RU2157518C1 - Standard sample of radionuclide composition based on natural soil and method of preparation thereof - Google Patents

Abstract

FIELD: radiation control. SUBSTANCE: sample is attested for specific radionuclide activities as follows: U²³⁸-34,7±3,5, -34.7+/-3.5, U²³⁴-37,3±3,7, -37.3+/-3.7, Th²³²-43±4,3, - 43+/-4.3, Th²³⁰-50±7,5, -50+/-7.5, Th²²⁸-44±4,4, -44+/-4.4, Ra²²⁶-135±13,5, -135+/-13.5, Ra²²⁸-36,4±5,5, -36.4+/-5.5, Ra²²⁴-48,8±7,3, Pb-36±3,6, Po-36±3,6, -48.8+/-7.3, Pb 36+/-3.6, Po 36+/-3.6, K⁴⁰-460±32, -460+/-32, Pu²³⁹⁺⁴⁰-10±1,0, - 10+/-1.0, Pu²³⁸ < 0,5, <0.5, Am²⁴¹-12±1,8, - 12+/-1.8, Cs¹³⁷-30±2,1, - 30+/-2.1, Sr⁹⁰-18±2,7, - 18+/-2.7, Σ_α-590±88,5, - 590+/-88.5, Σ_β-900±135 - 900+/-135. Also attested are summary alpha- and beta- emitting radionuclides for analytical 1-g weight representative of all volume of standard sample. To prepare standard samples, natural soil (13- 15.6 kg) is dried in the open air, disintegrated to particle size at most 0.074 mm. Sample is placed in polyethylene container, stirred to avoid segregation. Inert organic liquid (10-11.5 l) is added for 12-15 min. Sample is further stirred, neutral radionuclide solution is added, mixture is settled, and liquid phase decanted. Precipitate is dried at room temperature at stirring. Sample is broken to particle size at most 0.074 mm and stirred to give air-dry material of sample with homogeneous distribution of radionuclides. Deviations from mean values of measured counting velocities 7-10% are caused by measurement error. EFFECT: increased measurement accuracy. 2 cl, 9 tbl

Description

The invention relates to a method for producing a standard sample of a radionuclide composition based on natural soil and can be used for:
- monitoring the accuracy of measurements of radionuclide composition;
- metrological certification of methods for measuring radionuclides (LV) by radiometric and radiochemical methods;
- calibration and calibration of measuring instruments;
- interlaboratory comparison experiments;
- the implementation of control, certification, expert and arbitration definitions of the radionuclide composition of similar facilities;
- accreditation of radiation monitoring laboratories;
- conducting radioecological monitoring in the areas of development of brown, gray and chernozem soils.

 There is a method of obtaining a standard sample of a radionuclide composition based on natural soil, in which soil samples weighing 500 kg from a depth of 20 cm are sampled, dried, crushed, sifted through a 0.3 mm sieve, mixed in a 3000 l drum for 24 hours and obtained standard sample (IAEA AQCS CATALOG FOR REFERENCE MATERIALS AND INTERCOMPARISON EXERCISES 1998/1999 IAEA-375 Soil).

 However, in the known method, sampling is carried out from a depth of 20 cm. This depth is quite accessible for filtration processes, which can lead to the dissolution of technogenic radionuclides and their penetration to depths of up to 40 cm with possible binding by soil material and subsequent precipitation. In addition, the presence of “hot particles” in the sample affects the level of certified radionuclide activities.

Closest to the proposed standard sample is a standard sample, certified for the activity of the following man-made and natural pH (Bq / kg):
Sr ⁹⁰ - 30.34 Cs ¹³⁷ - 53.65
Ra ²²⁶ - 79.92 Pu ^239,240 - 1.04
(IAEA AQCS CATALOG FOR REFERENCE MATERIALS AND INTERCOMPARISON EXERCISES 1998/1999 IAEA / SOIL6)
The standard sample was prepared on the basis of a soil sample taken from a depth of 10 cm. Its material is considered homogeneous with a confidence level of 0.95 for a sample of at least 250 g.

 However, a known standard sample can be infected with man-made pH due to the fact that the soil sample on the basis of which it was prepared was taken from a depth of 10 cm. This depth is quite accessible for filtration processes, which can lead to the dissolution of man-made pH and penetration of solutions to depths. up to 40 cm with possible binding by soil substance and subsequent loss. The well-known standard sample is certified for specific activity of only four pH. In addition, the well-known standard is characterized by homogeneity at the level of 250 g, which is significantly higher than the weight quantities used as standard weights in radiometric measurements and radiochemical analyzes.

Closest to the technical result of the proposed method is a method of obtaining a standard sample of pH composition, in which soil sampling, drying at 110 ^o C for 8-10 hours, crushing lumps, sifting through sieves of 0.074 mm and 0.043 mm, removal of non-sifting residue , pouring 100 g of the obtained sample into a platinum cup, adding water to the sample with constant stirring until the consistency of "liquid sour cream", pouring 1 ml of a solution of radionuclides in 10% HNO ₃ with stirring after each drop, drying under infrared ampoule at 80 ^o C, grinding to a size of no more than 0.074 mm and mixing the sample with clean soil with the same particle size, the weight of which complements the sample up to 1800 (Sill Claude W. And Hindman Forest D. Preparation And Testing of Standard Soils Containing Known Quantities of Radionuclides. Analytical Chemistry, Vol. 46, N 1, 1, Jan. 1974. page 113-118.)
However, in the known method, after sieving the sample through a sieve of 0.074 mm, the non-sifting residue is removed, which contradicts the concept of representativeness of the sample, because without the granulometric representativeness the representativeness of the mineral and chemical composition and, consequently, physical properties are not achieved. In addition, the water added to the sample can chemically bind the introduced radionuclides, which will lead to their precipitation and complicate the achievement of the homogeneity of the resulting standard.

 The technical result of the proposed solution is to ensure the full representativeness of the standard sample achieved by processing the entire sample volume, and to obtain optimal homogeneity of the standard sample with a minimum analytical sample, as well as expanding the scope of the sample.

To achieve a technical result in a standard sample of a radionuclide composition based on natural soil, certified for specific activities Sr ⁹⁰ , Cs ¹³⁷ , Pu ^{239 + 240} , Ra ²²⁶ , radionuclides U ²³⁸ , U ²³⁴ , Th ²³² , Th ²³⁰ , Th ²²⁸ Ra are additionally certified ²²⁸ , Ra ²²⁴ , Pb ²¹⁰ , Po ²¹⁰ , K ⁴⁰ , Am ²⁴¹ , as well as the total activity of alpha and beta emitting radionuclides with a representative 1 g analytical sample, relative to the entire volume of the standard sample; while the standard sample is certified for activity in (Bq / kg):
U ²³⁸ - 34.7 ± 3.5 U ²³⁴ - 37.3 ± 3.7 Th ²³² - 43 ± 4.3
Th ²³⁰ - 50 ± 7.5 Th ²²⁸ - 44 ± 4.4 Ra ²²⁶ - 135 ± 13.5
Ra ²²⁸ - 36.4 ± 5.5 Ra ²²⁴ - 48.8 ± 7.3 Pb ²¹⁰ - 36 ± 3.6
Po ²¹⁰ - 36 ± 3.6 K ⁴⁰ - 460 ± 32 Pu ^{239 + 40} - 10 ± 1.0
Pu ²³⁸ <0.5 Am ²⁴¹ 12 ± 1.8 Cs ¹³⁷ - 30 ± 2.1
Sr ⁹⁰ - 18 ± 2.7 Σ _α - 590 ± 88.5 Σ _β - 900 ± 135
In the method for producing a standard sample of a radionuclide composition based on natural soil, including soil sampling, drying, crushing, abrasion, adding liquid to a sample, mixing and adding a solution of a given radionuclide with constant stirring, drying and grinding, a natural soil sample weighing 13-15 , 6 kg, dried in the open air, crushed the entire sample volume to a final grain size of not more than 0.074 mm, put it in a plastic container, mix to eliminate possible delamination, added 10–11.5 L of inert organic liquid are poured over 12-15 minutes, stirred to the consistency of “liquid sour cream”, a continuously neutral solution of the given radionuclides is added with constant stirring, then mixed again, settled, decanted settled liquid, dried in a fume hood at room temperature with periodic stirring, crushed to a final grain size of not more than 0.074 mm, mixed to eliminate possible separation, obtaining an air-dry mass of a standard sample with a homogeneous dispersion definiteness of radionuclides.

 The proposed method is as follows.

 From the horizon of 60-80 cm, which excludes infection with man-made pH, including "hot particles", take a sample of natural background soil weighing 13-15.60 kg. The weight is determined by the modern needs of the radiation monitoring laboratories of the Russian Federation, owning complexes of radiochemical and spectrometric methods (Table 1).

 The sample is dried to prevent sticking of the material during further crushing and abrasion.

 Dry material is crushed to a particle size of not more than 2 mm. The crushed material is abraded to a particle size of not more than 0.074 mm and placed in a plastic container.

 To eliminate possible gravimetric differentiation, the worn mass is mixed for 10 minutes with an electric drill with a two-blade screw nozzle. The optimum speed of rotation of the screw nozzle is determined experimentally and is equal to 75-100 rpm, since at this speed the mixing time is minimal in the absence of spraying material (table. 2).

 In the resulting mass with constant stirring with the same nozzle, but with a hand drill, for the possibility of varying the number of revolutions, 10 to 11.5 liters of an organic liquid inert with respect to the introduced radionuclides are injected within 12-15 minutes (table 3) (table 4) unlike water, which can bind and precipitate radionuclides, which would make it impossible to create a homogeneous standard.

 Laboratory experiments on 15 g of dry soil established the optimal rate of fluid injection of 5-10 ml / sec, which avoids the formation of lumps. The experimental results are shown in table. 5.

 The resulting sample volume is mixed for 30-35 minutes with the same nozzle with an electric drill at a rotation speed of 200-300 rpm until a homogeneous mass with the consistency of "liquid sour cream" is obtained. This consistency allows intensive mixing with a minimum flow rate. Laboratory experiments established that 200-300 rpm is the maximum speed at which spraying does not occur (Table 6). The same experiments showed that 25 g of material acquire the indicated consistency in 2 -2.5 seconds (table. 7). Thus, the mixing time of the total sample volume of 26 kg will be about 30-33 minutes (tab. 6, 7).

 Then, a neutral solution is introduced into the resulting mass continuously for 5-10 minutes with constant stirring, which is the sum of the solutions of technogenic pH.

The neutral solution is pre-prepared as follows. The volumes of solutions of introduced radionuclides with certified specific activities (Am ²⁴¹ - 3.63 Bq / kg, Pu ²³⁹ - 2.35 Bq / kg, Cs ¹³⁷ 64 Bq / kg, Sr ⁹⁰ 73 Bq / kg) are selected taking into account the mass of natural background soil (15.35 kg) in order to reach the values of specific activities (Bq / kg) in the standard sample that correspond to the upper values of the global fallout background, namely: Cs ¹³⁷ - 20, Sr ⁹⁰ - 20, Pu ²³⁹ - 10, Am ²⁴¹ -10.

For this, 4 solutions were prepared separately:
45 ml Am ²⁴¹ in 15% HNO ₃ ,
65 ml Pu ²³⁹ in 15% HNO ₃ ,
5 ml Cs ¹³⁷ in 15% HNO ₃ ,
4 ml Sr ⁹⁰ in 15% HNO ₃
Then the solutions were combined to obtain a total volume of 119 ml and immediately before introducing into the sample the natural background soil to avoid a possible reaction, this volume was neutralized by adding 32 ml of 30% NH ₄ OH (ammonia). The pH value measured after neutralization should be equal to 7. Then this solution is continuously introduced into the sample with constant stirring for 5 minutes.

 Subsequent homogenization of the sample is performed by periodic mixing at a rotation speed of up to 300 rpm for 70-75 minutes. Laboratory experiments have established that an analytical sample of 1 g is representative with respect to a mass of 25 g, if it is mixed for at least 4-6 seconds.

 After mixing, the sample is set to sediment the soil mass until complete transparency (absence of visible suspension) for 70-75 hours.

 The liquid formed above the surface of the settled sample is decanted, and the wet mass is laid out in a fume hood on trays of neutral material and kept at room temperature until completely dry. Laboratory experiments established the time of complete drying of various weight quantities of the sample under the indicated conditions.

 Thus, the time to complete drying of the sample mass after decantation is about 45-50 hours.

 The dry material is placed in a container of neutral material and crushed with a cylinder of inert material until the lumpiness is completely eliminated.

 The resulting mass is crushed to a final grain size of not more than 0.074 mm.

 The weakened sample is stirred for 10-15 minutes at a speed of 100 rpm to eliminate possible delamination.

 The result is an air-dry fine-erased mass of a standard sample with a homogeneous distribution of natural and man-made pH.

 To assess the uniformity of pH distribution, at least two (for interlaboratory control) series of aliquots and at least 20 samples in each series are taken from the obtained sample. The selection is carried out in several stages with mixing of the material after the selection of each batch. The weight of the sample must correspond to the claimed representativeness with respect to the bulk. Measurements are performed on low-background flow alpha-beta radiometers; the measurement time of each sample is 3x1000-3x1500s.

 An example of obtaining a standard sample of a radionuclide composition based on natural background soil.

 The base soil in the amount of 15.6 kg was selected in the Kirovograd region from a depth of 40-60 cm, which corresponds to horizon "B" of typical chernozems. The measured activity of natural pH corresponded to background values; The measured activity of technogenic pH was lower than the background of global fallout.

 The entire volume of the initial mass of the sample was dried, crushed to a particle size of not more than 2 mm and rubbed to a homogeneous material with a final particle size of not more than 0.074 mm. The frayed sample was placed in a polyethylene container, where for 10 minutes it was mixed with an electric drill with a two-blade screw nozzle at 100 rpm.

 In the resulting mass with constant stirring with the same nozzle, but on a hand drill, 11 l of a neutral organic liquid, for example ethyl alcohol, was introduced for 15 minutes. The resulting volume of the substance was mixed with the same nozzle at 300 rpm until a homogeneous mass with the consistency of "liquid sour cream" was obtained for 30 minutes.

Then, a neutral solution containing Am ²⁴¹ , Pu ²³⁹ , Cs ¹³⁷ , Sr ⁹⁰ was continuously introduced into the resulting mass with constant stirring for 5 minutes. Subsequent homogenization of the sample was carried out by periodic mixing (14 cycles of 5 minutes) at 300 rpm. The mixing cycle is due to restrictions on the continuous operation of the electric drill.

 After mixing, the sample was set for sedimentation of the solid mass until the liquid is completely transparent for 72 hours. The liquid layer formed above the sample surface was decanted, and the wet mass was removed from the container and laid out for drying at room temperature in a fume hood on trays 40x60 cm in size for 48 hours.

 After that, the dry material is placed in a plastic container, where it is crushed with an ebonite cylinder for 10 minutes until the lumpiness is completely eliminated, after which it is brought to a fineness of not more than 0.074 mm. The resulting mass was stirred at 100 rpm for 10 minutes.

 To assess the degree of homogeneity of the pH distribution, two series of 1 g aliquots of 22 samples in each series were selected from the obtained sample. The selection was carried out in random order in several stages with mixing of the material after the selection of each batch.

 The first series of samples was measured on a NRR-610 TESLA low-background alpha-beta flow radiometer (measurement time 3 times 1000 s for each sample), the second - on an NT-1000 CANBERRA four-channel low-frequency alpha-beta flow radiometer (measurement time 3 times 1500 s for each sample).

 The results of assessing the uniformity of the distribution of radionuclides in the mass of the obtained standard sample, shown in table 8, indicate that the analytical sample of the standard of 1.0 g is representative of the bulk. Deviations from the average values of the measured counting speed of 7-10% are determined by the measurement error, which is confirmed by repeated measurements of the same weights (table. 8).

 The obtained standard sample is characterized by the specific activity values of natural and technogenic radionuclides indicated in the table. nine.

Claims (2)

1. A standard sample of a radionuclide composition based on natural soil, certified for specific activity Sr ⁹⁰ , Cs ¹³⁷ , Pu ^{239 + 240} , Ra ²²⁶ , characterized in that it additionally certified radionuclides U ²³⁸ , U ²³⁴ , Th ²³² , Th ²³⁰ , Th ²²⁸ , Ra ²²⁸ , Ra ²²⁴ , Pb ²¹⁰ , Po ²¹⁰ , K ⁴⁰ , Am ²⁴¹ , as well as the total activity of alpha and beta emitting radionuclides with a representative sample of 1 g relative to the entire volume of the standard sample, while the standard sample certified for the following specific radionuclide activities:
U ²³⁸ 34.7 ± 3.5; U ²³⁴ 37.3 ± 3.7; Th ²³² 43 ± 4.3;
Th ²³⁰ 50 ± 7.5; Th ²²⁸ 44 ± 4.4; Ra ²²⁶ 135 ± 13.5;
Ra ²²⁸ 36.4 ± 5.5; Ra ²²⁴ 48.8 ± 7.3; Pb ²¹⁰ 36 ± 3.6;
Po ²¹⁰ 36 ± 3.6; K ⁴⁰ 460 ± 32; Pu ^{239 + 40} 10 ± 1.0;
Pu ²³⁸ <0.5; Am ²⁴¹ 12 ± 1.8; Cs ¹³⁷ 30 ± 2.1;
Sr ⁹⁰ 18 ± 2.7; Σ _α 590 ± 88.5; Σ _β 900 ± 135.  2. A method of obtaining a standard sample of a radionuclide composition based on natural soil, including soil sampling, drying, crushing, abrasion, adding liquid to a sample, mixing and adding a solution of a given radionuclide with constant stirring, drying and grinding, characterized in that a natural sample is taken soil weighing 13 - 15.6 kg, dried in the open air, crushed the entire sample to a final grain size of not more than 0.074 mm, placed it in a plastic container, mixed to eliminate possibly about separation, add 10 - 11.5 L of inert organic liquid for 12 - 15 minutes, mix to the consistency of liquid sour cream, add a continuously neutral solution of the given radionuclides with constant stirring, then mix again, settle, decant the settled liquid, dry in a fume hood at room temperature with periodic stirring, grind to a final grain size of not more than 0.074 mm, mix to eliminate possible separation, obtaining an air-dry mass of a standard sample but with a homogeneous distribution of radionuclides.

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