Device and method for accurately measuring activity of radioactive body sources

Abstract

The present invention discloses a device and method for accurately measuring the activity of a radioactive body source, aiming to address the technical problem of high uncertainty in existing methods for measuring the activity of radioactive body sources. Specifically, the device and method comprise a first detector, a radioactive body source, a second detector, and a radioactive standard surface source. The radioactive body source contains radioactive nuclides and is a centrally symmetrical structure with two mutually symmetrical and parallel symmetry planes on its left and right sides, respectively. The first and second detectors are disposed on the left and right sides of the radioactive body source, respectively. The central axes of the first and second detectors lie on the same straight line as the line connecting the midpoints of the two symmetry planes of the radioactive body source. The distance between the first detector and the radioactive body source and the distance between the second detector and the radioactive body source are both L. The radioactive standard surface source is placed on the left or right side of the radioactive body source during measurement to calibrate the absorption coefficient μ of the radioactive body source.

Description

Technical Field

[0001] The present invention relates to a device for measuring body source radioactivity, and in particular to a device and method for accurately measuring the activity of a radioactive body source. Background Art

[0002] Radioactivity is a key physical quantity in radioactivity measurement. In many scenarios, the measurement object is a volume source of a certain thickness, such as filter media, soil, and rock samples used in environmental sampling. During measurement, these volume sources absorb gamma rays emitted by the contained radioactive source, and the absorption rate varies with the thickness of the medium. Furthermore, the uniformity of the distribution of radioactive material within the volume source is a key factor influencing measurement accuracy. Existing research on radioactive volume source measurement technology has primarily focused on two aspects: how to accurately calibrate efficiency and how to prepare uniform volume source samples. Patent document No. 201410264382.9, entitled "Method and Apparatus for Simulating Detection Efficiency of Calibrated Detectors Using Virtual Sources," discloses a solution that uses virtual source equivalence technology to equate the efficiency of a volume source to that of a point or area source. This technique, which replaces measured efficiency with simulated efficiency, is often used in applications with low accuracy requirements, but is generally not feasible for high-precision measurement applications. In 2019, Yao Jianfeng published a master's thesis at Chengdu University of Technology titled "Study on Volume Source Efficiency Calibration and Rapid Pollutant Detection Methods." He also described using a virtual point source to simulate the volume source efficiency. This work, verified with a standard source, showed a -5.36% deviation from the measured value in the gamma ray energy range of 200keV to 1500keV. Above 1500keV, the deviation reached a staggering -21.21%. This simulation method is not very accurate and has significant limitations. In addition, for bulk sources of multiple matrices, it is impossible to make a standard bulk source for each matrix. The usual practice is to use a standard bulk source and perform an efficiency transition by measuring the ratio of the absorption coefficients of the standard bulk source and the bulk source to the same gamma ray. This further introduces a transition error (Zhang Xiaolin et al., "γ Energy Spectrum Analysis of Natural Radioactivity in Building Materials", Nuclear Electronics and Detection Technology, 2005, Vol. 25, No. 3; Masayasu Noguchi, et al. Correction methods of γ-ray self-absorption in bulk sample. Radioisotopes, 2000, 49(4): 189). Even so, there is still the problem of uneven distribution of radioactive nuclides in each bulk source. So far, the evaluation technology of this uneven effect is not mature enough; therefore, the results obtained by the existing radioactive bulk source activity measurement method still have the problem of high uncertainty. Summary of the Invention

[0003] The purpose of the present invention is to provide a device and method for accurately measuring the activity of a radioactive body source, so as to solve the technical problem of high uncertainty in existing methods for measuring the activity of radioactive body sources.

[0004] In order to achieve the above object, the present invention provides a device for accurately measuring the activity of a radioactive body source, which is special in that it includes a first detector, a radioactive body source, a second detector and a radioactive standard surface source;

[0005] The radioactive body source contains radioactive nuclides, and the radioactive body source as a whole is a centrally symmetrical structure, with two mutually symmetrical and parallel symmetry planes on its left and right sides respectively;

[0006] The first detector and the second detector are respectively arranged on the left and right sides of the radioactive body source; the central axes of the first detector and the second detector and the line connecting the midpoints of the two symmetry planes of the radioactive body source are located on the same straight line; the distance between the first detector and the radioactive body source and the distance between the second detector and the radioactive body source are both L;

[0007] The radioactive standard surface source is placed on the left or right side of the radioactive body source during measurement to calibrate the absorption coefficient μ of the radioactive body source.

[0008] Furthermore, in order to ensure the accuracy of measuring the absorption coefficient μ of the radioactive body source, the distance between the two symmetry planes of the radioactive body source is d; L / d≥4.5; the cross-section of the radioactive standard surface source along the perpendicular line of the central axis of the first detector matches the size of the symmetry plane of the radioactive body source.

[0009] Furthermore, the radioactive body source is a cylindrical structure as a whole, and its two ends are two symmetric planes of the radioactive body source.

[0010] Furthermore, the radioactive body source is a rectangular parallelepiped structure as a whole, and the end faces located at both ends of its long sides are two symmetric planes of the radioactive body source.

[0011] Furthermore, the radioactive body source is a cube structure as a whole, and any corresponding two end faces thereof are two symmetric faces of the radioactive body source.

[0012] Furthermore, the radioactive body source further includes a container located outside the radioactive body source and having a shape adapted thereto, for containing the radioactive body source, so that the radioactive body source as a whole has a centrally symmetrical structure.

[0013] Furthermore, the first detector and the second detector are both coaxial high-purity germanium detectors, and their outer diameters are adapted to the symmetry plane of the radioactive standard surface source.

[0014] The present invention also provides a method for accurately measuring the activity of a radioactive body source, which is based on the above-mentioned device for accurately measuring the activity of a radioactive body source and has the following characteristics:

[0015] Step 1: At time t, the characteristic gamma rays in the radioactive body source are detected by the first detector and the second detector to obtain the count rate n of the first detector. At and the second detector count rate n Bt ;

[0016] Step 2: Place the radioactive standard surface source on the left or right side of the radioactive body source to calibrate the dielectric absorption coefficient μ of the radioactive body source to the characteristic gamma rays;

[0017] Step 3: Remove the radioactive body source and place a radioactive standard surface source in the middle between the first detector and the second detector to calibrate the detection efficiency ε1 of the first detector and the detection efficiency ε2 of the second detector;

[0018] Step 4: Calculate the activity A of the radioactive nuclide in the radioactive source N :

[0019]

[0020] Among them, P γ is the characteristic γ emission probability, and e is a natural constant.

[0021] Beneficial effects of the present invention:

[0022] 1. The present invention is based on the basic principle that the sum of the distances traveled by gamma rays in a body source when emitted in two opposite directions is only related to the overall thickness of the body source. The activity of the radioactive body source is solved by multiplying the energy spectrum peak count rates measured by two detectors, thereby converting local self-absorption with uncertain attenuation thickness into overall body self-absorption with a determined attenuation thickness. The self-absorption coefficient can be accurately measured directly by experimental methods, thereby improving the reliability of the activity measurement.

[0023] 2. The present invention converts the problem of accurate calibration of bulk source efficiency during single-detector measurement into a dual-detector efficiency product calibration problem, significantly reducing measurement uncertainty. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the structure of an embodiment of a device for accurately measuring the activity of a radioactive body source according to the present invention (radioactive standard surface source is not shown);

[0025] Figure 2 This is a schematic structural diagram of a method for accurately measuring the activity of a radioactive body source in step 2 of an embodiment of the present invention, in which a radioactive standard surface source is placed on the right side of the radioactive body source;

[0026] Figure 3 This is a structural diagram of the step 3 of an embodiment of a method for accurately measuring the activity of a radioactive body source of the present invention, in which the radioactive body source is removed and a radioactive standard surface source is placed in the middle of the first detector and the second detector.

[0027] Figure Number:

[0028] 1-first detector, 2-second detector, 3-radioactive body source, 4-radioactive nuclide, 5-radioactive standard surface source. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0030] An embodiment of the present invention provides a device for accurately measuring the activity of a radioactive body source, such as Figure 1 As shown, the measuring device includes a first detector 1 , a second detector 2 , a radioactive body source 3 and a radioactive standard surface source 5 , and is used to measure the activity of the radioactive body source 3 .

[0031] The radioactive source 3 to be tested has a centrally symmetrical structure as a whole, with two mutually symmetrical and parallel symmetry planes on its left and right sides respectively. Specifically, it can be a cylindrical structure, a rectangular parallelepiped structure, or a cube structure. If it is a cylindrical structure, the two ends of the cylindrical structure are the two symmetry planes of the radioactive source 3 respectively. If it is a rectangular parallelepiped structure, the two end faces located at the two ends of the long side of the rectangular parallelepiped structure are the two symmetry planes of the radioactive source 3 respectively. If it is a cube structure, any two corresponding faces on the cube structure can serve as the two symmetry planes of the radioactive source 3. In order to make the radioactive source 3 form a centrally symmetrical structure as a whole, two methods can generally be used: the first method is generally applicable to granular radioactive sources 3, which can be molded into a cylindrical structure, a rectangular parallelepiped structure, or a cube structure by glue; the second method is applicable to both granular radioactive sources 3 and liquid radioactive sources 3, and specifically uses a container with a centrally symmetrical structure and fills it with the radioactive source 3, so that the overall structure of the radioactive source 3 becomes a centrally symmetrical structure. The radioactive source 3 in this embodiment is a cylindrical structure, and the distance between its two symmetry planes (ie, thickness) is d.

[0032] The first and second detectors 1 and 2 are coaxial high-purity germanium detectors with outer diameters larger than the diameter of the cylindrical radioactive source 3. The first and second detectors 1 and 2 are positioned on the left and right sides of the radioactive source 3, respectively. The detection surfaces of the first and second detectors 1 and 2 are opposite and parallel to the end faces of the radioactive source 3. The central axes of the first and second detectors 1 and 2 are aligned with the central axis of the cylindrical radioactive source 3, i.e., they are coaxially positioned.

[0033] The radioactive standard surface source 5 is placed on the left or right side of the radioactive body source 3 and is close to the radioactive body source 3 to calibrate the absorption coefficient μ of the radioactive body source 3. In this embodiment, the diameter of the calibrated radioactive body source 3 is consistent with the outer diameter of the first detector 1 and the second detector 2. In other embodiments, the radioactive standard surface source 5 can also be of the same size as the symmetry plane of the radioactive body source 3.

[0034] The steps for accurately measuring the activity of the radionuclide 4 in the radioactive source 3 are as follows:

[0035] Step 1: Figure 1 As shown, the first detector 1 and the second detector 2 are placed on the left and right sides of the radioactive source 3 in the above manner. The distance between the first detector 1 and the second detector 2 is 30 cm. The distance between the detection surface of the first detector 1 and the left end face of the radioactive source 3 is L, and the distance between the detection surface of the second detector 2 and the right end face of the radioactive source 3 is also L. The thickness of the radioactive source 3 is d = 2 cm, and both satisfy L / d ≥ 4.5. At time t, the characteristic gamma rays in the radioactive source 3 are detected by the first detector 1 and the second detector 2 respectively, and the count rate n of the first detector 1 is obtained. At and the second detector 2 count rate n Bt .

[0036] Step 2: Figure 2 As shown, the radioactive standard surface source 5 is placed on the right side of the radioactive body source 3 to calibrate the dielectric absorption coefficient μ of the radioactive body source 3 to the characteristic gamma rays;

[0037] Step 3: Figure 3 As shown, the radioactive body source 3 is removed, and the radioactive standard surface source 5 is placed in the middle position between the first detector 1 and the second detector 2 to calibrate the detection efficiency ε1 of the first detector 1 and the detection efficiency ε2 of the second detector 2;

[0038] Step 4: Calculate the activity A of the radionuclide 4 in the radioactive source 3 N ;

[0039] Since the measurement count rate of the first detector 1 at time t is The measured count rate of the second detector 2 at time t Multiplying the two count rates gives:

[0040]

[0041] Transforming formula (1) can obtain the activity A of radionuclide 4 N for:

[0042]

[0043] Among them, P γ is the characteristic γ emission probability, d1 is the distance from the radionuclide 4 to the left symmetry plane of the radioactive body source 3, d2 is the distance from the radionuclide 4 to the right symmetry plane of the radioactive body source 3, and e is a natural constant.

[0044] Based on the fundamental principle that the sum of the distances traveled by gamma rays in a radioactive source when emitted in two opposite directions is related only to the overall thickness of the source, this method solves for the activity of the radioactive source by multiplying the peak count rates of the energy spectrum measured by two detectors. A corresponding measurement device is designed based on this method. This method transforms local self-absorption, where the attenuation thickness is uncertain, into self-absorption of the entire radioactive source, where the attenuation thickness is determined. This method also transforms the difficulty of accurately calibrating the source efficiency when measuring with a single detector into a dual-detector efficiency product calibration problem, significantly reducing measurement uncertainty.

[0045] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present invention shall be covered by the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A method for accurately measuring the activity of a radioactive body source, characterized by: A radioactive body source activity precision measuring device is used, the precision measuring device comprising a first detector (1), a second detector (2), a radioactive body source (3) and a radioactive standard surface source (5); The radioactive body source (3) contains a radioactive nuclide (4). The radioactive body source (3) is a centrally symmetrical structure as a whole, and two mutually symmetrical and parallel symmetry planes are respectively provided on its left and right sides. The first detector (1) and the second detector (2) are respectively arranged on the left and right sides of the radioactive body source (3); the central axes of the first detector (1) and the second detector (2) and the connecting line of the midpoints of the two symmetry planes of the radioactive body source (3) are located on the same straight line; the distance between the first detector (1) and the radioactive body source (3) and the distance between the second detector (2) and the radioactive body source (3) are both L; The radioactive standard surface source (5) is placed on the left or right side of the radioactive body source (3) during measurement to calibrate the absorption coefficient μ of the radioactive body source (3); The distance between the two symmetric planes of the radioactive body source (3) is d; L / d≥4.5; the cross section of the radioactive standard surface source (5) along the perpendicular line of the central axis of the first detector (1) matches the size of the symmetric plane of the radioactive body source (3); The precise measurement method comprises the following steps: Step 1: At time t, the characteristic gamma rays in the radioactive source (3) are detected by the first detector (1) and the second detector (2), and the counting rate n of the first detector (1) is obtained. At and the second detector (2) count rate n Bt ; Step 2: placing the radioactive standard surface source (5) on the left or right side of the radioactive body source (3) to calibrate the dielectric absorption coefficient μ of the radioactive body source (3) to the characteristic gamma rays; Step 3, removing the radioactive body source (3), and placing the radioactive standard surface source (5) in the middle between the first detector (1) and the second detector (2) to calibrate the detection efficiency ε1 of the first detector (1) and the detection efficiency ε2 of the second detector (2); Step 4: Calculate the activity A of the radionuclide (4) in the radioactive source (3) N : Among them, P γ is the characteristic γ emission probability, and e is a natural constant.

2. The method for accurately measuring the activity of a radioactive body source according to claim 1, wherein: The radioactive body source (3) is a cylindrical structure as a whole, and its two ends are respectively two symmetrical planes of the radioactive body source (3).

3. The method for accurately measuring the activity of a radioactive source according to claim 1, wherein: The radioactive body source (3) is a rectangular parallelepiped structure as a whole, and the end faces located at both ends of its long sides are respectively two symmetrical faces of the radioactive body source (3).

4. The method for accurately measuring the activity of a radioactive body source according to claim 1, wherein: The radioactive body source (3) is a cubic structure as a whole, and any two corresponding end faces thereof are two symmetrical faces of the radioactive body source (3).

5. The method for accurately measuring the activity of a radioactive body source according to claim 2, 3 or 4, characterized in that: The radioactive body source (3) further comprises a container located outside the radioactive body source and having a shape adapted thereto, for containing the radioactive body source (3), so that the radioactive body source (3) as a whole has a centrally symmetrical structure.

6. The method for accurately measuring the activity of a radioactive body source according to claim 5, wherein: The first detector (1) and the second detector (2) are both coaxial high-purity germanium detectors; the outer diameters of the detectors are adapted to the symmetry plane of the radioactive body source (3).

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