A method for manufacturing an electron source for alpha spectrometer calibration

Abstract

This invention relates to the field of alpha ray detection equipment technology, specifically to a method for fabricating an electron source for alpha spectrometer calibration. A pulse signal generator is connected to the input terminal of the preamplifier circuit of the alpha spectrometer to which the electron source is to be fabricated. The pulse signal generator includes an FPGA module and connected to a DAC chip, a voltage-controlled current output module, and an analog switch. The FPGA module controls the DAC chip to output pulse signals of arbitrary amplitude, and controls the analog switch to open and close at different frequencies, outputting pulses of different period frequencies. The pulse signal generator generates pulse signals to simulate an alpha ray source to prepare the electron source. This method eliminates the need for a standard source when calibrating related indicators of the alpha spectrometer, such as energy scale, energy nonlinearity, energy resolution, and electronic detection efficiency. The calibration is simple and convenient, and the electron source has low cost, good operability, practicality, and safety.

Description

Technical Field

[0001] This invention relates to the field of alpha ray detection equipment technology, and specifically to a method for manufacturing an electron source for alpha spectrometer calibration. Background Technology

[0002] In the nuclear radiation measurement industry, alpha spectrometers, as alpha ray detection devices, have wide applications, such as nuclear radioactivity investigation, radioactivity detection in nuclear wastewater, detection of nuclear contamination in seafood, and medical examinations. An alpha spectrometer system mainly consists of a vacuum system and an electronic system. The electronic system primarily includes a semiconductor detector (such as a PIPS detector), a preamplifier circuit, and a digital multichannel module. The semiconductor detector efficiently captures alpha particles from the radioactive source, generating a small, second-decaying pulse signal (charge signal). The preamplifier circuit, composed of a charge-sensitive amplifier circuit and an adjustment amplifier circuit, converts the charge signal into a pulse signal with a certain amplitude. The adjustment amplifier circuit then adjusts the pulse amplitude and pulse width to a suitable multichannel sampling range. Finally, the digital multichannel module performs functions such as pulse amplitude extraction, counting, and spectral line output. The pulse amplitude in the output spectrum corresponds to the alpha energy of the radioactive source, and the number of pulses per unit time represents the activity of the radioactive source.

[0003] To ensure the accuracy of measurement results, the alpha spectrometer should be calibrated regularly. Alpha spectrometer calibration methods include energy calibration using an alpha standard source with known energy and activity calibration using standard samples of known concentrations. Energy calibration maps the known energy of the alpha ray to the amplitude of the generated signal. For example, if an alpha standard source (Am241) emits an alpha ray with an energy of 5.486 MeV with the highest probability, and the amplitude is extracted by the alpha spectrometer's electronics system to be 500 mV, then it can be assumed that if the system extracts many 500 mV pulse signals within a certain period, an Am241 source exists. This correspondence is the energy calibration and the fundamental theory of nuclide identification. Alpha spectrometer calibration relies on one or more different standard sources. However, the fabrication process of alpha standard sources is complex and costly. Furthermore, they are radioactive, requiring strict management and storage of radioactive sources, and limiting the types and activity levels of nuclides that can be obtained, thus restricting the research and manufacturing of alpha spectrometer equipment. Summary of the Invention

[0004] To address the aforementioned shortcomings in the existing technology, this invention provides a method for fabricating an electron source for alpha spectrometer calibration. The electron source is prepared by generating pulse signals using a pulse signal generator to simulate an alpha ray source. This eliminates the need for a standard source when calibrating related indicators of the alpha spectrometer, such as energy scale, energy nonlinearity, energy resolution, and electronic detection efficiency. The calibration is simple and convenient, and the electron source has a low cost, demonstrating good operability, practicality, and safety.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0006] A method for fabricating an electron source for alpha spectrometer calibration includes the following steps:

[0007] S1. Connect a pulse signal generator to the input terminal of the preamplifier circuit of the α-spectrum instrument whose electronic source is to be made;

[0008] The pulse signal generator includes an FPGA module and a connected DAC chip, analog switch, and voltage-controlled current output module. The FPGA module is connected to the DAC chip and controls the DAC chip to output a voltage signal. The voltage-controlled current output module converts the voltage signal into a current signal. The voltage-controlled current output module is connected to a preamplifier circuit and inputs the current signal into the preamplifier circuit. The FPGA module is connected to the analog switch and controls the analog switch to open or close, thereby controlling the on / off state of the current signal. Thus, the FPGA module controls the output of pulse signals of arbitrary amplitude with different period frequencies.

[0009] S2. The α spectrometer in S1 is calibrated with energy using a standard source to obtain the correspondence between the center channel address of the output spectral line and the energy.

[0010] S3. Take out the standard source, and use the FPGA module to control the DAC chip and analog switch to continuously generate pulse signals at a certain frequency, so that the center channel address of the energy peak of the digital multichannel module output spectrum corresponds one-to-one with the center channel address of the energy peak of the standard source in S2. The FPGA module records the output voltage V of the DAC chip, such as... Figure 4 As shown, based on the correspondence between the energy peak center address and the energy obtained in S2, the correspondence between the energy peak center address, the energy and the output voltage of the pulse signal generator is obtained. Thus, the energy peak is generated at any energy peak center address through the FPGA module, and the electronic source of the α spectrometer is fabricated.

[0011] Step S2 is as follows: Select a standard source, place the standard source at the detector end of the α spectrometer detector, output the spectrum through the digital multichannel module, and record the center channel address of the energy peak in the output spectrum as H. Look up the energy of the standard source in the nuclide table to obtain the correspondence between the center channel address and energy of the energy peak in the whole spectrum, and complete the energy calibration of the α spectrometer.

[0012] In step S3, the activity of the electron source is simulated by controlling the number of pulses per unit time through the FPGA module.

[0013] When simulating a hybrid source using an electronic source, the FPGA module controls the alternating generation of pulse signals corresponding to each standard source based on the proportion of each standard source in the hybrid source and the energy branch ratio of each standard source in the hybrid source as found in the nuclide table, thereby simulating the output of the hybrid source through the electronic source.

[0014] The electron source can be used to calibrate the energy scale, energy nonlinearity, energy resolution, and electronic detection efficiency of the alpha spectrometer.

[0015] Compared with the prior art, the beneficial effects of the present invention are: (1) In the present invention, an electron source is prepared by generating a pulse signal to simulate an α-ray source through a pulse signal generator. When calibrating the relevant indicators such as energy scale, energy nonlinearity, energy resolution, and electronic detection efficiency of the α-spectrum, a standard source is not required, the calibration is simple and convenient, and the electron source has a low cost. The electron source has good operability, practicality and safety.

[0016] (2) The pulse signal generator in this invention includes an FPGA module and a connected DAC chip, voltage-controlled current output module and analog switch. The FPGA module controls the DAC chip to output a pulse signal of arbitrary amplitude, and controls the analog switch to open and close at different frequencies to output pulses of different period frequencies. It has the characteristics of small size, controllable output charge, and adjustable pulse generation frequency.

[0017] (3) The electronic source in this invention can simulate a single standard source or a mixed source of multiple standard sources, avoiding mixed interference when two or more standard sources are used together. It is highly efficient when used for calibration of energy nonlinearity of α spectrometer. Attached Figure Description

[0018] Figure 1 A schematic diagram of the pulse signal output from the digital multichannel module for the detector to capture alpha particles;

[0019] Figure 2 This is a schematic diagram of the pulse signal generator connected to the input terminal of the preamplifier circuit in this invention;

[0020] Figure 3 This is a schematic diagram showing the connections of the various modules of the pulse signal generator in this invention;

[0021] Figure 4 This is a flowchart illustrating how the FPGA module controls the DAC chip to output a voltage signal corresponding to the energy of a certain standard source in this invention.

[0022] Figure 5 Record the energy and energy branching ratio of the standard source (Am241) in the standard nuclide library;

[0023] Figure 6 This is a schematic diagram of the spectrum after 1000 seconds of continuous measurement using the Am241 standard source as an electronic source. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] The output of the alpha spectrometer detector is sequentially connected to a preamplifier circuit and a digital multichannel module. A sample or standard source containing alpha particles is placed at the detector probe. Upon receiving alpha rays, the detector depletes the positively charged alpha particles, generating a tiny current and outputting a charge signal. Taking a standard source (Am241) as an example, its main energy is 5.486 MeV. This energy, when received by the detector, generates approximately 2.41 × 10⁻¹³ C of charge. The preamplifier circuit collects and amplifies the charge to form a pulse signal. Next, adjustments and amplification are performed to adjust the pulse signal to an appropriate amplitude. The digital multichannel module records the pulse signal and outputs the spectral lines, such as... Figure 1 As shown.

[0026] This invention provides a method for fabricating an electron source for alpha spectrometer calibration, comprising the following steps:

[0027] S1. Connect a pulse signal generator to the input terminal of the preamplifier circuit of the α-spectrum instrument to be used as the electron source, such as... Figure 2 As shown;

[0028] The pulse signal generator includes an FPGA module and connected DAC chip, analog switch, and voltage-controlled current output module, such as... Figure 3 As shown, the FPGA module is connected to the DAC chip and controls the DAC chip to output a voltage signal. The voltage-controlled current output module converts the voltage signal into a current signal. The voltage-controlled current output module is connected to the preamplifier circuit and inputs the current signal into the preamplifier circuit. The FPGA module is connected to the analog switch and controls the analog switch to open or close, thereby controlling the on / off state of the current signal. Thus, the FPGA module controls the output of pulse signals of arbitrary amplitude and different period frequencies. In other words, the FPGA module controls the DAC chip to output pulse signals of arbitrary amplitude and controls the analog switch to open and close at different frequencies to output pulses of different period frequencies.

[0029] S2. The α-spectrum in S1 is calibrated using a standard source to obtain the correspondence between the center channel address of the output spectral line and the energy. Specifically, a standard source is selected and placed at the detector end of the α-spectrum detector. The spectral line is output through the digital multichannel module. The center channel address of the energy peak in the output spectral line is recorded as H. The energy of the standard source is looked up in the nuclide table to obtain the correspondence between the center channel address of the energy peak and the energy of the entire spectrum, thus completing the energy calibration of the α-spectrum.

[0030] S3. Take out the standard source, and use the FPGA module to control the DAC chip and analog switch to continuously generate pulse signals at a certain frequency, so that the center channel address of the energy peak of the digital multichannel module output spectrum corresponds one-to-one with the center channel address of the energy peak of the standard source in S2. The FPGA module records the output voltage V of the DAC chip, such as... Figure 4As shown, based on the correspondence between the energy peak center address and energy obtained in S2, the correspondence between the energy peak center address, energy, and the output voltage of the pulse signal generator can be obtained. Thus, an energy peak can be generated at any energy peak center address using the FPGA module, thereby fabricating the electron source for the α-spectrum. That is, based on the nuclide library records, the electron source can output an analog signal from any standard source.

[0031] Taking the standard source (Am241) as an example, according to the nuclide library, it emits a signal with an energy of 5485.7 keV with a probability of 0.852 and a signal with an energy of 5443 keV with a probability of 0.128. Placing the standard source (Am241) in the detector and outputting the spectrum through the digital multichannel module, two distinct energy peaks will appear in the output spectrum. The center channel addresses of these peaks are denoted as H1 and H2, respectively. H1 corresponds to 5485.7 keV, and H2 corresponds to 5443 keV. Using these two energy points, the channel address and energy correspondence for the entire spectrum can be established, thus completing the energy calibration of the alpha spectrometer. After removing the standard source (Am241), the pulse amplitude generated by the pulse signal generator is adjusted so that a peak is also generated at the center of channel address H1 in the output spectrum. At this time, the energy generated by the output voltage V of the DAC chip controlled by the FPGA module is 5485.7 keV. Similarly, a peak is generated at the center of channel H2, and the energy generated by the DAC chip and analog switch controlled by the FPGA module is 5443 keV. Finally, based on the correspondence between channel addresses and energies in the full spectrum, an energy peak can be generated at the center of any channel address through the FPGA module, thus completing the construction of the electronic source for this alpha spectrometer.

[0032] Any standard source can be simulated using an electron source. Taking the standard source (Am241) as an example, according to the standard nuclide library, it emits pulses of six energies, and its energies and energy branches are as follows: Figure 5As shown, it emits 5485.7 KeV with a probability of 0.852, 5443 KeV with a probability of 0.128, 5485.7 KeV with a probability of 0.014, 5544.3 KeV with a probability of 0.0034, 5512 KeV with a probability of 0.002, and 5308.2 KeV with a probability of 0.000339. The FPGA module generates pulse signals corresponding to each energy level by controlling a DAC chip and analog switches. Specifically, the FPGA module randomly generates pulse signals corresponding to these six energies, with the random probability controlled to correspond to the energy branch ratio of each energy. This results in the emission of 5485.7 keV with a probability of 0.852, 5443 keV with a probability of 0.128, 5485.7 keV with a probability of 0.014, 5544.3 keV with a probability of 0.0034, 5512 keV with a probability of 0.002, and 5308.2 keV with a probability of 0.000339. The remaining probability does not generate pulses. This successfully simulates the decay event of a standard source (Am241), obtaining the electron source of the standard source (Am241). Standard sources typically have two measurement parameters: energy and activity. In this embodiment, the activity of the electron source is simulated by controlling the number of pulses per unit time through the FPGA module. For example, if 10 pulses are generated per second, the activity q = 10 becquerels (Bq) is generated, thus creating an Am241 electron source with an activity of 10 Bq.

[0033] The electron source can also be used to simulate a mixed source. Based on the proportion of each standard source in the mixed source and the energy branch ratio of each standard source in the mixed source as looked up in the nuclide table, the FPGA module controls the alternating generation of pulse signals corresponding to each standard source. That is, it alternately generates different energy pulses at a certain count rate, thereby simulating the output of the mixed source through the electron source. For example, the mixed source includes standard source S1 and standard source S2. Standard source S1 generates only one energy E1 with a probability of 0.5, and another standard source S2 generates only one energy E2 with a probability of 0.5. Controlling the generation of 10 pulses of energy E1 and 10 pulses of energy E2 per second simultaneously generates a 10Bq S1 electron source and a 10Bq S2 electron source, i.e., a mixed source of S1 and S2. According to the clauses of standard JJF1851-2020 "Alpha Spectrometer Calibration Specification", two or more standard sources can be used for energy nonlinearity calibration. Here, only one electronic source system is needed to achieve the effect of two standard sources simultaneously, and the efficiency is more than twice that of using standard sources. This is because when using one standard source, you cannot use another standard source at the same time, while electronic sources can and there is no mixing interference.

[0034] The electron source provided in this embodiment can be used to calibrate related indicators of the alpha spectrometer, such as energy scale, energy nonlinearity, energy resolution, and electronic detection efficiency.

[0035] (1) The method for calibrating the energy scale using an electronic source is as follows: by simulating the Am241 standard source with an electronic source, two obvious energy peaks will appear in the spectrum (the probability of the last four energies of the Am241 source is very small, so the energy peaks appearing in the spectrum are not obvious and are generally not analyzed; only the first two energies are studied). The highest energy peak of 5485.7 KeV corresponds to channel address h1, and the second highest energy peak of 5443 KeV corresponds to channel address h2. The energy E corresponding to any channel address hx is E=hx*(5485.7-5443) / (h1-h2). In this way, the energy scale is calibrated using an electronic source.

[0036] (2) The calibration method for energy nonlinearity of the electron source is as follows: The electron source is set to a mixture of Am241 and Cm244. The output spectrum will show four distinct energy peaks. Analyzing the spectrum, the peak center energies are Ea1, Ea2, Ec1, and Ec2. By consulting the nuclide library, the standard values ​​for the four peak center energies are found to be 5485.7 keV, 5443 keV, 5805 keV, and 5762.8 keV, respectively. According to the energy nonlinearity formula... We can obtain:

[0037] ;

[0038] ;

[0039] ;

[0040] ;

[0041] The maximum value among U1, U2, U3, and U4 is U.

[0042] (3) The method for calibrating the energy resolution of the electron source is as follows:

[0043] The electron source was set to an Am241 source, generating 10 pulses per second. The activity q = 10 becquerels (Bq), thus creating a 10 Bq Am241 electron source. The spectrum obtained after continuous measurement of this simulated standard source for 1000 seconds is shown below. Figure 6As shown, the vertical axis count values ​​N1 and N2 for H1 and H2 are taken respectively, and then the horizontal axis corresponding to the N / 2 counts on the energy peaks is taken as the energies E1l and E1r, E2l and E2r. According to the definition of energy resolution, the energy resolution of H1 is ΔE1 = E1r - E1l, and the energy resolution of H2 is ΔE2 = E2r - E2l. ΔE1 and ΔE2 represent the energy resolution of the equipment for the 5485.7 KeV and 5443 KeV energy peaks of Am241 nuclide, respectively. ΔE1 and ΔE2 represent the best resolution achieved by the equipment for both Am241 nuclides.

[0044] (4) Methods for using electronic sources in background calibration tests

[0045] Background calibration involves obtaining the background count of the equipment and then calculating the background count rate nb, where nb = Nb / t. According to the definition of background, it is independent of the source; therefore, during alpha spectrometer background calibration, the electron source is turned off, and the detector is connected for continuous 24-hour measurement to obtain Nb.

[0046] (5) The calibration method for the electronic source's electronic detection efficiency is as follows:

[0047] The electron source was set to an Am241 source, generating 10 pulses per second, resulting in an activity q = 10 Bq. Thus, a 10 Bq Am241 electron source was created. Measurements were continuously performed for 1100 seconds, and the total count N in the 5000 KeV~6000 KeV energy range was calculated. The background count Nb in the same energy range was then calculated using the method for electron source-based background measurements. The detection efficiency ε of the device was calculated using the formula: The detection efficiency ε represents the best detection efficiency that the equipment's electronic system can achieve for the Am241.

Claims

1. A method for fabricating an electron source for α-spectrum calibration, characterized in that... Includes the following steps: S1. Connect a pulse signal generator to the input terminal of the preamplifier circuit of the α-spectrum instrument whose electronic source is to be made; The pulse signal generator includes an FPGA module and a connected DAC chip, analog switch, and voltage-controlled current output module. The FPGA module is connected to the DAC chip and controls the DAC chip to output a voltage signal. The voltage-controlled current output module converts the voltage signal into a current signal. The voltage-controlled current output module is connected to a preamplifier circuit and inputs the current signal into the preamplifier circuit. The FPGA module is connected to the analog switch and controls the analog switch to open or close, thereby controlling the on / off state of the current signal. Thus, the FPGA module controls the output of pulse signals of arbitrary amplitude with different period frequencies. S2. The α spectrometer in S1 is calibrated with energy using a standard source to obtain the correspondence between the center channel address of the output spectral line and the energy. S3. Take out the standard source, and use the FPGA module to control the DAC chip and analog switch to continuously generate pulse signals at a certain frequency, so that the energy peak center channel address of the output spectrum of the digital multichannel module corresponds one-to-one with the energy peak center channel address of the standard source in S2. The FPGA module records the output voltage V of the DAC chip, as shown in Figure 4. According to the correspondence between the energy peak center channel address and the energy obtained in S2, the correspondence between the energy peak center channel address, the energy and the output voltage of the pulse signal generator is obtained. Thus, the FPGA module generates an energy peak at any energy peak center channel address, and the electronic source of the α spectrometer is made.

2. The method for manufacturing an electron source for α-spectrum calibration according to claim 1, characterized in that: Step S2 is as follows: Select a standard source, place the standard source at the detector end of the α spectrometer detector, output the spectrum through the digital multichannel module, and record the center channel address of the energy peak in the output spectrum as H. Look up the energy of the standard source in the nuclide table to obtain the correspondence between the center channel address and energy of the energy peak in the whole spectrum, and complete the energy calibration of the α spectrometer.

3. The method for fabricating an electron source for α-spectrum calibration according to claim 1, characterized in that: In step S3, the activity of the electron source is simulated by controlling the number of pulses per unit time through the FPGA module.

4. The method for manufacturing an electron source for α-spectrum calibration according to claim 1, characterized in that: When simulating a hybrid source using an electronic source, the FPGA module controls the alternating generation of pulse signals corresponding to each standard source based on the proportion of each standard source in the hybrid source and the energy branch ratio of each standard source in the hybrid source as found in the nuclide table, thereby simulating the output of the hybrid source through the electronic source.

5. The method for manufacturing an electron source for α-spectrum calibration according to claim 1, characterized in that: The electron source can be used to calibrate the energy scale, energy nonlinearity, energy resolution, and electronic detection efficiency of the alpha spectrometer.

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