RU2267800C1 - Alpha-emitting radionuclide identification method - Google Patents

Abstract

FIELD: environmental protection.

SUBSTANCE: invention relates to radio-ecological monitoring that can be used to determine alpha-emitting radionuclides in environmental samples, in particular for alpha-spectrometric determination of isotope proportions of ²⁴⁰Pu and ²³⁹Pu, ²³⁸Pu and ²⁴¹Am, ²³⁵U and ²³⁶U. Technical result of invention resides in possibility of simultaneously determining activities of all alpha-emitting radionuclides, increased accuracy of simultaneous determination of isotope proportions of energetically close isotopes, and separating above-indicated duplets. Identification of alpha-emitting radionuclides involves environmental and technological sampling, treating samples, preparing samples for measurements, measuring and recording spectrum of sample, minimizing deviations of model spectrum from sample spectrum, and determining content of alpha-emitting radionuclides in the sample. When sample is being prepared, summary activity of sample is preliminarily determined, after which isotope solution is introduced into sample as internal standard with known energy and specified activity of alpha-emission of the sample. Based on sample spectrum measurement results and minimizing deviations of model spectrum from sample spectrum in internal standard region, parameters of asymmetric Gauss distribution describing internal standard peak are determined. Identification of alpha-emitting radionuclides is accomplished using semiconductor spectrometer and total energy scale of spectrometer is utilized, whereas spectrum of individual radionuclide is described according to proposed proportion. Minimization of deviations of model spectrum from sample spectrum is effected in three steps.

EFFECT: enabled simultaneous accurate determination of activities of energetically close isotopes.

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Description

The present invention relates to the field of radioecological monitoring, environmental protection and can be used to determine alpha-emitting radionuclides in environmental samples, in particular for alpha-spectrometric determination of isotopic ratios of ²⁴⁰ Pu and ²³⁹ Pu, ²³⁸ Pu and ²⁴¹ Am, ²³⁵ U and ²³⁶ U, by the quantitative characteristics of which it is possible to trace the nature of global radiation fallout, the change in environmental pollution after radiation accidents and nuclear weapons tests.

A known method of alpha spectrometric determination of isotopic ratios of ²⁴⁰ Pu / ²³⁹ Pu, ²³⁸ Pu / ²⁴¹ Am, in which the analysis of isotopic pairs is carried out using semiconductor alpha spectrometry on a serial Si (Au) detector of the DKD type, the processing of the obtained spectra of alpha radiation of radionuclides is carried out on a microcomputer "Electronics" by decomposing complex peaks into components of the alpha line.

The processing method is based on the determination of a single alpha line and the calculation of the isotopic composition of the source using the least squares method. Peaks of the spectra are processed in turn. The relative error depends on the statistics of the account at the peak and lies in the range of 0.7-10%. The spectrum analysis time for one isotope is 2-3 minutes.

However, the known method does not allow with sufficient accuracy to simultaneously determine the activity of alpha-emitting radionuclides in weakly active samples [1].

Closest to the claimed method according to the technical nature and the achieved effect, is a method for identifying radionuclides in samples using a liquid scintillation counter LSS [2].

The method includes taking environmental and technological samples, processing samples, preparing samples for measurement on a liquid scintillation counter, measuring and recording the spectrum of the sample and measurement parameters, creating a model spectrum of the sample, minimizing the deviation of the model spectrum from the spectrum of the sample, and determining the content of alpha-emitting radionuclides in the sample. When preparing the sample, the total activity of the analyzed sample and the energy interval of alpha-emitting radionuclides in the sample are preliminarily determined, and then the isotope solution is introduced into the sample as an internal standard with a certain energy and a given alpha radiation activity, the alpha-emission spectrum of the sample is measured and recorded, on based on the results of measuring the spectrum of the sample, minimizing the deviation of the model spectrum from the spectrum of the sample in the field of the internal standard, determine the parameters of the asymmetric distribution Auss, describing the peak of the internal standard, according to these parameters, using empirical formulas of the dependences of the parameters on the quenching for the alpha-energy of the internal standard, determine the magnitude and type of quenching of the analyzed sample, from the obtained values and type of quenching of the sample, using the formulas for the dependence of the parameters of the asymmetric Gaussian distribution from energy and quenching and reference data on alpha-emitting radionuclides make up the model spectrum.

The known method does not allow to simultaneously determine the activity of all alpha-emitting radionuclides in the sample and at the same time determine the isotopic ratios of such radionuclides as ²⁴⁰ Pu and ²³⁹ Pu, ²³⁸ Pu and ²⁴¹ Am, ²³⁵ U and ²³⁶ U, to separate doublets of radionuclides with close energies; to determine the activity of alpha-emitting radionuclides in a weakly active sample at the level of global fallout, because there is not enough energy resolution when using LSS; a limited part of the energy scale is used.

The technical result of the proposed method is the ability to simultaneously determine the activity of all alpha-emitting radionuclides, increase the accuracy of the simultaneous determination of isotopic ratios with close energies, separation of doublets of radionuclides such as ²⁴⁰ Pu and ²³⁹ Pu, ²³⁸ Pu and ²⁴¹ Am, ²³⁵ U and ²³⁶ U.

To achieve a technical result, a method for identifying alpha-emitting radionuclides is proposed, including sampling the environment and process samples, processing samples, preparing samples for measurement, measuring and recording the spectrum of the sample and measurement parameters, creating a model spectrum of the sample, minimizing the deviation of the model spectrum from the spectrum of the sample and determining the content of alpha-emitting radionuclides in the sample, when preparing the sample, the total activity of the analyzed sample is preliminarily determined, then in the sample in the isotope solution is used as an internal standard with a certain energy and a given alpha radiation activity, the spectrum of the alpha radiation of the sample is measured and recorded, based on the results of measuring the spectrum of the sample, minimizing the deviation of the model spectrum from the spectrum of the sample in the region of the internal standard, the parameters of the asymmetric Gaussian distribution are determined describing the peak of the internal standard, the method for identifying alpha-emitting radionuclides is carried out using a semiconductor spectrometer and use the entire energy scale of the spectrometer, and the spectrum of an individual radionuclide is described by the formula:

Where:

N (n _k ) is the differential account in the n _k channel;

E ^α _I is the energy of the i-line of the radionuclide;

S _i - peak area (integral count), which determines the content of the radionuclide in the sample, the parameter is minimized;

δ _i - the relative output of the i-th line of the radionuclide in its activity,

G (n _k , E ^α _i ) - asymmetric Gauss:

where: n _k is the channel number of the spectrometer;

Δ and (1-Δ) - the contribution of the first and second peaks of the double Gauss in the total area of the line;

σ ₁ and σ ₂ are the dispersion of the Gaussian distribution for the first and second peaks, respectively;

μ ₁ = k ₁ · ^Еα ₁ -k ₂ is the position of the first peak of the double Gauss;

k ₁ , k ₂ - calibration parameters of the spectrometer,

n _k (E ^α _i ) = k _{1 ·} E ^α _i -k ₂ ; (2)

μ ₂ = μ ₁ -Δμ is the position of the second peak of the double Gauss;

Δμ is the shift of the first peak relative to the second,

and minimizing the deviation of the model spectrum from the spectrum of the sample is carried out in three stages: at the first stage, the peak areas S _i and variances σ ₁ and σ _{2 are} preliminarily calculated with constant calibration coefficients k ₁ and k ₂ ; at the second stage, the calibration of the energy scale is made by clarifying the calibration coefficients k ₁ and k ₂ at the obtained values of S _i , the variance of σ ₁ and σ ₂ at the first stage; at the third stage, the peak areas S _i and, correspondingly, the isotope content in the sample, their dispersion σ ₁ and σ ₂ are calculated at constant calibration coefficients k ₁ and k ₂ , thereby making a correction to the calibration scale.

Distinctive features of the proposed method is that the method for determining alpha-emitting radionuclides is carried out using a semiconductor spectrometer and the entire energy scale of the spectrometer is used, and the spectrum of an individual radionuclide is described by the formula:

Where:

N (n _k ) is the differential account in the n _k channel;

E _i is the energy of the i-line of the radionuclide;

S _i - peak area (integral count), which determines the content of the radionuclide in the sample, the parameter is minimized;

δ _i - the relative output of the i-th line of the radionuclide in its activity,

G (n _k , E ^α _i ) is the asymmetric Gaussian distribution:

where: n _k is the channel number of the spectrometer;

Δ and (1-Δ) is the contribution of the first and second peaks of the double Gaussian distribution to the total area of the line;

σ ₁ and σ ₂ are the dispersion of the Gaussian distribution for the first and second peaks, respectively;

μ ₁ = k ₁ · E ^α ₁ -k ₂ - position of the first peak of the double Gaussian distribution;

k ₁ , k ₂ - calibration parameters of the spectrometer:

n _k (E ^α _i ) = k ₁ · E ^α _i -k ₂ ; (2)

μ ₂ = μ ₁ -Δμ is the position of the second peak of the double Gaussian distribution;

Δμ is the shift of the first peak relative to the second,

and minimizing the deviation of the model spectrum from the spectrum of the sample is carried out in three stages: at the first stage, the peak areas S _i and variances σ ₁ and σ _{2 are} preliminarily calculated with constant calibration coefficients k ₁ and k ₂ ; at the second stage, the calibration of the energy scale is made by clarifying the calibration coefficients k ₁ and k ₂ at the obtained values of S _i , the variance of σ ₁ and σ ₂ at the first stage; at the third stage, the peak areas S _i and, correspondingly, the isotope content in the sample, their dispersion σ ₁ and σ ₂ are calculated at constant calibration coefficients k ₁ and k ₂ , thereby making a correction to the calibration scale.

The use of a semiconductor spectrometer to identify alpha-emitting radionuclides in samples allows one to obtain spectra with lower resolution, which leads to an increase in the accuracy of simultaneous determination of isotopic ratios with close energies and the separation of doublets of such radionuclides as ²⁴⁰ Pu and ²³⁹ Pu, ²³⁸ Pu and ²⁴¹ Am, ²³⁵ U and ²³⁶ U.

Graduation of the spectrometer.

To calibrate the spectrometer for energy and energy resolution, an exemplary spectrometric alpha radiation source is used.

The alpha radiation spectrum of the reference source is measured over a time at which the number of readings in the main peak of each nuclide exceeds 10 ² . The acquired hardware spectrum is recorded in a spectral file.

Processing of measurement results.

When processing the measurement results, the acquired hardware spectrum and model spectrum are used.

The method for processing alpha spectra works the better, the lower the energy resolution of the alpha spectrometer, therefore, samples with a total resolution of <30 keV are analyzed.

Based on the reference data on the energies E _α and the outputs δ _i using the formula, a model spectrum is constructed that is closest to the measured one.

To build a model spectrum, split multiplets and calculate peak areas, a description of each possible multiplet energy line using a double Gaussian distribution is used, having the following form:

where: n _k is the channel number of the spectrometer;

Δ and (1-Δ) - the contribution of the first and second peaks of the double Gauss in the total area of the line;

σ ₁ and σ ₂ are the dispersion of the Gaussian distribution for the first and second peaks, respectively;

μ ₁ = k ₁ · E ^α ₁ -k ₂ is the position of the first peak of the double Gauss;

k ₁ , k ₂ - calibration parameters of the spectrometer:

n _k (E ^α _i ) = k ₁ · E ^α _i -k ₂ ;

μ ₂ = μ ₁ -Δμ is the position of the second peak of the double Gauss;

Δμ is the shift of the first peak relative to the second.

The spectrum of an individual radionuclide is described as follows:

Where:

N (n _k ) is the differential account in the n _k channel;

E ^α _i is the energy of the α-line of the radionuclide;

S _i - peak area (integral count), which determines the content of the radionuclide in the sample, the parameter is minimized;

δ _i is the relative yield of the i-th α-line of the radionuclide in its activity.

Figure 1 shows the first step in constructing a model spectrum, in connection with fluctuations in the calibration parameters of the spectrometer and their differences for different PDPs, preliminary calibration of the spectrometer (i.e., coefficients k ₁ and k ₂ ) relative to the library spectrum is carried out.

Table 1 Maximum channel number Maximum value The values of the maxima of the nearest lines 492 382 94 262 446 238 316 379 382 Deviation 288 120 -64 144 66 3 0

Table 1 shows the results of preliminary adjustment of the calibration of the spectrometer.

Maximum channel number - the maximum in the hardware spectrum is automatically searched.

Maximum value - the number of pulses in the maximum channel.

The maxima of the nearest lines are the number of pulses in the channels, depending on the relative output of the nearest α-lines of the library spectrum radionuclides.

Deviation - the automatically calculated parameter is expressed in the minimum deviation and the maximum value, in the form of the number of channels, on both sides of the maximum.

The entire hardware spectrum is shifted, if necessary, by the desired number of channels to either side relative to the maximum, so that the deviation is 0.

Spectrum correction is carried out in a semi-automatic mode.

Next, the hardware spectrum is simulated by minimizing the sum of the squared deviations of the model and hardware spectra. Variable minimization parameters are the areas S _{i of the} peaks of individual radionuclides, their dispersions σ ₁ , σ ₂ and k ₁ and k _{2 are the} calibration coefficients of the spectrometer.

Peak dispersions are determined by the quality of the sample (thickness, substrate material, etc.) and are the same for all radionuclides of a given sample.

Using the entire energy scale and describing the spectrum of an individual radionuclide according to the proposed formula in the subject of the invention allows the use of all spectrometric information about the radionuclide and significantly increase the accuracy of the simultaneous determination of alpha-emitting radionuclides with similar energies.

Minimization in three stages allows you to more accurately adjust the energy calibration of the spectrometer scale, which significantly increases the accuracy of determination of alpha-emitting radionuclides.

Minimization is carried out in three stages.

At the first stage, the peak areas S and variances σ ₁ and σ _{2 are} preliminarily calculated with constant coefficients k ₁ and k ₂ . Thus, the approximate content of alpha-emitting radionuclides and the quality of sample preparation are determined.

Table 2. σ ₁ = 2.9 σ ₂ = 1594.7 k ₁ = 249.7 k ₂ = 9.8

Table 2 presents the results of the first minimization stage and the ratio of the coefficients k ₁ and k ₂ with the variances σ ₁ and σ ₂ for the hardware spectrum depicted in FIG. 2.

At the second stage, calibration is adjusted, i.e. with the obtained values of S, σ ₁ and σ _{2, the} coefficients k ₁ and k _{2 are} adjusted.

At the last stage, the areas of S peaks (and, correspondingly, the content of isotopes in the sample) are calculated, their dispersions are σ ₁ and σ ₂ at constant calibration coefficients k ₁ and k ₂ , and the calibration scale is corrected.

The calculated peak areas determine simultaneously the activity of all alpha-radionuclides of the sample, a fragment of the results is presented in table 3.

Table 3. Pu-240 Pu-238 Pu-242 Bq / sample 116 169 108 μ ₁ 1269.48 1280.62 1352.79 1363.48 1202.55 1213.64 S ₁ 31.045 83.3975 47.4175 119.968 23.981 83.5052 μ ₂ 1268.07 1279.21 1351.38 1362.07 1201.14 1212.23 S ₂ 0.31359 0.8424 0.47896 1.2118 0.24223 0.84349 Δ 0.271 0.728 0.283 0.716 0.224 0.780 E (keV) 5.124 5.168 5.457 5.499 4.856 4.901

In the presence of complex (merged) doublets ( ²⁴⁰ Pu / ²³⁹ Pu, ²³⁸ Pu / ²⁴¹ Am, ²³⁵ U / ²³⁶ U) in the sample, the presence of separately standing radionuclides is used. If such nuclides are not present in the sample, then additional reference nuclides are introduced into the sample. This is necessary for accurate correction of the calibration of the energy scale of the spectrometer.

Figure 1 shows the correction of fluctuations in the calibration characteristics of the alpha spectra.

Figure 2 presents the hardware spectrum of the sample alpha radiation of isotopes of plutonium and americium, decoded during processing on the components of the alpha line.

Figure 3 presents a typical hardware spectrum of a sample of alpha radiation from plutonium isotopes.

Figure 4 presents the spectrum of alpha radiation 239 + 240Pu, 238Pu.

Figure 5 presents the spectrum of alpha radiation of the sample 239 + 240Pu, 238Pu, bottom sediments of the Yenisei River.

Figures 6 and 7 show a view of the alpha spectra of uranium isotopes presented at different scales.

Example 1

An averaged sample of an air-dry sample weighing 10 g is placed in a porcelain cup and calcined in a muffle furnace at a temperature of 500-550 ° C for 4-6 hours. After calcination, the cooled sample is transferred into a beaker with a capacity of 100 cm ³ , 0.12 Bq of isotope label ²⁴² Pu is added, a mixture of concentrated nitric, hydrochloric and hydrofluoric acids 30: 10: 1 by volume is added to a ratio of liquid to solid phases of 5: 1 and boiled at periodic stirring for two hours.

Cool the sample, decant and filter the liquid phase into a beaker, evaporate on a tile. The solid residue is treated a second time with a mixture of acids. After separation, the liquid phase is attached to the first decantate and evaporated together to form a wet salt.

10-15 cm ^{3 of} concentrated nitric acid are added to a beaker with wet salts with the addition of 4-5 ml of 30% hydrogen peroxide and evaporated. Repeat this operation 3-4 times, after which the salt residue is dissolved in 30-50 cm ^{3 of} 7.5 M nitric acid.

Sorption release of plutonium.

40-60 mg of crystalline sodium nitrite are added to the sample solution with stirring, the beaker is kept with the sample for 30 minutes in a water bath. The prepared sample is filtered through a column with anianite AB-17 at a rate of 1 drop per second. After passing the sample, the column is washed first with 100 cm ³ 7.5 M HNO ₃ and then with 100 cm ³ 9 M HCl at the same rate. Plutonium is eluted by passing 100 cm ^{3 of a} 0.4 M HCl solution. Evaporate the resulting eluate to dryness. Contribute to a beaker with a dry residue of 3-5 cm ^{3 of} concentrated nitric acid with the addition of 4-5% hydrogen peroxide, and evaporate. Dissolve the dry residue in 2 cm ³ 1 M HNO ₃ .

Extraction purification of plutonium.

15-20 mg of crystalline sodium nitrite are added to the sample solution with stirring, the sample is kept in a water bath for 30 minutes. Plutonium is extracted with 1.5 cm ³ of a TTA solution in toluene for 15 minutes. Separate the phases. Re-extraction of plutonium from the aqueous phase is carried out. Combine the organic phases and wash them 2 times for 5 minutes with a 1 M HNO ₃ solution in 3 cm ³ portions. Plutonium is re-extracted 2 times for 5 minutes with a 9 M HNO ₃ solution in 3 cm ³ portions. The aqueous phases are combined, evaporated to dryness. Pour into a beaker with a dry residue of 2-3 cm ³ concentrated HNO ₃ with the addition of 4-5 drops of 30% H ₂ O ₂ . Repeat this operation until complete decomposition of the residues of organic matter. The dry residue is dissolved by heating in 1.5 cm ^{3 of a} 0.5 M solution of H ₂ SO ₄ .

Preparation of a spectrometric source.

The polished stainless steel substrate is degreased with acetone and fixed to the bottom of the electrolytic cell. In the solution obtained by extraction, add 1 drop of a solution of methyl orange indicator with a transition interval of pH 3.1-4.3. Adding dropwise 1 M aqueous ammonia solution, neutralize the solution until the color of the indicator turns yellow. The solution is acidified with 0.05 M sulfuric acid until the indicator changes color (turning red), after which 2 more drops of acid are added. The resulting solution was transferred by a capillary pipette into the electrolytic cell. Lower the cathode into the solution, turn on the current. Conduct electrolysis for 2 hours at a current density of 300-320 mA / cm ² . Before the end of the process, without turning off the current, chloroform is introduced into the cell with a 0.7-1.2 cm capillary pipette. Turn off the current source. Drain the electrolyte. The electrolytic cell is disassembled and the disk made of corrosion-resistant steel is washed with plutonium deposited on it, distilled water and acetone. The disk is dried under an infrared lamp, after which it is calcined for 5-7 minutes on an electric stove at a temperature of 200-250 ° C. The calcined disk is a spectrometric source.

Spectrometric detection of α particles was carried out using a 4-channel Canberra α-spectrometer based on PD-600 semiconductor surface-barrier PIPS detectors with a window area of 600 mm ² and FWHM of 22 keV, which make it possible to convert radiation energy into an electrical pulse a certain amplitude corresponding to this energy. The measurement time of the sample on an alpha spectrometer was 40 hours. The relative measurement error is not more than 10%.

Figure 3 shows the alpha spectrum of radiochemically extracted plutonium from a soil sample taken in the area of the Chernobyl accident.

Processing of measurement results.

When processing the measurement results use the dialed hardware spectrum (figure 3) and the model spectrum.

Based on the reference data on the energies E and the outputs of δ _i using the formulas (1) - (3), a model spectrum is constructed that is closest to the measured one.

To build a model spectrum, split multiplets and calculate peak areas, a description of each possible multiplet energy line using a double Gaussian distribution is used, having the following form:

The spectrum of individual radionuclides ( ²³⁸ Pu, ²³⁹ Pu, ²⁴⁰ Pu, ²⁴¹ Am) is described as follows:

Figure 1. shows the first step in constructing a model spectrum for a given sample. A preliminary calibration of the spectrometer calibration (i.e., the coefficients k ₁ and k ₂ ) relative to the library spectrum is carried out.

Table 1 Channel number Value The values of the maxima of the nearest lines maximum maximum 492 382 94 262 446 238 316 379 382 Deviation 288 120 -64 144 66 3 0

Table 1 shows the results of preliminary adjustment of the calibration of the spectrometer.

Maximum channel number - the maximum in the hardware spectrum is automatically searched.

Maximum value - the number of pulses in the maximum channel.

The maxima of the nearest lines are the number of pulses in the channels, depending on the relative output of the nearest α-lines of the library spectrum radionuclides.

Deviation - the automatically calculated parameter is expressed in the minimum deviation and the maximum value, in the form of the number of channels, on both sides of the maximum.

Spectrum correction is carried out in a semi-automatic mode.

Next, the hardware spectrum is simulated by minimizing the sum of the squared deviations of the model and hardware spectra. Variable minimization parameters are the areas S _{i of the} peaks of individual radionuclides, their dispersions σ ₁ , σ ₂ and k ₁ and k _{2 are the} calibration coefficients of the spectrometer.

Peak dispersions are determined by the quality of the sample (thickness, substrate material, etc.) and are the same for all radionuclides of a given sample.

Minimization is carried out in three stages.

At the first stage, the peak areas S and variances σ ₁ and σ _{2 are} preliminarily calculated with constant coefficients k ₁ and k ₂ . Thus, the approximate content of radionuclides and the quality of sample preparation are determined.

Table 2. σ ₁ = 2.9 σ ₂ = 1594.7 k ₁ = 249.7 k ₂ = 9.8

Table 2 presents the results of the first minimization stage and the ratio of the coefficients k ₁ and k ₂ with the variances σ ₁ and σ ₂ for the hardware spectrum of this sample (figure 2).

At the second stage, calibration is adjusted, i.e. with the obtained values of S, σ ₁ and σ _{2, the} coefficients k ₁ and k _{2 are} adjusted.

At the last stage, the areas S _{i of} peaks (and, correspondingly, the content of isotopes in the sample) are calculated, their dispersion is σ ₁ and σ ₂ at constant calibration coefficients k ₁ and k ₂ , and the calibration scale is corrected.

In the presence of complex (merged) doublets ( ²⁴⁰ Pu / ²³⁹ Pu, ²³⁸ Pu / ²⁴¹ Am, ²³⁵ U / ²³⁶ U) in the sample, the presence of separately standing radionuclides is used. If such nuclides are not present in the sample, then additional reference nuclides are introduced into the sample, in this case ²⁴² Pu. This is necessary for accurate correction of the calibration of the energy scale of the spectrometer.

As a result of the disaster, dispersed nuclear fuel fell on the soil, poorly enriched ²³⁵ U, and, naturally, ²³⁴ U, in addition, the soil was contaminated with plutonium isotopes and fragmented fission products. The ratio of ²³⁸ Pu / ^{239 + 240} Pu in the analyzed soil samples in the area of the Chernobyl NPP corresponds to plutonium of spent fuel and ranged from 25-55%. In the analyzed sample, the time interval between radiochemical isolation and measurement on an α-spectrometer is more than 4 years. During this time, ²⁴¹ Am accumulated in the preparation due to the decay of ²⁴¹ Pu (T _1/2 = 14.4 years), and the activity of ²⁴¹ Am shows the amount of maternal ²⁴¹ Pu that fell on the ground as a result of the Chernobyl accident.

After processing this alpha spectrum with the program, the following results were obtained:

²³⁹ Pu = 10.3 Bq / pr; ²⁴⁰ Pu = 10.6 Bq / pr; ²³⁸ Pu = 9.5 Bq / pr; ²⁴¹ Am = 6.0 Bq / pr.

The ratios of plutonium and americium are:

²⁴⁰ Pu / ²³⁹ Pu = 1.03; ²³⁹ Pu / ^{240 + 239} Pu = 0.46; ²³⁸ Pu / ²⁴¹ Am = 1.59.

Knowing the activity of ²⁴¹ Am accumulated over 4 years, we can calculate the value of the activity of maternal ²⁴¹ Pu. At the time of preparation of the drug (1995), the activity of ²⁴¹ Pu = 1450 Bq / pr.

The calculation data are in good agreement with the data obtained at the time of the accident, when the activities of ²³⁹ Pu and ²⁴⁰ Pu in the reactor were approximately the same, and the content of ²⁴¹ Pu was 98% of the activity of all plutonium.

Example 2. Figure 4 shows the alpha spectrum of the preparation of soil samples taken in the region of the Semipalatinsk nuclear test site. It can be seen that the instrument peaks ²³⁹ Pu and ²⁴⁰ Pu are not allowed. After processing the instrumental spectrum by deciphering the alpha spectra, the following plutonium isotope activity values were obtained:

²³⁹ Pu = 1.09 Bq / pr; ²⁴⁰ Pu = 0.74 Bq / pr; ²³⁸ Pu = 0.05 Bq / pr.

The plutonium ratios are:

²⁴⁰ Pu / ²³⁹ Pu = 0.7; ²³⁸ Pu / ^{240 + 239} Pu = 0.032.

The relations obtained are in good agreement with published data on weapons-grade plutonium.

Example 3. Figure 5 presents the alpha spectrum of a sample of bottom sediment taken from the river. Yenisei. The study of bottom sediments is one of the most effective methods that allow us to evaluate the further fate of radionuclides released into the environment. Such studies make it possible to predict the further behavior of radionuclides and their redistribution between ecosystem components over a sufficiently long period of time. Bottom sediments are a unique object in which, under certain conditions, the state of the external environment is “preserved” for various periods of time.

Studying the alpha spectrum of plutonium presented allows us to assess the pollution of the water ecosystem of the Yenisei River as a result of the activities of the fuel cycle enterprises, as well as to predict the radioecological situation.

During mathematical processing of the presented hardware alpha spectrum, the following results were obtained:

²³⁹ Pu = 37.4 Bq / kg; ²⁴⁰ Pu = 26.3 Bq / kg; ²³⁸ Pu = 12.7 Bq / kg.

The specific activity of plutonium was calculated relative to the known activity of the ²⁴² Pu tracer, which was previously introduced into the sample.

The ratios of plutonium and americium are:

²⁴⁰ Pu / ²³⁹ Pu = 0.70; ²³⁸ Pu / ^{240 + 239} Pu = 0.20

In this case, it can be assumed that the obtained values of the relations turned out to be a superposition of weapons-grade and fuel-grade plutonium, analyzed in bottom sediments.

Example 4. Technogenic soil pollution by uranium isotopes is shown in Fig.6 and 7, in which the spectrum of the same sample is presented at different scales. In this trial the soil sampled in an area Primorye, alpha-spectrometric analysis gave the uranium content of the samples with an abnormal ratio of ²³⁵ U / ²³⁸ U isotope ratio and ²³⁴ U / ²³⁸ U. This plutonium isotopes and ²³⁵ U fission fragment products absent. The information obtained allowed us to confirm the assumption that an accident occurred on a nuclear submarine at a given site during a fuel reload, as a result of which uranium was emitted from a nuclear installation, highly enriched with light isotopes. After processing by our program, the following contents and ratios of uranium isotopes were obtained.

²³⁴ U = 2.14 Bq / pr; ²³⁸ U = 0.07 Bq / pr; ²³⁵ U = 0.12 Bq / pr; ²³⁶ U = 0.05 Bq / ave.

The values of the uranium relations are:

²³⁴ U / ²³⁸ U = 30.4; ²³⁵ U / ²³⁸ U = 1.7; ²³⁶ U / ²³⁸ U = 0.41; ²³⁵ U / ²³⁶ U = 2.4.

The uranium relations obtained, as noted above, are characteristic of the fuel of compact power plants, including those used in nuclear submarines.

The technical effectiveness of the proposed method compared with the prototype is to increase the reliability of identification of radionuclides in samples. This method, due to the better resolution of the detector and the proposed method for processing the measurement results, allows one to isolate and identify with sufficient accuracy such alpha-active radionuclides as ²⁴¹ Am and ²⁴¹ Am, ²³⁹ Pu and ²⁴² Pu in the mixture, which allows the separation of radionuclides with close energies, such like ²⁴⁰ Pu and ²³⁹ Pu, ²³⁸ Pu and ²⁴¹ Am, ²³⁵ U and ²³⁶ U, ²⁴³ Cm and ²⁴³ Cm, which is impossible to implement in the prototype method. On Fig presents a sample of industrial uranium, measured using a semiconductor detector and decoded by the proposed method. The table shows the spectrum decryption data (uranium and its decay products). In Fig.9, the spectrum of the same sample measured using LSS. It is not possible to identify the decay products of uranium, perhaps only to say that the main contribution to the activity comes from ²³⁴ U.

Table 3. Nuclide Number of pulses Activity, Bq 2σ,% 212-B1 63 6.65E-03 32 212-RO 66 6.97E-03 26 216-RO 149 1.57E-02 eighteen 220-rn 175 1.85E-02 16 222-rn 37 3.92E-02 82 224-RA 209 2.21E-02 16 228-TH 222 2.35E-02 22 232-u 194 2.05E-02 38 234-u 623297 65.8 one 235-u 17752 1.88 2 236-u 2585 0.273 16 238-u 698 7.37E-02 twenty 239-PU 706 7.46E-02 8 Amount 646153 68.3

The proposed method for determining alpha-emitting radionuclides can be carried out on standard equipment. This development is included in the R&D plan of the State Unitary Enterprise MosNPO Radon, as has great applied value.

References.

1. Anichenkov S.V., Popov Yu.S. "Alpha spectrometric determination of isotopic ratios of ²³⁹ Pu / ²⁴⁰ Pu, ²³⁸ Pu / ²⁴¹ Am." M., Radiochemistry, No. 4, 1990, pp. 110-112 (analogue).

2. Patent No. 2191409, G 01 T 1/204, 1/36 (prototype).

Claims (1)

A method for identifying alpha-emitting radionuclides, including taking environmental and process samples, processing samples, preparing samples for measurement, measuring and recording the spectrum of the sample and measurement parameters, creating a model spectrum of the sample, minimizing the deviation of the model spectrum from the spectrum of the sample, and determining the alpha content emitting radionuclides in the sample, when preparing the sample, the total activity of the analyzed sample is preliminarily determined, then an isotope solution is introduced into the sample as an internal standard and with a certain energy and a given alpha radiation activity, the alpha spectrum of the sample is measured and recorded, based on the results of measuring the spectrum of the sample, minimizing the deviation of the model spectrum from the spectrum of the sample in the region of the internal standard, the parameters of the asymmetric Gaussian distribution describing the peak of the internal standard are determined, characterized in that the method for identifying alpha-emitting radionuclides in samples is carried out using a semiconductor spectrometer, while using all the energy nical scale spectrometer and a separate spectrum radionuclide described by the formula

where N (n _k ) is the differential account in the n _k channel; E ^α _i is the energy of the i-th line of the radionuclide; S _i - peak area (integral count), which determines the content of the radionuclide in the sample, the parameter is minimized; δ _i - the relative output of the i-th line of the radionuclide in its activity, G (n _k , Е ^α _i ) is the asymmetric Gaussian distribution:

where n _k is the channel number of the spectrometer; Δ and (1-Δ) is the contribution of the first and second peaks of the double Gaussian distribution to the total area of the line; σ ₁ and σ ₂ are the dispersion of the Gaussian distribution for the first and second peaks, respectively; μ ₁ = k ₁ · ^Еα ₁ -k ₂ is the position of the first peak of the double Gaussian distribution; k ₁ , k ₂ - calibration parameters of the spectrometer: n _k (E ^α _i ) = k ₁ · E ^α _i -k ₂ ; μ ₂ = μ ₁ -Δμ is the position of the second peak of the double Gaussian distribution; Δμ is the shift of the first peak of the relative second, and minimizing the deviation of the model spectrum from the spectrum of the sample is carried out in three stages: at the first stage, the peak areas S _i and variances σ ₁ and σ _{2 are} preliminarily calculated with constant calibration coefficients k ₁ and k ₂ ; at the second stage, the calibration of the energy scale is made by clarifying the calibration coefficients k ₁ and k ₂ at the obtained values of S _{i of the} variance σ ₁ and σ ₂ at the first stage; at the third stage, they calculate the areas of Si peaks and, correspondingly, the content of isotopes in the sample, their dispersion σ ₁ and σ ₂ at constant calibration coefficients k ₁ and k ₂ , making a correction of the calibration scale.

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