JP4193981B2 - Isotope analysis method using laser - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an isotope analysis method using a laser.
[0002]
[Prior art]
As an apparatus for selectively detecting a specific atom, molecule or isotope and performing mass spectrometry on these, as shown in FIG. 5, a laser beam having a wavelength corresponding to the energy between specific levels of atoms and molecules is used. There is a laser resonance ionization mass spectrometer that is based on resonance absorption excitation, and is excited to a higher excitation level by several photons and finally excited and ionized until it exceeds the ion potential. This apparatus has a feature that specific atoms and molecules can be detected selectively and with high sensitivity.
[0003]
Currently, these instruments are often used in the field of environmental measurement such as dioxin analysis and have already been commercialized, but at present, this laser resonance ionization mass spectrometry has been established for gas samples. The solid sample is still under development.
[0004]
The energy level of an atom is basically determined by the element, but even for the same element, as shown in FIG. 6, the difference in mass number, that is, a slight shift in the energy level due to the isotope, that is, isotope shift. There is. Using this isotope shift, a method for selectively detecting and exciting each isotope by resonance excitation and ionization has been realized.
[0005]
As a simple solid sample vaporization method for analyzing a solid sample by laser resonance ionization, as shown in FIG. 7, a sample vapor is generated by irradiating the sample with a vaporization laser, and a normal resonance is generated. Similar to ionization, there is a laser ablation method in which analysis is performed by irradiating a resonance ionization laser.
[0006]
The feature of this method is that it is not necessary to pre-process the sample before analysis, is very simple, and can be applied to high boiling point materials. However, in this method, in order to increase the sensitivity, it is necessary to pass a resonance ionization laser in the vicinity of the vaporization spot and introduce more vapor atoms into the resonance ionization laser.
[0007]
At this time, the temperature of the sample vapor atom is very high. In particular, in the case where isotope selective excitation is performed using a slight isotope shift, it is indispensable to suppress the Doppler spreading effect of FIG. Yes. One way of suppressing the Doppler spreading effect as described above is to narrow the velocity distribution of vapor atoms. For example, a supersonic molecular beam valve, a small-diameter Knudsen cell, or the like is used to align the traveling direction of vapor atoms.
[0008]
As an Na isotope ratio analyzer, metal Na vapor and laser light for photoionizing Na atoms are introduced into a predetermined position of an electron lens system composed of one metal electrode and three grit electrodes. Thus, it is known that metal Na atoms are photoionized and the isotope ratio of Na atoms is analyzed from the difference in flight time of the generated ions (see, for example, Patent Document 1).
[0009]
[Patent Document 1]
JP-A-7-209217
[Problems to be solved by the invention]
In this way, when vaporizing by laser ablation and passing a selective excitation laser very close to the vaporization spot, it is very difficult to narrow the velocity distribution, including the method of aligning the traveling direction of the vapor atoms. The sensitivity was difficult to increase. Accordingly, an object of the present invention is to provide an isotope analysis method using a laser capable of analyzing trace isotopes very simply and with high accuracy by utilizing the Doppler effect.
[0011]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the isotope analysis method using a laser according to claim 1 of the present invention provides a Doppler velocity component corresponding to each isotope shift even at the time of irradiation of a resonance absorption wavelength laser of a certain isotope. Each isotope has its own velocity component, and each isotope has a slightly different initial velocity. Each isotope is separated using a slight difference in ion orbit.
[0012]
Thereby, the isotope analysis method and apparatus using the laser of the present invention does not require various pretreatments for performing selective ionization on the solid sample, and each isotope to be excited has its own characteristic. Because each isotope ion has a velocity component and each has a slightly different initial velocity, a specific isotope, especially a very high amount, is obtained by taking advantage of the slightly different ion trajectory when extracting ions to the detector. Simple isotopes can be analyzed easily and with high accuracy.
[0013]
The isotope analysis method using a laser according to claim 2 of the present invention is such that, even when a certain isotope is irradiated with a resonance absorption wavelength laser, an isotope having a Doppler velocity component corresponding to each isotope shift is generated by resonance absorption excitation. Because they are excited, each isotope has its own unique velocity component and takes advantage of slight differences in ion trajectories when extracting ions to the detector, based on the fact that each isotope ion has a slightly different initial velocity. However, the slight differences in the initial velocities between the isotopes caused by the small isotope shifts of the resonance excitation levels are emphasized by the ion extraction means so that a large ion orbital difference is generated, and each isotope is separated. It was set as the structure to do.
[0014]
As a result, since the isotope shift of the resonance excitation level is small, the difference in the initial velocity between the isotopes is slight, but the slight difference in the initial velocity is emphasized by the ion extraction means, and the difference in the large ion trajectory is increased. As it occurs, particularly very isotopes can be easily and accurately analyzed.
[0015]
The isotope analysis method using a laser according to claim 3 of the present invention is such that, even when a certain isotope is irradiated with a resonance absorption wavelength laser, an isotope having a Doppler velocity component corresponding to each isotope shift is generated by resonance absorption excitation. Because they are excited, each isotope has its own unique velocity component and takes advantage of slight differences in ion trajectories when extracting ions to the detector, based on the fact that each isotope ion has a slightly different initial velocity. In order to separate each isotope, a pulsed laser is used, and information on the arrival time difference to the ion detector caused by the mass difference of each isotope is taken into account. The isotope analysis was performed.
[0016]
As a result, the isotope analysis method using the laser of the present invention does not require various pretreatments for selective ionization of a solid sample, and does not require a specific isotope, particularly a very abundant isotope. The body can be analyzed easily and with higher resolution.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
The present invention reversely utilizes the Doppler effect in order to solve the problems of the prior art. Next, an embodiment of the present invention will be described in detail below with reference to FIGS. A conceptual diagram of an apparatus for carrying out the present invention is shown in FIG. In the figure, 1 is a solid sample, 2 is a resonance excitation laser, 3 is an ion extraction electrode, and 4 is a position sensitive ion detector.
[0026]
The Doppler velocity (Δν = ν · v / c, ν: frequency, v: velocity) corresponding to the isotope shift even when irradiated with a resonance absorption wavelength laser of a certain isotope contained in the solid sample 1 by the resonance excitation laser 2. , C: speed of light) components cause resonance absorption excitation, so that each isotope to be excited has a unique velocity component.
[0027]
Since each isotope ion has a slightly different initial velocity, the ion trajectory at the time of ion extraction to the detector is slightly different, and “Isotopes of interest” and “Isotopes of no interest” in the figure And reaches the plane of the position sensitive ion detector 4. Using this, each isotope is separated.
[0028]
However, since the isotope shift of the resonance excitation level is small, the initial velocity difference between the isotopes is also small. Therefore, to emphasize a slight difference in initial speed, so a large difference in ion trajectories occurs, Ru provided an ion extracting electrode structure 3. In FIG. 2 , the potential distribution is displayed on the vertical axis, and the distance from one end to the other end of the electrode structure 3 is displayed on the horizontal axis. If the “Isotope of interest” passes through the center of the electrode structure 3, the “Isotope of interest” is off the center, so it shifts outward. In this way, the plane of the position sensitive ion detector 4 is reached.
[0029]
By adopting a position sensitive ion detector 4 that can obtain position information with high resolution, such as a movable slit on the front of the detector or a fluorescent screen output type microchannel plate ion detector, etc. At the same time, it is possible to measure many types of isotopes and to have a very wide dynamic range.
[0030]
Further, by using those pulsed laser, it is considering the information of the arrival time difference of the ion detector caused by the mass difference between the isotope that Ki out to perform a higher resolution isotope analysis. According to the present invention, trace isotopes can be analyzed very easily and with high accuracy.
[0031]
As a specific example, the principle of this method was verified by Monte Carlo calculation of ion orbits. FIG. 3 is an equivalent view of an apparatus for carrying out the present invention. The same components as those in FIG. 1 are denoted by the same reference numerals, 1 is a solid sample, 2 is a resonance excitation laser, 3 is an ion extraction electrode, 4 is It is a position sensitive ion detector. When calculating with the configuration of this equivalent diagram, assuming that the sample temperature is 3000 degrees, the arrival position of ions on the detector surface when irradiated with a laser having a resonance absorption wavelength of ⁴⁰ Ca (422.792 nm) in the sample gas The distribution is as shown in FIG.
[0032]
From the display of the ion arrival position on the detector surface in FIG. 4, it was found that ⁴⁰ Ca and ⁴² Ca (isotope shift: 400 MHz) and other isotopes can be distinguished in the present invention. Thus, it can be understood that the present invention can be sufficiently implemented.
[0033]
The isotope analysis method and apparatus using a laser of the present invention can be used for analysis of a very small amount of nuclear transmutation (artificial) generation long-life nuclide. As an example, analysis of ⁴¹ Ca generated as a result of neutron irradiation in concrete occupying most of the reactor building structural material can be mentioned.
[0034]
A large amount of concrete is generated as waste material at the time of demolition of the reactor, which will increase in the future, and the level of whether concrete waste material is radioactive waste is determined by the accuracy of the evaluation method of whether it is below the natural radioactivity level This greatly affects the amount of radioactive waste to be disposed of.
[0035]
In order to properly evaluate whether it is below the natural radioactivity level, it is necessary to analyze nuclides with a trace amount and a long half-life such as ⁴¹ Ca. However, there is currently no effective analyzer, The invention can be one of the promising candidates for that tool.
[0036]
Further, the present invention may be one of the promising candidates as a tool for ¹⁴ C dating, and may be used. Currently, ¹⁴ to do C dating requires large acceleration mass spectrometer, and various ago treatment it takes a very troublesome because it is necessary, increase the isotope analysis method of the present invention It can be expected to be improved.
[0037]
【The invention's effect】
As described above, the isotope analysis method using the laser according to the present invention selectively excites and ionizes isotopes, and therefore, analyzes specific isotopes, especially extremely isotopes, with high sensitivity. Can do. Conventionally, in order to perform isotope selective ionization on a solid sample, various pre-treatments have been required, which is very time-consuming. However, this extra pre-treatment process generates errors in analysis results. Although it was a source, to say that no pre-processing is required means to be highly accurate. Therefore, the isotope analysis method of the present invention makes it possible to analyze the collected isotopes very easily and with high accuracy. Further, by using a position sensitive ion detector such as a fluorescent channel output type microchannel plate, it is possible to simultaneously measure many kinds of isotopes and to have a very wide dynamic range.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of an apparatus for carrying out the present invention.
FIG. 2 is a potential distribution diagram that emphasizes a speed difference.
FIG. 3 is an equivalent diagram of an apparatus for carrying out the present invention.
FIG. 4 is a distribution diagram of arrival positions of ions on a detector surface.
FIG. 5 is a resonance absorption excitation diagram of laser light.
FIG. 6 isotope shift diagram.
FIG. 7 is a conceptual diagram of a laser ablation method.
FIG. 8 is an explanatory diagram of the Doppler effect.
[Explanation of symbols]
1 Solid Sample 2 Resonance Excitation Laser 3 Ion Extraction Electrode 4 Position Sensitive Ion Detector

Claims (3)

  Even when a certain isotope is irradiated with a resonance absorption wavelength laser, isotopes having Doppler velocity components corresponding to the respective isotope shifts are excited by resonance absorption excitation, so each isotope has its own unique velocity component. Using a laser characterized in that each isotope is separated using a slight difference in ion trajectory when extracting ions to the detector, based on each having a slightly different initial velocity. Wasotope analysis method.   Separation of each isotope by emphasizing slight differences in initial velocities between each isotope due to small isotope shifts of resonance excitation levels by ion extraction means so that a large ion orbital difference is generated. The isotope analysis method using a laser according to claim 1.   2. A high-resolution isotope analysis is performed by using a pulse oscillation laser and taking into account the information on the arrival time difference to the ion detector caused by the mass difference of each isotope. Alternatively, an isotope analysis method using the laser according to claim 2.

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