Method for simultaneous analysis of multiple alpha-emitting radionuclides

Abstract

To provide a method that enables quantitative analysis of multiple α-ray discharge nuclear species to be performed simultaneously without complicated processes.SOLUTION: A method includes steps of: introducing a sample solution into a column 2 equipped with a solid-phase extraction resin; adsorbing α-ray discharge nuclear species contained in the sample solution onto the solid-phase extraction resin of the column 2; eluting the α-ray discharge nuclear species adsorbed on the solid-phase extraction resin into an eluent for each group; atomizing the eluent and introducing it into a plasma ion source 5 to ionize; introducing oxygen or ammonia into the ion groups to convert the mass of ions of the elements concerned through reaction with those gases; and then removing ions with a specific mass number in a quadrupole mass filter 9 and measuring a specific signal of the α-ray discharge nuclear species that have passed through the quadrupole mass filter 9.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for analyzing alpha-emitting radionuclides, such as thorium (Th), neptunium (Np), americium (Am), curium (Cm), plutonium (Pu), and uranium (U). In particular, it relates to a method that can simultaneously analyze multiple nuclides by applying a high-frequency inductively coupled plasma mass spectrometer.

Background Art

[0002] Radioactive substances emit radiation such as alpha rays, beta rays, and gamma rays, and decay to become more stable atomic nuclei. At that time, the quantification of radioactive nuclides that emit alpha rays can be measured by measuring alpha rays using a ZnS(Ag) scintillation counter, a gas flow counter, a silicon semiconductor detector, etc. However, it was not possible to simultaneously analyze nuclides with similar alpha-ray energies. In order to quantify each nuclide, generally, various separation and concentration operations have been performed, and complicated processes have been required.

[0003] Also, according to the generally known high-frequency inductively coupled plasma mass spectrometry method, for nuclides with different masses, quantification for each nuclide is possible without a prior separation operation. However, even then, for example, the isotopes 238U and 238Pu, 241Am and 241Pu could not be separated and quantified. In addition, since the sample introduced into the apparatus is a radioactive substance, it is more preferable to have a low concentration on the order of ppt. However, when the concentration is low, for example, the influence of interference of multiple nuclides and multiple elements due to contamination becomes stronger, and as a result, there is also a problem that the measurement accuracy decreases.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide a method that can simultaneously analyze multiple nuclides without requiring complicated processes.

Means for Solving the Problems

[0005] To achieve the above objective, the inventors diligently investigated measurement methods that take advantage of the strengths of high-frequency inductively coupled plasma mass spectrometers (ICP-MS, ICP-MS / MS).

[0006] 《High frequency inductively coupled plasma mass spectrometer: ICP-MS》 Generally, liquid samples are introduced into a nebulizer in the sample introduction section and aerosolized. This aerosol is then introduced into a plasma ion source. In the plasma ion source, argon gas is introduced into the center of a high-frequency coil to which high-frequency energy is applied. The powerful high-frequency energy causes argon atoms to collide with each other, generating a high-energy argon plasma. The aerosolized sample is instantly decomposed in the plasma (temperature 6000-10000K), and the elements to be measured are atomized and then ionized. These ions pass through a pair of orifices called a sampling cone and a skimmer cone (some devices have a hyperskimmer cone), with pores of about 1 mm, and are introduced into the ion lens section. The ion lens section focuses the ions, separates ions from neutral matter, and blocks photons entering from the plasma. A collision-reaction cell either eliminates interference by introducing an unreactive gas (He) into the cell and causing it to collide with interfering ions, utilizing the kinetic energy difference with the element to be analyzed (collision mode), or by introducing a highly reactive gas (oxygen, methane, ammonia, etc.) into the cell and reacting it with the interfering ions to eliminate interference (reaction mode). A quadrupole mass filter consists of four parallel rod-shaped electrodes, and a quadrupole electric field is formed by applying a voltage that is a superposition of a DC voltage and a high-frequency AC voltage with the polarity of the opposing electrodes being the same. When ions are introduced into the quadrupole electric field along the rod-shaped electrodes with a low acceleration voltage, the ions move while oscillating in the vertical and horizontal directions. However, if the voltage is changed while keeping the DC / AC voltage ratio constant, at a certain moment only ions with a specific mass number will oscillate stably, pass through the quadrupole, and reach a detector equipped with a secondary electron multiplier tube. On the other hand, ions with other mass numbers will have a large amplitude, diverge, collide with the electrodes, and disappear. Secondary electron multiplier tubes are detectors capable of detecting weak ion flows with high precision. They utilize the property that secondary electrons are emitted when ions collide with a metal surface or a specially processed ceramic surface. These emitted secondary electrons are accelerated by an electric field and further amplified exponentially through repeated collisions. Ultimately, the secondary electrons are amplified hundreds of thousands to over ten million times, allowing them to be extracted as large signal currents per mass.

[0007] ICP-MS (ICP-MS / MS) has many advantages, including 1) miniaturization is possible, 2) high-speed scanning is possible, 3) it is relatively inexpensive due to its widespread use, 4) no special national qualifications are required, and 5) it is easy to operate. However, ICP-MS (ICP-MS / MS) has a drawback: it has a limited mass resolution, and while it can separate ions with a mass difference of one unit, it cannot separate isobaric ions.

[0008] 《Key Features of the Invention》 Therefore, in order to overcome the above-mentioned disadvantages, the present invention features "coarse separation of isobars using a column" and "precise separation of isobars by reaction with gas" as its key characteristics. (1) Crude separation of isobars using a column Separation of plutonium and uranium, which are alpha-emitting radionuclides that often have isobars and are present in excess. The sample solution containing the alpha-emitting radionuclides is introduced into a column or filter packed with solid-phase extraction resin, and these are separated. As the solid-phase extraction resin, for example, DGA resin (manufactured by EICHROM TECHNOLOGIES) or TRU resin (manufactured by EICHROM TECHNOLOGIES) can be used, but it is not particularly limited as long as it can achieve the above objective. For example, when using DGA resin, the sample to be measured is prepared into a nitric acid solution (4M HNO3 + 0.1% H2O2 or 4M HNO3 + 0.1M NaNO2). Then, when the alpha-emitting radionuclide sample solution prepared into a 4M HNO3 + 0.1% H2O2 nitric acid solution is introduced into a column or filter packed with DGA resin, uranium, plutonium, amenicium, curium, etc. are adsorbed onto the DGA resin. Subsequently, when a low-grade nitric acid solution (0.2M HNO3 + 0.1% H2O2; if 4M HNO3 + 0.1M NaNO2 is used as the nitric acid solution, 0.1M NaNO2 is used instead of 0.1% H2O2; the same applies hereafter) is passed through, uranium leaches from the DGA resin. Then, for example, when a 0.5M HCl + 0.1% H2O2 solution is passed through, americium and curium, etc., leaches from the DGA resin, and when a 0.5M HCl + 1% ascorbic acid solution is passed through, plutonium leaches from the DGA resin. Furthermore, when TRU resin is used as another solid-phase extraction resin, for example, americium and plutonium can be separated by using 4M HCl. (2) Precise separation of isobars by reaction with gases By passing high-purity oxygen and ammonia gases through the collision-reaction cell of an ICP-MS (ICP-MS / MS), elements that are highly reactive with these gases are converted into other masses, thereby eliminating interference. For example, americium and plutonium can be converted to AmO and plutonium to PuO2 by adjusting the amount of oxygen gas within a predetermined range. Also, by adjusting the amount of oxygen gas within a predetermined range, plutonium can be converted to PuO and uranium to UO2, making it possible to separate and measure the isobars of plutonium and uranium. In addition, by adjusting the amount of ammonia gas within a predetermined range, it is possible to separate and measure isobaric plutonium and uranium by converting only uranium into an ammonia adduct (such as UN2H4).

[0009] 《Method for Analyzing Alpha-Particle Emitting Radionuclides According to the Present Invention》 The analytical method of the present invention, possessing the above important features, is characterized by introducing a sample solution into a column or filter packed with a solid-phase extraction resin, adsorbing alpha-emitting radionuclides contained in the sample solution onto the solid-phase extraction resin, then separately eluting elements, particularly those having isobars, into an eluent, atomizing the eluent and introducing it into a plasma ion source for ionization, introducing oxygen or ammonia gas into the resulting ion group to convert the mass of ions of elements highly reactive with these gases, and then measuring a specific signal that has passed through a quadrupole mass filter. Depending on the target of measurement, only the column may be used, or only the ion mass conversion using oxygen or ammonia gas may be used, but by using both, for example, even with low-concentration samples on the order of ppt, it is possible to reliably eliminate interference from other elements and radionuclides and quantify with high accuracy without complex pretreatment. Furthermore, this analytical method can be automatically controlled using appropriate software. In addition, the sample solution can be concentrated to an appropriate concentration before being introduced into the column or filter. [Effects of the Invention]

[0010] According to the present invention, alpha-emitting radionuclides can be quantified for each radionuclide without requiring complicated pretreatment, by separating substances using a column packed with a solid-phase extraction resin, precisely separating isobars using a collision-reaction cell, and separating ions other than those with a specific mass number using a quadrupole mass filter. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 shows a schematic configuration of an apparatus suitable for carrying out the analytical method of the present invention. [Figure 2]Figure 2 shows an example of separating a mixed standard solution containing alpha-emitting radionuclides using a column. [Figure 3] Figure 3 shows the changes in plutonium and americium due to oxidation reactions in a collision reaction cell. [Figure 4] Figure 4 shows the changes in plutonium and americium due to the reaction with ammonia gas in a collision reaction cell. [Figure 5] Figure 5 shows the results of simultaneously measuring 10 alpha-emitting radionuclides using the method of the present invention. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described below with reference to the accompanying drawings. It goes without saying that the present invention is not limited to the embodiments described below, and various modifications and alterations are possible.

[0013] 《Analyzer》 Figure 1 shows a schematic configuration of an apparatus suitable for carrying out the analytical method of the present invention. In Figure 1, 1 is an autosampler (automatic preparative device) that stores sample containers filled with sample solutions obtained by eluting the sample to be analyzed in a suitable dissolving solution, 2 is a column, and 3 is a high-frequency inductively coupled plasma mass spectrometer, which includes a nebulizer (coaxial nebulizer or ultrasonic nebulizer) 4, a plasma ion source 5, an interface cone 6, an ion lens 7, a collision / reaction cell 8 equipped with a gas supply means 8a, a quadrupole mass filter 9, and a detector 10.

[0014] "column" In Figure 1, the sample solution filled in the sample container stored in the autosampler (automatic sorting device) 1 is supplied to column 2. Alpha-emitting radionuclides and the like are adsorbed onto the solid-phase extraction resin (not shown) packed in column 2.

[0015] 《Adsorption process》 The autosampler (automatic sample preparation device) 1 draws up a sample solution filled in a specific sample container and supplies it to column 2 using a pump (not shown), allowing the alpha-emitting radionuclide to be adsorbed onto the solid-phase extraction resin packed in column 2. After supplying a certain amount of sample solution to column 2, the probe of the autosampler 1 moves to the position containing the eluent. The sample solution after passing through column 2 may be directly introduced into an inductively coupled plasma mass spectrometer (ICP-MS, ICP-MS / MS), or it may be drained through a drain (not shown), and is not particularly limited.

[0016] 《Elution process》 In the process of eluting alpha-emitting radionuclides adsorbed on the solid-phase extraction resin packed in column 2, the eluent is supplied from the pump and delivered to column 2. In column 2, the alpha-emitting radionuclides adsorbed on the solid-phase extraction resin are eluted according to the supplied eluent and introduced into an inductively coupled plasma mass spectrometer (ICP-MS). For introduction, a coaxial nebulizer or an ultrasonic nebulizer (USN) is used.

[0017] 《Separation of alpha-emitting radionuclides》 Figure 2 shows an example of separating a mixed solution containing an alpha-emitting nuclide using the column configured as described above. The composition of this mixed solution is a nitric acid (4M HNO3 + 0.1M NaNO2) solution containing 235U, 238U, 241Am, 244Cm, 245Cm, 246Cm, 240Pu, 242Pu, 232Th, and 237Np. The resin for solid phase extraction (DGA resin) was packed into the column with 220 mg. In this example, after passing the mixed solution through the column and adsorbing the alpha-emitting nuclide onto the solid phase extraction resin, the eluent was passed through the column, and the eluent after passing through the column was sequentially introduced into an inductively coupled plasma mass spectrometer (ICP-MS) to quantify the alpha-emitting nuclide contained in the eluent after passing through the column. In Figure 2, the horizontal axis represents time, and at the top of the graph, the correspondence with each step in the table described on the graph is shown. The vertical axis is the detection intensity obtained by the inductively coupled plasma mass spectrometer (ICP-MS). Since high purity oxygen was introduced into the collision / reaction cell of the ICP-MS during detection, all the alpha-emitting nuclides in the mixed solution were detected as oxides. As shown in Figure 2, by using the solid phase extraction resin, the alpha-emitting nuclide could be separated.

[0018] 《Removal of interference of isomers by collision / reaction cell》 As shown in Figure 2, uranium among the alpha-emitting nuclides can be separated, but for example, americium and plutonium having isomers (241Am and 241Pu) are not separated and remain contained in the solution. If this solution is introduced into an inductively coupled plasma mass spectrometer, isomers having the same mass number cannot be separated. Therefore, in Figure 1, by supplying a gas (oxygen or ammonia gas) from the gas supply means 8a into the collision / reaction cell 8, due to the difference in reactivity between these gases and each alpha-emitting nuclide, for example, by setting the amount of oxygen gas within a predetermined range, americium is converted to AmO and plutonium is converted to PuO2. Also, if the amount of oxygen gas is set within a predetermined range, only plutonium is converted to PuO, uranium is converted to UO2, and it becomes possible to separately measure the isomeric plutonium and uranium.

[0019] Figure 3 shows the difference in the flow rate of oxygen gas and the products of the oxidation reaction of americium and plutonium in the collision reaction cell. The horizontal axis represents the introduction flow rate of oxygen gas into the collision reaction cell, and the vertical axis represents the detection intensity obtained by a high-frequency inductively coupled plasma mass spectrometer (ICP-MS). It can be seen that when the oxygen flow rate is 2 mL / min or more, americium forms AmO, and plutonium forms PuO2 rather than PuO. The oxygen flow rate is preferably 2.0 mL / min or more and 3.0 mL / min or less. As shown in Figure 3, if the oxygen flow rate is too high, the detection intensities of both AmO and PuO2 decrease, so it is preferably 3.0 mL / min or less. From the above, it can be seen that by setting the oxygen flow rate to 2 mL / min or more and 3.0 mL / min or less, 241Pu and 241Am can be separated and analyzed.

[0020] Figure 4 shows the difference in the flow rate of ammonia gas and the products of the reaction of uranium and plutonium with ammonia gas in the collision reaction cell. The horizontal axis represents the introduction flow rate of ammonia gas into the collision reaction cell, and the vertical axis represents the detection intensity obtained by a high-frequency inductively coupled plasma mass spectrometer (ICP-MS). From Figure 4, it can be seen that when the ammonia gas flow rate is 1.0 ml / min or more, uranium forms an ammonia adduct (e.g., UN2H4), and plutonium remains approximately as Pu. From the above, it can be seen that by setting the ammonia gas flow rate to 1.0 ml / min or more and 2.0 ml / min or less, 238Pu and 238U can be separated and analyzed. Also, since the detection intensity of plutonium decreases as the ammonia gas flow rate increases, the introduced ammonia gas flow rate is more preferably 1.0 ml / min or more and 1.5 ml / min or less. In addition, for quantification, usually, a calibration curve is created by the method performed by a high-frequency inductively coupled plasma mass spectrometer (ICP-MS, ICP-MS / MS), and quantification can be performed from the detected values.

[0021] Figure 5 shows the results of simultaneously measuring 10 types of alpha-emitting nuclides by the method of the present invention. A DGA resin is used as the resin for solid-phase extraction.First, in step 1, the column packed with DGA resin was washed with 8 ml of washing solution (4M HNO3 + 0.1% H2O2 solution). Then, in step 2, a sample solution containing Th, Np, Am, Cm, Pu, and U (5 ml of 4M HNO3 + 0.1% H2O2 solution, Th 20 ppt, 241Am 20 ppt, 244Cm 5.36, 242Pu 1 ppt, U 20 ppt, 237Np originated from the 241Am sample, and 240Pu, 245Cm, and 246Cm originated from the 244Cm sample) was introduced into the column, and the above alpha-emitting radionuclides were adsorbed onto the DGA resin. Subsequently, in step 3, the column was washed with 8 ml of the above washing solution. Next, in step 4, 45 ml of uranium eluent (0.2 M HNO3 + 0.1% H2O2) was introduced into the column to elute the uranium. This eluent was then introduced directly into a high-frequency inductively coupled plasma mass spectrometer (ICP-MS / MS; NexION Perkin Elmer) at a solution flow rate of 300 μl / min, and the detection intensity shown as step 4 in Figure 5 was obtained. The solution flow rate was kept constant until the end of step 7, and oxygen gas was introduced into the collision / reaction cell at a rate of 2.0 ml / min from the start to the end of detection. After confirming that the uranium elution was approximately complete by checking the detection intensity, in the next step 5, 17 ml of americium and curium eluent (0.5 M HCl + 0.1% H2O2) was introduced into the column to elute americium and curium. The detection intensity shown as step 5 in Figure 5 was obtained by directly introducing the eluent into an inductively coupled plasma mass spectrometer (ICP-MS / MS). Confirmation of the detection intensity confirmed that the elution of americium and curium was approximately complete. As the next step, step 6, 26 ml of plutonium eluent (0.5 M HCl + 1% ascorbic acid) was introduced into the column to elute plutonium. The detection intensity shown as step 6 in Figure 5 was obtained by directly introducing this eluent into an inductively coupled plasma mass spectrometer (ICP-MS / MS) and simultaneously introducing oxygen gas at 2.0 ml / min into the collision / reaction cell.Finally, in step 7, 16 ml of thorium-neptunium eluent (0.01 M ammonium oxalate) was introduced into the column to elute thorium and neptunium. The eluent was then introduced directly into an inductively coupled plasma mass spectrometer (ICP-MS / MS), and oxygen gas was introduced into the collision reaction cell at a rate of 2.0 ml / min. The detection intensity shown as step 7 in Figure 5 was obtained. Thus, the method of the present invention eliminates interference from other elements and nuclides such as rhenium trioxide (mass number 235) and lead dioxide (mass number 239), and allows for the simultaneous measurement of 10 alpha-emitting nuclides with higher accuracy, even at low concentrations of a few ppt, without the need for complicated pretreatment.

[0022] Based on the above, by adjusting the type of gas introduced into the collision reaction cell of the present invention and the flow rate of that gas, alpha-emitting radionuclides can be separated and quantified without complicated processes, even if they are isobars. [Industrial applicability]

[0023] The method of the present invention can quantitatively analyze multiple alpha-emitting radionuclides simultaneously without requiring complicated steps, and can therefore be applied to various environmental analysis institutions and businesses. [Explanation of Symbols]

[0024] 1. Autosampler (Automatic Sampler) 2 α-nuclide enrichment and separation column or filter 3. Radiofrequency inductively coupled plasma mass spectrometer 4. Coaxial nebulizer or ultrasonic nebulizer 5. Plasma Ion Source 6 Interface cone 7 Ion Lens 8a High-purity oxygen supply means 8 Collision Reaction Cells 9. Quadrupole Mass Filter 10 detectors

Claims

1. A method for analyzing a sample containing multiple alpha-emitting radionuclides, A solution of the sample is introduced into a column equipped with a solid-phase extraction resin that adsorbs at least one of the aforementioned plurality of alpha-emitting radionuclides. The above-mentioned solid-phase extraction resin is used to adsorb at least one of the multiple alpha-emitting radionuclides contained in the sample solution. A step of separating at least one of the plurality of alpha-emitting radionuclides by eluting the alpha-emitting radionuclides adsorbed on the solid-phase extraction resin into an eluent, The process includes the steps of atomizing the eluent and introducing it into a plasma ion source for ionization, introducing oxygen gas into the ion group to convert the mass of at least one ion of an alpha-emitting nuclide contained in the ion group, and then measuring the signal of a specific mass that has passed through a quadrupole mass filter. The eluent after the separation step contains plutonium and americium. A method for analyzing a sample containing multiple alpha-emitting radionuclides, characterized in that the oxygen gas introduction flow rate is 2 ml / min or more and 3 ml / min or less.

2. A method for analyzing a sample containing multiple alpha-emitting radionuclides, A solution of the sample is introduced into a column equipped with a solid-phase extraction resin that adsorbs at least one of the aforementioned plurality of alpha-emitting radionuclides. The above-mentioned solid-phase extraction resin is used to adsorb at least one of the multiple alpha-emitting radionuclides contained in the sample solution. A step of separating at least one of the plurality of alpha-emitting radionuclides by eluting the alpha-emitting radionuclides adsorbed on the solid-phase extraction resin into an eluent, The process includes the steps of atomizing the eluent and introducing it into a plasma ion source for ionization, introducing ammonia gas into the ion group to convert the mass of at least one ion of an alpha-emitting nuclide contained in the ion group, and then measuring the signal of a specific mass that has passed through a quadrupole mass filter. The eluent after the separation step contains plutonium and uranium. A method for analyzing a sample containing multiple alpha-emitting radionuclides, characterized in that the flow rate of the ammonia gas introduced is 1 ml / min or more and 2 ml / min or less.

3. In the separation step, a plurality of alpha-emitting radionuclides are adsorbed onto the solid-phase extraction resin. In the separation step, the first nuclide is eluted using an eluent that elutes the first nuclide among the plurality of alpha-emitting nuclides. The measurement process is performed using the obtained eluent. After measuring the first nuclide, in the separation step, the second nuclide is eluted using an eluent that elutes a second nuclide different from the first nuclide. A method for analyzing a sample containing a plurality of alpha-emitting radionuclides according to claim 1 or 2, wherein the measurement step is performed using the obtained eluent.

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