A system and method for measuring contamination photons in a beta reference radiation field

Abstract

The present application relates to the field of beta reference radiation fields and provides a system and method for measuring contamination photons in a beta reference radiation field. The system comprises an energy spectrometer, a collimator, a beta ray absorber, a photon absorber, and a processing device. The energy spectrometer comprises a detector and a measuring device connected to the detector. The collimator has a through-hole through which both beta rays emitted by a radiation source and contamination photons can be emitted to the detector. The beta ray absorber is movably disposed on the collimator to block or open the through-hole and absorb beta rays. The photon absorber is movably disposed on the collimator to block or open the through-hole and absorb contamination photons and beta rays. The processing device establishes a Monte Carlo model of the detector and the beta ray absorber and calculates the actual fluence spectrum of the contamination photons using the Monte Carlo model. Finally, the dose contribution caused by the contamination photons is calculated using the Monte Carlo model and the actual fluence spectrum of the contamination photons.

Description

Technical Field

[0001] The present application relates to the field of β reference radiation field, and in particular to a system and method for measuring contamination photons in a β reference radiation field. Background Art

[0002] A reference radiation field is an essential testing environment for calibrating radiation monitoring instruments and determining their metrological performance. Any radiation monitoring instrument will experience varying degrees of measurement error due to various factors. For example, measurement errors may arise from various factors, including design, processing, assembly, and component quality. Therefore, newly manufactured radiation monitoring instruments must be calibrated and verified in a reference radiation field to determine whether they meet the technical requirements of relevant standards. Furthermore, after a period of use, the metrological performance of radiation monitoring instruments that have passed calibration may be affected by factors such as environmental conditions, improper use, poor maintenance, and internal component quality variations. Therefore, radiation monitoring instruments must be calibrated regularly, and the results are used to determine whether they can continue to be used or require repair. Repaired radiation monitoring instruments must also be calibrated in a reference radiation field to determine whether they meet the specified requirements.

[0003] Beta radiation hazards are widespread in nuclear medicine and nuclear industry workplaces, including those involved in radioisotope production and application, radiopharmaceutical preparation, nuclear fuel production and reprocessing, reactor maintenance and decommissioning, and nuclear waste disposal. Beta radiation is a weakly penetrating radiation, capable of delivering an equivalent dose exceeding 25 times the effective dose to any small area of ​​the sensitive skin layer. Direct exposure to beta-radioactive materials and substances can result in a beta radiation dose exceeding 50 times that of gamma radiation under the same exposure conditions. Therefore, radiation monitoring instruments are required in these nuclear industry and nuclear medicine workplaces to monitor beta radiation doses, prevent the occurrence of definite effects, and safeguard the occupational health of radiation workers.

[0004] Currently, the BSS2 (Beta Secondary Standard type 2) is widely used internationally to generate beta-ray radiation fields for calibration and determination of the response of radiation monitoring instruments. This device is equipped with a radioactive source. The radiation field generated by the source contains contaminant photons, which affect instrument calibration results. These contaminant photons originate from characteristic X-rays and bremsstrahlung generated when gamma and beta rays emitted by the source pass through the source window (titanium or stainless steel). When calibrating beta-ray radiation monitoring instruments, the contribution of contaminant photons to the total beta-ray dose at the calibration location should be as small as possible. This requirement is particularly important for calibrating instruments with high photon sensitivity. Therefore, measuring the fluence spectrum of contaminant photons in the beta reference radiation field is crucial for fully understanding the beta reference radiation field and ensuring the accuracy of instrument calibration results. Summary of the Invention

[0005] In view of this, the present application hopes to provide a system and method for measuring contamination photons in a β reference radiation field, which can measure the fluence spectrum of contamination photons.

[0006] To achieve the above objectives, an embodiment of the present application provides a system for measuring contamination photons in a β reference radiation field, comprising:

[0007] An energy spectrometer comprising a detector and a measuring device connected to the detector;

[0008] A collimator, wherein the collimator is formed with a through hole, through which the beta rays and contamination photons emitted by the radiation source can be emitted to the detector;

[0009] a beta-ray absorbing member movably disposed on the collimator to block or open the through hole, the beta-ray absorbing member being capable of absorbing the beta-ray;

[0010] a photon absorber movably disposed on the collimator to block or open the through hole, wherein the photon absorber is capable of absorbing the contamination photons and the beta rays;

[0011] A processing device is communicatively connected to the measuring device, wherein the processing device establishes a Monte Carlo model of the detector and the beta-ray absorbing element, and calculates an actual fluence spectrum of contamination photons through the Monte Carlo model.

[0012] In some embodiments, the energy spectrometer includes a connecting tube, the collimator includes a front part and a rear part, the front part is connected to the side of the rear part away from the detector, the rear part is formed with a receiving hole, the through hole passes through the front part and connects to the receiving hole, and the connecting tube is inserted into the receiving hole to connect the through hole and the detector.

[0013] In some embodiments, the β-ray absorber has an axial length of not less than 20 mm.

[0014] In some embodiments, the beta-ray absorbing member is made of PMMA; and / or

[0015] The photon absorber is made of lead.

[0016] In some embodiments, the beta ray absorber is in sliding engagement with the collimator; and / or,

[0017] The photon absorber is in sliding cooperation with the collimator.

[0018] In some embodiments, the measurement system includes an adjustment platform, the spectrometer is placed on the adjustment platform, and the axis of the radiation source, the axis of the detector, and the axis of the collimator are made to coincide with each other by adjusting the adjustment platform.

[0019] Another embodiment of the present application provides a method for measuring contamination photons in a β reference radiation field, using any of the above-described measurement systems, including:

[0020] The beta-ray absorbing element is used to block the through hole, and the radiation source is activated to enable the detector to generate a first pulse, and the measuring device is capable of generating a first energy spectrum according to the first pulse;

[0021] The photon absorption element is used to block the through hole, and the radiation source is activated to enable the detector to generate a second pulse, and the measuring device is capable of generating a second energy spectrum according to the second pulse;

[0022] The processing device calculates the actual fluence spectrum of the contamination photons using the Monte Carlo model according to the first energy spectrum and the second energy spectrum.

[0023] In some embodiments, the processing device calculates an actual fluence spectrum of contamination photons using the Monte Carlo model based on the first energy spectrum and the second energy spectrum, including:

[0024] Obtaining a response function of the detector to incident particles within a set energy range based on the Monte Carlo model;

[0025] The actual fluence spectrum is obtained by calculating using a least squares method based on the response function, the first energy spectrum, the second energy spectrum and a reference fluence spectrum of contamination photons.

[0026] In some embodiments, the set energy range of the incident particles is between 1 keV and 3600 keV, with an energy interval of 5 keV.

[0027] In some embodiments, the calculation method includes:

[0028] The proportion of the dose caused by the contamination photons to the dose caused by the beta rays is obtained according to the actual fluence spectrum and the reference beta energy spectrum of the radiation source.

[0029] In some embodiments, obtaining the proportion of the dose caused by the contamination photons to the dose caused by the beta rays based on the actual fluence spectrum and the reference energy spectrum of the beta rays of the radioactive source includes:

[0030] The actual fluence spectrum and the reference β energy spectrum are simulated to irradiate the same phantom respectively to obtain a first absorbed dose of the actual fluence spectrum at a specific tissue depth and a second absorbed dose of the reference β energy spectrum at a tissue depth of 0.07 mm, respectively. The ratio of the first absorbed dose to the second absorbed dose is the proportion of the dose caused by the contamination photons.

[0031] The measurement system provided in the embodiments of the present application utilizes a photon absorber capable of absorbing contamination photons and beta rays, and a beta-ray absorber capable of absorbing beta rays, thereby enabling measurement of the pulse amplitude spectrum of contamination photons. Due to the detector's detection efficiency, the area of ​​the full-energy peak in the measured pulse amplitude spectrum of contamination photons does not equal the number of contamination photons actually emitted by the radiation source. Therefore, a Monte Carlo model of the detector and beta-ray absorber is established using a processing device. The response matrix derived from the Monte Carlo model is used to convert the pulse amplitude spectrum of contamination photons into their actual fluence spectrum. This allows the actual number of contamination photons emitted by the radiation source to be determined, allowing the energy spectrum distribution of contamination photons in the beta reference radiation field to be directly obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of the structure of the measurement system in one embodiment of the present application;

[0033] Figure 2 is a perspective schematic diagram of a collimator in one embodiment of the present application;

[0034] Figure 3 for Figure 2 A schematic structural diagram of the collimator from another perspective;

[0035] Figure 4 Schematic diagram of the structure of a beta-ray absorber in one embodiment of the present application;

[0036] Figure 5 This is a schematic structural diagram of a photon absorption element in one embodiment of the present application;

[0037] Figure 6 Schematic diagram of the structure of the Monte Carlo model in one embodiment of the present application;

[0038] Figure 7 A flowchart of a measurement method in an embodiment of the present application;

[0039] Figure 8 Schematic diagram of the structure of a phantom in one embodiment of the present application.

[0040] Description of Reference Numerals

[0041] Energy spectrometer 1; connecting tube 11; collimator 2; through hole 2a; first section 2aa; second section 2ab; front portion 21; rear portion 22; receiving hole 22a; beta-ray absorber 3; photon absorber 4; first portion 41; second portion 42; Monte Carlo model 5; housing 51; vacuum chamber 51a; detection core 52; incident window 53; adjustment platform 6;

[0042] Phantom 10; Sensitive Volume 101; DETAILED DESCRIPTION

[0043] It should be noted that, unless there is a conflict, the embodiments and technical features in the embodiments of this application can be combined with each other, and the detailed description in the specific implementation method should be understood as an explanation of the purpose of this application and should not be regarded as an improper restriction on this application.

[0044] The present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. The descriptions of "first", "second", etc. in the embodiments of the present application are for descriptive purposes only and should not be understood as indicating or implying their relative importance or implicitly including at least one feature. In the description of the embodiments of the present application, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. In the embodiments of the present application, the unit "mm" is millimeter and the unit "eV" is electron volt.

[0045] See also Figures 1 to 6 On the one hand, an embodiment of the present application provides a system for measuring contamination photons in a β reference radiation field, the measuring system including an energy spectrometer 1, a collimator 2, a β ray absorber 3, a photon absorber 4 and a processing device.

[0046] The energy spectrometer 1 includes a detector and a measuring device connected to the detector. For example, the detector and the measuring device are electrically connected. The measuring device generates an energy spectrum in response to the detector.

[0047] Collimator 2 is formed with a through hole 2a, through which both beta rays and contamination photons emitted by the radiation source can be emitted to the detector. For example, collimator 2 is located between the radiation source and the detector, with a pipe connecting through hole 2a and the detector. Both beta rays and contamination photons emitted by the radiation source can be emitted through through hole 2a along the axial direction of collimator 2 to the detector.

[0048] Beta-ray absorber 3 is movably mounted on collimator 2 to block or open aperture 2a. Beta-ray absorber 3 is capable of absorbing beta rays. When beta-ray absorber 3 blocks aperture 2a, the radiation source causes the detector to generate a first pulse, and the measurement device can generate a first energy spectrum based on the first pulse. When beta-ray absorber 3 blocks aperture 2a, beta rays emitted by the radiation source are absorbed by beta-ray absorber 3, and the detector generates the first pulse in response to contamination photons emitted by the radiation source and background. In other words, the first energy spectrum includes the pulse amplitude spectrum of the contamination photons and the pulse amplitude spectrum of the background.

[0049] The photon absorber 4 is movably disposed on the collimator 2 to block or open the through hole 2a. The photon absorber 4 can absorb contamination photons and beta rays. When the photon absorber 4 blocks the through hole 2a, the radiation source causes the detector to generate a second pulse, and the measuring device can generate a second energy spectrum based on the second pulse. When the photon absorber 4 blocks the through hole 2a, both the beta rays and contamination photons emitted by the radiation source are absorbed by the photon absorber 4, and the detector generates a second pulse in response to the background. In other words, the second energy spectrum is the pulse amplitude spectrum of the background. In this way, the measuring device can obtain the pulse amplitude spectrum of the contamination photons based on the first and second energy spectra, that is, subtracting the second energy spectrum from the first energy spectrum to obtain the pulse amplitude spectrum of the contamination photons.

[0050] It is understood that, when the beta-ray absorber 3 is required to block the through hole 2a, the photon absorber 4 opens the through hole 2a to avoid the beta-ray absorber 3. Similarly, when the photon absorber 4 is required to block the through hole 2a, the beta-ray absorber 3 opens the through hole 2a to avoid the photon absorber 4.

[0051] The processing device is in communication with the measuring device. The processing device establishes a Monte Carlo model 5 of the detector and the beta-ray absorber 3 and calculates an actual fluence spectrum of the contamination photons using the Monte Carlo model 5. Specifically, the processing device calculates the actual fluence spectrum of the contamination photons based on the response matrix obtained from the Monte Carlo model 5 based on the first energy spectrum and the second energy spectrum.

[0052] The measurement system provided in the embodiments of the present application utilizes the photon absorber 4 to absorb contamination photons and β-rays, and the β-ray absorber 3 to absorb β-rays, thereby enabling measurement of the pulse amplitude spectrum of contamination photons. Due to the detector's detection efficiency, the area of ​​the full-energy peak in the measured pulse amplitude spectrum of contamination photons does not equal the number of contamination photons actually emitted by the radiation source. Therefore, a Monte Carlo model 5 of the detector and β-ray absorber 3 is established using a processing device. The response matrix is ​​calculated using the Monte Carlo model 5, and the pulse amplitude spectrum of the contamination photons is converted into the actual fluence spectrum of the contamination photons. This allows the actual number of contamination photons emitted by the radiation source to be determined, thereby directly obtaining the energy spectrum distribution of the contamination photons in the β reference radiation field.

[0053] In some embodiments, the actual fluence spectrum can be compared with the reference fluence spectrum of contamination photons to determine whether there are unknown components in the radiation source, thereby obtaining more information about the β reference radiation field.

[0054] It should be noted that particle fluence is the number of particles per unit area that pass perpendicularly through the recording plane. Fluence spectrum is the process of dividing the recording plane into multiple recording grids, recording the fluence for different energy intervals within each grid. The Monte Carlo N-Particle Transport Code (MCNP) model uses a computer to simulate particle transport in space using random methods to estimate the mathematical expectation of particles.

[0055] In some embodiments, a Monte-Carlo (MC) model can be established in a processing device based on the size and material of the detector. The size and material of the detector can be obtained from the detector's product manual. For example, the detector model can be established in MCNP5 of the processing device.

[0056] For example, see Figure 6 The Monte Carlo model 5 of the detector includes a housing 51, a detection core 52, and an entrance window 53. The housing 51 defines a vacuum chamber 51a and a window communicating with the vacuum chamber 51a. The entrance window 53 seals the window, and the detection core 52 is located within the vacuum chamber 51a. The entrance window 53 maintains a vacuum within the vacuum chamber 51a, allowing radiation from the radiation source to irradiate the detection core 52 through the entrance window 53.

[0057] In some embodiments, the material of the housing 51 may include but is not limited to aluminum, the material of the detection core 52 may include but is not limited to germanium, etc. The material of the incident window 53 may include but is not limited to beryllium.

[0058] The collimator 2 plays the role of shielding and collimating. The collimator 2 can shield the heat photons in the external environment from entering the detector, and can also facilitate the β rays and contamination photons emitted by the radiation source to be irradiated on the detector. In one embodiment, please refer to Figure 2 and Figure 3 Through hole 2a consists of a first section 2aa and a second section 2ab. The second section 2ab extends axially from the first section 2aa near the detector port. The diameter D1 of the first section 2aa is 15 mm, and the diameter D2 of the second section 2ab is 14 mm. This limits the number of particles that enter the detector, reduces detector dead time, prevents "blocking," and minimizes the impact of ambient scattered radiation on the measured energy spectrum.

[0059] In one embodiment, please refer to Figures 1 to 3The energy spectrometer 1 includes a connecting tube 11, and the collimator 2 includes a front portion 21 and a rear portion 22. The front portion 21 is connected to the side of the rear portion 22 away from the detector. The rear portion 22 is formed with a receiving hole 22a. The through hole 2a passes through the front portion 21 and connects to the receiving hole 22a. The connecting tube 11 is inserted into the receiving hole 22a to connect the through hole 2a and the detector.

[0060] In some embodiments, the thickness of the front portion 21 is 70 mm, and the thickness of the rear portion 22 is 40 mm. Thus, the thickness of the front portion 21 prevents contaminating photons in the beta radiation field from penetrating the front portion 21 and entering the external environment, ensuring that contaminating photons in the beta radiation field can only enter the connecting tube 11 through the through hole 2a. The thickness of the rear portion 22 is sufficient to shield scattered photons from the external environment, limiting the entry of scattered photons into the connecting tube 11.

[0061] In some embodiments, the outer contour of the collimator 2 is cylindrical, and the cross-section of the receiving hole 22a is circular.

[0062] In one embodiment, please refer to Figure 2 and Figure 3 The through hole 2a is a straight hole extending in the axial direction, and the cross-sectional shape of the through hole 2a is circular.

[0063] The shape of the beta ray absorber 3 can be adapted to the shape of the through hole 2a, and the beta ray absorber 3 can block the through hole 2a. Figure 2 The cross-sectional shape of the through hole 2a is circular, and the cross-sectional shape of the β-ray absorber 3 is also circular.

[0064] For example, in some embodiments, the cross-sectional area of ​​the beta-ray absorber 3 is not less than the cross-sectional area of ​​the through-hole 2a. For example, the beta-ray absorber 3 can completely cover the through-hole 2a, thereby blocking the through-hole 2a. In another example, the beta-ray absorber 3 can be inserted into the through-hole 2a. In this manner, the beta-ray absorber 3 can also block the through-hole 2a.

[0065] The shape of the photon absorber 4 can be adapted to the shape of the through hole 2a, and the photon absorber 4 can block the through hole 2a. Figure 2 The cross-sectional shape of the through hole 2a is circular, and the cross-sectional shape of the photon absorber 4 is also circular.

[0066] For example, in some embodiments, the cross-sectional area of ​​the photon absorber 4 is not less than the cross-sectional area of ​​the through hole 2a. For example, the photon absorber 4 can completely cover the through hole 2a, thereby blocking the through hole 2a. In another example, the photon absorber 4 can be inserted into the through hole 2a. In this way, the photon absorber 4 can also block the through hole 2a.

[0067] It should be noted that the cross sections in the embodiments of the present application are all taken as cross sections on a plane perpendicular to the axial direction of the collimator 2 .

[0068] In some embodiments, the total photon fluence of the collimator 2 penetrating the shield is less than 10% of the photon fluence passing through the through hole 2a. -4 In this way, it is ensured that the collimator 2 does not excessively affect the measurement results. For example, the fluence of the collimator 2 can be obtained by Monte Carlo simulation.

[0069] In one embodiment, please refer to Figure 4 The axial length L of the beta-ray absorber 3 is not less than 20 mm. For example, the axial length L of the beta-ray absorber 3 is 20 mm, 21 mm, 21.5 mm, or 22 mm, etc., to ensure that beta rays generated by a radiation source such as Sr-90 / Y-90 can be prevented from entering the detector.

[0070] In one embodiment, the beta-ray absorbing element 3 is made of PMMA, which is polymethyl methacrylate.

[0071] In one embodiment, the photon absorber 4 is made of lead.

[0072] In one embodiment, please refer to Figures 2 to 4 , the beta ray absorbing member 3 is slidably matched with the collimator 2. For example, in one embodiment, please refer to Figures 2 to 4 The beta ray absorber 3 can be inserted into the through hole 2a, such as the first section 2aa. This facilitates the assembly of the beta ray absorber 3 into the collimator 2 and prevents external light from interfering with the test.

[0073] In one embodiment, please refer to Figure 2 、 Figure 3 and Figure 5 , the photon absorber 4 is slidably matched with the collimator 2. For example, in one embodiment, please refer to Figure 2 、 Figure 3 and Figure 5 , the photon absorber 4 can be inserted into the through hole 2a. In this way, the photon absorber 4 is easily assembled into the collimator 2 and external light is prevented from interfering with the test.

[0074] For example, in one embodiment, please refer to Figure 2 、 Figure 3 and Figure 5The photon absorber 4 includes a first portion 41 and a second portion 42. The second portion 42 is connected to the end of the first portion 41 closest to the detector. The first portion 41 is inserted into the first segment 2aa, and the second portion 42 is inserted into the second segment 2ab. In other words, the shape of the first portion 41 matches the shape of the first segment 2aa, enabling it to block the first segment 2aa. The shape of the second portion 42 matches the shape of the second segment 2ab, enabling it to block the second segment 2ab. For example, if the diameters of the first portion 41 and the first segment 2aa are both 15 mm, the diameters of the second portion 42 and the second segment 2ab can be 14 mm.

[0075] In one embodiment, the through hole 2a may have an axial length of 70 mm, and the photon absorber 4 may have an axial length of 70 mm. In this way, the photon absorber 4 may completely fill the through hole 2a.

[0076] In one embodiment, please refer to Figure 1 The measurement system includes an adjustment platform 6, on which the spectrometer 1 is placed. The adjustment platform 6 is adjusted so that the axis of the radiation source, the axis of the detector, and the axis of the collimator 2 coincide. In other words, the position of the spectrometer 1 can be changed by adjusting the adjustment platform 6 so that the axis of the radiation source, the axis of the detector, and the axis of the collimator 2 coincide.

[0077] In some embodiments, the adjustment platform 6 can adjust the height of the spectrometer 1 in the vertical direction and the position in the horizontal plane. Exemplarily, the adjustment platform 6 includes a support platform, a lifting foot and two sets of linear guide rails. The support platform is used to support the spectrometer 1, and the lifting foot is provided on the support platform to adjust the height of the support platform in the vertical direction. One set of linear guide rails extends in the left-right direction, and the other set of linear guide rails extends in the front-back direction, and the support platform slides with the linear guide rails. In this way, by moving the support platform to slide along the linear guide rails, the position in the left-right direction and / or in the front-back direction, that is, the position of the support platform in the horizontal plane, can be adjusted.

[0078] Exemplarily, the lifting foot may be a jackscrew.

[0079] The detector type is not limited. Crystals used in the detector include, but are not limited to, Ge (germanium), NaI (sodium iodide), Si(Li) (lithium silicon), CdTe (cadmium antimonide), Cd(Zn)Te (cadmium zinc telluride), or PIPS (Passivated Implanted Planar Silicon). For example, the detector can be a low-energy Ge detector.

[0080] For example, the detector is made of germanium crystal, such as ultrapure germanium. The active area of ​​the detector is 2000mm 2(square millimeters), the thickness of the germanium crystal is 20.5 mm (millimeters), and the energy measurement range is 5 keV (kiloelectron volts) to 500 keV. For example, in some embodiments, the detector has a resolution of 315 eV (electron volts) for 5.9 keV X-rays of Fe-55 (iron with a mass number of 55).

[0081] In some embodiments, the measurer may be a digital multiplexer.

[0082] The measuring device can be connected to the processing device via wireless communication and / or wired communication. For example, in some embodiments, the measuring device includes a data port, and is communicatively connected to the processing device via the data port. The data port includes, but is not limited to, a USB (Universal Serial Bus) and / or RS-232 port, etc.

[0083] In some embodiments, the measuring instrument is integrated with energy spectrum analysis software, such as Genie2000, to implement functions such as energy spectrum measurement and analysis. For example, the measuring instrument uses the energy spectrum analysis software to implement functions such as energy spectrum measurement, peak finding, peak area calculation, background subtraction, efficiency calibration, and / or nuclide identification.

[0084] Radioactive sources include but are not limited to 147 Pm (promethium with a mass number of 147), 85 Kr (krypton with a mass number of 85) and 90 Sr / 90 Y (strontium and yttrium with a mass number of 90). For example, the radiation source may be from BSS2 (Beta Secondary Standard type 2).

[0085] See also Figure 7 Another embodiment of the present application provides a method for measuring contamination photons in a β reference radiation field. The method uses the measuring system in any embodiment of the present application, and the measuring method includes:

[0086] S100 , blocking the through hole with the β-ray absorbing element, starting the radiation source to enable the detector to generate a first pulse, and the measuring device to generate a first energy spectrum according to the first pulse.

[0087] S200 , blocking the through hole with the photon absorption element, starting the radiation source to enable the detector to generate a second pulse, and the measuring device to generate a second energy spectrum according to the second pulse.

[0088] In this way, the first energy spectrum and the second energy spectrum are measured and obtained respectively through steps S100 and S200.

[0089] It should be noted that, in some embodiments, step S100 may be performed first, and then step S200. In other embodiments, step S200 may be performed first, and then step S100.

[0090] In a specific embodiment, the axes of the detector, collimator 2 and radiation source are aligned by adjusting the adjustment platform 6. The beta-ray absorber 3 is used to block the through hole 2a of the collimator 2. Turn on the irradiation device, load the detector in Genie2000, click to start the energy spectrum measurement, and set the measurement time to 12 hours. The first energy spectrum is obtained through the above measurement, and the first energy spectrum includes the pulse amplitude spectrum of the contamination photons and the pulse amplitude spectrum of the background. Thereafter, the beta-ray absorber 3 is removed, and the photon absorber 4 is used to block the through hole 2a of the collimator 2. The remaining measurement conditions are the same as above, and the second energy spectrum is obtained through measurement, and the second energy spectrum only includes the pulse amplitude spectrum of the detector background. The counts in the same channel address in the first energy spectrum and the second energy spectrum are subtracted to obtain the pulse amplitude spectrum of the contamination photons.

[0091] S300: The processing device calculates an actual fluence spectrum of the contamination photons using the Monte Carlo model according to the first energy spectrum and the second energy spectrum.

[0092] After completing step S100 and step S200 , the processing device calculates the actual fluence spectrum of the contamination photons using the response matrix obtained by the Monte Carlo model 5 .

[0093] The measurement method provided in the embodiment of the present application obtains the pulse amplitude spectrum of the contamination photons through the coordinated measurement between the detector, the β-ray absorber 3, the photon absorber 4 and the collimator 2, and then converts the pulse amplitude spectrum of the contamination photons into an actual fluence spectrum through the response matrix obtained by the Monte Carlo model 5. In this way, the actual fluence spectrum of the contamination photons in the β reference radiation field can be obtained by combining measurement with model calculation, thereby reducing the deviation caused by the detector efficiency.

[0094] In one embodiment, the processing device calculates the actual fluence spectrum of the contamination photons using the Monte Carlo model according to the first energy spectrum and the second energy spectrum, including:

[0095] S310: Obtaining a response function of the detector to incident particles within a set energy range based on the Monte Carlo model.

[0096] The response function refers to the probability that a monoenergetic incident particle can generate a pulse of a certain energy amplitude in the detector. For example, the response function of the detector's Monte Carlo model 5 to different monoenergetic incident particles within a set energy range can be calculated using MCNP5 of the processing device.

[0097] In some embodiments, the set energy range of the incident particles is between 1keV and 3600keV, with an energy interval of 5keV. Specifically, the number of particles running during the calculation is 1×10 8 (10 to the power of 8). Parallel calculation of the monoenergetic photon response function within the above-set energy range can be completed on the processing device.

[0098] The detector response matrix is ​​calculated using the Monte Carlo model 5.

[0099] S320 . Calculate the actual fluence spectrum using a least squares method based on the response function, the first energy spectrum, the second energy spectrum, and a reference fluence spectrum of contamination photons.

[0100] Exemplarily, the processing device has UMG (Unfolding with Maxed and Gravel) spectrum analysis software, and the actual fluence spectrum corresponding to the pulse amplitude spectrum of the contamination photons is calculated using the GRV_MC33 program of the UMG spectrum analysis software. Specifically, before using the GRV_MC33 program, the necessary control files and input files can be written. The control file contains the pulse amplitude spectrum file name, the initial spectrum file name, the response function file name, the number of iterations, the set energy range of the incident particles during the calculation, and the chi-squared value of the degree of freedom of the calculation result. 2 . The input file consists of a response function file, a pulse amplitude spectrum file and an initial spectrum file, wherein the response function file contains the response function of the detector, for example, the response function of a monoenergetic particle with an energy range of 1keV to 3600keV and an interval of 5keV. The pulse spectrum amplitude spectrum file is the pulse amplitude spectrum of the contamination photons obtained by the first energy spectrum and the second energy spectrum. The initial spectrum file can be the reference fluence spectrum of the contamination photons. The reference fluence spectrum of the contamination photons can be the fluence spectrum of the contamination photons recommended by PTB (German Federal Institute of Physics). The actual fluence spectrum can be obtained by calculating the least squares method using the UMG spectrum decomposition software. In this way, the measured pulse amplitude spectrum of the contamination photons is converted into an actual fluence spectrum.

[0101] In one embodiment, the calculation method includes:

[0102] S400: Obtain a proportion of the dose caused by the contamination photons to the dose caused by the beta rays according to the actual fluence spectrum and a reference beta energy spectrum of the radiation source.

[0103] In the beta radiation field generated by a radioactive source, the physical quantity of interest at the calibration position is the tissue absorbed dose caused by the beta radiation. However, contamination photon radiation also exists at the calibration position. Relevant standards, such as ISO 6980-1, stipulate that the dose rate caused by contamination photons should be less than 5% of the total beta radiation dose received by the dosimeter. Therefore, accurately measuring the tissue absorbed dose caused by contamination photons at the calibration position in the beta reference radiation field is crucial to fully understand the reference radiation field and ensure the accuracy of instrument calibration results.

[0104] ISO 6980-1 standard defines photon pollution as: the ratio of the photon dose rate generated by gamma, X-ray and bremsstrahlung pollution in the reference radiation to H p The contribution of (0.07) should be less than 5% of the beta particle dose rate recorded by the calibrated detector.

[0105] H p (0.07) means that the personal dose equivalent of weak penetrating radiation refers to the dose equivalent of soft tissue at a depth of 0.07mm at a specified point on the body.

[0106] The reference β energy spectrum can be a β ray energy spectrum obtained by simulation calculation, so that a β ray energy spectrum measurement device such as an ionization chamber can be saved.

[0107] In this embodiment, the share of the dose caused by the contamination photons is obtained through the actual fluence spectrum and the reference β energy spectrum, which is simple and convenient.

[0108] In one embodiment, obtaining the proportion of the dose caused by the contamination photons to the dose caused by the beta rays based on the actual fluence spectrum and the reference beta energy spectrum of the radiation source includes:

[0109] The actual fluence spectrum and the reference β energy spectrum are simulated to irradiate the same phantom respectively to obtain a first absorbed dose of the actual fluence spectrum at a specific tissue depth and a second absorbed dose of the reference β energy spectrum at a tissue depth of 0.07 mm, respectively. The ratio of the first absorbed dose to the second absorbed dose is the proportion of the dose caused by the contamination photons.

[0110] In this embodiment, a simulation method is used to calculate and obtain the proportion of the dose caused by the contamination photons, which does not rely on equipment such as an ionization chamber. The method is simple and low in cost.

[0111] In some embodiments, the specified tissue depth includes 0.07 mm, 3 mm, and / or 10 mm.

[0112] For example, see Figure 8, using the actual fluence spectrum and the reference β energy spectrum as input energy spectra, respectively, to simulate irradiation of the same phantom 10, and obtaining the deposition energies of the two radiations in the sensitive volume 101 of the phantom 10, respectively. That is, the first absorbed dose of the actual fluence spectrum at a specific tissue depth and the second absorbed dose of the reference β energy spectrum at a tissue depth of 0.07 mm are obtained, respectively. The ratio of the two deposition energies is the share of the dose caused by contamination photons.

[0113] For example, the absorbed dose at a tissue depth of 0.07 mm in the phantom can be calculated using EGSnrc software.

[0114] EGSnrc (NRC's electron gamma shower software) is an extension and upgrade of EGS4 (electron gamma shower version 4). EGS4 is a Monte Carlo program for simulating photon and electron transport, jointly developed by the Stanford Linear Accelerator Center (SLAC) and the National Research Council of Canada (NRCC). Compared to EGS4, EGSnrc improves the accuracy of charged particle transport and atomic scattering cross sections.

[0115] Here, the measured actual fluence spectrum serves as the input spectrum for the Monte Carlo program, directly simulating the absorbed dose of contamination photons at tissue depths of 0.07 mm, 3 mm, and 10 mm. Furthermore, the reference β spectrum serves as the input spectrum for the Monte Carlo program, directly simulating the absorbed dose of β rays at a tissue depth of 0.07 mm. The ratio of the two yields the contribution of the photon-induced dose to the β-ray-induced dose at different tissue depths (0.07 mm, 3 mm, and 10 mm). This ratio is then compared with the contamination photon-induced dose contribution requirement in the ISO 6980-1 standard to determine whether the reference radiation field meets the ISO standard.

[0116] By determining the dose fraction caused by contamination photons at different tissue depths, it is equivalent to determining the conventional true value of the dose caused by contamination photons at different tissue depths in the β radiation field. Therefore, this conventional true value can be used to analyze H p (0.07) dose meter, H p (3) Dosimeter and H p (10) The response of the dosimeter, that is, when the dose caused by the contaminating photons is known, the energy of the β-rays deposited in the dosimeter is determined, and then whether the dosimeter meets the sensitivity requirements of the relevant IEC standards.

[0117] In dosimetry, the phantom 10 is a structure that simulates the equivalent of skin tissue.

[0118] The phantom 10 includes but is not limited to a plate mold. For example, the plate mold may be a plate mold recommended by the ISO standard.

[0119] The reference β spectrum may be a β spectrum recommended by the ISO standard.

[0120] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Those skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, and improvements that fall within the spirit and principles of the present application are intended to be within the scope of protection of the present application.

Claims

1. A system for measuring contamination photons in a β reference radiation field, characterized in that: include: An energy spectrometer comprising a detector and a measuring device connected to the detector; A collimator, wherein the collimator is formed with a through hole, through which the beta rays and contamination photons emitted by the radiation source can be emitted to the detector; a beta-ray absorbing member movably disposed on the collimator to block or open the through hole, the beta-ray absorbing member being capable of absorbing the beta-ray; a photon absorber movably disposed on the collimator to block or open the through hole, wherein the photon absorber is capable of absorbing the contamination photons and the beta rays; A processing device is communicatively connected to the measuring device, wherein the processing device establishes a Monte Carlo model of the detector and the beta-ray absorbing element, and calculates an actual fluence spectrum of contamination photons through the Monte Carlo model.

2. The measurement system according to claim 1, characterized in that: The energy spectrometer includes a connecting tube, the collimator includes a front part and a rear part, the front part is connected to the side of the rear part away from the detector, the rear part is formed with a receiving hole, the through hole passes through the front part and connects with the receiving hole, and the connecting tube is inserted into the receiving hole to connect the through hole and the detector.

3. The measurement system according to claim 1, characterized in that: The β-ray absorbing member has an axial length of not less than 20 mm.

4. The measurement system according to claim 1, characterized in that: The material of the beta-ray absorbing member is PMMA; and / or, The photon absorber is made of lead.

5. The measurement system according to claim 1, characterized in that: The beta ray absorbing member is in sliding engagement with the collimator; and / or, The photon absorber is in sliding cooperation with the collimator.

6. The measurement system according to claim 1, characterized in that: The measurement system includes an adjustment platform, the energy spectrometer is placed on the adjustment platform, and the adjustment platform is adjusted so that the axis of the radiation source, the axis of the detector, and the axis of the collimator coincide with each other.

7. A method for measuring contamination photons in a β reference radiation field, characterized in that: The measurement system according to any one of claims 1 to 6 comprises: The beta-ray absorbing element is used to block the through hole, and the radiation source is activated to enable the detector to generate a first pulse, and the measuring device is capable of generating a first energy spectrum according to the first pulse; The photon absorption element is used to block the through hole, and the radiation source is activated to enable the detector to generate a second pulse, and the measuring device is capable of generating a second energy spectrum according to the second pulse; The processing device calculates the actual fluence spectrum of the contamination photons using the Monte Carlo model according to the first energy spectrum and the second energy spectrum.

8. The calculation method according to claim 7, characterized in that: The processing device calculates an actual fluence spectrum of contamination photons using the Monte Carlo model according to the first energy spectrum and the second energy spectrum, including: Obtaining a response function of the detector to incident particles within a set energy range based on the Monte Carlo model; The actual fluence spectrum is obtained by calculating using a least squares method based on the response function, the first energy spectrum, the second energy spectrum and a reference fluence spectrum of contamination photons.

9. The calculation method according to claim 8, characterized in that: The set energy range of the incident particles is between 1 keV and 3600 keV, and the energy interval is 5 keV.

10. The calculation method according to claim 7, characterized in that: The calculation method includes: The proportion of the dose caused by the contamination photons to the dose caused by the beta rays is obtained according to the actual fluence spectrum and the reference beta energy spectrum of the radiation source.

11. The calculation method according to claim 10, characterized in that: Obtaining, according to the actual fluence spectrum and a reference energy spectrum of beta rays from the radioactive source, a proportion of the dose caused by the contamination photons to the dose caused by the beta rays, comprising: The actual fluence spectrum and the reference β energy spectrum are simulated to irradiate the same phantom respectively to obtain a first absorbed dose of the actual fluence spectrum at a specific tissue depth and a second absorbed dose of the reference β energy spectrum at a tissue depth of 0.07 mm, respectively. The ratio of the first absorbed dose to the second absorbed dose is the proportion of the dose caused by the contamination photons.

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