RU2713813C2 - Method of radionuclide activity determination in samples of environmental objects - Google Patents

Abstract

FIELD: chemistry; physics.

SUBSTANCE: invention relates to organization and methods of monitoring radioactivity of environment during extraction and analysis of low-active samples. Summary of invention consists in development of algorithm (sequence of performance of technological operations) when analyzing low-active samples, in accordance with which in determining level of activity of beta-active nuclides, their radiochemical extraction, spectrometric measurement and calculation of activity, and then remaining filtrate containing other radionuclides is directed to alpha emitting nuclides release circuit. When analyzing low-active samples for content of alpha-active nuclides, their radiochemical release, spectrometric measurement and calculation of activity are carried out, and then the remaining filtrate containing other radionuclides is directed to a scheme for extraction of beta-emitting nuclides.

EFFECT: technical result is higher information value and reliability of results of determining activity of radionuclides of γ-, β-, α- radiating nuclides when analyzing low-active samples.

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Description

The technical field to which the invention relates.

The invention relates to the organization and methods of monitoring environmental radioactivity in the selection and analysis of samples of various levels of activity.

The technical problem to which the invention is directed.

Currently, it is urgent to develop a system of radionuclide studies, including both hardware and methodological support, and the organization of research, which allows to obtain information on the qualitative and quantitative composition of radioactive contamination of various samples of environmental objects with a high level of sensitivity and reliability of measurement results . This problem is especially relevant in the analysis of inactive samples.

The prior art.

The analogue.

A typical method for radionuclide research of each selected sample of environmental objects includes preliminary dosimetric monitoring, gamma spectrometric analysis, beta, alpha - radiometric analysis in combination with radiochemical methods for the separation and concentration of radionuclides. The task is time-consuming, expensive and inefficient when analyzing a large volume of samples.

Prototype.

A known method of conducting radionuclide analysis of samples ["Guide to methods for monitoring environmental radioactivity", ed. I.A. Soboleva, E.N. Belyaeva, Moscow: “Medicine”, 2002, p. 25], based on a preliminary assessment by radiometric methods of the total beta, alpha activity of nuclides for sorting environmental samples against threshold (regulated) levels of activity with further determination of the content of activity and the composition of the identified abnormal (above the threshold level established depending on the research task) samples gamma, beta, alpha spectrometric methods with appropriate radiochemical sample preparation. A diagram of this method is shown in FIG. 1.

However, this method has several limitations associated with a previously unknown radionuclide composition.

When making absolute measurements, it is necessary to take into account a number of corrections in the calculation of activity (decay scheme, self-absorption, self-scattering, counter efficiency, radiation absorption by a layer of a separating medium, etc.), which directly depend on the radiation energy, and the absence of preliminary information on the composition of pollution makes it practically impossible to implement this method.

The use of the relative method in the selection of appropriate standards facilitates the problem under consideration, since it eliminates most of the corrections, however, with an unknown radionuclide composition, it is difficult to estimate the exact value of the total efficiency of the radiometer, due to the different sensitivity of the detector in different energy regions of the spectrum. In addition, it is necessary to assume the expected radionuclide composition in the selection of reference samples. For example, when examining areas with a significant loss of decay products (emergency facilities, the Chernobyl nuclear power plant area, test sites), the composition of the comparison sample should include natural radionuclides, as well as ¹³⁷ Cs, ⁹⁰ Sr + ⁹⁰ Y, fissile material in the ratio typical for deposition at the test site . For areas with a low probability of contamination with technogenic radionuclides, the spectral composition of the reference sample should be close to the spectrum of natural radionuclides in a typical ratio for a given territory. Given the variety of samples (soil, vegetation, water samples, etc.), it is necessary to have a set of comparison samples for calibrating the equipment in several geometry variants depending on the type of samples being analyzed.

Thus, the considered method is quite time-consuming, requires a lot of preliminary preparation when selecting comparison samples

The present invention allows to optimize research in this area and in a short time with minimal cost to obtain information about radioactive contamination of the territory and other objects.

The technical result of the invention.

The technical result of the proposed method is to increase the efficiency of radionuclide studies in the following areas:

- increase in the volume of analyzed samples (~ 10 times) and the information content of radionuclide studies due to the use of mathematical methods for decoding spectrometric information during the express analysis of all analyzed samples;

- increasing the reliability of measurement results by combining mathematical methods of decoding spectrometric information with classical methods of γ-, β-, α-spectrometry;

- obtaining complete information about the composition of the radioactive contamination of low activity samples without dividing the sample;

- reduction of material, labor and time costs through the use of the minimum necessary composition of hardware and methodological support for radionuclide studies.

The way to achieve a technical result.

The specified result is achieved by the fact that in the proposed method the following research algorithms are developed:

- the general algorithm of radionuclide studies with a sufficient amount of experimental material (soil, vegetation, water, etc.) based on a combination of spectrometric and radiochemical research methods with preliminary mathematical decoding of spectrometric information;

- an algorithm for radionuclide studies of inactive samples with an insufficient amount of experimental material (smears, tablets), excluding the division of the sample, allowing you to get the full amount of information about the radionuclide contamination of each sample sample.

The measuring instruments used were a DGDK-63 semiconductor gamma-spectrometer based on a Ge (Li) detector and a TRI-CARB 2750 / LL liquid scintillation alpha, beta radiometer from Canberra Parcard, complete with Moc software of NPO Radon with mathematical decoding of complex spectra (base includes ³ N, ¹⁴ C, ¹³⁷ Cs, ⁹⁰ Sr + ⁹⁰ Y, ²³⁹ Pu, ^234,235,238 U)

SUMMARY OF THE INVENTION

The general algorithm for radionuclide studies after sampling involves the following steps:

- preliminary radiation monitoring on the ground;

- gamma spectrometric analysis of all samples taken;

- identification of alpha-, beta-emitting nuclides by mathematical decryption methods in all samples without separation (at this stage, a qualitative assessment of radioactive contamination in the "search mode" with a preliminary quantitative assessment due to the limitations of the decryption program);

- confirmation of the detected contamination composition by the methods of radiochemical separation of radionuclides and determination of their activity;

- conclusions about the condition of the investigated object according to the results of radionuclide analysis.

The algorithm for radionuclide analysis, taking into account the specifics of the selected experimental material, is shown in FIG. 2.

A more difficult task is to obtain information about the radionuclide contamination of objects using the tablet method (analysis of tablets) and the method of removing unfixed pollution (analysis of smears). Both methods have the following limitations:

- insufficient amount of experimental material (due to sampling technology);

- low activity of radionuclide contamination of smears and tablets due to low exposure.

These factors, as well as the lack of preliminary information on the qualitative and quantitative composition of the radioactive contamination of the studied samples, exclude the possibility of their division during a comprehensive study of all the analyzed radionuclides.

In this regard, an algorithm for radionuclide analysis of smear and tablet samples was developed, which provides for obtaining the maximum possible information about the composition of radioactive contamination in the sample. The problem was solved for beta-emitting nuclides ⁹⁰ Sr + ⁹⁰ Y and alpha-emitting nuclides ²³⁹ Pu, ^234,235,238 U.

The algorithm for radionuclide studies in the analysis of smear samples and tablets provides the following steps in accordance with the scheme in FIG. 3:

Stage 1 (preliminary study):

- preliminary gamma-spectrometric analysis of all selected samples;

- preliminary radiochemical sample preparation in order to maximize the conversion of all available radionuclides into the solution (ashing and acid leaching);

- clarification of the resulting solution by chemical methods and the preparation of a counting sample for measurements on a liquid crystal radiometer;

- processing the information obtained using mathematical methods of decoding and identification of radionuclides ³ N, ^l4 C, ¹³⁷ Cs, ⁹⁰ Sr + ⁹⁰ Y, ²³⁹ Pu, ^234,235,238 U in the analyzed samples of smears and tablets.

At the preliminary stage, all selected samples are analyzed.

Samples whose absolute activity in beta and alpha radiation does not exceed 0.1 Bq are excluded from further analysis (the limit of the measured activity is determined by the sensitivity of the measuring equipment and the forecast of the chemical yield of radiochemical sample preparation).

Samples whose absolute beta and alpha radiation activity exceeds 0.1 Bq, as well as samples whose preliminary analysis revealed significant quantities of technogenic origin radionuclides, are examined in detail by radiochemical methods in order to confirm the identification results by mathematical decryption methods.

Stage 2 Detailed investigation ( ⁹⁰ Sr + ⁹⁰ Y, ²³⁹ Pu, ^234,235,238 U)

The material of the counting samples of samples taken for a detailed study by chemical methods (ashing) is cleaned of a liquid scintillator, the resulting solid residue is subjected to acid leaching in order to re-transfer the radionuclides into solution. Next, the radionuclide analysis is carried out according to the following scheme:

- if a significant amount of ⁹⁰ Sr + ⁹⁰ Y radionuclides is detected at the preliminary stage of research, radiochemical isolation of the indicated radionuclides is carried out and their activity is determined by appropriate methods; while the filtrate containing interfering radionuclides is discarded or sent to the radionuclide separation scheme ²³⁹ Pu, ^234,235,238 U;

- when a significant amount of radionuclides ²³⁹ Pu, ^234,235,238 U is detected at the preliminary stage of research, radiochemical isolation of these radionuclides is carried out by appropriate methods; while the filtrate containing interfering radionuclides is discarded or sent to the ⁹⁰ Sr + ⁹⁰ Y radionuclide release circuit.

Thus, this algorithm allows you to analyze the qualitative and quantitative composition of the radioactive contamination of smears and tablets in full without dividing the sample. If necessary, algorithms can be developed for other beta-alpha-emitting nuclides.

Justification of compliance with the eligibility criterion of "inventive step".

The proposed technical solution has an inventive step, since it does not explicitly follow from published scientific data and known technical solutions that the claimed radionuclide research algorithms lead to an increase in the volume of analyzed samples, to increase the information content and reliability of the results of determining the activity of γ-, β-, α-emitting radionuclides nuclides, including the analysis of inactive samples without their division.

Justification of compliance with the eligibility criterion "industrial applicability".

The proposed technical solution is industrially applicable, as for its implementation can be used serial measuring equipment (including foreign production) in combination with methodological support, developed and certified in accordance with the tasks in carrying out radiation monitoring.

The results of experimental verification of the implementation of the method.

The proposed method according to the first algorithm is implemented during radiation monitoring at emergency facilities with a high level of contamination, according to the second algorithm, when radioactive contamination is detected with sampling by the tablet method and the method of removing unfixed contamination using smears. Both algorithms worked out on a single hardware and methodological support.

The rationale for the technical and economic effectiveness of the invention.

The technical and economic efficiency of the proposed method consists in increasing the number of analyzed samples, increasing the information content and reliability of the results of determining the activity of radionuclides of γ-, β-, α-emitting nuclides in the analysis of samples of various levels of activity using the minimum necessary composition of hardware and methodological support.

Claims (3)

1. A method for determining the activity of radionuclides in samples of environmental objects, which consists in sampling and preparation of samples, determining the total beta, alpha activity with a breakdown of environmental samples relative to threshold activity levels, followed by determining the activity of gamma, beta, alpha-emitting nuclides in selected samples, characterized in that a gamma-spectrometric analysis of all samples is preliminarily performed, alpha-, beta-emitting nuclides in the mixture are identified, and a detailed research by radiochemical and spectrometric methods and establish the activity of detected radionuclides only in those samples in which the activity level exceeds the regulated level. 2. The method according to p. 1, characterized in that when analyzing inactive samples for the content of beta-active nuclides, they are radiochemically isolated, spectrometric measured and calculated, and then the remaining filtrate containing other radionuclides is sent to the alpha-emitting nuclide isolation scheme . 3. The method according to p. 1, characterized in that when analyzing inactive samples for the content of alpha-active nuclides, they perform radiochemical isolation, spectrometric measurement and calculation of activity, and then the remaining filtrate containing other radionuclides is sent to the beta-emitting nuclide isolation scheme .

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