Single-nuclide gamma radioactive sample activity measuring system and measuring method

Abstract

The invention relates to a single-nuclide gamma radioactive sample activity measuring system and method, and the system comprises a shielding box body which is located outside a measuring cavity; the measuring cavity comprises a cube detection area formed by six flat-plate-shaped detectors; the height-adjustable bracket is arranged on the flat-plate-shaped detector at the bottom during use and is used for placing a sample to be detected; and the weight sensor is arranged in the shielding box body and is supported at the bottom of the measuring cavity. The measurement method comprises the following steps: calculating the relative deviation of the detection efficiency of each point location and a central point location in a detection area by adopting a Monte Carlo simulation method, and finding a sensitive area; simulating and calculating self-absorption correction factors of different characteristic samples in the sensitive area, and constructing a database; and experimental measurement: placing a sample to be measured in the sensitive area for measurement, automatically weighing, calling the database through sample parameters, and automatically calculating to obtain a measurement result. The method has the advantages of low requirement on sample positioning precision, simplicity and convenience in operation, short measurement time and high efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of single-nuclide radioactivity detection, and in particular to a single-nuclide gamma radioactivity sample activity measurement system and a measurement method. BACKGROUND

[0002] Single-nuclide gamma radioactivity sample activity measurement is commonly applied to the measurement of total gamma radioactivity levels of liquid samples and solid samples in the field of environmental monitoring, as well as to the evaluation of the radioactivity levels of building materials in the construction industry to ensure the safety of the building environment. At present, the commonly used equipment for single-nuclide gamma radioactivity sample activity measurement is a low-background multi-channel gamma spectrometer, which is mainly used for the measurement and analysis of the gamma radioactivity content in environmental samples such as building materials, soil, and water. Such equipment generally includes a gamma spectrometer (a scintillator gamma spectrometer or a high-purity germanium gamma spectrometer) and a low-background measurement chamber. The measurement chamber is generally no larger than Ф40 cm × 40 cm and is composed of a lead main body, a tin gasket, a copper plate lining, and a carbon steel shell. The gamma spectrometer is usually a cylindrical sodium iodide detector of about 3 inches or a high-purity germanium detector with a relative detection efficiency of more than 30%. The placement of the measured single-nuclide gamma radioactivity sample has strict requirements. The sample needs to be placed at the efficiency calibration reference point in the measurement chamber, generally coaxially close to the surface of the probe, to ensure the accuracy of the calculation of the detection efficiency of the measured sample. Single-nuclide gamma radioactivity samples have different shapes, including point-shaped forms such as point-shaped radioactive sources and bulk-shaped forms such as water or soil radioactive sources or environmental samples. Before testing, the sample to be measured needs to be pre-made into a state as close as possible to the material, density, and size of the efficiency calibration reference material. One sample is measured at a time, and each sample measurement time can reach several hours. The sample needs to be weighed before measurement, and the weight needs to be input into the upper computer to calculate and give the activity concentration level of the measured sample. Through this set of equipment, the collection, storage, processing, and spectrum analysis of the gamma spectrum of the measured sample can be realized, and finally the qualitative and quantitative analysis of the radioactive nuclides in the measured sample can be realized.

[0003] However, the current measurement device and method have the following problems: first, the sample measurement time is relatively long, especially for environmental level samples, which generally requires several hours of measurement time, and the measurement efficiency is low. Second, the sample positioning accuracy requirement is high. The actual placement position of the measured sample generally deviates from the placement position of the efficiency calibration source, which affects the accuracy of the sample measurement result. Third, the weighing and measurement are two separate steps, and the degree of automation is low. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides a single-nuclide gamma radioactivity sample activity measurement system and a measurement method, aiming to reduce the requirement for sample positioning accuracy and improve the simplicity and efficiency of measurement operation.

[0005] The technical solution adopted by the present application is as follows: The application provides a single-nuclide gamma radioactivity sample activity measurement system, comprising: A shielding box is located outside the measurement cavity and comprises an openable and closable door. The measurement cavity comprises a cubic detection area surrounded by six flat plate-shaped detectors, the flat plate-shaped detectors are flat plate-shaped, and the six flat plate-shaped detectors are parallel to each sides of the cubic detection area, respectively. A support is height-adjustable and is placed on the flat plate-shaped detector at the bottom during use, and is used for placing a sample to be measured. A weight sensor is arranged in the shielding box and is supported on the bottom of the measurement cavity, and is used for automatically weighing the sample to be measured.

[0006] Further technical solutions are as follows: Five of the flat plate-shaped detectors constitute a cubic detection area with one side open, and the remaining one flat plate-shaped detector is arranged on the inner wall of the door and opens or closes the detection area with the opening and closing of the door.

[0007] The flat plate-shaped detector is one of a plastic scintillator detector, a sodium iodide detector and a lanthanum bromide detector.

[0008] The shielding box has a cubic structure.

[0009] The application further provides a measurement method of the single-nuclide gamma radioactivity sample activity measurement system, comprising: Simulation calculation: A Monte Carlo simulation method is used to model the measurement cavity, a plurality of points are arranged in the detection area, and the detection efficiency of gamma rays with different energies at each point is calculated, respectively; the plurality of points are symmetrically distributed with the center point of the detection area as the center; The relative deviation of the detection efficiency at each point in the detection area and the center point is calculated, respectively; A sensitive area is divided in the detection area, so that the relative deviation of the detection efficiency at each point in the sensitive area and the detection efficiency at the center point of the detection area does not exceed a set threshold; Different characteristic samples are arranged in the sensitive area, the corresponding self-absorption correction factors are simulated and calculated, the corresponding relationship between the characteristic parameters of the samples and the self-absorption correction factors is established, and a database is constructed; Experimental measurement: The characteristic parameters of the sample to be measured are obtained; The sample to be measured is placed in the detection area, the sample to be measured is adjusted by the support so that the sample to be measured is entirely in the sensitive area and the center of the sample to be measured coincides with the center of the sensitive area, and the sample to be measured is measured; The measuring system automatically weighs and records the weight of the measured sample, calls the corresponding self-absorption correction factor in the database based on the weight and the characteristic parameter, combines the count of each flat plate-shaped detector, and calculates the activity measurement result of the radionuclide contained in the measured sample.

[0010] Further technical solutions are: The Monte Carlo simulation method is used to model the measuring cavity, a plurality of point positions are arranged in the detection area, and the detection efficiency of different energy gamma rays at each point position is calculated, including: The geometric center of the detection area is taken as the origin of the three-dimensional coordinate axis, and the detection area is equally divided into a plurality of unit regions by using the XY plane, the XZ plane and the YZ plane, the number and distribution form of point positions in each unit region are the same; The detection efficiency of each point position in one of the unit regions is calculated, the calculation result is assigned to other unit regions according to the symmetry of space, and then the detection efficiency of all point positions in the whole detection area is obtained.

[0011] The detection area is equally divided into eight regions.

[0012] The characteristic parameters include sample size, shape, sample matrix material, matrix material density, nuclide distribution characteristics, nuclide type, and gamma ray energy.

[0013] The plurality of point positions are distributed from dense to sparse in the direction away from the center point of the detection area.

[0014] The gamma ray energy range is 59 keV to 3 MeV.

[0015] The beneficial effects of the present application are as follows: The measuring system of the present application has the advantages of short measuring time, low sample positioning accuracy requirement, simple operation and high automation degree, and has the following advantages: 1. The present application has the advantages of short measuring time and high detection efficiency.

[0016] The measuring system of the present application is provided with six flat plate-shaped detectors on the front, rear, left, right, top and bottom of the measuring cavity, which constitutes a cubic detection area, can greatly shorten the measuring time of the sample, and greatly increases the detection efficiency of the measuring system.

[0017] 2. The present application has the advantages of low sample positioning accuracy requirement and simple operation.

[0018] The application finds a sensitive area in the constructed cubic detection area through simulation calculation, and the detection efficiency of the spatial point source in the area is similar, and the influence difference of the self-absorption correction factor is negligible. Therefore, the operator only needs to place the measured sample in the area to complete the activity measurement, and compared with the traditional measurement that the sample must be coaxially arranged with the probe, the requirement for positioning accuracy of the sample placement position during activity measurement is reduced, and the operation is more simple and convenient.

[0019] 3. The application is based on simulation calculation, and a database based on the correlation between the sample characteristics and the self-absorption correction factor is constructed, so that the subsequent experimental measurement process can automatically call the database to complete the assignment of the self-absorption correction factor, and the calculation efficiency of the measurement system is improved.

[0020] 4. The sample weighing function is provided, and the self-absorption correction calculation efficiency of the sample is further improved.

[0021] The weight sensor is installed between the bottom flat plate-shaped detector and the shielding shell, the automatic weighing of the measured sample is realized, the matrix density is obtained based on the weighing result, and then the self-absorption correction calculation of the measurement result is automatically completed.

[0022] Other features and advantages of the application will be described in the subsequent description, or can be understood through the implementation of the application. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is a structural schematic diagram of the measurement system of the embodiment of the application.

[0024] Figure 2 It is a point distribution diagram in the detection area during simulation calculation of the embodiment of the application.

[0025] Figure 3 It is a relative deviation distribution of the detection efficiency of each point position and the center point position in the detection area under the simulation calculation of the embodiment of the application at the gamma ray energy of 59 keV.

[0026] Figure 4 It is a relative deviation distribution of the detection efficiency of each point position and the center point position in the detection area under the simulation calculation of the embodiment of the application at the gamma ray energy of 662 keV.

[0027] Figure 5 It is a relative deviation distribution of the detection efficiency of each point position and the center point position in the detection area under the simulation calculation of the embodiment of the application at the gamma ray energy of 1332 keV.

[0028] Figure 6 It is a position point distribution diagram for the self-absorption correction simulation calculation of the embodiment of the application.

[0029] Figure 7 It is a schematic diagram of the experimental measurement process of the embodiment of the application.

[0030] In the figure: 1, flat panel detector; 2, shielded box; 3, equipment shell; 4, support; 5, weight sensor; 6, equipment support. DETAILED DESCRIPTION

[0031] The specific embodiments of the present application are described below with reference to the accompanying drawings.

[0032] Example 1 Referring to Figure 1 The present embodiment provides a single-nuclide gamma radioactivity sample activity measurement system, comprising: a shielded box 2 located outside the measurement cavity, comprising a closable door; a measurement cavity comprising a cubic detection region composed of six flat panel detectors 1, each of which is parallel to a side of the cubic detection region; a support 4, which is adjustable in height and is placed on the bottom flat panel detector 1 when in use, for placing the sample to be measured; a weight sensor 5 arranged in the shielded box 2 and supported on the bottom of the measurement cavity.

[0033] Five of the flat panel detectors 1 form a cubic detection region with one side open, and the remaining flat panel detector 1 is arranged on the inner wall of the door, which opens or closes the detection region when the door is opened or closed.

[0034] As a preferred mode, the shielded box 2 is in a cubic structure, and the door is preferably opened or closed along its door axis from the front side; the five flat panel detectors 1 located at the back, left, right, top, and bottom are fixedly installed, and the flat panel detector 1 at the front side can be rotated along the door axis together with the door to open or close the measurement cavity, facilitating the sample to be measured to be placed into or removed from the front side.

[0035] As a specific embodiment, the six flat panel detectors 1 are respectively installed at the front, back, left, right, top, and bottom of the measurement cavity, and can be used to measure the gamma rays emitted by the radioactive sample. Each flat panel detector 1 is flat (i.e., the detector crystal structure is flat), and the size is preferably 40 cm × 40 cm × 5 cm, thereby constructing a closed detection region with a size of 40 cm × 40 cm × 40 cm covering a 4π angle range.

[0036] The flat panel detector 1 can be one of a plastic scintillator detector, a sodium iodide detector, and a lanthanum bromide detector. Preferably, a sodium iodide detector is used.

[0037] As a preferred mode, the support 4 is made of light material such as plastic to reduce the attenuation effect on the sample radioactive gamma rays, preferably the height is adjustable in the range of 10 cm to 30 cm. In use, it can be arranged at the center position of the bottom plate-shaped detector 1.

[0038] As a preferred mode, the shielding box 2 is composed of flat lead shielding plates, which cover the detector in all directions to build a low-background measurement environment and reduce the interference of the environmental background on the measurement results. Preferably, each lead shielding plate has a size of 50 cm x 50 cm x 5 cm, the main material is lead, and the outer layer is wrapped with an aluminum metal skin with a thickness of 2 mm.

[0039] As a preferred mode, the shielding box 2 is composed of flat lead shielding plates, which cover the detector in all directions to build a low-background measurement environment and reduce the interference of the environmental background on the measurement results. Preferably, each lead shielding plate has a size of 50 cm x 50 cm x 5 cm, the main material is lead, and the outer layer is wrapped with an aluminum metal skin with a thickness of 2 mm.

[0040] As a preferred mode, the weight sensor 5 has a scale size of 40 cm x 40 cm, a maximum weighing capacity of 50 kg, and a weighing accuracy of 0.1 g. It is preferably installed between the bottom plate-shaped detector 1 and the bottom lead shielding plate to realize automatic weighing of the measured sample.

[0041] As a specific embodiment, the measurement system further comprises a device support frame 6 for supporting the entire measurement device. The main material is carbon steel, and the outer surface is painted to prevent rust.

[0042] It can be understood that the above are all recommended design sizes, which can be adjusted according to actual use.

[0043] Example 2 The present embodiment provides a measurement method of a single-nuclide gamma radioactive sample activity measurement system based on example 1, comprising the following steps: S1. Simulation calculation: S11. The Monte Carlo simulation method is used to model the measurement cavity, a plurality of points are set in the detection area, and the detection efficiency of gamma rays of different energies at each point is calculated; the plurality of points are symmetrically distributed around the center point of the detection area.

[0044] As a preferred mode, the gamma ray energies calculated in this embodiment include 59 keV, 662 keV and 1332 keV.

[0045] As a preferred mode, since the center point of the detection area is away from each detector, the plurality of points are distributed from dense to sparse in the direction away from the center point of the detection area.

[0046] As a preferred mode, in order to improve the calculation efficiency, the detection efficiency of each point position is calculated in the following manner, including: S111. Taking the geometric center of the detection region as the origin O of the three-dimensional coordinate axis, the detection region is equally divided into several unit regions by using the XY plane, the XZ plane and the YZ plane, and preferably eight unit regions are set; the number and distribution form of point positions in each unit region are the same.

[0047] Wherein, the point position distribution refers to Figure 2 . Figure 2 Figure (a) in the middle is a structural schematic diagram of the detection region after being equally divided into eight regions. Figure 2 Figure (b) in the middle is Figure 2 Figure (a) in the middle is a point position distribution diagram on any XY plane, and each black solid circle represents a point position.

[0048] S112. The detection efficiency of each point position in one of the unit regions is calculated, and according to the symmetry of the space, the calculation result is assigned to other unit regions, and then the detection efficiency of all point positions in the entire detection region, i.e. the point source space detection efficiency, is obtained.

[0049] S12. The relative deviation of the detection efficiency of each point position in the detection region from the detection efficiency of the central point position is calculated.

[0050] For the measurement system of the present embodiment, the relative deviation of the detection efficiency simulation calculation result of each point position from the detection efficiency simulation calculation result of the central point position under the γ-ray energy of 59 keV, 662 keV and 1332 keV is shown in Figure 3 , Figure 4 , Figure 5 .

[0051] S13. A sensitive region is divided in the detection region, so that the relative deviation of the detection efficiency of each point position in the sensitive region from the detection efficiency of the central point position does not exceed a set threshold.

[0052] Figures 3 to 5 In the middle, (a) to (e) are the relative deviation distributions on the XY plane at Z=0 cm, Z=±4 cm, Z=±8 cm, Z=±13 cm and Z=±19 cm, respectively. The closed curve in the figure represents the "equal relative deviation line". Analysis of the calculation results of the relative deviation shows that there is a region in the detection region, so that the detection efficiency of each point position in the region is similar, the relative deviation of the detection efficiency simulation calculation result of each point position in the region from the detection efficiency simulation calculation result of the central point position is less than the set threshold of 5%, and the size of the region is about 15 cm × 15 cm × 15 cm. The present embodiment names it as the sensitive region.

[0053] S14. Setting samples with different features in the sensitive region, simulating the corresponding self-absorption correction factors, establishing the corresponding relationship between the feature parameters of the sample and the self-absorption correction factors, and constructing a database.

[0054] Wherein, the sample is completely placed in the sensitive region.

[0055] Wherein, the feature parameters preferably include sample size, shape, sample matrix material, matrix material density, nuclide distribution characteristics, nuclide species, and gamma ray energy, etc.

[0056] As a specific embodiment, the sample feature parameters are: the container size of the bulk sample is Ф7.5 cm × 7 cm, the top, bottom and wall thickness are all 0.25 cm, the container matrix material is ABS plastic (density is 1.1 g / cm 3 ), the sample matrix material includes water (density is 1.0 g / cm 3 ) and soil (density is 1.5 g / cm 3 ), the matrix and gamma nuclides are uniformly distributed in the sample container, and the gamma ray energy involved in the calculation includes 662 keV and 1332 keV.

[0057] As a specific embodiment, the sample position is preferably set at the center point A (O) of the sensitive region, i.e. the center point of the 15 cm × 15 cm × 15 cm cube.

[0058] In order to verify the influence of the sample placement position in the sensitive region on the calculation results, the following working conditions are further set for simulation calculation: As shown in Figure 6 , six additional position points are set: 2.5 cm (B1 point) and 5 cm (B2 point) away from the center point A (O) along the X axis, 2.5 cm (C1 point) and 5 cm (C2 point) away from the center point along the Y axis, and 2.5 cm (D1 point) and 5 cm (D2 point) away from the center point along the Z axis. For samples with gamma nuclides uniformly distributed in the sample, the measurement system response of the sample at each position point and the measurement system response of the corresponding position bare source (i.e. the point does not set sample container material and sample matrix material) are simulated and calculated, and the self-absorption correction factors of different position points are obtained, as shown in Table 1. For gamma nuclides with extreme point source distribution at the center of the sample, the self-absorption correction factors of different position points are calculated, as shown in Table 2.

[0059] From Table 1 and Table 2, for the sample with stable distribution of gamma radionuclide, in the sensitive region with similar detection efficiency at each point, the influence of sample measurement position on the measurement system response, self-absorption correction and activity measurement result can be reduced or even ignored. Moreover, the arrangement of the six scintillator detectors at the front, back, left, right, top and bottom positions greatly increases the detection efficiency of the measurement system, and can greatly shorten the measurement time of the sample.

[0060] Table 1 Self-absorption correction factor simulation calculation of different measurement points for the sample with uniform distribution of gamma radionuclide in the sample Table 2 Self-absorption correction factor simulation calculation of different measurement points for the sample with concentrated distribution of gamma radionuclide in the sample center S2. Experimental measurement, see Figure 7 , including the following flow: S21. Obtain the characteristic parameters of the sample to be measured.

[0061] S22. Open the door of the measurement cavity, place the sample to be measured in the detection area, adjust the support to make the sample to be measured entirely in the sensitive region, and preferably make the center of the sample to be measured coincide with the center of the sensitive region, then close the door of the measurement cavity, and open each flat panel detector to measure the sample to be measured.

[0062] Specifically, before the measurement starts, the type of the flat panel detector, the measurement time and other measurement parameters need to be set.

[0063] Specifically, for the measurement system using plastic scintillator detectors as flat panel detectors, only single gamma radionuclide samples with known nuclide species can be measured, and the nuclide species to be measured needs to be manually selected before the sample is measured. Moreover, since the energy resolution of the plastic scintillator detector is poor, it is generally unable to distinguish the characteristic information of the measured gamma radionuclide, and therefore the full spectrum efficiency is used as the detection efficiency of the measured gamma radionuclide in the simulation calculation. For the sodium iodide detector or lanthanum bromide detector with higher energy resolution, the nuclide identification and activity calculation functions can be automatically completed.

[0064] S23. The measurement system automatically weighs and records the weight of the sample to be measured through the weight sensor, calls the corresponding self-absorption correction factor in the database established in step S14 based on the weight and the characteristic parameters, and calculates the activity measurement result of the radionuclide contained in the sample to be measured by combining the counts of each flat panel detector, which includes the activity or activity concentration level of the radionuclide contained in the sample.

[0065] It can be understood that if it is necessary to add new sample size or sample material, the database is updated by repeating step S14.

[0066] Those skilled in the art can understand that the above only describes the preferred embodiments of the present application and is not used to limit the present application, and although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or make equivalent replacements to some technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A single isotope gamma radioactivity sample activity measurement system, characterized by, The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system.

2. The mono-isotope gamma radioactivity sample activity measurement system of claim 1, wherein, The application relates to a gamma-ray activity measurement system.

3. The mono-isotope gamma radioactivity sample activity measurement system of claim 1, wherein, The application relates to a gamma-ray activity measurement system.

4. The mono-isotope gamma radioactivity sample activity measurement system of claim 1, wherein, The application relates to a gamma-ray activity measurement system.

5. A measurement method using the single nuclide gamma radioactivity sample activity measurement system according to any one of claims 1 to 4, characterized by, The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system.

6. The measurement method according to claim 5, characterized in that, The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system.

7. The measuring method according to claim 6, characterized in that, The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. The application relates to a gamma-ray activity measurement system. 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The measurement method according to claim 5, characterized by, The characteristic parameters include sample size, shape, sample matrix material, matrix material density, nuclide distribution characteristics, nuclide type, and gamma ray energy.

9. The measurement method according to claim 5, characterized by, The several points are distributed from dense to sparse in a direction away from the center point of the detection area.

10. The measurement method according to claim 5, characterized by, The gamma ray energy ranges from 59 keV to 3 MeV.

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