A temperature compensation method for alpha radioactive aerosol measurement

Abstract

The invention discloses a temperature compensation method for alpha radioactive aerosol measurement. The method is based on the temperature compensation system, and a gain coefficient is set before the division operation of a trapezoidal forming algorithm. Before the trapezoidal forming algorithm is run each time to filter and form a digitized quasi-exponential decay signal, the gain coefficient is adjusted according to the real-time temperature of the detector. Since the signal entering the multiplier is hundreds of signal filtering and superposition data, the number of bits is much larger than the number of bits of the initial data, and therefore, data splitting will not occur after processing with the multiplier and divider. The method can realize temperature compensation for each alpha particle signal, so that the signal affected by the temperature can be corrected in time, thereby ensuring the accuracy of the obtained alpha energy spectrum, having a good spectrum stabilization effect, and effectively improving the accuracy of nuclide identification.

Description

Technical Field

[0001] The invention belongs to the technical field of radioactive measurement, and in particular relates to a temperature compensation method for alpha radioactive aerosol measurement. Background Art

[0002] The pollution of air by long-lived α radioactive aerosols is the main factor that constitutes the irradiation hazard of nuclear radiation to the human body. Therefore, it is particularly important to quickly determine the types and concentrations of long-lived α radioactive aerosols and nuclides in the air. The identification of the types of α radioactive aerosol nuclides requires the use of an α radioactive aerosol measuring instrument. The principle is that different nuclides emit different α energies, and the obtained α energy spectra are different. The number of channels corresponding to the α energy peak in the α energy spectrum is also different. Therefore, the nuclides can be identified according to the number of channels corresponding to the α energy peak in the α energy spectrum. However, since temperature will affect the gain of the radioactive aerosol measuring instrument, the energy of the obtained α particles will drift, and the number of channels corresponding to the α energy peak in the α energy spectrum will change, which will lead to errors in nuclide identification; therefore, it is necessary to correct the α energy spectrum through temperature compensation, that is, to stabilize the spectrum, so as to ensure the accuracy of nuclide identification.

[0003] At present, there are several methods for temperature compensation of various measuring instruments: First, the working voltage of the detector in the measuring instrument is adjusted to change the gain of the detector itself, thereby achieving temperature compensation. However, the measurement of the α energy spectrum generally uses semiconductor detectors such as PIPS. The gain of this type of detector is independent of the working voltage, so it is impossible to achieve spectrum stability by adjusting the working voltage. The second is to use a voltage-controlled gain amplifier, but the voltage-controlled gain amplifier cannot achieve fine gain adjustment. Since the temperature drift of α radioactive aerosols is often less than 10%, this method is not suitable for α radioactive aerosol measuring instruments and will increase measurement noise. The third is to first obtain the real-time temperature of the detector, then calculate the temperature compensation coefficient, and finally correct the obtained α energy spectrum according to the temperature compensation coefficient; this method is to split and combine the data of each channel on the α energy spectrum through the temperature compensation coefficient. For example, the count of 500 channels of the α energy spectrum is N. 500 According to the temperature compensation coefficient, N 500 Split into αN 500 and (1-α)N 500 ,αN 500 The data of 499 channels are integrated into the new N 499 Data, (1-α)N 500 With N 501 The split data is integrated into a new N 500 Data; This method corrects the α energy spectrum over a period of time according to the temperature correction coefficient, which cannot achieve real-time temperature compensation, has a poor spectrum stabilization effect, and is prone to errors in nuclide identification.

[0004] Therefore, it is necessary to design a temperature compensation method that can perform real-time temperature compensation in α-radioactive aerosol measurement to enhance the spectrum stabilization effect and improve the accuracy of nuclide identification. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a temperature compensation method for α-radioactive aerosol measurement, so as to solve the technical problem that the current temperature compensation method is difficult to achieve real-time temperature compensation, and achieve the effect of improving the accuracy of nuclide identification.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A temperature compensation method for alpha radioactive aerosol measurement comprises the following steps:

[0008] 1) Obtain the charge signal generated by the detector due to the injection of α-particle signals;

[0009] 2) Amplify the charge signal into a quasi-exponential decay signal;

[0010] 3) digitizing the quasi-exponential decay signal;

[0011] 4) Adjust the filter shaping algorithm according to the real-time temperature of the detector;

[0012] 5) Using a filter shaping algorithm to filter and shape the digitized quasi-exponential decay signal;

[0013] 6) extracting the peak value of the signal after filtering and shaping to obtain the α energy spectrum;

[0014] 7) Identify the type of nuclide based on the α energy spectrum.

[0015] Furthermore, in step 4), the filtering shaping algorithm is a trapezoidal shaping algorithm; in step 5), the digitized quasi-exponential decay signal is filtered and shaped into a trapezoidal signal.

[0016] Further, step 4) includes the following sub-steps:

[0017] 41) calculating the peak drift ratio at the current temperature according to a preset linear equation of the peak drift ratio and the temperature;

[0018] 42) The peak drift ratio at the current temperature is used as the gain coefficient, and the gain coefficient is multiplied before the division operation in the trapezoidal shaping algorithm.

[0019] Furthermore, the method for obtaining the linear equation of the peak drift ratio and temperature is as follows: set the gain coefficient to 1, and obtain multiple α energy spectra corresponding to α particles of any nuclide type in the detector at multiple temperatures according to steps 1) to 6); extract the peak values ​​of the multiple α energy spectra; calculate the peak drift ratios at multiple temperatures according to each peak value and the peak value of the standard α energy spectrum; and fit the linear equation of the peak drift ratio and temperature according to multiple temperatures and the corresponding peak drift ratios.

[0020] Furthermore, the temperature compensation method uses a temperature compensation system, which includes an amplifier module, an ADC chip, an FPGA chip, an MCU and a temperature sensor that are electrically connected in sequence;

[0021] The amplification module is used to amplify the charge signal and shape it into a quasi-exponential decay signal. The ADC chip is used to digitize the quasi-exponential decay signal. The FPGA chip is used to run the filtering and shaping algorithm to filter and shape the digitized quasi-exponential decay signal. The MCU is used to determine the type of nuclide based on the energy spectrum, and is also used to send instructions to the FPGA chip according to the real-time temperature of the detector to adjust the filtering and shaping algorithm. The temperature sensor is used to obtain the real-time temperature of the detector.

[0022] Furthermore, the amplification module includes a charge-sensitive preamplifier and an operational amplifier, and the operational amplifier is electrically connected to the charge-sensitive preamplifier and the ADC chip respectively; the charge-sensitive preamplifier is used to amplify the charge signal into a quasi-exponential decay signal, and the operational amplifier is used to further amplify the quasi-exponential decay signal.

[0023] Furthermore, a multiplier and a divider are provided in the FPGA chip, the value of the divider is a fixed value, and when the FPGA chip runs the filter shaping algorithm, the ratio of the value of the multiplier to the value of the divider is used as a gain coefficient;

[0024] The linear equation of the peak drift ratio and temperature is preset in the MCU to calculate the peak drift ratio at the current temperature. The MCU calculates the value of the multiplier according to the peak drift ratio and the value of the divider and generates corresponding instructions. The MCU sends instructions to the FPGA chip to modify the value of the multiplier.

[0025] Further, the value of the divider is 32768, the value of the multiplier is initially 32768, and the initial value of the gain coefficient is 1.

[0026] Further, step 7) includes the following sub-steps:

[0027] 71) The channel number of the α energy peak is obtained by using the digital second-order derivative method according to the α energy spectrum;

[0028] 72) Determine the nuclide type of the alpha particle by comparing the channel number of the alpha energy peak with the nuclide library.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The temperature compensation method for α radioactive aerosol measurement of the present invention is based on the temperature compensation system, and there is no need to set up an additional gain adjustment circuit, thereby reducing external signal noise and cost. Before the FPGA chip runs the filter shaping algorithm to filter and shape the digitized quasi-exponential decay signal each time, the MCU will send instructions to the FPGA chip to adjust the filter shaping algorithm according to the real-time temperature of the detector; temperature compensation of the signal is performed according to the real-time temperature during filtering and shaping, so that the signal affected by the temperature can be corrected in time, thereby ensuring the accuracy of the obtained α energy spectrum, having a good spectrum stabilization effect, and effectively improving the accuracy of nuclide identification.

[0031] 2. The temperature compensation method for α radioactive aerosol measurement of the present invention sets a gain coefficient before the division operation of the trapezoidal forming algorithm. Since the signal entering the multiplier is the data of hundreds of signal filtering superpositions, the number of bits is much larger than the number of bits of the initial data. Therefore, there will be no data splitting after processing with the multiplier and divider. This method can achieve temperature compensation for each α particle signal, so that the signals affected by temperature can be corrected in time, thereby ensuring the accuracy of the obtained α energy spectrum, having a good spectrum stabilization effect, and can effectively improve the accuracy of nuclide identification.

[0032] 3. The temperature compensation system of the present invention sets a multiplier and a divider in the FPGA chip, takes the ratio of the multiplier to the divider as the gain coefficient, fixes the value of the divider, and generates corresponding instructions to adjust the value of the multiplier according to the real-time temperature of the detector, thereby adjusting the gain coefficient according to the real-time temperature of the detector. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of the components and connection relationship of the temperature compensation system described in the embodiment;

[0034] Figure 2 A schematic diagram of the composition and connection relationship of the α-radioactive aerosol measuring instrument described in the embodiment;

[0035] Figure 3 It is a schematic diagram of filtering and shaping the quasi-exponential decay signal into a trapezoidal signal in the embodiment;

[0036] Figure 4 The flowchart of the processing of the exponential decay signal in the FPGA chip and the MCU in the embodiment is shown. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0038] It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. In the description of the present invention, it should be noted that the orientation or position relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the invention product is usually placed when used, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance. In addition, the terms "horizontal", "vertical", etc. do not mean that the components are absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted. In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" 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 an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of 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.

[0039] Example:

[0040] See also Figure 1A temperature compensation method for measuring α-radioactive aerosols, the temperature compensation method uses a temperature compensation system, the temperature compensation system includes an amplifier module, an ADC chip, an FPGA chip, an MCU and a temperature sensor electrically connected in sequence; the ADC chip is an analog-to-digital converter, the FPGA chip is a programmable logic gate chip, and the MCU is a single-chip microcomputer; in this embodiment, the ADC chip uses 12 bits so that the temperature compensation system can obtain 1024 energy spectra.

[0041] The temperature compensation method comprises the following steps:

[0042] 1) The amplification module receives the charge signal generated by the detector due to the injection of the α-particle signal; in this embodiment, the detector is a PIPS detector;

[0043] 2) The amplification module amplifies the charge signal into a quasi-exponential decay signal and transmits it to the ADC chip; in this embodiment, the amplification module includes a charge-sensitive preamplifier and an operational amplifier, and the operational amplifier is electrically connected to the charge-sensitive preamplifier and the ADC chip respectively; the charge-sensitive preamplifier is used to amplify the charge signal into a quasi-exponential decay signal, and the operational amplifier is used to further amplify the quasi-exponential decay signal;

[0044] 3) The ADC chip digitizes the quasi-exponential decay signal, that is, converts the quasi-exponential decay signal from an analog signal to a digital signal, and transmits it to the FPGA chip;

[0045] 4) The temperature sensor obtains the real-time temperature of the detector and transmits it to the MCU. The MCU sends instructions to the FPGA chip to adjust the filter shaping algorithm according to the real-time temperature of the detector;

[0046] 5) The FPGA chip runs a filter shaping algorithm to filter and shape the digitized quasi-exponential decay signal;

[0047] 6) The FPGA chip extracts the peak value of the filtered and formed signal to obtain the α energy spectrum and transmits it to the MCU;

[0048] 7) MCU identifies the type of nuclide based on the α energy spectrum.

[0049] The composition and connection relationship of general α-radioactive aerosol measuring instruments are as follows: Figure 2 As shown, it includes an air pump, filter paper, PIPS, electronics, screen, buttons and a power supply system; when working, the air pump inhales air, the filter paper intercepts the aerosol in the air on the surface of the filter paper, the PIPS is the PIPS detector, the PIPS detector is close to the surface of the filter paper to measure the α particles on the surface of the filter paper, and the electronics is the central control of the α radioactive aerosol measuring instrument; the temperature compensation system described in this embodiment is integrated in the electronics.

[0050] The temperature compensation method for α radioactive aerosol measurement described in the present invention is based on the temperature compensation system, and does not need to additionally set up a gain adjustment circuit, thereby reducing external signal noise and cost; before the FPGA chip runs the filter shaping algorithm to filter and shape the digitized quasi-exponential decay signal each time, the MCU sends an instruction to the FPGA chip to adjust the filter shaping algorithm according to the real-time temperature of the detector; temperature compensation is performed on the signal according to the real-time temperature during filtering and shaping, so that the signal affected by the temperature can be corrected in time, thereby ensuring the accuracy of the obtained α energy spectrum, having a good spectrum stabilization effect, and effectively improving the accuracy of nuclide identification.

[0051] Further, in step 4), the filtering shaping algorithm is a trapezoidal shaping algorithm; in step 5), the digitized quasi-exponential decay signal is filtered and shaped into a trapezoidal signal; that is, the quasi-exponential decay signal is filtered and shaped into a trapezoidal signal by the trapezoidal shaping algorithm, such as Figure 3 shown.

[0052] The essence of the trapezoidal forming algorithm is to average multiple samples in proportion, reduce the noise level by averaging, and improve the signal-to-noise ratio. For the trapezoidal forming algorithm, the more filtering points there are, the higher the signal-to-noise ratio is, but the lower the pass rate is. To ensure the pass rate, hundreds of filtering points are generally used. Since the division operation is completed in the last step, the signal amplitude is continuously accumulated to a large value before this, and finally divided by a fixed value (usually related to the number of filtering points and the signal shape) to convert the quasi-exponential signal into a trapezoidal signal. The basic algorithm formula is as follows:

[0053] v1(k)=2×v1(k-1)-v1(k-2)+v i (k)

[0054]

[0055] Among them, n a 、n b 、n c is the waveform sampling point, v i is the input, v o is the output; from the formula, it can be seen that the output needs to be scaled through a division operation;

[0056] Therefore, in the temperature compensation method of the present invention, in step 4), the filter shaping algorithm is adjusted by multiplying a gain coefficient before the division operation of the trapezoidal shaping algorithm, and the gain coefficient is determined by the real-time temperature of the detector. Specifically, step 4) includes the following sub-steps:

[0057] 41) calculating the peak drift ratio at the current temperature according to a preset linear equation of the peak drift ratio and the temperature;

[0058] 42) The peak drift ratio at the current temperature is used as the gain coefficient, and the gain coefficient is multiplied before the division operation in the trapezoidal shaping algorithm.

[0059] To implement step 4), a multiplier and a divider are provided in the FPGA chip, the multiplier is represented by M, the divider is represented by D, and the gain coefficient G=M / D is defined, that is, when the FPGA chip runs the filter shaping algorithm, the ratio of the value of the multiplier to the value of the divider is used as the gain coefficient, and the value of the divider is a fixed value; in this embodiment, the value of the divider V d =32768 (FPGA chip is implemented by right shifting 15 bits to reduce the resource consumption of FPGA chip), the initial value of the multiplier is V m =32768, the initial value of the gain coefficient G=1, and the temperature compensation system has no additional gain in the initial state;

[0060] The linear equation of the peak drift ratio and temperature is preset in the MCU to calculate the peak drift ratio at the current temperature. The MCU calculates the value of the multiplier according to the peak drift ratio and the value of the divider and generates a corresponding instruction. The MCU sends an instruction to the FPGA chip to modify the value of the multiplier; for example, when the temperature of the detector changes and the gain coefficient needs to be modified, the MCU sends an instruction to modify the multiplier V m When you need to double the value, change the multiplier value to 65536. When you need to reduce it to half, change V m Modify it to 16384 to achieve temperature compensation by adjusting the gain coefficient.

[0061] Among them, the method for obtaining the linear equation of the peak drift ratio and temperature is as follows: set the gain coefficient to 1. In this embodiment, the value of the multiplier is first fixed at 32768, and the temperature compensation system does not perform temperature compensation at this time; according to steps 1) to 6), multiple α energy spectra corresponding to α particles of any nuclide type in the detector at multiple temperatures are obtained; the peak values ​​of the multiple α energy spectra are extracted; the peak drift ratios at multiple temperatures are calculated based on each peak value and the peak value of the standard α energy spectrum; the linear equation of the peak drift ratio and temperature is fitted based on multiple temperatures and the corresponding peak drift ratios; that is, y=ax+b is used to represent the linear equation of the peak drift ratio and temperature, the x-coordinate represents the real-time temperature of the detector, and the y-coordinate represents the peak drift ratio, and the coefficients a and b are obtained through multiple sets of data and written into the MCU.

[0062] The process from step 4) to step 6) is as follows Figure 4 As shown, whenever the temperature of the detector changes, the MCU will generate instructions based on the current temperature and send them to the FPGA chip, so that the FPGA chip will immediately change the multiplier and perform amplitude correction on the signal corresponding to each subsequent alpha particle;

[0063] In this way, if the input 12-bit data is directly multiplied and divided, decimals will be obtained, and the decimal resolution is poor, which can easily lead to uneven data distribution; however, in the method described in the present invention, since the signal entering the multiplier is the data of hundreds of signal filtering and superposition, the number of bits is much larger than the number of bits of the initial data, and therefore, data splitting will not occur after processing with the multiplier and divider. This method can achieve temperature compensation for each α particle signal, so that the signals affected by temperature can be corrected in time, thereby ensuring the accuracy of the obtained α energy spectrum, having a good spectrum stabilization effect, and effectively improving the accuracy of nuclide identification.

[0064] In addition, step 7) is implemented based on MCU and includes the following sub-steps:

[0065] 71) The channel number of the α energy peak is obtained by using the digital second-order derivative method according to the α energy spectrum;

[0066] 72) The nuclide type of the alpha particle is determined by comparing the channel number of the alpha energy peak with the nuclide library; the nuclide library is preset in the MCU, and the nuclide library is a database that includes a one-to-one correspondence between the nuclide types, energy spectra and other parameters of various alpha particles.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Those skilled in the art should understand that those modifications or equivalent substitutions of the technical solution of the present invention that do not depart from the purpose and scope of the technical solution should be included in the scope of the claims of the present invention.

Claims

1. A temperature compensation method for alpha radioactive aerosol measurement, characterized in that: The steps include: 1) Obtain the charge signal generated by the detector due to the injection of α-particle signals; 2) Amplify the charge signal into a quasi-exponential decay signal; 3) Digitize the quasi-exponential decay signal; 4) Adjust the filter shaping algorithm according to the real-time temperature of the detector; 5) Using the filter shaping algorithm to filter and shape the digitized quasi-exponential decay signal; 6) Extract the peak value of the filtered and formed signal to obtain the α energy spectrum; 7) Identify the nuclide type based on the α energy spectrum; In step 4), the filter shaping algorithm is a trapezoidal shaping algorithm; in step 5), the digitized quasi-exponential decay signal is filtered and shaped into a trapezoidal signal; Step 4) includes the following sub-steps: 41) Calculate the peak drift ratio at the current temperature according to the preset linear equation of the peak drift ratio and temperature; 42) Use the peak drift ratio at the current temperature as the gain coefficient, and multiply the gain coefficient before the division operation in the trapezoidal shaping algorithm; The temperature compensation method uses a temperature compensation system, which includes an amplifier module, an ADC chip, an FPGA chip, an MCU and a temperature sensor that are electrically connected in sequence; The amplification module is used to amplify the charge signal into a quasi-exponential decay signal, the ADC chip is used to digitize the quasi-exponential decay signal, the FPGA chip is used to run the filter shaping algorithm to filter and shape the digitized quasi-exponential decay signal, the MCU is used to determine the type of nuclide according to the energy spectrum, and is also used to send instructions to the FPGA chip according to the real-time temperature of the detector to adjust the filter shaping algorithm, and the temperature sensor is used to obtain the real-time temperature of the detector; The FPGA chip is provided with a multiplier and a divider, the value of the divider is a fixed value, and when the FPGA chip runs the filter shaping algorithm, the ratio of the value of the multiplier to the value of the divider is used as a gain coefficient; The linear equation of the peak drift ratio and temperature is preset in the MCU to calculate the peak drift ratio at the current temperature. The MCU calculates the value of the multiplier according to the peak drift ratio and the value of the divider and generates corresponding instructions. The MCU sends instructions to the FPGA chip to modify the value of the multiplier.

2. A temperature compensation method for alpha radioactive aerosol measurement according to claim 1, characterized in that: The method for obtaining the linear equation of the peak drift ratio and temperature is as follows: set the gain coefficient to 1, and obtain multiple α energy spectra corresponding to α particles of any nuclide type in the detector at multiple temperatures according to steps 1) to 6); extract the peak values ​​of the multiple α energy spectra; calculate the peak drift ratios at multiple temperatures according to each peak value and the peak value of the standard α energy spectrum; and fit the linear equation of the peak drift ratio and temperature according to multiple temperatures and the corresponding peak drift ratios.

3. A temperature compensation method for alpha radioactive aerosol measurement according to claim 1, characterized in that: The amplification module includes a charge-sensitive preamplifier and an operational amplifier, and the operational amplifier is electrically connected to the charge-sensitive preamplifier and the ADC chip respectively; the charge-sensitive preamplifier is used to amplify the charge signal into a quasi-exponential decay signal, and the operational amplifier is used to further amplify the quasi-exponential decay signal.

4. A temperature compensation method for alpha radioactive aerosol measurement according to claim 1, characterized in that: The value of the divider is 32768, the value of the multiplier is initially 32768, and the initial value of the gain coefficient is 1.

5. The temperature compensation method for alpha radioactive aerosol measurement according to claim 1, characterized in that: Step 7) includes the following sub-steps: 71) According to the α energy spectrum, the channel number of the α energy peak is obtained by using the digital second-order derivative method; 72) Determine the nuclide type of the alpha particle by comparing the channel number of the alpha energy peak with the nuclide library.

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