Granular radioactive rice standard substance, and preparation method and application thereof

Abstract

The present application relates to the technical field of radio-labeling, in particular to a granular radioactive rice standard substance, a preparation method and application thereof. The present application carries out first drying on a rice sample at ≤50℃ to obtain a dried rice sample; carries out radionuclide spiking (when the mass is ≥1 kg, second drying at ≤50℃ after soaking is adopted; when the mass is <1 kg, rotary evaporation drying after soaking and mixing by rotary evaporation is adopted) on the dried rice sample by using a spiking solution to obtain a granular radioactive rice standard substance; the composition of the spiking solution comprises: a radionuclide, a non-radioactive nuclide carrier, an acid and a solvent; the characteristic gamma ray energy of the radionuclide is ≥500 keV. The granular radioactive rice standard substance prepared by the present application is basically the same as the rice sample in terms of matrix structure, stacking state and gamma ray self-absorption characteristics, thereby improving the test accuracy of the radionuclide activity concentration.

Description

Technical Field

[0001] This invention relates to the field of radiolabeling technology, specifically to a granular radioactive rice standard substance, its preparation method, and its application. Background Technology

[0002] Against the backdrop of the continuous expansion of nuclear energy utilization and the increasing demand for nuclear accident emergency response and radioactive event prevention, rapid screening of gamma radionuclides in food is of great significance for protecting public health, maintaining food safety, and supporting emergency decision-making. Nuclear accidents, radioactive material release events, and the cross-regional distribution of contaminated food can all lead to a significant increase in the workload of food radioactivity testing in a short period. Therefore, it is necessary to establish rapid screening and performance verification methods suitable for large-scale food sample testing.

[0003] Among the many artificial radionuclides 137 Cs is a typical focus of attention in the assessment of nuclear fission products and food contamination caused by nuclear accidents. 137 Cs has a long half-life and strong environmental persistence, enabling it to enter agricultural product systems through the soil-crop pathway and exert long-term effects on public internal radiation dose. Meanwhile, 137 Cs emits characteristic 661.7 keV gamma rays, making it suitable for rapid detection and identification using conventional gamma spectroscopy systems. Therefore, with 137 Using Cs as a target nuclide for rapid screening methods and sample preparation in food radioactivity has strong representativeness and practical application value. In gamma-ray energy spectroscopy measurements, detection efficiency is crucial for measuring radionuclide activity. While there are many methods for obtaining detection efficiency, such as Monte Carlo simulations, semi-empirical methods, or numerical calculations, using radioactive standard materials that are as similar as possible to the sample in terms of measurement geometry, matrix composition, and packing density for experimental calibration remains one of the most direct and reliable methods. For staple food products such as rice, rapid gamma-ray screening in the fully packaged state is closer to actual regulatory and emergency testing scenarios. However, the measurement results are significantly affected by factors such as sample geometry, packing density, packaging condition, self-absorption effects, and spatial distribution of nuclides. Therefore, when calibrating detection efficiency, standard or validation samples with known activity concentrations, stable morphology, and packaging conditions as close as possible to actual packaging conditions are required.

[0004] Currently, relevant institutions both domestically and internationally, such as the National Institute of Standards and Technology (NIST) of the United States, the Joint Research Centre (JRC) of the European Commission, and the International Atomic Energy Agency (IAEA), have established various systems of radioactive reference materials for food and environmental matrices. However, existing radioactive food reference materials are mostly in powder form or small packaged samples, which are difficult to directly meet the physical verification needs for calibration, detection efficiency verification, and algorithm performance evaluation of dynamic screening devices for whole-bag foods.

[0005] Standard materials related to rice mainly include two categories: naturally contaminated samples and artificially incorporated powdered matrices. The occurrence state of radionuclides in naturally contaminated samples is closer to the actual contamination situation, but they usually have problems such as high acquisition cost, limited quantity, and difficulty in adjusting the activity level and nuclide composition as needed. Although artificially incorporated powdered matrices are convenient for adjusting the target activity level, their powder morphology differs from that of actual rice grains in terms of density and self-absorption characteristics, making it difficult to truly reflect the volume source detection response of rice grains.

[0006] Traditional methods typically involve grinding the matrix into a fine powder, then sieving it to obtain samples with particle sizes ranging from tens to hundreds of micrometers, followed by spiking and mixing. While this method is beneficial for improving the uniformity of radionuclide distribution, it disrupts the original particle morphology of the rice, causing the sample to differ from actual granular rice in terms of matrix structure, packing state, and gamma-ray self-absorption characteristics, thus affecting the accuracy of radionuclide activity concentration testing. Summary of the Invention

[0007] Therefore, the purpose of this invention is to provide a granular radioactive rice standard substance, its preparation method, and its application. The granular radioactive rice standard substance prepared by this invention retains the morphology and matrix characteristics of rice sample particles, improves the accuracy of radionuclide detection results, and allows for adjustment of the nuclide type and activity concentration as needed, providing greater flexibility.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing granular radioactive rice standard material, comprising the following steps: The rice sample was first dried to obtain a dried rice sample; The dried rice sample was spiked with a spiking solution to obtain granular radioactive rice standard material; When the mass of the rice sample is ≥1kg, the radionuclide is added after soaking and then drying. When the mass of the rice sample is less than 1 kg, the radionuclide is added by rotary evaporation soaking and mixing followed by rotary evaporation drying; The spiking solution comprises: a radionuclide, a non-radioactive nuclide carrier, an acid, and a solvent; the radionuclide has a characteristic gamma-ray energy ≥ 500 keV; The temperatures of the first drying, the second drying, and the rotary evaporation drying are independently ≤50°C.

[0009] Preferably, the concentration of the non-radioactive nuclide carrier in the spiking solution is 5~20 μg / g, and the concentration of the acid is 0.05~0.2 mol / L.

[0010] Preferably, the radionuclide includes 137 Cs、 134 Cs or 60 Co; The non-radioactive nuclide carrier includes 133 Cs or 59 Co.

[0011] Preferably, when the mass of the rice sample is ≥1kg, the solvent is water; When the mass of the rice sample is less than 1 kg, the solvent includes one or more of methanol, ethanol, and dimethyl ether.

[0012] Preferably, the soaking time is 1 to 4 hours.

[0013] Preferably, the mass ratio of the dried rice sample to the spiked solution is 1:1 to 3; The time for rotary evaporation soaking and mixing is 1 to 4 hours.

[0014] Preferably, the rotary evaporator has a rotational speed of 30~80 r / min, a pressure of -0.085~-0.095 MPa, and a temperature of 35~50℃.

[0015] Preferably, after the radionuclide is spiked, the process further includes testing the uniformity, stability, and radionuclide activity concentration of the rice sample after the radionuclide is spiked.

[0016] The present invention also provides a granular radioactive rice standard material prepared by the preparation method described in the above technical solution.

[0017] This invention also provides the application of the granular radioactive rice standard material described in the above technical solution in the detection of radioactive nuclides in rice; the characteristic gamma ray energy of the radioactive nuclide is ≥500keV.

[0018] Traditional methods for spiking radioactive rice samples typically require grinding the rice into powder before mixing it with a radioactive solution to ensure uniform nuclide distribution. While this method improves nuclide distribution uniformity, it disrupts the original grain morphology of the rice, resulting in differences in matrix structure, packing state, and gamma-ray self-absorption characteristics compared to actual granular rice. For whole-bag rice samples, simple dripping or surface spraying can lead to radioactive nuclides concentrating in localized areas or on the grain surface, causing uneven activity distribution within the sample and affecting the reliability of device calibration and screening method verification results. The preparation method provided by this invention achieves uniform introduction of radioactive nuclides into granular rice samples. While maintaining the grain morphology, this invention reduces the initial moisture content of the rice sample through a first drying process (pre-drying treatment), improving the stability and consistency of the spiking solution's penetration into the rice grains during subsequent soaking, thereby improving the uniformity of radioactive nuclide spiking and recovery rate. Subsequent impregnation with the spiking solution allows the radioactive nuclides to penetrate into the interior of the rice grains or their pore structure. Compared with powder mixing and spiking, simple drop addition, or surface spraying, the preparation method provided by the present invention can improve the spatial distribution uniformity of radionuclides in granular rice samples while maintaining the morphology of rice particles, and reduce the risk of local enrichment of radionuclides.

[0019] In this invention, all drying temperatures are below 50°C. This removes free water (or solvent) and improves the absorption capacity of subsequent spiking solutions while avoiding thermal denaturation, starch gelatinization, particle adhesion, or changes in matrix morphology of rice particles caused by excessively high temperatures. The resulting radioactive rice samples retain the original physical morphology and matrix characteristics of granular rice, more closely resembling the state of actual food samples. This improves the matrix matching between the radioactive detection sample and the actual test sample, reducing the impact of matrix effects on measurement results.

[0020] For gamma-ray radioactivity detection in rice, the particle morphology, packing state, and matrix structure of the sample affect gamma-ray self-absorption, detection efficiency, and energy spectrum response. Traditional powder-spikened samples differ from the actual granular rice samples being tested in matrix state, reducing the accuracy of the detection results. The granular radioactive rice standard material prepared in this invention maintains the particle morphology and matrix characteristics of the rice sample, improving the accuracy of radionuclide activity concentration detection results.

[0021] The preparation method provided by this invention yields granular radioactive rice standard materials with clearly defined and adjustable activity concentrations. While naturally contaminated rice samples more closely resemble the actual contamination state, they are difficult to obtain, limited in quantity, and their nuclide composition and activity levels are difficult to adjust as needed. Existing standard materials are mostly small-packaged powder samples, which are insufficient to meet the calibration and performance evaluation requirements of rapid screening devices for whole-bag rice. This invention allows for the determination of the amount of radioactive nuclide standard solution to be added based on the target activity concentration, rice sample mass, the activity concentration of the radionuclide in the spiking solution, decay correction results, and experimental recovery rate results, thereby preparing radioactive rice samples with different activity concentration levels. The preparation method provided by this invention can meet the calibration and verification requirements of rapid food radioactivity screening devices at different screening levels and activity ranges.

[0022] This invention selects appropriate radionuclide spiking methods based on the preparation quantity of granular radioactive rice standard material. For large quantities of rice samples (≥1 kg, e.g., whole-bag rice samples), this invention employs immersion-penetration spiking, allowing the spiking solution to fully penetrate the rice grains, improving the uniformity of the spatial distribution of radionuclides in large-mass samples and the reproducibility of preparation. Drying at below 50°C removes free water from the rice sample while avoiding thermal denaturation, starch gelatinization, particle adhesion, or matrix morphology changes caused by excessively high temperatures, thus maintaining the physical consistency between the granular radioactive rice standard material and actual rice. For small quantities of rice samples (<1 kg), this invention employs rotary evaporation spiking. After thoroughly mixing the spiking solution with the dried rice sample, the solvent is gradually removed under rotation, reduced pressure, and low-temperature (below 50°C) heating conditions, allowing the radionuclides to be uniformly adsorbed and fixed within the rice grains during solution concentration, thereby obtaining small-mass granular radionuclide rice standard material with better uniformity.

[0023] The granular radioactive rice standard material prepared by this invention has good uniformity and can be used as a standard for detecting radionuclides in rice and as a metrological standard to calibrate measuring instruments and evaluate the accuracy of measurement methods.

[0024] Furthermore, by controlling the acidity and non-radioactive nuclide carrier concentration, this invention can maintain the chemical stability of radionuclides in the spiking solution, reduce adsorption, local enrichment or precipitation loss on the container wall, and promote the uniform penetration, dispersion and adsorption fixation of radionuclides in rice particles, thereby improving the uniformity, stability and recovery rate of granular radioactive rice standard material (spiked sample).

[0025] Furthermore, the preparation method provided by this invention improves the stability of granular radioactive rice standard material in preservation, transportation, and repeated measurements. Traditional food samples are prone to mold growth, moisture absorption, clumping, or morphological changes during preservation and transportation, leading to alterations in sample geometry and density distribution, thus affecting the repeatability of gamma spectroscopy measurements. For whole-bag samples, changes in packaging state and stacking morphology further impact detection efficiency and dynamic transport measurement response. This invention removes free water from the sample through low-temperature drying (≤50℃), which can be combined with sterilization irradiation and vacuum sealing to reduce the risk of microbial growth, moisture absorption, and mold growth, improving sample stability during long-term preservation and transportation. Simultaneously, vacuum sealing allows the sample to form more stable geometric dimensions, stacking density, and packaging morphology, which is beneficial for improving the repeatability of subsequent gamma spectroscopy measurements, dynamic transport measurements, and whole-bag screening experiments. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating the preparation and evaluation process of granular radioactive rice standard material in this invention. Detailed Implementation

[0027] This invention provides a method for preparing granular radioactive rice standard material, comprising the following steps: The rice sample was first dried to obtain a dried rice sample; The dried rice sample was spiked with a spiking solution to obtain granular radioactive rice standard material; When the mass of the rice sample is ≥1kg, the radionuclide is added after soaking and then drying. When the mass of the rice sample is less than 1 kg, the radionuclide is added by rotary evaporation soaking and mixing followed by rotary evaporation drying; The spiking solution comprises: a radionuclide, a non-radioactive nuclide carrier, an acid, and a solvent; the radionuclide has a characteristic gamma-ray energy ≥ 500 keV; The temperatures of the first drying, the second drying, and the rotary evaporation drying are independently ≤50°C.

[0028] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0029] This invention involves a first drying process on rice samples to obtain dried rice samples; the temperature of the first drying is ≤50℃. In this invention, the temperature of the first drying is ≤50℃, and can be 35~50℃, or even 40~45℃; the drying time can be 24~72h, or 30~60h, or even 40~50h. This invention's first drying of the rice samples brings the rice matrix to a relatively constant weight state. By reducing the initial moisture content of the rice, the stability and consistency of the penetration of the spiking solution into the rice particles during subsequent soaking are improved, thereby improving the uniformity and recovery rate of radionuclide spiking. By controlling the first drying temperature below 50℃, this invention can remove free water and improve the absorption capacity of subsequent spiking solutions while avoiding thermal denaturation, starch gelatinization, particle adhesion, or changes in matrix morphology of rice particles caused by excessively high temperatures, thus maintaining the physical consistency between the granular radioactive rice standard and actual rice.

[0030] After obtaining the dried rice sample, the present invention uses a spiking solution to spike the dried rice sample with radioactive nuclides to obtain granular radioactive rice standard material.

[0031] In this invention, the spiking solution comprises: a radionuclide, a non-radioactive nuclide carrier, an acid, and a solvent. In this invention, the radionuclide has a characteristic gamma-ray energy ≥500 keV, and may specifically include... 137 Cs、 134 Cs or 60 Co. In this invention, the non-radioactive nuclide carrier may include 133 Cs or 59 Co; the elements in the radioactive nuclide and the non-radioactive nuclide carrier are the same. In this invention, when the mass of the rice sample is ≥1kg, the solvent is water, specifically ultrapure water; when the mass of the rice sample is <1kg, the solvent includes one or more of methanol, ethanol, and dimethyl ether. This invention selects methanol, ethanol, and dimethyl ether as solvents for the rotary evaporation method, which can dissolve the radioactive nuclide standard solution and the non-radioactive nuclide carrier, and can also remove volatile solvents under low temperature and reduced pressure conditions. Furthermore, the above solvents do not react with nuclide ions to form a precipitation reaction, do not significantly damage the morphology of rice particles, and do not affect the requirements of subsequent gamma spectroscopy measurements and sample stability.

[0032] In this invention, the concentration of the non-radioactive nuclide carrier in the spiking solution can be 5-20 μg / g, or 8-18 μg / g, or further 10-16 μg / g, specifically 10 μg / g, 12 μg / g, 14 μg / g, or 15 μg / g. In this invention, the concentration of the acid in the spiking solution can be 0.05-0.2 mol / L, or 0.08-0.18 mol / L, or further 0.1-0.16 mol / L, specifically 0.1 mol / L, 0.12 mol / L, 0.14 mol / L, or 0.15 mol / L. This invention does not specifically limit the activity value of the radionuclide in the spiking solution; it can be determined according to actual needs. This invention maintains the chemical stability of radionuclides in the spiking solution by controlling acidity and the concentration of non-radioactive nuclide carriers, reducing adsorption, local enrichment, or precipitation losses on container walls, and promoting the uniform penetration, dispersion, adsorption, and fixation of radionuclides in rice grains. This improves the uniformity, stability, and recovery rate of granular radioactive rice standard materials (spiked samples). When using an immersion method for spiking, this invention successfully solves problems such as insufficient uniformity of radionuclides in the sample, unstable recovery rates, particle adhesion, or changes in matrix morphology by controlling immersion conditions, the acidity of the spiking solution, and drying conditions.

[0033] In this invention, the mass ratio of the spiking solution to the dried rice sample can be 1~3:1, or 1~2:1, or even 1~1.5:1.

[0034] In this invention, when the mass of the spiked solution rice sample is ≥1kg, the radionuclide spiking is performed by soaking followed by a second drying. In this invention, the soaking temperature can be room temperature (18~30℃); the soaking time can be 1~4h, 1.5~3.5h, 2~3h, specifically 2.5h; the soaking can include static soaking or low-speed stirring soaking; the low-speed stirring speed can be 30~80r / min, 40~70r / min, specifically 50~60r / min. In this invention, the second drying temperature is ≤50℃, 35~50℃, specifically 40~45℃; the second drying can be forced air drying; this invention does not specifically limit the second drying time, drying is sufficient until the mass loss rate is less than 0.1g / h.

[0035] For large quantities of rice samples (≥1kg, such as whole-bag rice samples), this invention employs an immersion-penetration spiking method, allowing the spiking solution to fully penetrate the rice grains, thereby improving the uniformity of the spatial distribution of radionuclides in large-mass samples and the reproducibility of the preparation. By drying at temperatures below 50°C, free water in the rice samples can be removed, while avoiding thermal denaturation, starch gelatinization, particle adhesion, or changes in matrix morphology of the rice grains due to excessively high temperatures. This maintains the consistency of the granular radioactive rice standard material with the actual rice in terms of physical morphology.

[0036] In this invention, when the mass of the rice sample is <1 kg, the radionuclide spiking is performed by rotary evaporation soaking and mixing followed by rotary evaporation drying. In this invention, the temperature for rotary evaporation soaking and mixing can be room temperature, and the time for rotary evaporation soaking and mixing can be 1-4 h, 1.5-3.5 h, 2-3 h, or specifically 2.5 h. In this invention, the rotation speed for rotary evaporation soaking and mixing and rotary evaporation drying can be independently 30-80 r / min, 40-70 r / min, or specifically 50-60 r / min; the pressure for rotary evaporation drying can be -0.085 to -0.095 MPa, -0.088 to -0.092 MPa, or specifically -0.09 MPa; the temperature for rotary evaporation drying is ≤50℃, 35-50℃, or specifically 40-45℃. This invention uses rotary evaporation drying at ≤50℃, which can remove solvents while avoiding thermal denaturation, starch gelatinization, particle adhesion, or changes in matrix morphology of rice particles caused by excessively high temperatures, thereby maintaining the physical consistency between granular radioactive rice standard material and actual rice.

[0037] For small rice samples (mass <1kg, specifically from grams to tens of grams), this invention employs a rotary evaporation method for spiking. The acidic carrier solution of the radionuclide is thoroughly mixed with the dried rice sample, and the solvent is gradually removed under conditions of rotation, reduced pressure, and low temperature (below 50°C). This allows the radionuclide to be uniformly adsorbed and fixed inside the rice grains during the solution concentration process, thereby obtaining a small-mass radionuclide granular rice standard with good uniformity.

[0038] After the radionuclide spiking is completed, the present invention may further include irradiating the spiked sample to sterilize it, thereby obtaining a radionuclide granular rice standard. In the present invention, the irradiation sterilization conditions may include: the radiation source includes... 60 Co gamma-ray source or 137The Cs radiation source has an irradiation dose (total) of 17-25 kGy, which can also be 18-24 kGy, and further 19-23 kGy, specifically 20 kGy, 21 kGy, or 22 kGy. This invention, through irradiation sterilization, can inhibit microbial growth and improve the storage stability of granular radioactive rice standard materials.

[0039] After the irradiation sterilization is completed, the present invention may further include: performing uniformity testing, stability testing, and radionuclide activity concentration determination on the radionuclide granular rice standard after irradiation sterilization.

[0040] In this invention, the method for uniformity testing may include the following steps: placing granular radioactive rice standard material into a sample box, measuring the net peak area at the characteristic gamma-ray peak of the radionuclide using a traceable high-purity germanium gamma-ray spectrometer, and calculating the radionuclide activity concentration of the granular radioactive rice standard material. The cumulative net count at the characteristic gamma-ray peak of the radionuclide is not less than 10,000. The activity concentration calculation formula is shown in Equation 1: ; in: C A,i For the first i The activity concentration of each sample, in becquerels per kilogram (Bq / kg). e ( E The detection efficiency is 661.66 keV γ-rays; N s Count the net area of ​​the total energy peaks measured for standard substances; T s The measurement time for rice is in seconds (s). N b Count the net area of ​​the background peak; T b The baseline measurement is live time, measured in seconds (s). P The branching ratio of gamma-ray emission at the corresponding energy; m The unit for measuring the mass of a standard substance is kilogram (kg). l The decay constant of a radionuclide is expressed in seconds (s). -1 ); Δt The interval between the reference time and the start time of measurement for granular radioactive rice standard material is expressed in seconds (s).

[0041] In this invention, the 137 The characteristic gamma-ray peak energy of Cs is 661.66 keV; 60The characteristic gamma-ray peak energy of Co is 1173 keV or 1332 keV. In this invention, during the homogeneity test, 7-15 (or 8-12, or even 9-11, specifically 10) granular radioactive rice standard materials already packed in a sample box can be selected as samples. The specific activity of each sample is measured repeatedly 2-5 times (or 2-4 times, or even 2-3 times, specifically 2 or 3 times). A one-way ANOVA method is used to compare the variances between groups and within groups to determine whether there is a statistically significant difference between the measured values ​​of each group. F =2.695, P =0.069>0.05, then it is considered that in α At the 0.05 level, there is no significant difference in the specific activity of radionuclides among different samples, and the sample homogeneity of the granular radioactive rice standard material meets the requirements. In this invention, the stability test method may include the following steps: The granular radioactive rice standard material is placed in a sample box and stored in a cool, ventilated location for 1-12 months. It is taken out and tested once each month from the 1st to the 12th month, and the radioactive nuclide activity concentration is measured using the same stable high-purity germanium gamma spectrometer. After the measurement results are decay-corrected to the same reference time, a linear regression method is used to evaluate the trend of activity concentration change over time. The slope and standard deviation of the linear fitting equation are calculated using equations 2-4, and the slope is evaluated to determine if there is a significant difference compared to 0. If the difference is not statistically significant, the granular radioactive rice standard material meets the stability requirements under the corresponding storage conditions.

[0042] ; in, X For time, Y for X The activity concentration of radionuclides measured over time. b 1 For regression coefficients, s The standard deviation of each point in the straight line. S(b 1 ) for b 1 The standard deviation.

[0043] In this invention, the determination of radionuclide activity concentration may include: randomly selecting 2-5 (or 2-4, specifically 3) granular radioactive rice standard materials and 1-3 (or 1-2, specifically 2) blank samples (i.e., dried rice samples), placing them separately in a sample box, and then determining the radionuclide activity concentration. In this invention, the granular radioactive rice standard materials and blank samples can be provided to various laboratories for measurement. In this invention, the measuring instrument for determining the radionuclide activity concentration can be a high-purity germanium gamma spectrometer. In this invention, the determination of radionuclide activity concentration can be performed using destructive or non-destructive measurement methods. In this invention, during the determination of radionuclide activity concentration, the detection efficiency can be obtained through a radionuclide standard solution, or by using the LabSOCS passive efficiency calibration method, or by calculating the detector model using Monte Carlo software such as EGS4, MCNP, or Geant4. Based on the obtained radionuclide activity concentration results, the recommended value and uncertainty of granular radioactive rice standard material can be determined by using the power-moderated mean method (PMM), arithmetic mean method, uncertainty-weighted average method, median method, robust average method, or other methods applicable to standard sample value determination.

[0044] In this invention, the sample boxes used for uniformity testing, stability testing, and radionuclide activity concentration determination can include sample boxes with known geometric dimensions suitable for gamma-ray spectroscopy measurements, such as the 7570 type cylindrical sample box or the 7535 type cylindrical sample box. This invention can select the appropriate sample box based on the minimum sampling amount and the actual application scenario. When using different sample boxes, the detection efficiency should be re-determined or efficiency correction should be performed based on the corresponding geometric dimensions and filling height.

[0045] The present invention also provides a granular radioactive rice standard material prepared by the preparation method described in the above technical solution.

[0046] This invention also provides the application of the granular radioactive rice standard material described in the above technical solution in the detection of radionuclides in rice; the characteristic gamma-ray energy of the radionuclides is ≥500 keV, and may specifically include... 137 Cs、 134 Cs or 60 Co.

[0047] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0048] In the following examples, the water is ultrapure water.

[0049] Example 1 according to Figure 1 The flowchart shown illustrates the preparation of granular radioactive rice standard material.

[0050] Step 1: Rice pre-drying treatment. The specific steps are as follows: Place the rice sample (the rice to be spiked) in a forced-air drying device and dry it at 40℃ until the water loss rate is low (0.07g / h, about 48h) to obtain a dried rice sample.

[0051] Step 2: Preparation of the spiking solution: [The text abruptly ends here, likely due to an incomplete sentence 137 Cs radioactive standard solution, non-radioactive cesium carrier ( 133 Cs), nitric acid, and solvent are mixed thoroughly to obtain a spiked solution. The spiked solution contains... 137 The activity of Cs is 4000 Bq, the concentration of the non-radioactive cesium carrier is 10 μg / g, and the concentration of nitric acid is 0.1 mol / L. The solvent is water or methanol.

[0052] Step 3: Select the spiking method based on the sample preparation volume.

[0053] Step 3A: Immersion Spiking of Large Batch of Whole-Bag Samples: When preparing large batches of whole-bag rice samples ranging from kilograms to tens of kilograms, an immersion spiking method combined with low-temperature drying using forced air is employed. The specific procedure is as follows: The dried rice sample is completely immersed in the spiking solution (solvent is water), allowed to stand for 1 hour, and then dried at 40°C using forced air for 48 hours to obtain the dried sample. 137 Cs granular rice. The mass ratio of the spiked solution to the dried rice sample was 1:1.

[0054] Step 3B: Spiking of small-mass samples by rotary evaporation: When preparing small-mass rice samples, the rotary evaporation method is used for spiking. The specific procedure is as follows: The dried rice sample and the spiking solution (solvent: methanol) are mixed and evaporated at room temperature and a rotation speed of 50 r / min for 1 hour. Then, the sample is dried by rotary evaporation at 40℃, 50 r / min, and -0.085 MPa (until it is loose or not adherent to the wall), resulting in a dried sample. 137 Cs granular rice. The mass ratio of the spiked solution to the rice sample was 1:1.

[0055] Step 4: Sterilization irradiation treatment, the specific steps are as follows: using... 60 Coγ-ray source for drying 137 Cs granular rice was sterilized by irradiation with a total irradiation dose of 17-25 kGy to obtain granular radioactive rice standard material.

[0056] Step 5: Uniformity Test. The granular radioactive rice standard material was placed into a 7570 cylindrical marinade cup and measured using a traceable high-purity germanium gamma spectrometer.137 The net peak area at the characteristic gamma-ray peak with Cs energy of 661.66 keV was used to calculate the granular radioactive rice standard material. 137 Cs activity concentration, 137 The cumulative net count at the characteristic gamma-ray peak of Cs with energy 661.66 keV is not less than 10,000. The activity concentration calculation formula is shown in Equation 1: ; in: C A,i For the first i The activity concentration of each sample, in becquerels per kilogram (Bq / kg). e(E) The detection efficiency is 661.66 keV γ-rays; N s Count the net area of ​​the total energy peaks measured for standard substances; T s The measurement time for rice is in seconds (s). N b Count the net area of ​​the background peak; T b The baseline measurement is live time, measured in seconds (s). P The branching ratio of gamma-ray emission at the corresponding energy; m The unit for measuring the mass of a standard substance is kilogram (kg). l The decay constant of a radionuclide is expressed in seconds (s). -1 ); Δt The interval between the reference time and the start time of measurement for granular radioactive rice standard material is expressed in seconds (s).

[0057] Ten granular radioactive rice standard materials pre-packed in a 7570 sample box were selected as samples. Each sample was measured twice. One-way ANOVA was used to compare the between-group and within-group variances to determine whether there were statistically significant differences between the measured values ​​of each group. The results are shown in Table 1. F =2.695, P =0.069>0.05, then it is considered that in α At the 0.05 level, the differences between different samples 137 There was no significant difference in Cs specific activity, and the sample uniformity of the granular radioactive rice standard material prepared by this invention met the requirements.

[0058] Table 1. Results of homogeneity test of granular radioactive rice standard material

[0059] Step 6: Stability Test. Through stability testing, the granular radioactive rice standard material...137 The characteristics of Cs activity concentration changes over time were studied to determine suitable storage and transportation conditions for granular radioactive rice standard materials. The granular radioactive rice standard materials were placed in 7570 cylindrical marinade cups and stored in a cool, ventilated location for 12 months. They were tested monthly using the same stable high-purity germanium gamma spectrometer. 137 Cs activity concentration. After the measurement results were decay-corrected to the same reference time, the trend of activity concentration over time was evaluated using linear regression. The slope and standard deviation of the linear fitting equations were calculated using Equations 2-4, and the difference between the slope and 0 was assessed. If the difference was not statistically significant, the test results indicate that the granular radioactive rice standard material prepared in this invention has good stability under the corresponding storage conditions.

[0060] ; in, X For time, Y for X Measured over time 137 Cs activity concentration, b 1 is the regression coefficient. s The standard deviation of each point in the straight line. S ( b 1) For b The standard deviation of 1.

[0061] Step 7: In granular radioactive rice standard material 137 Cs activity concentration determination. This was achieved through collaboration with multiple laboratories to determine the concentration of Cs in granular rice standard materials. 137 Cs activity concentration. Three samples and two blank samples were randomly selected from all samples and provided to each laboratory for measurement. The measuring instrument was a high-purity germanium gamma spectrometer. Measurements could be performed using either destructive or non-destructive methods. Detection efficiency can be determined by... 137 The Cs standard solution was used for experimental calibration, or the LabSOCS passive efficiency calibration method can be used, or the detector model can be built using Monte Carlo software such as EGS4, MCNP, and Geant4 for calculation. Based on the obtained... 137 The Cs activity concentration results were used to determine the recommended value and uncertainty of the granular radioactive rice standard material using the power-moderated mean method (PMM).

[0062] Step 8: Vacuum sealing. The granular radioactive rice standard material after being calibrated is placed into a polyethylene bag and then placed into a rice brick mold for shaping, followed by vacuum sealing.

[0063] Comparative Example 1 10 kg of rice dried at 40℃ for 48 h was soaked in 10 kg of spiked solution (prepared according to Example 1) for 1 h. After soaking, the rice was spread evenly on a tray and placed in a high and low temperature humidity test chamber (temperature 40℃, relative humidity 5%) for drying for 48 h. The resulting radioactive rice sample was divided into 4 equal portions and added to 10 kg of non-radioactive rice sample. The mixture was then carried out in an all-around planetary ball mill for a total mixing time of 140 h for each portion. After mixing, the sample was dispensed into 10 N-type Marin cups and measured using a BE5030 wide-energy HPGeγ spectrometer. Each sample was measured twice. The results showed that the differences between groups were statistically significant. F =7.855, P =0.002), indicating that in α At the 0.05 level, the differences between different samples 137 The difference in Cs activity concentration was statistically significant, but the uniformity requirement was not met.

[0064] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a granular radioactive rice standard material, comprising the following steps: The rice sample was first dried to obtain a dried rice sample; The dried rice sample was spiked with a spiking solution to obtain granular radioactive rice standard material; When the mass of the rice sample is ≥1kg, the radionuclide is added after soaking and then drying. When the mass of the rice sample is less than 1 kg, the radionuclide is added by rotary evaporation soaking and mixing followed by rotary evaporation drying; The spiking solution comprises: a radionuclide, a non-radioactive nuclide carrier, an acid, and a solvent; the radionuclide has a characteristic gamma-ray energy ≥ 500 keV; The temperatures of the first drying, the second drying, and the rotary evaporation drying are independently ≤50°C.

2. The preparation method according to claim 1, characterized in that, The concentration of the non-radioactive nuclide carrier in the spiking solution is 5~20 μg / g, and the concentration of acid is 0.05~0.2 mol / L.

3. The preparation method according to claim 1 or 2, characterized in that, The radionuclides include 137 Cs、 134 Cs or 60 Co; The non-radioactive nuclide carrier includes 133 Cs or 59 Co.

4. The preparation method according to claim 1 or 2, characterized in that, When the mass of the rice sample is ≥1kg, the solvent is water; When the mass of the rice sample is less than 1 kg, the solvent includes one or more of methanol, ethanol, and dimethyl ether.

5. The preparation method according to claim 1 or 2, characterized in that, The soaking time is 1 to 4 hours.

6. The preparation method according to claim 1 or 2, characterized in that, The mass ratio of the dried rice sample to the spiked solution was 1:1~3; The time for rotary evaporation soaking and mixing is 1 to 4 hours.

7. The preparation method according to claim 1, characterized in that, The rotary evaporator is operated at a speed of 30-80 r / min, a pressure of -0.085--0.095 MPa, and a temperature of 35-50 °C.

8. The preparation method according to claim 1, characterized in that, After the radionuclide is spiked, the process also includes testing the uniformity, stability, and activity concentration of the rice sample after the radionuclide is spiked.

9. The granular radioactive rice standard material prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the granular radioactive rice standard material according to claim 9 in the detection of radioactive nuclides in rice; wherein the characteristic gamma ray energy of the radioactive nuclide is ≥500keV.

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