Microwave plasma assisted laser spectroscopy system for radionuclides

Abstract

The present application relates to radionuclide spectrum analysis technical field, provide a kind of microwave plasma assisted laser spectrum measurement system for radionuclide, the pulsed laser generated by pulsed laser unit is handled after passing through optical path shaping unit, and is vertically applied to sample surface ablation in sample processing unit in laser-induced plasma optical spectrum signal;Microwave plasma torch generator unit generates microwave plasma, and plasma optical spectrum signal is enhanced;Optical path collection unit is used to collect plasma optical spectrum signal;PC control unit includes pulse delay generator, and pulse delay generator is used to provide timing control, avoid the interference of initial plasma radiation continuous spectrum;Radionuclide harmless treatment unit is used to extract radioactive aerosol in sample processing unit and is dissolved;The present application can effectively obtain strong spectrum signal at low laser energy, and can reduce laser ablation volume, improve spectrum stability.

Description

Technical Field

[0001] This invention relates to the field of radionuclide spectral analysis technology, and more specifically, to a microwave plasma-assisted laser spectral measurement system for radionuclides. Background Technology

[0002] Laser-induced breakdown spectroscopy (LIBS) is an atomic emission spectroscopy technique that generates a plasma emission source by ablating and exciting sample materials with a pulsed laser. Due to its advantages such as speed, portability, and on-site analysis, LIBS has been widely used in various fields, including industrial processes, mineral exploration, and environmental monitoring. The operation of nuclear facilities inevitably results in the diffusion of radioactive materials into the equipment environment, necessitating frequent inspections and maintenance to determine the material composition and wear status of various components. Currently, existing LIBS methods mostly use laser energies higher than 50 mJ to obtain distinctive spectral signals. Excessive laser energy can cause unavoidable damage to the sample, which does not comply with nuclear industry safety regulations, hindering the widespread application of LIBS technology in the nuclear industry. Therefore, there is an urgent need for a device that can rapidly and non-destructively detect radioactive elements in nuclear facilities at low laser energies. Researchers have developed various LIBS signal enhancement methods to improve the detection sensitivity of LIBS and better meet application requirements. Common LIBS signal enhancement methods include dual-pulse LIBS, spatially constrained LIBS, and laser-induced fluorescence combined with other techniques. While these methods can achieve certain signal enhancement effects, they require expensive experimental setups, increasing instrument costs and the overall complexity of the detection system. Summary of the Invention

[0003] The present invention provides a microwave plasma-assisted laser spectroscopy measurement system for radionuclides, which is simple, practical, and low in cost, and can effectively obtain strong spectral signals at low laser energy.

[0004] The microwave plasma-assisted laser spectroscopy measurement system for radionuclides according to the present invention includes a pulsed laser unit, an optical path shaping unit, an optical path collecting unit, a PC control unit, a sample processing unit, a microwave plasma torch generator unit, and a radionuclide detoxification unit. The pulsed laser unit is used to generate pulsed lasers. After being processed by the optical path shaping unit, the pulsed lasers are applied perpendicularly to the sample surface in the sample processing unit to ablate and generate laser-induced plasma spectral signals. The microwave plasma torch generator unit is used to generate microwave plasma, which is located in front of the sample on one side and enhances the plasma spectral signal. The optical path collection unit is used to collect plasma spectral signals; The PC control unit includes a pulse delay generator, which is used to provide timing control to avoid interference from the continuous spectrum of the initial plasma radiation. The radionuclide detoxification unit is used to extract and dissolve radioactive aerosols from the sample processing unit.

[0005] Preferably, the pulsed laser unit includes a pulsed laser generator.

[0006] Preferably, the optical path shaping unit includes a laser reflector, a half-wave plate, a polarizer, and a focusing lens; the laser reflector is located on the outgoing optical path of the pulsed laser generator; the laser reflector is located on the incoming optical path of the half-wave plate; the polarizer is located on the outgoing optical path of the half-wave plate; the focusing lens is located on the outgoing optical path of the polarizer; the sample is located on the outgoing optical path of the focusing lens; the laser reflector, the half-wave plate, the polarizer, and the focusing lens are coaxial, and the included angle between the laser reflector and the half-wave plate is 45°.

[0007] Preferably, the microwave plasma torch generator unit includes an outer tube, a middle tube, an inner tube, a microwave input terminal, and a reflection tuning terminal. The outer tube, the middle tube, and the reflection tuning terminal form an open-ended resonant cavity, into which an inert gas is input.

[0008] Preferably, the optical path collection unit includes a spectrometer, an optical fiber, and an optical fiber probe, with the optical fiber probe located above the other side of the sample surface; the optical fiber probe is connected to one end of the optical fiber, and the other end of the optical fiber is connected to the spectrometer.

[0009] Preferably, the fiber optic probe has a collection angle of 45° with the sample surface.

[0010] Preferably, the PC control unit also includes a PC controller, which is connected to the spectrometer, and the pulse delay generator is connected to both the spectrometer and the pulsed laser generator.

[0011] Preferably, the sample processing unit also includes a sample stage and a shielding cover, with the sample located on the sample stage and the sample stage located inside the shielding cover.

[0012] Preferably, the sample stage is a three-dimensional displacement sample stage, used to compensate for the thickness difference between different samples.

[0013] Preferably, the radionuclide harmless treatment unit includes a vacuum pump and a radionuclide absorbing solvent. The vacuum pump extracts the radioactive aerosol from the shielding cover and dissolves it by the radionuclide absorbing solvent.

[0014] The beneficial effects of this invention are as follows: The device for enhancing laser-induced breakdown spectral signals provided in this invention adds a microwave plasma torch generator to the existing LIBS spectral detection system. This microwave plasma torch generator is located in front of the sample surface. When the pulsed spectrum generated by the pulsed laser generator acts perpendicularly to the sample surface, the microwave plasma generated by the microwave plasma torch generator directly acts on the laser-induced plasma on the sample surface. This results in laser-induced plasma with higher temperature and electron density under microwave plasma excitation. Because the microwave plasma torch generator is small, low-power, and easy to assemble, the overall cost of the device remains relatively unchanged. Adding the microwave plasma torch generator also does not alter the layout of the original LIBS detection system, making operation convenient. Furthermore, the technical solution of this invention can effectively enhance the LIBS spectral signal, improve spectral stability, and thus increase the detection sensitivity of LIBS. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a microwave plasma-assisted laser spectroscopy measurement system for radionuclides in one embodiment.

[0016] Figure 2 This is a schematic diagram of the structure of the microwave plasma torch generator unit in the embodiment.

[0017] Figure 3 The figures show the experimental results, where (a) is the LIBS spectrum of national standard T1 copper obtained using the device of the present invention at a laser energy of 0.55 mJ; (b) is the LIBS spectrum of national standard T1 copper obtained using conventional LIBS equipment at a laser energy of 0.55 mJ; (c) is the LIBS spectrum of national standard T1 copper obtained using the device of the present invention at a laser energy of 0.01 mJ; and (d) is the LIBS spectrum of national standard T1 copper obtained using conventional LIBS equipment at a laser energy of 0.4 mJ.

[0018] In the picture: 1 is the pulsed laser unit, 2 is the optical path shaping unit, 3 is the optical path collection unit, 4 is the PC control unit, 5 is the sample processing unit, 6 is the microwave plasma torch generator unit, 7 is the radioactive nuclide harmless treatment unit, 1-1 is the pulsed laser generator, 2-1 is the laser reflector, 2-2 is the half-wave plate, 2-3 is the polarizer, 2-4 is the focusing lens, 3-1 is the spectrometer, 3-2 is the optical fiber, 3-3 is the optical fiber probe, 4-1 is the pulse delay generator, 4-2 is the PC controller, 5-1 is the sample stage, 5-2 is the sample, 5-3 is the shielding protective cover, 6-1 is the microwave plasma, 6-2 is the outer tube, 6-3 is the middle tube, 6-4 is the inner tube, 6-5 is the microwave input terminal, 6-6 is the reflection tuning terminal, 7-1 is the vacuum pump, 7-2 is the radioactive nuclide absorption solvent. Detailed Implementation

[0019] To further understand the content of this invention, a detailed description of the invention will be provided in conjunction with the accompanying drawings and embodiments. It should be understood that the embodiments are merely illustrative and not limiting of the invention.

[0020] Implementation List like Figure 1 As shown, this embodiment provides a microwave plasma-assisted laser spectroscopy measurement system for radionuclides, which includes a pulsed laser unit 1, an optical path shaping unit 2, an optical path collecting unit 3, a PC control unit 4, a sample processing unit 5, a microwave plasma torch generator unit 6, and a radionuclide harmless treatment unit 7. The pulsed laser unit 1 includes a pulsed laser generator 1-1, which generates pulsed laser. After being processed by the optical path shaping unit 2, the pulsed laser acts perpendicularly on the surface of the sample 5-2 in the sample processing unit 5 to ablate and generate a laser-induced plasma spectral signal. The microwave plasma torch generator unit 6 is used to generate microwave plasma 6-1, which is located in front of one side of sample 5-2. Microwave plasma 6-1 enhances the plasma spectral signal. Microwave plasma 6-1 is inverted funnel-shaped and has a "cross zone" with optimal enhancement effect. During the enhancement process, its central axis is parallel to and covers the sample surface. The length of microwave plasma is 12±1mm. After the pulsed laser passes vertically through the "cross zone" of microwave plasma, it is focused on the surface of sample 5-2. Optical path collection unit 3 is used to collect plasma spectral signals; PC control unit 4 includes pulse delay generator 4-1, which is used to provide timing control for the LIBS system and avoid interference from the continuous spectrum of initial plasma radiation. The radionuclide harmless treatment unit 7 is used to extract and dissolve the radioactive aerosols in the sample treatment unit 5.

[0021] The optical path shaping unit 2 includes a laser reflector 2-1, a half-wave plate 2-2, a polarizer 2-3, and a focusing lens 2-4. The laser reflector 2-1 is located on the output optical path of the pulsed laser generator 1-1. The laser reflector 2-1 is located on the incident optical path of the half-wave plate 2-2. The polarizer 2-3 is located on the output optical path of the half-wave plate 2-2. The focusing lens 2-4 is located on the output optical path of the polarizer 2-3. The sample 5-2 is located on the output optical path of the focusing lens 2-4. The laser reflector 2-1, the half-wave plate 2-2, the polarizer 2-3, and the focusing lens 2-4 are coaxial, and the included angle between the laser reflector 2-1 and the half-wave plate 2-2 is 45°.

[0022] The microwave plasma torch generator unit 6 includes an outer tube 6-2, a middle tube 6-3, an inner tube 6-4, a microwave input terminal 6-5, and a reflection tuning terminal 6-6. The outer tube 6-2, the middle tube 6-3, and the reflection tuning terminal 6-6 form an open-ended resonant cavity, into which an inert gas is introduced. The inert gas can be helium, argon, or neon, preferably argon. The input power of the microwave plasma torch generator unit 6 is preferably 100W, and the argon flow rate is preferably 1.5L / min. The plasma obtained under the above conditions is microwave plasma, which is a non-thermal equilibrium plasma.

[0023] The optical path collection unit 3 includes a spectrometer 3-1, an optical fiber 3-2, and an optical fiber probe 3-3. The optical fiber probe 3-3 is located above and on the other side of the surface of the sample 5-2. The optical fiber probe 3-3 is connected to one end of the optical fiber 3-2, and the other end of the optical fiber 3-2 is connected to the spectrometer 3-1. The collection angle between the optical fiber probe 3-3 and the surface of the sample 5-2 is 45°.

[0024] The PC control unit 4 also includes a PC controller 4-2, which is connected to the spectrometer 3-1. The pulse delay generator 4-1 is connected to both the spectrometer 3-1 and the pulse laser generator 1-1.

[0025] The sample processing unit 5 also includes a sample stage 5-1 and a shielding cover 5-3. The sample 5-2 is located on the sample stage 5-1, which is located inside the shielding cover 5-3. The sample stage 5-1 is a three-dimensional displacement sample stage used to compensate for the thickness difference between different samples 5-2.

[0026] The radionuclide harmless treatment unit 7 includes a vacuum pump 7-1 and a radionuclide absorbing solvent 7-2. The vacuum pump 7-1 extracts the radioactive aerosol from the shielding protective cover 5-3 and dissolves it through the radionuclide absorbing solvent 7-2.

[0027] The following experiment will verify the technical effect of this embodiment: In the experiment, national standard T1 copper was used as the analytical sample, and high-purity argon was used as the carrier gas to generate microwave plasma. A pulsed laser generator was used as the excitation source. The maximum single-pulse energy of the pulsed laser generator was 200 mJ, the pulse duration was 7 ns, and the frequency was 10 Hz. In this experiment, the single-pulse energy was scanned from 0.01 mJ to 1 mJ. The sample was fixed on a three-dimensional displacement sample stage, and the sample position was changed after each measurement to ensure that the pulsed laser excited different positions on the sample surface. The distance from the sample surface to the focusing lens was set to 50 mm. The pulsed laser was focused vertically onto the sample surface through the focusing lens to obtain a hemispherical plasma.

[0028] The emission spectrum of the plasma was collected using a spectrometer via a lateral plasma signal collection method. The fiber optic probe was positioned at a 45° angle to the sample surface to maximize signal reception. A pulse delay generator provided timing control for the LIBS system, avoiding interference from the continuous spectrum of the initial plasma radiation and yielding better discrete atomic spectra. In this experiment, to achieve a better signal-to-noise ratio (SNR), each LIBS spectral signal was obtained by accumulating 20 excitation signals at different locations on the sample surface.

[0029] Figure 3 Part (a) of the text Figure 3 Part (b) shows the spectra obtained by the device in this embodiment and conventional LIBS devices at 0.55 mJ. It can be seen that the LIBS spectral signal is significantly enhanced after microwave plasma is applied to the laser focal point. The LIBS spectral signal can be enhanced up to 140 times. For some non-metallic elements, such as Si, the emission spectral signal of plasma is almost undetectable under existing technologies, but a significant spectral signal can be detected using this method. Therefore, combining microwave plasma with a pulsed laser source will become a novel, low-cost, and highly efficient LIBS excitation source.

[0030] Figure 3 Part (c) is the LIBS spectrum of national standard T1 copper obtained by using the equipment of this embodiment, which can be adjusted to the lowest laser energy of 0.01mJ; Figure 3 Part (d) shows the LIBS spectrum of standard T1 copper obtained using conventional instruments adjusted to the minimum laser energy of 0.4 mJ required to generate the signal. It can be seen that using the equipment of this embodiment, the instrument can still obtain very strong emission spectral signals of the target elements at 324 nm and 327 nm even with laser energy as low as 0.01 mJ.

[0031] This embodiment provides a microwave plasma-assisted laser spectroscopy (LIBS) measurement device for online detection of radionuclides. Based on an existing LIBS spectral detection system, a microwave plasma torch generator is added, positioned in front of the sample. When the pulsed spectrum generated by the pulsed laser generator acts perpendicularly on the sample surface, the microwave plasma generated by the microwave plasma torch generator directly acts on the laser-induced plasma on the sample surface. This results in a higher temperature and greater electron density laser-induced plasma under microwave excitation, thus obtaining an enhanced laser-induced breakdown spectral signal. Because the microwave plasma torch generator is small, low-power, and easy to assemble, it does not significantly change the overall cost of the device. A modular design allows for flexible selection of whether to add the microwave plasma torch generator to the LIBS system, making operation convenient. Furthermore, the technical solution of this embodiment can effectively enhance the LIBS spectral signal, thereby improving the detection sensitivity of LIBS. Experiments show that the technical solution of this embodiment has a signal enhancement effect on all major elements in the sample, and even low-content elements that are difficult to detect in the sample can obtain significant spectral signals using this method.

[0032] The present invention and its embodiments have been described above illustratively. This description is not restrictive, and the figures shown are only one embodiment of the present invention; the actual structure is not limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, such designs should fall within the protection scope of the present invention.

Claims

1. A microwave plasma-assisted laser spectroscopy measurement system for radionuclides, characterized in that: It includes a pulsed laser unit (1), an optical path shaping unit (2), an optical path collection unit (3), a PC control unit (4), a sample processing unit (5), a microwave plasma torch generator unit (6), and a radionuclide harmless treatment unit (7); The pulsed laser unit (1) is used to generate pulsed laser. After being processed by the optical path shaping unit (2), the pulsed laser acts perpendicularly on the surface of the sample (5-2) in the sample processing unit (5) to ablate and generate a laser-induced plasma spectral signal. The pulsed laser unit (1) includes a pulsed laser generator (1-1), and the single pulse energy of the pulsed laser generator is scanned from 0.01mJ to 1mJ. The optical path shaping unit (2) includes a laser reflector (2-1), a half-wave plate (2-2), a polarizer (2-3), and a focusing lens (2-4); the laser reflector (2-1) is located on the outgoing optical path of the pulsed laser generator (1-1); the laser reflector (2-1) is located on the incident optical path of the half-wave plate (2-2); the polarizer (2-3) is located on the outgoing optical path of the half-wave plate (2-2); the focusing lens (2-4) is located on the outgoing optical path of the polarizer (2-3); the sample (5-2) is located on the outgoing optical path of the focusing lens (2-4); the laser reflector (2-1), the half-wave plate (2-2), the polarizer (2-3), and the focusing lens (2-4) are coaxial, and the angle between the laser reflector (2-1) and the half-wave plate (2-2) is 45°; The optical path collection unit (3) includes a spectrometer (3-1), an optical fiber (3-2), and an optical fiber probe (3-3). The optical fiber probe (3-3) is located above the other side of the sample (5-2) surface. The optical fiber probe (3-3) is connected to one end of the optical fiber (3-2), and the other end of the optical fiber (3-2) is connected to the spectrometer (3-1). The collection angle between the optical fiber probe (3-3) and the sample (5-2) surface is 45°. The microwave plasma torch generator unit (6) is used to generate microwave plasma (6-1). The microwave plasma (6-1) is located in front of the sample (5-2) on one side. The microwave plasma (6-1) enhances the plasma spectral signal. The microwave plasma torch generator unit (6) includes an outer tube (6-2), a middle tube (6-3), an inner tube (6-4), a microwave input end (6-5), and a reflection tuning end (6-6). The outer tube (6-2), the middle tube (6-3), and the reflection tuning end (6-6) form an open-end resonant cavity. Inert gas is input into the resonant cavity. The microwave plasma (6-1) is inverted funnel-shaped and has a cross-region with optimal enhancement effect. During the enhancement process, the central axis is parallel to and covers the sample surface. After the pulsed laser passes vertically through the cross-region of the microwave plasma (6-1), it is focused on the surface of the sample (5-2). The optical path collection unit (3) is used to collect plasma spectral signals; The PC control unit (4) includes a pulse delay generator (4-1), which is used to provide timing control to avoid interference from the continuous spectrum of the initial plasma radiation. The radionuclide harmless treatment unit (7) is used to extract and dissolve the radioactive aerosols in the sample treatment unit (5).

2. The microwave plasma-assisted laser spectroscopy measurement system for radionuclides according to claim 1, characterized in that: The PC control unit (4) also includes a PC controller (4-2), which is connected to the spectrometer (3-1). The pulse delay generator (4-1) is connected to the spectrometer (3-1) and the pulse laser generator (1-1) respectively.

3. The microwave plasma-assisted laser spectroscopy measurement system for radionuclides according to claim 2, characterized in that: The sample processing unit (5) also includes a sample stage (5-1) and a shielding cover (5-3). The sample (5-2) is located on the sample stage (5-1), and the sample stage (5-1) is located inside the shielding cover (5-3).

4. The microwave plasma-assisted laser spectroscopy measurement system for radionuclides according to claim 3, characterized in that: The sample stage (5-1) is a three-dimensional displacement sample stage used to compensate for the thickness difference between different samples (5-2).

5. The microwave plasma-assisted laser spectroscopy measurement system for radionuclides according to claim 4, characterized in that: The radionuclide harmless treatment unit (7) includes a vacuum pump (7-1) and a radionuclide absorbing solvent (7-2). The vacuum pump (7-1) extracts the radioactive aerosol from the shielding cover (5-3) and dissolves it through the radionuclide absorbing solvent (7-2).

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