Method for verifying the uniformity of the beta reference radiation field ocular lens personal dose equivalent rate

Abstract

The present application relates to the personal dose equivalent rate uniformity verification method in the beta reference radiation field, including the following steps: measuring the beta radiation field absorption dose rate and its uniformity distribution; the energy spectrum of Sr / Y-90 beta radiation field is measured; the conversion coefficient database of corresponding absorption dose rate-personal dose equivalent rate is established when the energy spectrum regional distribution of Sr / Y-90 beta radiation field changes, the regional distribution measurement result of personal dose equivalent rate in beta radiation field is obtained; the personal dose equivalent rate uniformity region of Sr / Y-90 beta radiation field is determined.The method provided by the present application can measure the personal dose equivalent rate uniformity region of beta radiation level of human eye lens in the beta radiation field of BSS 2 standard device, solve the problem that the directional dose equivalent rate uniformity region in the beta radiation field changes due to the deformation and aging of the flattening filter after long-term use, and cause a certain difference between the personal dose equivalent rate in the beta radiation field and the PC end indication value.

Description

Technical Field

[0001] This invention belongs to the field of metrology and testing technology, specifically relating to the personal dose equivalent rate within a β reference radiation field. A method for verifying uniformity. Background Technology

[0002] Absorbed radiation dose is a physical quantity used to represent the amount of ionizing radiation energy absorbed per unit mass of irradiated material when ionizing radiation interacts with matter. The absorbed radiation dose is the quotient obtained by dividing the average energy imparted by ionizing radiation deposited in an infinitesimally small volume element by the mass of the material in that volume element.

[0003] Beta absorbed dose is an indispensable part of ionizing radiation metrology. In my country, beta absorbed dose reference radiation is mostly provided by the Beta Secondary Standard Type 2 (BSS2) standard device, which is based on beta radioisotopes. 90 Sr- 90 Y、 85 Kr、 147 The emitted beta rays from Pm, after being bundled by a flattened filter, can provide a radiation field with a uniform dose rate within a range of tens of centimeters in diameter at the measurement point.

[0004] In workplace or environmental monitoring, dose equivalent values ​​are measured under "receptor-free" conditions. This means the location of interest is a place where a person might reside, but no person or model is actually present there; various other objects far from the receptor, along with their absorption and scattering, are present. (This refers to the individual dose equivalent rate of beta radiation.) This refers to the dose equivalent per unit time at a specified depth of 3 mm in human tissue, measured in Sv / h. Typically, Used to describe the level of beta radiation in the lens of the human eye. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a personal dose equivalent rate within a β reference radiation field. The uniformity verification method is used to address the issue that factors such as deformation and aging of the flattened filter after long-term use cause changes in the uniformity region of the personal dose equivalent rate in the β radiation field, leading to changes in the personal dose equivalent rate in the β radiation field. The problem is that there is a certain difference between the values ​​displayed on the PC and the values ​​displayed on the PC.

[0006] To achieve the above objectives, the technical solution adopted by this invention is as follows: personal dose equivalent rate within the β reference radiation field. A method for verifying uniformity, the method comprising the following steps:

[0007] S1. Measure the absorbed dose rate in the β radiation field. and its uniform distribution;

[0008] S2. Measure the energy spectrum of the Sr / Y-90β radiation field;

[0009] S3. Establish a database of conversion coefficients between absorbed dose rate and personal dose equivalent rate when the energy spectrum distribution of the Sr / Y-90β radiation field changes, and obtain the personal dose equivalent rate in the β radiation field. Regional distribution measurement results;

[0010] S4. Determine the individual dose equivalent rate of the Sr / Y-90β radiation field. Uniform region.

[0011] Furthermore, step S1 includes the following specific steps:

[0012] S11. Place the sensitive volume center of the ionization chamber at the measurement point at the center of the normal of the Sr / Y-90β radiation field to ensure that the β rays are incident perpendicularly into the ionization chamber.

[0013] S12. Based on the accumulated charge J fed back by the electrometer connected to the ionization chamber. a The absorbed dose rate at the measurement point is calculated by taking the reading and combining it with formulas (1) to (3).

[0014]

[0015]

[0016]

[0017] in:

[0018] J a : Cumulative charge, C;

[0019] The average ionization energy of air, eV;

[0020] The ratio of the average mass blocking power of the entrance window of the ionization chamber to that of the air is a constant without dimensions.

[0021] Sensitive volume air mass, m 3 / kg;

[0022] k PT Temperature and pressure correction factor, where P is the ambient air pressure (kPa) and T is the ambient temperature (°C).

[0023] t: Measurement time, in seconds;

[0024] D: Absorbed dose, J / kg;

[0025] Absorbed dose rate, J / (kg·h);

[0026] S13. Using the measurement point as the center, on the vertical plane where the sensitive volume center of the ionization chamber is located, move the sensitive volume center of the ionization chamber 20.0 cm in each of the four directions: up, down, left, and right. Set the movement step size to 1.0 cm to 2.0 cm, and obtain the cumulative charge J at each moving point. a The absorbed dose rate at each moving point was calculated. Thus, the absorbed dose rate in the β radiation field is obtained. The uniform distribution.

[0027] Furthermore, the energy spectrum of the Sr / Y-90β radiation field was measured using a SiPIN detector; the SiPIN detector is connected to a matching preamplifier, main amplifier, and digital multichannel.

[0028] Furthermore, when performing energy spectrum measurements of the Sr / Y-90β radiation field using the SiPIN detector, a 3 mg·cm⁻¹ area is placed in front of the SiPIN detector window. 2 Aluminized polyester film.

[0029] Furthermore, the sensitive volume center of the SiPIN detector is placed at a position coinciding with the sensitive volume center of the ionization chamber; an H is placed immediately behind the SiPIN detector. p (3) Phantom

[0030] Furthermore, when using the SiPIN detector to perform energy spectrum measurements of the Sr / Y-90β radiation field, the absorbed dose rate in step S1 is compared with that in step S1. The method for measuring the uniformity distribution is the same as that for the ionization chamber. After each set of cumulative charge readings is measured, the sensitive volume center of the SiPIN detector is placed at a position that coincides with the sensitive volume center of the ionization chamber. The SiPIN detector is then replaced to measure and record the energy spectrum distribution of the Sr / Y-90β radiation field at the current position.

[0031] Furthermore, step S3 includes the following specific steps:

[0032] S31. Using MCNP simulation to establish human tissue and H p (3) Phantom, to obtain the calculation method of the conversion coefficient of absorbed dose rate - individual dose equivalent rate;

[0033] S32. Establish a database of conversion coefficients between absorbed dose rate and individual dose equivalent rate when the energy spectrum distribution of the Sr / Y-90β radiation field changes.

[0034] S33. Combining the measurement points obtained in step S1 with the absorbed dose rate at each moving point. Obtain the personal dose equivalent rate in the Sr / Y-90β radiation field The regional distribution measurement results.

[0035] Furthermore, step S32 includes the following specific steps:

[0036] S321. Based on the energy spectrum distribution results of the Sr / Y-90β radionuclide measured using the SiPIN detector and the matching device of BSS2, the energy spectrum distribution of the Sr / Y-90β radionuclide in H2O is calculated according to formula (5). p (3) Under the phantom, the conversion coefficient H of absorbed dose rate to personal dose equivalent rate corresponding to the change in the distribution of the β radiation field energy spectrum region. p (3,T) / D T ;

[0037]

[0038] Among them, H p (3,T) represents the individual dose equivalent of a small volume element at a depth of 3 mm inside a human tissue model when irradiated with Sr / Y-90β radionuclide, Sv;

[0039] Φ E The energy E of the Sr / Y-90β radionuclide, m -3 ;

[0040] Q is the β-particle quality factor, taken as Q = 1Sv / Gy;

[0041] Energy deposition per unit mass within a small volume element, J / kg;

[0042] D T,E For the injection volume Φ E The deposition energy of Sr / Y-90β radionuclides with energy E in a small volume element, J / kg;

[0043] D T The deposition energy of the Sr / Y-90β radionuclide in a small volume element, J / kg;

[0044] S322. Establish a database of conversion coefficients between absorbed dose rate and individual dose equivalent rate when the energy spectrum distribution of the Sr / Y-90β radiation field changes.

[0045] Furthermore, step S33 includes the following specific steps:

[0046] The measurement points and absorbed dose rates at each moving point obtained in step S1 are used to calculate the absorption dose rate. The measurement result is multiplied by the corresponding absorption dose rate-personal dose equivalent rate conversion factor H from the absorption dose rate-personal dose equivalent rate conversion factor database. p (3,T) / D T The individual dose equivalent rate at the measurement point and at each movement point was calculated. Thus, the personal dose equivalent rate in the β radiation field is obtained. The regional distribution of.

[0047] Furthermore, in step S4, the area where the personal dose equivalent rate deviation from the measurement point does not exceed ±5% is selected and identified as the personal dose equivalent rate of the β radiation field. Uniform region.

[0048] The beneficial effects of this invention are as follows: The personal dose equivalent rate within the β reference radiation field provided by this invention... The uniformity verification method can be achieved by measuring the absorbed dose rate in the β radiation field. Its uniform distribution; measuring the energy spectrum of the Sr / Y-90β radiation field; establishing a database of conversion coefficients between absorbed dose rate and personal dose equivalent rate when the energy spectrum distribution of the Sr / Y-90β radiation field changes, and obtaining the personal dose equivalent rate in the β radiation field. Regional distribution measurement results; determination of individual dose equivalent rate of Sr / Y-90β radiation field. Uniform region. The method provided by this invention enables the measurement of personal dose equivalent rate, representing the beta radiation level of the human eye lens, within the beta radiation field of a BSS2 standard device. In the uniform region, this addresses the issue of changes in the uniformity of the directional dose equivalent rate in the β-radiation field caused by factors such as deformation and aging of the flattened filter after long-term use, which leads to changes in the personal dose equivalent rate in the β-radiation field. The problem is that there is a certain difference between the values ​​displayed on the PC and the values ​​displayed on the PC. Attached Figure Description

[0049] Figure 1 Personal dose equivalent rate within the β reference radiation field provided for embodiments of the present invention A flowchart illustrating the uniformity verification method;

[0050] Figure 2 Absorbed dose rate in the β radiation field provided for embodiments of the present invention Measurement diagram;

[0051] Figure 3 A schematic diagram of energy spectrum measurement of the β radiation field provided for an embodiment of the present invention;

[0052] Figure 4 The human tissue and H established using MCNP provided for embodiments of the present invention p(3) Schematic diagram of the model. Detailed Implementation

[0053] The technical solutions in the embodiments of the present invention will be further clearly and completely described below with reference to the accompanying drawings and examples. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0054] It should be noted that in the description of the embodiments of the present invention, the terms "upper," "lower," "front," "rear," "front," "back," "left," "right," "horizontal," "vertical," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0055] The inventors discovered that flattened filters are prone to deformation and aging after long-term use, causing changes in the uniformity of the beta radiation dose rate at the reference point. However, the reference value at the PC only corrects for the decay of the radiation source itself and environmental factors at the measurement point, which also leads to a difference between the actual value at the measurement point and the reference value at the PC. This change is mainly reflected in two aspects: absorbed dose rate and dose equivalent rate. The uniformity change of absorbed dose rate can be directly measured using a thin-window ionization chamber, but the measurement of dose equivalent rate depends on the energy of beta rays and cannot directly measure the uniformity change.

[0056] Due to the personal dose equivalent rate of beta radiation It is used to characterize the dose equivalent level produced per unit time in an actual radiation field at a depth of 3 mm inside a human body (or a spherical phantom). In the β standard radiation field of the BSS2 standard device, only the energy of Sr / Y-90 has a significant impact on the individual dose equivalent rate. It makes a contribution, but other nuclides lack sufficient energy and therefore make no contribution. Furthermore, an H-type nuclide is placed immediately behind the SiPIN detector. p (3) Phantom (Φ20cm×20cm PMMA cylinder) is used to simulate the total internal reflection of the human head in the Sr / Y-90β radiation field.

[0057] like Figure 1-3 As shown, this embodiment provides a personal dose equivalent rate within a β reference radiation field. The homogeneity verification method involves verifying the individual dose equivalent rate in a Sr / Y-90β radiation field. A method for verifying uniformity, the method comprising the following steps:

[0058] S1. Measure the absorbed dose rate in the β radiation field. and its uniform distribution;

[0059] like Figure 2 In the experiment shown, the sensitive volume center of the ionization chamber was placed at the measurement point at the center of the normal to the Sr / Y-90β radiation field, ensuring that the β rays were incident perpendicularly into the ionization chamber; then, the accumulated charge J was fed back from the electrometer connected to the ionization chamber. a The absorbed dose rate at the measurement point can be calculated by referring to formulas (1) to (3).

[0060]

[0061]

[0062]

[0063] in:

[0064] J a : Cumulative charge, C;

[0065] The average ionization energy of air, eV;

[0066] The ratio of the average mass blocking power of the entrance window of the ionization chamber to that of the air is a constant without dimensions.

[0067] Sensitive volume air mass, m 3 / kg;

[0068] k PT Temperature and pressure correction factor, where P is the ambient air pressure (kPa) and T is the ambient temperature (°C).

[0069] t: Measurement time, in seconds;

[0070] D: Absorbed dose, J / kg;

[0071] Absorbed dose rate, J / (kg·h);

[0072] The ionization chamber is a thin-window ionization chamber, and the PTW34045 type thin-window ionization chamber can be selected.

[0073] Specifically, the accumulated charge J reported by the electrometer connected to the ionization chamber. aThe reading is obtained by recording the electrometer reading (i.e., current I) at the measurement point, and combining this reading with the residence time of the sensitive volume center of the ionization chamber at the measurement point to obtain the cumulative charge J at the measurement point. a .

[0074] Similarly, taking the measurement point as the center, on the vertical plane where the sensitive volume center of the ionization chamber is located, move the sensitive volume center of the ionization chamber 20.0 cm in each of the four directions: up, down, left, and right. The step size can be set to 1.0 cm to 2.0 cm. Record the electrometer reading at each moving point, and combine it with the dwell time at each moving point to obtain the cumulative charge J at each moving point. a Then, the absorbed dose rate at each moving point is calculated according to formulas (1) to (3). Therefore, the absorbed dose rate in the β radiation field can be obtained. The uniformity of the distribution.

[0075] S2. Measure the energy spectrum of the Sr / Y-90β radiation field;

[0076] Based on absorbed dose rate To determine the uniformity of the distribution, in order to further obtain the individual dose equivalent rate... In addition to obtaining a uniform region, it is also necessary to measure and provide the energy spectrum of the Sr / Y-90β radiation field (i.e., the energy spectrum region distribution of the Sr / Y-90β radiation field, or the energy spectrum region distribution of the β radiation field of the Sr / Y-90β radionuclides).

[0077] The energy spectrum of the Sr / Y-90β radiation field was measured using a SiPIN detector. In one specific embodiment, the SiPIN detector can be a BA-016-025-1500 type.

[0078] Specifically, when using a SiPIN detector to measure the energy spectrum of the Sr / Y-90β radiation field, the SiPIN detector is connected to a matching 142A preamplifier, a 575A main amplifier, and an MCA digital multichannel amplifier. The PC connected to the MCA digital multichannel amplifier can directly acquire the energy spectrum of the Sr / Y-90β radiation field through the matching software.

[0079] Specifically, such as Figure 3 As shown, when using a SiPIN detector to measure the energy spectrum of the Sr / Y-90β radiation field, a 3 mg·cm² coverage is applied to the front window of the SiPIN detector. 2The aluminum-coated polyester film is used for light shielding; the sensitive volume center of the SiPIN detector is placed at the same position as the sensitive volume center of the ionization chamber (i.e., the sensitive volume center of the SiPIN detector is placed at the measurement point at the center of the normal to the Sr / Y-90β radiation field, ensuring that β rays are incident perpendicularly on the SiPIN detector), and an H is placed immediately behind the SiPIN detector. p (3) Phantom (Φ20cm×20cm PMMA cylinder). When performing energy spectrum measurements of the Sr / Y-90β radiation field using a SiPIN detector, the absorbed dose rate in step S1 is compared with that in step S1. The method for measuring the uniformity distribution is consistent with that for each set of accumulated charge readings in the ionization chamber, the sensitive volume center of the SiPIN detector is placed at a position coinciding with the sensitive volume center of the ionization chamber. The SiPIN detector is then replaced to measure and record the energy spectrum distribution of the Sr / Y-90β radiation field at the current position (i.e., with the measurement point as the center, on the vertical plane where the sensitive volume center of the SiPIN detector is located, the sensitive volume center of the SiPIN detector is moved 20.0 cm in each of the four directions: up, down, left, and right, with each moving point coinciding with the sensitive volume center of the ionization chamber, and the energy spectrum distribution of the Sr / Y-90β radiation field at each moving point is recorded). Furthermore, H p (3) The phantom moves simultaneously with the SiPIN detector, and the relative positions between the two remain unchanged.

[0080] In one specific embodiment, the energy spectrum distribution of the Sr / Y-90β radionuclide associated with the BSS2 standard device was measured using a SiPIN detector.

[0081] S3. Establish a database of conversion coefficients between absorbed dose rate and personal dose equivalent rate when the energy spectrum distribution of the Sr / Y-90β radiation field changes, and obtain the personal dose equivalent rate in the β radiation field. Regional distribution measurement results;

[0082] Based on the above steps S1 and S2, the absorbed dose rate can be obtained. While the overall distribution of the β-ray spectrum in the Sr / Y-90β radiation field is known, the conversion from absorbed dose rate to personal dose equivalent rate requires appropriate conversion factors. Although ISO 6980-3 provides conversion factors for Sr / Y-90β nuclides at specified distances with and without flattening filters, these factors become inapplicable when the β-ray spectrum changes due to filter aging. Therefore, to obtain the distribution of personal dose equivalent rate in the Sr / Y-90β radiation field, a database of absorption dose rate-personal dose equivalent rate conversion factors is needed to account for changes in the Sr / Y-90β radiation field's spectral distribution.

[0083] Specifically, step S3 includes the following steps:

[0084] S31. Using MCNP simulation to establish human tissue and H p (3) Phantom, to obtain the calculation method of the conversion coefficient of absorbed dose rate - individual dose equivalent rate;

[0085] like Figure 4 As shown, human tissue and H were established using MCNP. p (3) Phantom: The human tissue is placed tightly against the phantom with the center normals of both aligned. Monoenergetic β particles with a fluence Φ and energy E are incident on the human tissue model and the phantom from an incident angle of 0°. According to the definition of personal dose equivalent, a small volume element with a depth of 3 mm inside the human tissue model is taken along the horizontal direction of the radiation field. The energy deposition dε and mass dm within the small volume element are simulated and obtained. Combined with the β particle quality factor Q (for weakly penetrating β particles irradiated externally, Q = 1Sv / Gy is usually taken), the personal dose equivalent H is calculated according to formula (4). p0 (3,T).

[0086]

[0087] Among them, H p0 (3,T) represents the individual dose equivalent of a small volume element at a depth of 3 mm inside a human tissue model under the condition of a given fluence Φ and energy E for monoenergetic β particles; Sv;

[0088] Q is the β-particle quality factor, taken as Q = 1Sv / Gy;

[0089] Energy deposition per unit mass within a small volume element, J / kg;

[0090] Subsequently, other structures in the tissue sphere model were removed, leaving only a small volume element at 3 mm. The deposition energy of monoenergetic β particles with fluence Φ and energy E within this small volume element was obtained, i.e., the absorbed dose D. T0 Therefore, under the condition of monoenergetic β particles with a given flux Φ and energy E, the conversion coefficient H of absorbed dose to individual dose equivalent for a small volume element at a depth of 3 mm inside a human tissue model is obtained. p0 (3,T) / D T0 This is the conversion factor between absorbed dose rate and individual dose equivalent rate.

[0091] S32. Establish a database of conversion coefficients between absorbed dose rate and individual dose equivalent rate when the energy spectrum distribution of the Sr / Y-90β radiation field changes.

[0092] Combining the energy spectrum distribution of the Sr / Y-90β radionuclide obtained by measuring the BSS2 standard device with a SiPIN detector in step S2, the energy spectrum distribution of the Sr / Y-90β radionuclide in H2O was calculated according to formula (5). p (3) Under the phantom, the conversion coefficient H of absorbed dose rate to personal dose equivalent rate corresponding to the change in the distribution of the β radiation field energy spectrum region. p (3,T) / D T That is, when the distribution of the β-radiation field energy spectrum of the Sr / Y-90β radionuclide changes (due to factors such as deformation and aging of the flattened filter), the conversion coefficient H of the absorbed dose rate to the personal dose equivalent rate of a small volume element at a depth of 3 mm inside the human tissue model can be obtained. p (3,T) / D T .

[0093]

[0094] Among them, H p (3,T) represents the individual dose equivalent of a small volume element at a depth of 3 mm inside a human tissue model when irradiated with Sr / Y-90β radionuclide, Sv;

[0095] Φ E The energy E of the Sr / Y-90β radionuclide, m -3 ;

[0096] Q is the β-particle quality factor, taken as Q = 1Sv / Gy;

[0097] Energy deposition per unit mass within a small volume element, J / kg;

[0098] D T,E For the injection volume Φ E The deposition energy of Sr / Y-90β radionuclides with energy E in a small volume element, J / kg;

[0099] D T The deposition energy of the Sr / Y-90β radionuclide in a small volume element is expressed in J / kg.

[0100] Furthermore, based on the aforementioned changes in the β-radiation field energy spectrum distribution of the Sr / Y-90β radionuclide, the conversion coefficient H of the absorbed dose rate - personal dose equivalent rate for a small volume element at a depth of 3 mm within the human tissue model is calculated. p (3,T) / D T It is possible to establish a database of conversion coefficients between absorbed dose rate and individual dose equivalent rate when the energy spectrum distribution of the Sr / Y-90β radiation field changes.

[0101] S33. Combining the measurement points obtained in step S1 with the absorbed dose rate at each moving point. Obtain the personal dose equivalent rate in the Sr / Y-90β radiation field Regional distribution measurement results;

[0102] According to formula (6), the absorbed dose rate at each measurement point and each moving point obtained in step S1 is calculated. The measurement result is multiplied by the corresponding absorption dose rate-personal dose equivalent rate conversion factor H from the absorption dose rate-personal dose equivalent rate conversion factor database. p (3,T) / D T This allows for the direct calculation of the individual dose equivalent rate at the measurement point and at each moving point. Measurement results.

[0103]

[0104] Therefore, the individual dose equivalent rate in the β radiation field can be obtained. The regional distribution measurement results.

[0105] S4. Determine the individual dose equivalent rate of the Sr / Y-90β radiation field. Uniform region;

[0106] The area whose personal dose equivalent rate deviates from the measurement point (center location) by no more than ±5% can be considered as the personal dose equivalent rate of the β radiation field. Uniform region.

[0107] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention is also intended to include these modifications and variations.

Claims

1. Personal dose equivalent rate within the β reference radiation field The uniformity verification method is characterized by, The method includes the following steps: S1. Measure the absorbed dose rate in the β radiation field. and its uniform distribution; S2. Measure the energy spectrum of the Sr / Y-90β radiation field; S3. Establish a database of conversion coefficients between absorbed dose rate and personal dose equivalent rate when the energy spectrum distribution of the Sr / Y-90β radiation field changes, and obtain the personal dose equivalent rate in the β radiation field. Regional distribution measurement results; S4. Determine the individual dose equivalent rate of the Sr / Y-90β radiation field. Uniform region.

2. The personal dose equivalent rate within the β reference radiation field according to claim 1 The uniformity verification method is characterized by, Step S1 includes the following specific steps: S11. Place the sensitive volume center of the ionization chamber at the measurement point at the center of the normal of the Sr / Y-90β radiation field to ensure that the β rays are incident perpendicularly into the ionization chamber. S12. Based on the accumulated charge J fed back by the electrometer connected to the ionization chamber. a The absorbed dose rate at the measurement point is calculated by taking the reading and combining it with formulas (1) to (3). in: J a : Cumulative charge, C; The average ionization energy of air, eV; The ratio of the average mass blocking power of the entrance window of the ionization chamber to that of the air is a constant without dimensions. Sensitive volume air mass, m 3 / kg; k PT : Temperature and pressure correction factor, where P is the ambient air pressure, kPa; T is the ambient temperature, °C; t: measurement time, seconds; D: Absorbed dose, J / kg; Absorbed dose rate, J / (kg·h); S13. Using the measurement point as the center, on the vertical plane where the sensitive volume center of the ionization chamber is located, move the sensitive volume center of the ionization chamber 20.0 cm in each of the four directions: up, down, left, and right. Set the movement step size to 1.0 cm to 2.0 cm, and obtain the cumulative charge J at each moving point. a The absorbed dose rate at each moving point was calculated. Thus, the absorbed dose rate in the β radiation field is obtained. The uniform distribution.

3. The personal dose equivalent rate within the β reference radiation field according to claim 2 The uniformity verification method is characterized by, The energy spectrum of the Sr / Y-90β radiation field was measured using a SiPIN detector; the SiPIN detector was connected to a matching preamplifier, main amplifier, and digital multichannel.

4. The personal dose equivalent rate within the β reference radiation field according to claim 3 The uniformity verification method is characterized by, When performing energy spectrum measurements of the Sr / Y-90β radiation field using the SiPIN detector, a 3 mg·cm² coverage is applied to the front window of the SiPIN detector. 2 Aluminized polyester film.

5. The personal dose equivalent rate within the β reference radiation field according to claim 3 The uniformity verification method is characterized by, The sensitive volume center of the SiPIN detector is placed at a position coinciding with the sensitive volume center of the ionization chamber; an H is placed immediately behind the SiPIN detector. p (3) Phantom 6. The personal dose equivalent rate within the β reference radiation field according to claim 5 The uniformity verification method is characterized by, When performing energy spectrum measurements of the Sr / Y-90β radiation field using the SiPIN detector, the absorbed dose rate in step S1 is compared with that in step S1. The method for measuring the uniformity distribution is the same as that for the ionization chamber. After each set of cumulative charge readings is measured, the sensitive volume center of the SiPIN detector is placed at a position that coincides with the sensitive volume center of the ionization chamber. The SiPIN detector is then replaced to measure and record the energy spectrum distribution of the Sr / Y-90β radiation field at the current position.

7. Personal dose equivalent rate within the β reference radiation field according to claim 6 The uniformity verification method is characterized by, Step S3 includes the following specific steps: S31. Using MCNP simulation to establish human tissue and H p (3) Phantom, to obtain the calculation method of the conversion coefficient of absorbed dose rate - individual dose equivalent rate; S32. Establish a database of conversion coefficients between absorbed dose rate and individual dose equivalent rate when the energy spectrum distribution of the Sr / Y-90β radiation field changes. S33. Combining the measurement points obtained in step S1 with the absorbed dose rate at each moving point. Obtain the personal dose equivalent rate in the Sr / Y-90β radiation field The regional distribution measurement results.

8. Personal dose equivalent rate within the β reference radiation field according to claim 7 The uniformity verification method is characterized by, Step S32 includes the following specific steps: S321. Based on the energy spectrum distribution results of the Sr / Y-90β radionuclide measured using the SiPIN detector and the matching device of BSS2, the energy spectrum distribution of the Sr / Y-90β radionuclide in H2O is calculated according to formula (5). p (3) Under the phantom, the conversion coefficient H of absorbed dose rate to personal dose equivalent rate corresponding to the change in the distribution of the β radiation field energy spectrum region. p (3,T) / D T ; Among them, H p (3,T) represents the individual dose equivalent of a small volume element at a depth of 3 mm inside a human tissue model when irradiated with Sr / Y-90β radionuclide, Sv; ω E The energy E of the Sr / Y-90β radionuclide, m -3 ; Q is the β-particle quality factor, taken as Q = 1Sv / Gy; Energy deposition per unit mass within a small volume element, J / kg; D T,E For the amount of injection ω E The deposition energy of Sr / Y-90β radionuclides with energy E in a small volume element, J / kg; D T The deposition energy of the Sr / Y-90β radionuclide in a small volume element, J / kg; S322. Establish a database of conversion coefficients between absorbed dose rate and individual dose equivalent rate when the energy spectrum distribution of the Sr / Y-90β radiation field changes.

9. Personal dose equivalent rate in the β reference radiation field according to claim 8 The uniformity verification method is characterized by, Step S33 includes the following specific steps: The measurement points and absorbed dose rates at each moving point obtained in step S1 are used to calculate the absorption dose rate. The measurement result is multiplied by the corresponding absorption dose rate-personal dose equivalent rate conversion factor H from the absorption dose rate-personal dose equivalent rate conversion factor database. p (3,T) / D T The individual dose equivalent rate at the measurement point and at each movement point was calculated. Thus, the personal dose equivalent rate in the β radiation field is obtained. The regional distribution of.

10. The personal dose equivalent rate within the β reference radiation field according to claim 1 The uniformity verification method is characterized by, In step S4, the area where the personal dose equivalent rate deviation from the measurement point does not exceed ±5% is selected and identified as the personal dose equivalent rate of the β radiation field. Uniform region.

Images