement result, using the following formula: in: P smooth (E) is the spectrum after smoothing; N is the window size; i is the index in the window; P measured (E)=P signal (E)+P backgruond (AND) in: P measured (E) is the measured total spectrum; P signal (E) is the signal spectrum of the target source; P backgruond (E) is the background spectrum; The second measurement result is processed to obtain a final third measurement result using the following formula: in: P(E) is the count rate at energy E (spectral data); A is the height of the peak (maximum count), indicating the intensity of the signal; E0 is the central energy of the peak (corresponding to the characteristic gamma energy of the nuclide); σ is the peak width and is related to the energy resolution of the NaI detector.

2. The non-destructive γ measurement method in the nuclear field according to claim 1, characterized in that: Before measuring and recording the first measurement result of the sample, the detection limit and detection time parameters of the NaI detector are obtained by calculation, and the NaI detector is set according to the parameters. The calculation formula is as follows: in: L min is the minimum detection limit; K is a constant that depends on the sensitivity of the detector; B is the background noise; t is the detection time; N signal and N background are the counts of signal and background, respectively.

3. The non-destructive γ measurement method in the nuclear field according to claim 2, characterized in that: The detection time t is based on 60 The control accuracy of the work shoes of the nuclear power plant workers of Co is determined.

4. The non-destructive gamma measurement method in the nuclear field according to claim 3, characterized in that: The control accuracy is such that the measurement reaches 1e-2Bq / g in 2 minutes.

5. The non-destructive γ measurement method in the nuclear field according to claim 1, characterized in that: The shielding box is provided with a shielding box body, a through hole is opened on the side wall of the shielding box body, the top of the NaI detector is configured as a cylinder, and the cylinder contacts the outside of the shielding box through the through hole.

6. The non-destructive gamma measurement method in the nuclear field according to claim 5, characterized in that: The nuclear electronics portion of the NaI detector is provided with a main amplifier circuit.

7. The non-destructive gamma measurement method in the nuclear field according to claim 6, characterized in that: The main amplifier circuit includes a voltage amplifier, a first connector and a second connector. The voltage amplifier is provided with an operational amplifier U19, a feedback resistor R74 and an input resistor R68 for signal amplification. The first connector and the second connector are used to transmit the amplified signal to the outside.

8. The non-destructive gamma measurement method in the nuclear field according to claim 7, characterized in that: The input resistor R68 is connected to the inverting input terminal of the operational amplifier U19, and the positive input terminal of the operational amplifier U19 is grounded.

9. The non-destructive γ measurement method in the nuclear field according to any one of claims 1 to 8, characterized in that: The size of the shielding box is 200mm×400mm×75mm.

10. The non-destructive gamma measurement method in the nuclear field according to claim 9, characterized in that: A lead plate is arranged inside the shielding box, and the thickness of the lead plate is 4-7 mm.

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