Laser device, element analysis system, and element analysis method

Abstract

To suppress the destruction of a surface of an object when analyzing elements contained in an object by using a laser beam, and to enable high-precision element analysis.SOLUTION: A laser device (30) having a laser irradiation part (40) for irradiating an object (M) with a laser beam (22) includes an acoustic wave acquisition part (50) for acquiring an acoustic wave (24) generated from the object (M) by irradiation with the laser beam (22). The laser irradiation part (40) is controlled to a predetermined focal position based on the acoustic wave acquired by the acoustic wave acquisition part (50).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a laser device, an elemental analysis system, and an elemental analysis method. [Background technology]

[0002] There are known techniques for analyzing elements contained in a target object using laser light. One example is Laser-Induced Breakdown Spectroscopy (LIBS), an elemental analysis technique that irradiates a sample with a pulsed laser, resolves the wavelength of the generated plasma using a spectrometer, and analyzes the light intensity for each wavelength to identify the elemental components contained.

[0003] As an analytical device using this LIBS, for example, Patent Document 1 describes an analytical device having a control device, a laser light source, a laser oscillator, an optical fiber for laser oscillation, an optical fiber for fluorescence detection, a spectrometer, and a fluorescence detector.

[0004] When analyzing elements in a melt using the analytical device described in Patent Document 1, an operator checks the position of the melt on a monitor, adjusts the positions of the tip of the optical fiber for laser oscillation and the tip of the optical fiber for fluorescence detection, and adjusts the distance from the tip of the optical fiber for laser oscillation to the surface of the melt and the distance from the tip of the optical fiber for fluorescence detection to the surface of the melt. Then, the laser oscillator oscillates a pulsed laser beam through the optical fiber for laser oscillation toward the surface of the melt, and the fluorescence detector detects the fluorescence generated at the surface of the melt via the optical fiber for fluorescence detection through a spectroscope. Based on this fluorescence, the elements contained in the melt are identified. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2015-190792 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the above-mentioned conventional technology, in order to perform elemental analysis of a molten material (target / sample) correctly, it is necessary to irradiate the molten material with a pulsed laser beam multiple times and adjust the focal position of the laser beam while checking the signal intensity at the time of plasma emission. Therefore, there is a concern that the surface of the molten material may be destroyed every time the focal position is adjusted, which may reduce the accuracy of elemental analysis of the molten material.

[0007] Therefore, an object of the present invention is to suppress damage to the surface of an object when analyzing elements contained in the object using laser light. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, a first aspect of the present invention is characterized in that a laser device including a laser irradiation unit that irradiates a target object with laser light, further including a sound wave acquisition unit that acquires sound waves generated from the target object by the irradiation of the laser light, and the laser irradiation unit is controlled to a predetermined focal position based on the sound waves acquired by the sound wave acquisition unit.

[0009] In addition, in order to achieve the above-mentioned object, a second aspect of the present invention is an elemental analysis system comprising a laser irradiation unit which irradiates a laser beam onto an object, and an analysis unit which analyzes elements contained in the object by the irradiation of the laser beam, characterized in that the system also comprises a sound wave acquisition unit which acquires sound waves generated from the object by the irradiation of the laser beam, a focal position determination unit which determines the focal position of the laser irradiation unit based on the sound waves acquired by the sound wave acquisition unit, and a position adjustment mechanism which aligns the laser irradiation unit to the focal position determined by the focal position determination unit.

[0010] In addition, in order to achieve the above-mentioned object, a third aspect of the present invention is an elemental analysis method including a first step of irradiating an object with laser light, a second step of acquiring sound waves generated from the object by the irradiation of the laser light, a third step of determining a focal position for irradiating the laser light based on the sound waves acquired in the second step, and a fourth step of irradiating the laser light from the focal position determined in the third step to analyze elements contained in the object. Effect of the Invention

[0011] According to the present invention, when analyzing elements contained in an object using a laser beam, damage to the surface of the object can be suppressed. Therefore, according to the present invention, high-precision element analysis is possible. Note that problems, configurations, and effects other than those described above will be made clear by the following description of the embodiment. [Brief description of the drawings]

[0012] [Figure 1] 1 is an overall configuration diagram of an elemental analysis system according to a first embodiment. [Diagram 2] FIG. 2 is a diagram showing the internal configuration of a probe. [Diagram 3] FIG. 2 is a model diagram showing the positional relationship between a probe and a molten material. [Figure 4] 1 is a diagram showing the attenuation rate of a sound wave versus the distance a between the laser optical axis and the microphone part. [Diagram 5] FIG. 13 is a graph showing the relationship between the acoustic amplitude value and the total count number in LIBS analysis relative to the distance between the irradiated part and the molten material. [Figure 6] 1 is a flowchart showing the procedure of elemental analysis. [Figure 7] 10A to 10C are diagrams showing the configuration of a probe according to a modified example, in which (a) is a top view of the probe, (b) is a front view of the probe, and (c) is a diagram showing the direction of sound waves incident on the probe. [Figure 8] FIG. 1 is a configuration diagram of an elemental analysis system according to a second embodiment. [Figure 9]FIG. 1 is a diagram showing an example in which the elemental analysis system is applied to elemental analysis of molten material inside a reactor building. [Figure 10] FIG. 11 is a configuration diagram of an elemental analysis system according to a third embodiment. [Figure 11] Figure 1 shows a sample made by uniformly mixing and sintering a mixed oxide of multiple elements simulating fuel debris. (a) shows the composition ratio of the sample, (b) shows a photograph of the sample's appearance, and (c) shows the outer dimensions of the sample. [Figure 12] FIG. 12 is a diagram showing the results of surface profile measurement of the sample shown in FIG. 11, measured using an elemental analysis system. [Figure 13] Figure 1 shows an oxide sample that is a heterogeneous mixture of multiple elements simulating fuel debris. (a) shows the composition ratio of the sample, and (b) shows a photograph of the sample's appearance. [Figure 14] FIG. 14 is a diagram showing a two-dimensional elemental mapping obtained for the sample shown in FIG. 13 using an elemental analysis system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a laser device, an elemental analysis system, and an elemental analysis method according to the present invention will be described with reference to the drawings.

[0014] (First embodiment) FIG. 1 is an overall configuration diagram of an elemental analysis system 100 according to a first embodiment. The elemental analysis system 100 shown in FIG. 1 is used for LIBS analysis. The elemental analysis system 100 includes a laser light source 10, a spectroscopic analysis section (analysis section) 15, a probe (laser device) 30, a controller (focal position determination section) 60, and a stage (position adjustment mechanism) 70. The laser light source 10 is connected to the probe 30 via an optical fiber cable 21 (hereinafter referred to as "optical fiber 21"). The spectroscopic analysis section 15 is also connected to the probe 30 via the optical fiber 21 in the same manner. In addition, the laser light source 10, the spectroscopic analysis section 15, the probe 30, and the stage 70 are electrically connected to the controller 60 via electric cables (dotted lines in the figure).

[0015] The elemental analysis system 100 according to this embodiment is used to analyze elements in a molten material M in a harsh environment (for example, an environment with a high radiation dose). Therefore, the probe 30 has resistance to radiation. In addition, a high-concentration OH-group doped type or hydrogen-doped annealed type optical fiber 21, which is resistant to radiation, is used.

[0016] In Fig. 1, reference numeral 22 denotes a laser beam, reference numeral 23 denotes plasma emission, and reference numeral 24 denotes a sound wave. Next, each component in Fig. 1 will be described in detail.

[0017] <Laser light source 10> The laser light source 10 oscillates a laser having a predetermined frequency. Here, it is preferable to use, for example, a semiconductor laser as the laser light source 10. This is a commonly used near-infrared or visible pulsed Nd 3+ This is because, compared to a YAG laser, it has advantages in the diameter and applicable length of the optical fiber 21 that transmits the laser light. In particular, in the above-mentioned harsh environment, analysis work needs to be performed by remote operation, and workability is important, so a semiconductor laser capable of long-distance transmission is preferable. The operation of the laser light source 10 is controlled by a controller 60.

[0018] <Spectral analysis section 15> The spectroscopic analysis unit 15 performs spectroscopic analysis of plasma emission 23 generated by irradiating the molten material (e.g., radioactive material / fuel debris) M with laser light 22. Specifically, the spectroscopic analysis unit 15 separates the plasma emission 23 into wavelength and intensity, and generates spectral information regarding the wavelength and intensity of the plasma emission 23. Then, this information is input to the controller 60.

[0019] <Probe 30> The probe 30 is provided at the tip of the optical fiber 21, and includes a laser irradiation unit 40 and a sound wave acquisition unit 50. The probe 30 is an example of a laser device according to the present invention.

[0020] Fig. 2 is a diagram showing the internal configuration of the probe 30. As shown in Fig. 2, the probe 30 has a laser irradiation unit 40 and a sound wave acquisition unit 50 arranged adjacent to each other with their longitudinal directions facing the irradiation direction (the left-right direction in Fig. 2), and both are integrated. However, as will be described in detail later, the two do not necessarily have to be integrated and may be separated from each other.

[0021] (Laser irradiation unit 40) The laser irradiation unit 40 includes a laser light transmission unit 41, a laser resonator 42, optical units 43, 44, 46, and 47, a window unit 45, a plasma emission transmission unit 48, and a housing 49. The laser light transmission unit 41 and the plasma emission transmission unit 48 are formed of optical fiber 21 (see FIG. 1). The housing 49 houses the laser resonator 42, the optical units 43, 44, 46, and 47, and the window unit 45.

[0022] The laser cavity 42 is made of Nd 3+ : YAG and Cr 4+ It is made of a composite crystal of Nd:YAG. The laser medium is placed on the incident side of the laser. 3+ :YAG crystal (hereinafter referred to as “Nd 3+ The saturable absorber Cr is placed on the output side of the laser. 4+ :YAG crystal (hereinafter referred to as “Cr 4+ The crystals are arranged in a Nd 3+ When a laser beam having a wavelength of 808 nm is quasi-continuously incident on the crystal from the laser source 10, the Nd 3+ is excited and emits a laser with a wavelength of 1064 nm. 4+ The crystal is usually opaque and does not transmit the laser. 4+ As the laser continues to be absorbed by the crystal, the crystal becomes transparent and emits a 1064 nm pulsed laser (<1000 ps). This type of laser is called a passive Q-switched pulsed laser oscillator.

[0023] In addition, Nd 3+ The 808 nm incidence surface of the crystal is coated with a coating that provides high reflectivity at 1064 nm and high transmittance at 808 nm. 4+The pulsed laser output face of the crystal is coated with a 1064 nm partially reflective coating. The crystal and coating form the laser cavity 42.

[0024] Since the light emitted from the end face of the optical fiber 21 must be a multiple-reflection light beam that satisfies the total reflection condition within the optical fiber 21, it is no longer parallel light but a collection of light beams having angles within the elevation angle defined by the refractive index of the optical fiber 21. For this reason, it is difficult to obtain a sufficient energy density since the light beams from the end face are only collected by the reduced image transfer by the optical system. Therefore, in this embodiment, a laser resonator 42, which is a laser medium, is provided at the tip of the optical fiber 21 to which the semiconductor laser light is transmitted.

[0025] The beam shape according to the present embodiment is a directional beam, which has the advantages of easily increasing the energy density, facilitating laser-produced plasma emission, and enabling efficient analysis at low energy.

[0026] A pulsed laser with a near-infrared wavelength is oscillated in the laser resonator 42, and a harmonic pulsed laser can be extracted by making the laser light incident on a nonlinear optical crystal. For example, when a pulsed laser light with a wavelength of 1064 nm emitted from the laser resonator 42 is made incident on an LBO (lithium triborate) crystal, light with a wavelength of 532 nm, which is half the wavelength, is generated, and this generates a pulsed laser light together with the 1064 nm light. The inventors have confirmed and demonstrated that the LBO crystal can maintain its function even under high radiation exposure.

[0027] In LIBS analysis, the emission spectrum of nuclear fuel materials has representative emission lines, especially from the ultraviolet to visible wavelength range. The use of short wavelength (high photon energy) laser light is an effective means for forming ions and more highly excited laser-produced plasma, i.e., the appearance of emission spectra from the ultraviolet to visible wavelength range, and the application of high-harmonic laser light is desirable in the final form.

[0028] By placing an LBO crystal after oscillating the 532 nm laser light, it is possible to generate a laser light with a wavelength of 1 / 3 of 1064 nm, i.e., 355 nm. The use of laser light with this wavelength is suitable for ion and higher excited state laser produced plasma emission spectroscopy.

[0029] The laser light 22 oscillated by the laser resonator 42 passes through the optical sections 43 and 44, and is irradiated onto the melt M via the window section 45. The plasma emission 23 generated in the melt M enters the laser irradiation section 40 from the window section 45, is reflected by the optical sections 44 and 46, passes through the optical section 47, and is incident on the plasma emission transmission section 48 and the spectroscopic analysis section 15 (see FIG. 1).

[0030] (Sound wave acquisition unit 50) The sound wave acquiring section 50 includes a microphone section 51 and a sound wave transmitting section 52. The sound wave transmitting section 52 is formed from an optical fiber 21 (see FIG. 1).

[0031] The microphone unit 51 is suitable for use in harsh environments with high radiation levels, for example, an optical microphone, a microphone using a glass thin film, or a fiber Bragg grating (hereinafter referred to as "optical microphone, etc."). These microphones are simple in structure and have excellent radiation resistance, making them suitable for use in harsh environments with high radiation levels. In terms of availability and cost, an optical microphone is the most desirable. In addition, for example, if a general microphone is used as the microphone unit, its electrical signal has a high output impedance, so it is generally difficult to transmit it over long distances. If it is transmitted as is, not only will it be attenuated, but loop noise and induced noise will be mixed in, making it unsuitable for use. However, if an optical microphone, etc., has a low output impedance, it is possible to transmit it over long distances, and it is possible to obtain the electrical signal remotely even in harsh environments. When the laser light 22 is irradiated onto the molten material M, a sound wave 24 is generated due to a change in the temperature of the molten material M. The microphone unit 51 obtains this sound wave 24. In addition, if the environment is not harsh and long-distance transmission of the electrical signal is not necessary, a general microphone can be used.

[0032] Next, a preferred mounting position of the microphone unit 51 relative to the laser irradiation unit 40 will be described with reference to Figs. 3 and 4. Fig. 3 is a model diagram showing the positional relationship between the probe 30 and the molten material M. Fig. 4 is a diagram showing the attenuation rate of the sound wave 24 relative to the distance a between the laser optical axis and the microphone unit 51 (i.e., the distance between the two in a direction perpendicular to the laser optical axis). In Fig. 4, the horizontal axis is the distance a (mm) between the microphone unit 51 and the laser optical axis, and the vertical axis is the sound wave amplitude value (peak value: V) from the molten material M acquired by the microphone unit 51. The graph shown in Fig. 4 shows the results when the distance Z (LTSD) between the laser irradiation unit 40 and the molten material M in Fig. 3 is constant (for example, 20 mm).

[0033] As shown in FIG. 4, it can be seen that the greater the distance a from the laser optical axis, the lower the sound wave amplitude value. If the distance a from the laser optical axis of the microphone unit 51 exceeds 100 mm, the sound wave amplitude value decreases, and noise components become predominant, making it difficult to measure the sound waves. In addition, the sound wave amplitude value is less than half when the distance a is 20 mm compared to when the distance a is 50 mm. Therefore, it is preferable to bring the microphone unit 51 closer to the laser optical axis, and it is desirable to place the microphone unit 51 on the same axis as the laser optical axis as much as possible. However, in reality, due to the structure of the laser irradiation unit 40, it is difficult to place the microphone unit 51 on the laser optical axis, so the distance a from the laser optical axis of the microphone unit 51 may be 100 mm or less, preferably 50 mm or less, and most preferably 20 mm or less. It is not necessary for the microphone unit 51 to be integrated with the laser irradiation unit 40, and it may be separated from the laser irradiation unit 40 as long as the distance a is within the range described above. In the LIBS analysis, the distance Z is approximately 20 mm, so in FIG. 3, when the distance a is 20 mm, the angle θ between the laser optical axis and the sound wave 24 is approximately 45 degrees.

[0034] <Controller 60> The controller 60 is composed of hardware including a CPU that performs various calculations, a storage device such as a ROM or HDD that stores programs for the CPU to execute the calculations, a RAM that serves as a work area when the CPU executes the programs, and a communication interface that is an interface for sending and receiving data with other devices, and software that is stored in the storage device and executed by the CPU. Each function of the controller 60 is realized by the CPU loading various programs stored in the storage device into the RAM and executing them.

[0035] The controller 60 controls the entire elemental analysis system 100. Specifically, the controller 60 controls the timing of irradiating the laser light from the laser light source 10 to the laser irradiation unit 40 and the timing of acquiring the sound wave 24 by the sound wave acquisition unit 50 so as to be synchronized. Then, based on the sound wave information input from the probe 30, the controller 60 controls the stage 70 to adjust the position of the melt M (described in detail later). Also, based on the result of the LIBS analysis input from the spectroscopic analysis unit 15, the controller 60 performs a predetermined display on a monitor (not shown).

[0036] <Stage 70> The stage 70 is a three-dimensional stage. The melt M is placed on the stage 70, and the stage 70 controls the relative position of the melt M with respect to the probe 30 (laser irradiation unit 40) in accordance with a command from the controller 60. In other words, the stage 70 moves the position of the melt M to a predetermined position on the three-dimensional coordinate system, thereby aligning the focal position of the laser irradiation unit 40. The stage 70 may be a two-dimensional stage.

[0037] In the elemental analysis system 100 configured as above, when the laser irradiation unit 40 irradiates the molten material M with laser light 22 of a predetermined intensity, the sound wave 24 generated thereby is acquired by the microphone unit 51. Based on the amplitude value (amplitude intensity) of the sound wave 24, the controller 60 calculates the focal position of the laser irradiation unit 40 (probe 30) and controls the driving of the stage 70. Then, the position of the molten material M changes, and the relative positions of the laser irradiation unit 40 and the molten material M are determined, and as a result, the laser irradiation unit 40 is aligned to the appropriate focal position.

[0038] Next, a method for determining the focal position of the laser irradiation unit 40 based on the sound wave amplitude value will be described with reference to Figs. 3 and 5. Fig. 5 is a diagram showing the relationship between the sound wave amplitude value and the total count number of the LIBS analysis (emission spectrum intensity for wavelength) with respect to the distance between the laser irradiation unit 40 and the molten material M. In Fig. 5, the horizontal axis is the distance LTSD (mm) between the window part 45 of the laser irradiation unit 40 and the molten material M (see Fig. 3), the left side of the vertical axis is the sound wave amplitude value (peak value: V), and the right side of the vertical axis is the LIBS intensity (au: arbitrary unit). Note that Fig. 5 shows the measurement results when copper (Cu) is used as the molten material M.

[0039] 5, the sound wave amplitude value acquired by the microphone unit 51 is high at a distance LTSD of 20 mm or 21 mm, and the LIBS intensity is also high at a distance LTSD of 20 mm or 21 mm. From this, if the distance LTSD (hereinafter referred to as the "specific distance") at which the amplitude value of the sound wave 24 is approximately maximum is known, if the laser irradiation unit 40 irradiates the molten material M with laser light from a position that is the specific distance away, a plasma emission 23 with high intensity can be obtained. In other words, the position that is the specific distance away from the molten material M is the optimal focal position of the laser irradiation unit 40.

[0040] In addition, the inventors performed similar experiments on other elements, such as Al, Fe, and Zr metals, and confirmed that they showed the same tendency as Cu. Therefore, it was found that by grasping the specific distance between the laser irradiation part 40 based on the sound wave and the molten material M, it is possible to obtain an appropriate focal position for the molten material M containing a wide range of metal elements. Based on this knowledge, the present invention is characterized in that the optimal focal position is calculated from the sound wave amplitude value and the focal position of the laser irradiation part 40 is controlled, which was not possible in the past.

[0041] Here, the sound wave can be generated even with a laser beam having a power density lower than that of plasma emission. For example, when the power density is 600 MW / cm, which is a predetermined threshold value, 2 If the power density is less than 400 MW / cm, the oxide will not emit plasma. However, the inventors have confirmed through experiments that even if an oxide is irradiated with a low-power density laser beam, an acoustic wave is generated from the oxide. Note that acoustic waves are generated at a power density of 400 MW / cm. 2 I found that more than that is good.

[0042] From this, in terms of generating sound waves while suppressing the destruction of the target object, for example, for the molten material M made of a metal material, a maximum of 400 MW / cm 2 More than 600MW / cm 2 By irradiating a pulsed laser beam having a low power density (predetermined power density) below this level, the controller 60 can calculate the focal position based on the sound wave 24. At this time, with a pulsed laser beam having a low power density, plasma emission does not occur from the melt M, so that destruction of the surface of the melt M can be suppressed. Note that the predetermined threshold value is set to 400 MW / cm. 2 More than 600MW / cm 2 Although the following is an example, this threshold value may be appropriately determined depending on the properties of the object to be irradiated with the pulsed laser light.

[0043] By controlling the power density of the laser light in this manner, it is possible to adjust the focal position of the laser irradiation unit 40 while suppressing damage to the surface of the molten material M, and subsequent elemental analysis of the molten material M can be performed with high accuracy.

[0044] Next, a description will be given of a method for analyzing elements of the melt M using the elemental analysis system 100. Fig. 6 is a flow chart showing the procedure of elemental analysis using the elemental analysis system 100.

[0045] First, the laser light source 10 outputs a laser (e.g., a semiconductor laser) (S1). Next, the laser resonator 42 emits a low power density (e.g., 400 MW / cm 2 More than 600MW / cm 2 The entire molten material M is irradiated with laser light 22 (S2). Next, the microphone unit 51 acquires sound waves 24 induced from the molten material M (S3). The controller 60 obtains a distance LTSD from the molten material M corresponding to the maximum value of the sound wave amplitude, and determines the focal position of the laser irradiation unit 40 with respect to the molten material M (S4). Next, the controller 60 controls the driving of the stage 70 to adjust the position of the molten material M so that the distance between the laser irradiation unit 40 and the molten material M becomes the obtained value (LTSD) (S5). As a result, the focal position adjustment of the laser irradiation unit 40 with respect to the molten material M is completed.

[0046] When the focal position adjustment of the laser irradiation unit 40 is completed in steps S1 to S5, the laser resonator 42 is irradiated with a high power density (for example, 600 MW / cm 2 The melt M is irradiated with laser light 22 of wavelength exceeding 100 nm, and elemental analysis is performed based on plasma emission 23 generated from the melt M (S6). In this manner, elemental analysis of the melt M is completed. Note that in S5, instead of the controller 60 controlling the driving of the stage 70, an operator may manually adjust the position of the probe 30 using a range finder or the like, and align the focal position of the laser irradiation unit 40 so that the distance between the laser irradiation unit 40 and the melt M becomes the distance (LTSD) calculated as described above.

[0047] Next, the effects of the present embodiment thus configured will be described.

[0048] Since the configuration is such that the low power density laser light 22 is irradiated and the sound wave 24 is detected, the focal position of the laser irradiation unit 40 (probe 30) can be adjusted while suppressing damage to the surface of the melt M in the preparation stage for elemental analysis. Therefore, elemental analysis can be performed with high accuracy. In particular, in the past, it was necessary to irradiate a laser with a high power density level that generates plasma emission in the preparation stage for elemental analysis to adjust the focal position, so there was a risk that correct elemental analysis could not be performed while suppressing damage to the surface of the melt M before the actual elemental analysis. However, according to the above-mentioned embodiment, LIBS analysis can be performed with high accuracy while suppressing damage to the surface of the melt M due to adjustment of the focal position.

[0049] As shown in Fig. 5, the characteristics of the sound wave amplitude value versus the distance LTSD and the characteristics of the plasma emission intensity versus the distance LTSD show the same tendency. Therefore, by irradiating the entire molten material M with the low power density laser beam 22, it is possible to grasp the element distribution and the overall shape of the molten material M while suppressing damage to the surface of the molten material M.

[0050] By using the microphone unit 51 such as an optical microphone having resistance to radiation, it is possible to align the focal position even in a harsh environment. Even if a laser range finder or the like is used instead of the microphone unit 51, it is possible to align the focal position while suppressing damage to the surface of the molten material M. However, since the laser range finder is not resistant to radiation, the configuration of this embodiment is advantageous when a harsh environment is assumed.

[0051] A probe 30 (laser emitting unit 40, sound wave acquiring unit 50) is attached to the tip of the optical fiber 21, and a pulsed laser is oscillated from the laser resonator 42 of the laser emitting unit 40, enabling long distance transmission. In particular, if a semiconductor laser is used as the laser light source 10, the transmission distance via the optical fiber 21 can theoretically be infinite. Furthermore, oscillating a pulsed laser in the laser resonator 42 eliminates the need to make the optical fiber 21 between the laser light source 10 and the probe 30 large in diameter. This improves the workability of elemental analysis work in harsh environments. Furthermore, since a small-diameter optical fiber 21 can be used, it is also economically advantageous.

[0052] The laser resonator 42 is made of Nd 3+ Since crystals are used, it is suitable for elemental analysis of the molten material M containing nuclear fuel material.

[0053] The controller 60 controls the timing of acquisition of the sound waves 24 by the sound wave acquisition unit 50 and the timing of irradiation of the laser light 22 by the laser irradiation unit 40 so that they are synchronized, so that the difference between the noise components and the sound waves can be determined with high accuracy, and the focal position can be controlled with high accuracy.

[0054] (Modification) In the above embodiment, a configuration using one microphone unit 51 has been described, but there may be a plurality of microphone units 51. Fig. 7 shows the configuration of a probe 30-1 according to a modified example, where (a) is a top view of the probe 30-1, (b) is a front view of the probe 30-1, and (c) is a view showing the direction of the sound wave 24 incident on the probe 30-1.

[0055] 7(a) and (b), the probe 30-1 includes four sound wave acquisition units 50a, 50b, 50c, and 50d. That is, the probe 30-1 includes four microphone units 51a, 51b, 51c, and 51d. The sound wave acquisition units 50a, 50b, 50d, and 50c (microphone units 51a, 51b, 51c, and 51d) are evenly arranged at 90-degree intervals around the laser irradiation unit 40 when viewed from the direction of the laser optical axis.

[0056] As shown in FIG. 7(c), if a convex portion M1 is formed on the surface of the molten material M, the sound wave 24-1 is blocked by the convex portion M1, and therefore the microphone portion 51b cannot acquire the sound wave 24-1. However, if a plurality of sound wave acquiring portions 50 are provided, the microphone portion 51d can acquire the sound wave 24-2 even if the convex portion M1 exists. Therefore, the sound wave acquiring portion 50 can reliably acquire the sound wave 24 from the molten material M. As a result, the focal position of the laser irradiation portion 40 is accurately determined, and elemental analysis can be performed with higher accuracy.

[0057] The number and arrangement of the sound wave acquiring units 50 are not limited to the configuration shown in Fig. 7. For example, the number may be less than four, or may be five or more. In addition, the multiple sound wave acquiring units 50 do not necessarily have to be evenly arranged around the laser irradiation unit 40. However, by evenly arranging the sound wave acquiring units 50 around the laser irradiation unit 40, the effect of more reliably acquiring the sound waves 24 is achieved.

[0058] Second embodiment Next, a second embodiment of the elemental analysis system according to the present invention will be described. Fig. 8 is a configuration diagram of an elemental analysis system 200 according to the second embodiment, showing a configuration example in which a robot arm 71 adjusts the focal position of a laser irradiation unit 40. In the following description, the same reference numerals are used for the configurations already described in the first embodiment, and the description thereof will be omitted.

[0059] In the elemental analysis system 200 shown in Fig. 8, a robot arm (position adjustment mechanism) 71 holds the probe 30. The controller 60 determines the focal position of the laser irradiation unit 40 based on the sound wave input from the probe 30, and controls the robot arm 71 so that the laser irradiation unit 40 is located at the focal position, thereby aligning the probe 30. That is, in the elemental analysis system 100, the position of the melt M is moved by the stage 70, thereby indirectly adjusting the focal position of the laser irradiation unit 40, but in the elemental analysis system 200, the position of the melt M is fixed, and the probe 30 is moved by the robot arm 71 to align the focal position of the laser irradiation unit 40.

[0060] Due to such a configuration, the elemental analysis system 200 is suitable for performing elemental analysis of molten material M, called fuel debris, formed in a nuclear reactor. Fig. 9 shows an example in which the elemental analysis system 200 is applied to elemental analysis of molten material M in a reactor building 80.

[0061] As shown in FIG. 9, the reactor building 80 contains a reactor vessel 85. Although not shown, the reactor vessel 85 stores fuel assemblies containing nuclear fuel material, control rods, and the like. When molten material M containing radioactive material accumulates in the reactor vessel 85 due to an unexpected event such as an accident, elemental analysis must be performed in order to process (transport) the molten material M. In a harsh environment with a high level of radiation, an operator cannot directly visually check the molten material M and perform elemental analysis. Therefore, as shown in FIG. 9, a robot arm 71 is inserted from an opening 81 of the reactor building 80, and the robot arm 71 is remotely operated to perform elemental analysis of the molten material M accumulated at the bottom of the reactor vessel 85.

[0062] In this case as well, first, the robot arm 71 is operated to bring the probe 30 close to the molten material M, and then the laser irradiation unit 40 irradiates the molten material M with a low power density laser beam. Then, the microphone unit 51 acquires sound waves generated from the molten material M, and the controller 60 determines the focal position of the laser irradiation unit 40 based on the peak of the sound waves, and controls the robot arm 71 to align the focal position of the laser irradiation unit 40. After the focal position of the laser irradiation unit 40 is controlled to an appropriate position, the controller 60 irradiates the molten material M with a high power density laser beam, analyzes the plasma emission generated from the molten material M, and analyzes the elements of the molten material M.

[0063] In this manner, according to the elemental analysis system 200, similarly to the first embodiment, it is possible to adjust the focal position of the laser irradiation unit 40 while suppressing damage to the surface of the melt M, and therefore it is possible to perform elemental analysis with high accuracy.

[0064] When processing the molten material M accumulated inside the reactor vessel 85, it is necessary to grasp the shape and the like of the molten material M. Conventionally, the shape has been grasped using radiation-resistant lighting and cameras in a harsh environment with high radiation levels. However, in a narrow environment, cameras and the like reduce workability, and there are problems such as the high cost of the system required to prepare these devices.

[0065] However, in the elemental analysis system 200 according to the second embodiment, since the shape of the molten material M can be grasped by the laser-induced sound waves, a camera or the like is not necessary. This allows for cost reduction. Furthermore, in a harsh environment, there is a risk that stable operation cannot be expected, such as an erroneous operation of the device, but the elemental analysis system 200 allows elemental mapping analysis to grasp the shape of the molten material M by the laser-induced sound waves (described in detail later). Therefore, the accuracy of the acquired data can be verified by superimposing the analysis result of the molten material M by the sound waves and the LIBS analysis result. Therefore, the elemental analysis system 200 allows elemental analysis to be performed with higher accuracy, particularly in a harsh environment.

[0066] The elemental analysis system 100 or 200 makes it possible to grasp the shape of the molten material M and perform elemental mapping analysis. For example, by repeating steps S1 to S6 in Fig. 6 while moving the probe 30 or the stage 70, the surface shape and element distribution of the molten material M can be obtained.

[0067] Fig. 11 shows a sample in which a mixed oxide of multiple elements simulating fuel debris is uniformly mixed and sintered, where (a) shows the composition ratio of the sample, (b) shows a photograph of the appearance of the sample, and (c) shows the outer dimensions of the sample. Fig. 12 shows the surface shape measurement results of the sample shown in Fig. 11, which was performed using elemental analysis system 100 while moving the stage at 800 points on the sample, 20 points vertically and 40 points horizontally. As shown in Fig. 12, it can be seen that the elemental analysis system 100 according to this embodiment can accurately reproduce the surface shape of the sample shown in Fig. 11.

[0068] The point cloud in the upper part of Figure 12 indicates the laser irradiation spot position. In this measurement, the laser light spot diameter was approximately 0.1 mm and the spatial resolution was 0.5 mm; however, by shortening the moving distance and reducing the spot diameter, it is possible to obtain detailed shape information with higher spatial resolution.

[0069] Fig. 13 shows an oxide sample in which multiple elements are mixed non-uniformly to simulate fuel debris, where (a) shows the composition ratio of the sample and (b) shows a photograph of the sample's appearance. Fig. 14 shows a two-dimensional elemental map obtained by using the elemental analysis system 100 for the sample shown in Fig. 13.

[0070] Figure 14(a) shows the results of LIBS analysis of the sample in Figure 13 in the LTSD environment optimized based on acoustic detection, and shows the emission intensity distribution at the representative wavelengths of the sample constituent elements Gd, Ce, Fe, and Zr. From this Figure 14(a), the qualitative distribution of the elements can be confirmed.

[0071] On the other hand, Figure 14(b) shows the element distribution of the same sample analyzed using an EDS (energy dispersive X-ray spectroscopy) attached to an electron microscope. As is clear from comparing the dotted areas in Figure 14(a) and (b), the results of LIBS and EDS show the same tendency for the element distribution, indicating that the qualitative analysis was performed correctly.

[0072] Third embodiment Next, a third embodiment of the elemental analysis system according to the present invention will be described. Fig. 10 is a configuration diagram of an elemental analysis system 300 according to the third embodiment. As shown in Fig. 10, the elemental analysis system 300 according to the third embodiment is an example applied to LA (Laser Ablation)-ICP-MS analysis. In the following description, the same reference numerals are used for the configurations already described in the first or second embodiment, and the description thereof will be omitted.

[0073] LA-ICP-MS performs elemental analysis by irradiating the surface of a sample with a laser and analyzing the resulting fine particles derived from the sample. In other words, LIBS analysis and LA-ICP-MS have in common the fact that they both irradiate a laser and perform elemental analysis of a sample.

[0074] In conventional LA-ICP-MS devices, the time that the laser was irradiated onto one point on the sample was lengthened in order to focus the probe and the sample, and the hole in the irradiated area became deeper, which could cause fluctuations in the focus of the laser light.

[0075] In this case, a stable signal cannot be obtained, which leads to the problem of inaccurate measurement. In addition, while LA-ICP-MS performs element mapping analysis such as depth profiling and surface analysis, there is also the problem that the analysis cannot be performed with high precision.

[0076] 10 includes a gas source 91, an ICP (inductively coupled plasma) source 92, and a mass analysis unit 93. The probe 30 and the stage 70 are housed in an enclosed space 90, and a sample S is fixed to the stage 70. The enclosed space 90 is connected to the gas source 91 via a pipe 25, and is filled with gas supplied from the gas source 91. The ICP source 92 is connected to the enclosed space 90 via a pipe 26, and is also connected to the mass analysis unit 93 via a pipe 27.

[0077] According to the elemental analysis system 300, in the LA-ICP-MS analysis, by irradiating the sample S with a laser beam of low power density, it is possible to adjust the optimal focal position while suppressing damage to the surface of the sample S. Therefore, when performing mass analysis of the sample S, a stable signal can be obtained, and a highly accurate analysis can be performed.

[0078] Here, the elemental analysis system 300 can adjust the focal position of the laser light while suppressing damage to the sample S, and thus can provide a means for solving the problems associated with the LA-ICP-MS described above. From this, too, the present invention is characterized by the fact that it calculates an optimal focal position from a sound wave amplitude value and controls the focal position of the laser irradiation unit 40, which is a feature not found in the past, and it can be seen that if this can be deployed in a field, it can be expected to be industrially applicable not only to LIBS measurement but also to various other fields.

[0079] Also, in the elemental analysis system 300, it is possible to grasp the shape of the sample, similarly to the elemental analysis system 100 or 200. For example, by moving the stage 70 in a two-dimensional or three-dimensional direction while irradiating the sample S with a laser for a predetermined time, it is possible not only to grasp the two-dimensional or three-dimensional shape of the sample S, but also to perform two-dimensional or three-dimensional mapping of the elements contained in the sample S. In this case, it is also possible to perform mapping by moving the probe 30.

[0080] Furthermore, by adjusting the spot diameter for laser irradiation, high-resolution imaging of the sample S can be obtained.

[0081] The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention, and all technical matters included in the technical ideas described in the claims are the subject of the present invention. The above-described embodiment shows a preferred example, but a person skilled in the art can realize various alternatives, modifications, variations, combinations, or improvements from the contents disclosed in this specification, and these are included in the technical scope described in the attached claims.

[0082] It goes without saying that the present invention can be applied not only to the field of elemental analysis in the above-mentioned harsh environments, but also to elemental analysis in any environment, such as a space environment or an undersea environment. [Explanation of symbols]

[0083] 10 Laser light source (semiconductor laser) 15 Spectroscopic Analysis Department (Analysis Department) 21 Optical fiber cable 22 Laser light 23 Plasma Emission 24. Sound Waves 30 Probe (laser device) 40 Laser irradiation unit 41 Laser light transmission unit 42 Laser resonator 43,44,46,47 Optical section 45 Window 48 Plasma light emission transmission unit 49 Case 50 Sonic acquisition unit 51 Microphone section 52 Sound wave transmission unit 60 Controller (Focus position determination unit) 70 Stage (position adjustment mechanism) 71 Robot arm (position adjustment mechanism) 80 Reactor Building 85 Reactor Vessel 90 Closed space 91 Gas Source 92 ICP source 93 Mass Spectrometry Department (Analysis Department) 100,200,300 Elemental Analysis System M Melt (target object) S Sample (object)

Claims

1. A laser device including a laser irradiation unit that irradiates a target with laser light, a sound wave acquiring unit for acquiring sound waves generated from the object by the irradiation of the laser light, The laser irradiation unit is controlled to a predetermined focal position based on the sound wave acquired by the sound wave acquisition unit. A laser device characterized by:

2. 2. The laser device according to claim 1, The laser irradiation unit and the sound wave acquisition unit are disposed adjacent to each other. A laser device characterized by:

3. 3. The laser device according to claim 2, The distance a between the laser irradiation unit and the sound wave acquisition unit in a direction perpendicular to the laser optical axis is 100 mm or less. A laser device characterized by:

4. 2. The laser device according to claim 1, The timing of irradiating the laser light by the laser irradiation unit and the timing of acquiring the sound wave by the sound wave acquisition unit are synchronized. A laser device characterized by:

5. 2. The laser device according to claim 1, A plurality of the ultrasonic wave acquiring units are provided. A laser device characterized by:

6. 6. The laser device according to claim 5, The plurality of sound wave acquiring units are evenly arranged around the laser irradiation unit as viewed from the laser optical axis direction. A laser device characterized by:

7. 2. The laser device according to claim 1, The sound wave acquisition unit is an optical microphone. A laser device characterized by:

8. 2. The laser device according to claim 1, the laser irradiation unit irradiates the object with the laser light, which is set to a predetermined power density at which the object cannot emit plasma light; The sound wave acquiring unit acquires the sound waves excited by the laser light irradiated at the predetermined power density. A laser device characterized by:

9. 9. The laser device according to claim 8, When the object is a metal material, the predetermined power density is 600 MW / cm ２ It is set to: A laser device characterized by:

10. a laser irradiation unit that irradiates a target object with laser light; an analysis unit that analyzes elements contained in the object by irradiating the object with the laser light, a sound wave acquiring unit for acquiring sound waves generated from the object by irradiation with the laser light; a focal position determination unit that determines a focal position of the laser irradiation unit based on the sound waves acquired by the sound wave acquisition unit; A position adjustment mechanism that aligns the laser irradiation unit with the focal position determined by the focal position determination unit. Elemental analysis system comprising:

11. 11. The elemental analysis system according to claim 10, A semiconductor laser for generating the laser light; an optical fiber that transmits the laser light generated by the semiconductor laser to the laser irradiation unit, The laser irradiation unit and the sound wave acquisition unit are disposed adjacent to each other at the tip end of the optical fiber. Elemental analysis system comprising:

12. 11. The elemental analysis system according to claim 10, a two-dimensional stage or a three-dimensional stage as the position adjustment mechanism, The two-dimensional stage or the three-dimensional stage controls the position of the laser irradiation unit according to a command from the focal position determination unit. Elemental analysis system comprising:

13. 11. The elemental analysis system according to claim 10, a robot arm as the position adjustment mechanism, the laser irradiation unit and the sound wave acquisition unit are provided at a tip of the robot arm, The robot arm controls a position of the laser irradiation unit according to a command from the focal position determination unit. Elemental analysis system comprising:

14. A first step of irradiating a target with laser light; a second step of acquiring a sound wave generated from the object by irradiation with the laser light; a third step of determining a focal position for irradiating the laser light based on the sound wave acquired in the second step; a fourth step of irradiating the object with the laser light from the focal position determined in the third step to analyze elements contained in the object; An elemental analysis method comprising:

15. 15. The elemental analysis method according to claim 14, In the third step, a position corresponding to a peak of the sound wave is determined as the focal position.

1. A method for elemental analysis comprising:

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