β radiation personal dose equivalent H p (3) Secondary standard ionization chamber and value transfer method

Abstract

The present invention relates to a beta radiation personal dose equivalent H p (3) A secondary standard ionization chamber and a quantity transfer method, belonging to the field of metrological measurement technology, comprises the following steps: S1, establishing a physical model of human tissue and a phantom, and obtaining the H of a typical β nuclide under the phantom at an incident angle of ‑45° to +45° by simulation calculation. p (3) / D T Conversion coefficient database; S2, place the ionization chamber under the β radiation field, place the phantom next to the rear end of the ionization chamber, and calculate the corresponding D at the measurement point based on the electrometer current reading T ; S3, according to D T The measurement result is multiplied by the conversion coefficient of the corresponding β nuclide in the database at the corresponding incident angle to obtain H at the measurement point. p (3) The agreed value; S4, placing the monitoring device in the β radiation field, close to the phantom, and achieving value transfer by calculating the relative inherent error, statistical fluctuation, and angular response of the monitoring device. The use of the ionization chamber and value transfer method provided by the present invention can ensure that the measurement results of the radiation monitoring device are accurate and reliable.

Description

Technical Field

[0001] The present invention belongs to the field of measurement technology, and is specifically a method for measuring the individual dose equivalent of beta radiation. p (3) Secondary standard ionization chamber and measurement value transfer method. Background Art

[0002] Personal monitoring dose of β radiation from occupational external exposure H p (3) Refers to the personal dose equivalent at a depth of 3 mm below the body surface, mostly used for the human eye lens. p (3) Relevant epidemiological studies have found that the incidence of cataracts is closely related to the degree of beta radiation exposure of the eye lens during interventional radiotherapy. For this reason, the dose limit for the eye lens is specified in the National Basic Safety Standards. However, the dose limit is a protective quantity that cannot be directly measured with existing equipment. Therefore, the operational practical quantity H that can be directly measured is used. p (3).

[0003] At present, it is difficult to ensure that the reading results of radiation monitoring equipment are accurate and reliable. p (3) Many problems caused by effective monitoring need to be solved urgently. Summary of the Invention

[0004] In order to solve the defects of the prior art, the present invention aims to provide a β radiation personal dose equivalent H p (3) A secondary standard ionization chamber and a measurement value transfer method, which can ensure that the measurement results of the radiation monitoring equipment are accurate and reliable.

[0005] In order to achieve the above purpose, a technical solution adopted by the present invention is:

[0006] A personal dose equivalent H p (3) Secondary standard ionization chamber, including:

[0007] An anti-scattering phantom, which is cylindrical in shape and is used to simulate the backscattering of beta rays by the human head. One end of the anti-scattering phantom has a cavity, which includes an upper cavity and a lower cavity.

[0008] A collecting electrode is provided at the middle of the bottom surface of the lower cavity, and is used to collect and read signals. The collecting electrode is connected to an electrometer via a signal lead wire.

[0009] A protective ring, which is a hollow ring structure and is sleeved outside the collecting electrode, and the outer circle of the protective ring cooperates with the inner wall of the lower cavity;

[0010] A metal ring having the same size as the protective ring is provided between the lower cavity and the upper cavity, and an incident window is attached in the middle of the metal ring;

[0011] The upper end surface of the backscatter phantom is provided with a protective cover for simulating the tissue absorption dose at a depth of 3 mm in the human body, and the space between the metal ring and the protective cover is free air;

[0012] The incident window and the collecting electrode together constitute a sensitive area of ​​the detection area, the metal ring and the guard ring together constitute an air-filled cavity, and the metal ring and the collecting electrode provide the ionization chamber with a detection high voltage with a parallel electric field through a high-voltage lead wire. When β radiation enters the sensitive area, it ionizes the free air and generates positive and negative charges, wherein the positive charge drifts to the collecting electrode under the action of the electric field to generate a current signal.

[0013] Furthermore, the personal dose equivalent H p (3) Secondary standard ionization chamber: the antiscattering phantom is a cylinder with a diameter of Φ80-100 mm and a height of 15-30 mm, and is made of a polymer material with good tissue equivalence.

[0014] Furthermore, the personal dose equivalent H p (3) A secondary standard ionization chamber, wherein the collecting electrode is a copper-clad gold-plated PCB board with a diameter of Φ35-45 mm and a thickness of 0.5-1 mm; the guard ring is a PMMA hollow ring with an outer diameter of 55-65 mm and a thickness of 0.5-1 mm, and the inner diameter thereof is spaced 0.4-0.6 mm from the collecting electrode.

[0015] Furthermore, the personal dose equivalent H p (3) The secondary standard ionization chamber, wherein the incident window is a graphite film with a diameter of 35 to 45 mm and a thickness of 30 to 35 μm.

[0016] Furthermore, the personal dose equivalent H p (3) A secondary standard ionization chamber, wherein a truncated cone structure with a 45° inclination angle is adopted between the metal ring and the protective cover.

[0017] A beta radiation personal dose equivalent H p (3) Quantity transfer method, which uses the above-mentioned personal dose equivalent H p (3) The secondary standard ionization chamber is realized, and the method comprises the following steps:

[0018] S1. Using a simulation method, establish a physical model of human tissue and a phantom, and obtain a database of absorbed dose-to-personal dose equivalent conversion coefficients for typical β nuclides in the phantom within an incident angle range of -45° to +45° through simulation calculations;

[0019] S2. Equivalent personal dose H p (3) The secondary standard ionization chamber is placed under the β radiation field, and a phantom is placed next to the rear end of the ionization chamber to ensure that the average incident direction of the β ray enters the sensitive area of ​​the ionization chamber vertically. The absorbed dose D corresponding to the measurement point is calculated based on the current reading measured by the electrometer. T , the calculation formula is:

[0020]

[0021] In the above formula:

[0022] J a —Accumulated charge;

[0023] —average ionization energy of air;

[0024] —Ratio of the average mass stopping power of PMMA and air;

[0025] —Air quality in sensitive areas;

[0026] k PT —Temperature and pressure correction factor, where P and T are the pressure and temperature at ambient conditions, respectively;

[0027] S3. Multiply the absorbed dose measurement result in step S2 by the conversion coefficient of the corresponding β nuclide at the corresponding incident angle in the absorbed dose-personal dose equivalent conversion coefficient database to obtain the personal dose equivalent H at the measurement point. p (3) the agreed value;

[0028] S4. The individual dose equivalent to be measured H p (3) The monitoring equipment is placed under the β radiation field, and the personal dose equivalent H p (3) The monitoring device is placed on the phantom so that the reference point of the monitoring device is located at a measurement point in the β radiation field where the agreed value of the personal dose equivalent (rate) is known. The reading value of the personal dose equivalent (rate) of the monitoring device at the measurement point is measured. The personal dose equivalent H is obtained by calculating the relative inherent error, statistical fluctuation and angular response of the monitoring device. p (3) Transmission of measurement values ​​of monitoring equipment.

[0029] Furthermore, the beta radiation personal dose equivalent H p (3) The value transfer method, step S1 is specifically as follows:

[0030] S11. A physical model of human tissue and a phantom is established using simulation modeling software, and monoenergetic beta particles with a set fluence Φ and energy E are incident on the physical model at an incident angle of 0°;

[0031] S12. Take a small volume element at a depth of 3 mm inside the human tissue along the horizontal direction of the radiation field, simulate the energy deposition and mass in the small volume element, and calculate the personal dose equivalent H. p (3), the calculation formula is:

[0032]

[0033] Where:

[0034] Q—β particle quality factor. For weakly penetrating β particles from external irradiation, Q=1Sv / Gy;

[0035] dε—energy deposition in a small volume element;

[0036] dm—mass of small volume element;

[0037] S13, only the small volume element at the depth of 3mm is retained, and other structural models are removed, and the absorbed dose D of the monoenergetic β particles incident at 0° with the set fluence Φ, energy E, and angle is obtained by simulation. T ;

[0038] S14, according to H p (3) and D T Obtain the conversion coefficient of absorbed dose-personal dose equivalent. The calculation formula of the conversion coefficient is: H p (3) / D T ;

[0039] S15. Changing the incident angle of the beta particle, repeating steps S11-S14, and finally establishing a conversion coefficient between the absorbed dose of a monoenergetic beta particle with energy E at a specific incident angle of the small volume element and the personal dose equivalent;

[0040] S16. Combined with the standard emission spectrum of typical β radionuclides, calculate the H emission of typical β nuclides under the phantom at an incident angle of -45° to +45°. p (3) and D T , thus obtaining H p (3) / D T Conversion coefficient database, the calculation formula is:

[0041]

[0042] Furthermore, the beta radiation personal dose equivalent H p (3) Value transfer method: The method for determining the relative inherent error of the monitoring equipment in step S4 is:

[0043] The dose equivalent rate measurement range covers at least 2 decimal levels within the effective measurement range of the monitoring equipment, and the dose equivalent measurement range covers at least 3 decimal levels within the effective measurement range of the monitoring equipment. There are at least 4 measurement points, and the number of repeated measurements of each measurement point is not less than 4 times. The measurement points within the lowest decimal level are repeated for not less than 7 times. The relative inherent error I of each measurement point is calculated according to the following formula: i :

[0044]

[0045] Where:

[0046] —The average value of the readings at the i-th measurement point;

[0047] H iC —The agreed value of the individual dose equivalent (rate) at the i-th measurement point.

[0048] Furthermore, the beta radiation personal dose equivalent H p (3) Value transfer method: The method for determining the statistical fluctuation of the monitoring device in step S4 is:

[0049] Repeat the measurement at the selected measurement point for no less than 10 times, and calculate the statistical fluctuation V of the monitoring equipment according to the following formula:

[0050]

[0051] Where: n is the number of repeated measurements.

[0052] Furthermore, the beta radiation personal dose equivalent H p (3) Value transfer method: The method for measuring the angular response of the monitoring device in step S4 is:

[0053] The monitoring device is changed to an angle α in two perpendicular planes passing through its reference point and including the reference direction, α = ±15°, ±30°, ±45°, and the angular response R of the monitoring device at the corresponding angle is measured according to the following formula:

[0054]

[0055] Where: H E,α —Personal dose equivalent (rate) readings measured by monitoring equipment;

[0056] H 0,α —Personal dose equivalent H p (3) The agreed value of personal dose equivalent (rate) given by the secondary standard ionization chamber.

[0057] The β radiation personal dose equivalent H of the present invention is used p (3) The secondary standard ionization chamber and the value transfer method have the following significant technical effects:

[0058] This invention aims at the fact that my country has not yet established a personal dose equivalent H p (3) The problem of lack of reference for the value transfer specification and relevant test methods of monitoring equipment provides a high-precision and accurate measurement of β radiation personal dose equivalent H p (3) The secondary standard ionization chamber was used to establish a conversion method from absorbed dose to personal dose equivalent based on the ionization chamber, and the personal dose equivalent H was formed. p (3) A series of test methods for the transmission of measurement values ​​of monitoring equipment can ensure that the measurement results of radiation monitoring equipment are accurate and reliable, and at the same time fill the gap in the current domestic personal dose equivalent H p (3) The gaps in the measurement value transfer specifications and related test methods of monitoring equipment are of great significance to the improvement of my country's personal dose equivalent H p (3) The traceability / transfer system of measurement values ​​is of great significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 is the personal dose equivalent H p (3) Schematic diagram of the structure of the secondary standard ionization chamber;

[0060] Figure 2 A β radiation personal dose equivalent H provided in an embodiment of the present invention p (3) Flowchart of the value transfer method;

[0061] Figure 3 It is a schematic diagram of MCNP modeling;

[0062] Figure 4 is based on the personal dose equivalent H p (3) Schematic diagram of the secondary standard ionization chamber for measuring absorbed dose;

[0063] Figure 5 It is a monitoring device that measures personal dose equivalent H p (3) Schematic diagram of value transfer;

[0064] Figure 1 Middle: 1-antiscattering phantom, 2-collecting electrode, 3-guard ring, 4-gas-filled cavity, 5-sensitive volume, 6-entrance window, 7-protective cover. DETAILED DESCRIPTION

[0065] The present invention will be further described below with reference to specific embodiments and the accompanying drawings.

[0066] Figure 1 The personal dose equivalent H provided by the embodiment of the present invention is shownp (3) Schematic diagram of the structure of the secondary standard ionization chamber, which includes an antiscattering phantom 1, a collecting electrode 2, a guard ring 3, a gas-filled cavity 4, a sensitive volume 5, an incident window 6, and a protective cover 7, wherein:

[0067] The antiscattering phantom 1 is cylindrical in shape and is used to simulate the backscattering of beta rays by the human head. One end of the antiscattering phantom 1 has a cavity, which includes a truncated cone-shaped upper cavity and a cylindrical lower cavity. The collecting electrode 2 is arranged in the middle of the bottom surface of the lower cavity for collecting and reading signals. The collecting electrode 2 has a ground lead and a signal lead. The ground lead is used to connect to the detection high voltage, and the signal lead is used to connect to the electrometer. The guard ring 3 is a hollow ring structure, which is sleeved on the outside of the collecting electrode 2. The outer circle of the guard ring 3 cooperates with the inner wall of the lower cavity. A metal ring of the same size as the guard ring 3 is provided at the connection between the lower cavity and the upper cavity. An incident window 6 is attached in the middle of the metal ring. The metal ring has a high-voltage lead for providing detection high voltage in the parallel electric field. The incident window 6 and the collecting electrode 2 together constitute the sensitive area 5 of the detection area, and the metal ring and the guard ring 3 together constitute the air-filled cavity 4. When β radiation enters the sensitive area 5, it ionizes the free air and generates positive and negative charges. The positive charges drift to the collecting electrode 2 under the action of the electric field to generate a current signal. A protective cover 7 is provided on the upper end surface of the backscattering phantom 1 to simulate the tissue absorption dose at a depth of 3 mm in the human body.

[0068] In the embodiment of the present invention, the antiscattering phantom 1 is a cylinder with a diameter of Φ (80-100) mm and a height of (15-30) mm, and is made of a polymer material with good tissue equivalence (such as polymethyl methacrylate PMMA, with a density of 1.19 g / m 3 , good tissue equivalence, low price, and easy processing). In addition, the human head is closer to a cylindrical structure, and the eye lens is located on the side of the human head, which is suitable for simulating the backscattering of beta rays by the human head.

[0069] In the embodiment of the present invention, the collecting electrode 2 is a copper-clad gold-plated PCB board with a diameter of Φ (35-45) mm and a thickness of (0.5-1) mm, which ensures the measurement stability of weak current.

[0070] In the embodiment of the present invention, the guard ring 3 is a PMMA hollow ring with an outer diameter of Φ (55-65) mm and a thickness of (0.5-1) mm. The inner diameter is spaced (0.4-0.6) mm from the collecting electrode 2. The guard ring 3 can reduce the leakage current from the gas-filled cavity 4 and even the parallel electric field.

[0071] In the embodiment of the present invention, the incident window 6 is made of a graphite film with a diameter of Φ (35-45) mm and a thickness of (30-35) μm. The graphite film is attached to a metal ring with the same size as the protective ring.

[0072] In the embodiment of the present invention, the applied detection high voltage range is +(200-300)V.

[0073] In the embodiment of the present invention, the protective cover 7 is made of PMMA, which has a tissue equivalent of 300 mg / cm 2 .

[0074] In the embodiment of the present invention, the volume range of the sensitive area 5 is 8 to 10 mL.

[0075] In the embodiment of the present invention, a 45°-inclined truncated cone structure is used between the metal ring and the protective cover 7, with free air in between. The truncated cone structure can ensure the beta radiation collection efficiency at an incident angle of ±45°, thereby improving the angular response capability of the ionization chamber.

[0076] Apply the detection high voltage to the high voltage lead-out wire of the metal ring and the collecting electrode 2, and then connect the electrometer to the signal lead-out wire of the collecting electrode 2. After preheating for 2 hours, the measurement work can be carried out under the β radiation field.

[0077] Although the personal dose equivalent H p (3) is the practical quantity of operation, but it cannot be determined by H p (3) Directly obtain the secondary standard ionization chamber, and indirectly obtain the personal dose equivalent H through the conversion of absorbed dose to personal dose equivalent p (3). Figure 2 The embodiment of the present invention provides a β radiation personal dose equivalent H p (3) Flowchart of the quantity transfer method. This method uses the above-mentioned personal dose equivalent H p (3) Implementation of the secondary standard ionization chamber, including the following steps:

[0078] S1. Use simulation methods to establish physical models of human tissue and phantoms, and obtain a database of absorbed dose-to-personal dose equivalent conversion coefficients for typical β nuclides under the phantom within an incident angle range of -45° to +45° through simulation calculations.

[0079] This step specifically includes the following processes:

[0080] S11. A physical model of human tissue and a phantom is established using simulation modeling software, and monoenergetic β particles with a set fluence Φ and energy E are incident on the physical model from an incident angle of 0°.

[0081] In the embodiment of the present invention, MCNP software (Monte Carlo N Particle Transport Code) can be used to establish human tissue and phantom models, such as Figure 3As shown, the phantom is a cylindrical phantom with dimensions of 20 cm × 20 cm, a PMMA wall material of 5 mm thickness, and a filling inside. Human tissue is placed close to the phantom, with the center normals of both aligned. Monoenergetic beta particles with a given fluence Φ and energy E are injected into the human tissue and the phantom at an angle of incidence of 0°.

[0082] S12. Take a small volume element at a depth of 3 mm inside the human tissue model along the horizontal direction of the radiation field, simulate the energy deposition and mass in the small volume element, and calculate the personal dose equivalent H according to formula (1): p (3), the calculation formula is:

[0083]

[0084] Where:

[0085] Q—β particle quality factor. For weakly penetrating β particles from external irradiation, Q=1Sv / Gy is usually taken;

[0086] dε—energy deposition in a small volume element;

[0087] dm—mass of small volume element.

[0088] S13, only the small volume element at the depth of 3mm is retained, and other structural models are removed. The absorbed dose D of the monoenergetic β particles incident at 0° with the set fluence Φ, energy E, and angle is obtained by simulation. T .

[0089] S14, according to H p (3) and D T Obtain the conversion coefficient of absorbed dose-personal dose equivalent. The calculation formula of the conversion coefficient is: H p (3) / D T .

[0090] S15. Change the incident angle of the β particles and repeat steps S11-S14 to finally establish a conversion coefficient between the absorbed dose of a monoenergetic β particle with energy E at a specific incident angle of the small volume element and the personal dose equivalent.

[0091] S16. Combined with the standard emission spectrum of typical β radionuclides, the H emission of typical β nuclides under the phantom and the incident angle range of -45° to +45° is calculated. p (3) and D T , thus obtaining H p (3) / D T Conversion factor database.

[0092] Typical β-radioactive nuclides include Sr / Y-90, Ru / Rh-106, Kr-85, Tl-204, Pm-147, etc. The H of a specific β-nuclides at a specific incident angle of the phantom is calculated according to formula (2). p (3) and D T , thus obtaining H p (3) / D T The conversion coefficient is finally established to establish the H of typical β nuclides under the phantom and within the incident angle range of -45° to +45°. p (3) / D T Conversion factor database.

[0093]

[0094] S2, the above H p (3) The secondary standard ionization chamber is placed under the β radiation field, and a phantom is placed next to the rear end of the ionization chamber to ensure that the average incident direction of the β ray enters the sensitive area of ​​the ionization chamber vertically. The absorbed dose D corresponding to the measurement point is calculated based on the current reading measured by the electrometer. T .

[0095] like Figure 4 As shown in FIG, in this embodiment, a cylindrical phantom is used because the cylindrical structure is closer to the human head. p (3) For the ocular lens monitoring device, it is recommended to use a cylindrical phantom with a size of Φ20cm×20cm, a wall material of PMMA, a wall thickness of 5mm, and a water-filled interior. The rear end of the ionization chamber is tightly attached to the phantom, and the normal line of the center of the phantom is consistent with the normal line of the ionization chamber surface, ensuring that the average incident direction of the β-ray enters the sensitive area of ​​the ionization chamber vertically. Record the temperature and atmospheric pressure under the ambient conditions, read the current reading given by the electrometer, and calculate the absorbed dose D at the measurement point (i.e., the geometric center of the sensitive area of ​​the ionization chamber) according to formulas (3) and (4): T .

[0096]

[0097] Where:

[0098] J a —Accumulated charge;

[0099] —average ionization energy of air;

[0100] —Ratio of the average mass stopping power of PMMA and air;

[0101] —Air quality in sensitive areas;

[0102] k PT—Temperature and pressure correction factor, where P and T are the pressure and temperature at ambient conditions, respectively.

[0103] S3. Multiply the absorbed dose measurement result measured by the ionization chamber in step S2 by the conversion coefficient of the corresponding β nuclide at the corresponding incident angle in the absorbed dose personal dose equivalent conversion coefficient database to obtain the personal dose equivalent H at the measurement point. p (3) The agreed value.

[0104] S4. The individual dose equivalent to be measured H p (3) The monitoring equipment is placed in the β radiation field, and the personal dose equivalent H p (3) The monitoring device is placed close to the phantom, so that the reference point of the monitoring device is located at a measurement point in the β radiation field where the agreed value of the personal dose equivalent (rate) is known. The reading of the personal dose equivalent (rate) of the monitoring device at the measurement point is measured. The personal dose equivalent H is obtained by calculating the relative inherent error, statistical fluctuation and angular response of the monitoring device. p (3) Transmission of measurement values ​​of monitoring equipment.

[0105] In the embodiment of the present invention, the personal dose equivalent H p (3) The value transfer of monitoring equipment includes three indicators: relative inherent error, statistical fluctuation and angular response. Figure 5 The method of transferring the values ​​of these three indicators is explained.

[0106] 1) Relative inherent error

[0107] like Figure 5 As shown, the monitoring device is placed close to the side of the phantom near the top, which is more consistent with the situation of the eye lens on the side of the human head, so that the reference point of the monitoring device is located at the agreed value H of the personal dose equivalent (rate) in the β radiation field. C At a known measurement point, the personal dose equivalent (rate) reading value H of the monitoring equipment at the measurement point is measured. i The dose equivalent rate measurement range covers at least 2 decimal levels within the effective measurement range of the monitor, the dose equivalent measurement range covers at least 3 decimal levels, there are at least 4 measurement points, the number of repeated measurements of each measurement point is not less than 4 times, and the measurement points within the lowest decimal level are repeated for not less than 7 times. The relative inherent error I of each measurement point is calculated according to formula (5): i :

[0108]

[0109] Where:

[0110] —The average value of the readings at the i-th measurement point, i = 1 ~ ω.

[0111] HiC —The agreed value of the individual dose equivalent (rate) at the i-th measurement point.

[0112] 2) Statistical fluctuations

[0113] The measurement of statistical fluctuations of monitoring equipment should use high-energy β radiation field as much as possible, and select the smallest possible dose rate measurement point. Repeat the measurement for no less than 10 times, and calculate the statistical fluctuation V of the monitoring equipment according to formula (6):

[0114]

[0115] Where: n is the number of repeated measurements.

[0116] 3) Angular response

[0117] The monitoring device is changed to an angle α in two vertical planes passing through its reference point and including the reference direction, α = ±15°, ±30°, ±45° (the agreed values ​​of personal dose equivalent (rate) at different incident angles are given by the ionization chamber at the above incident angles), and the angular response R of the monitoring device is measured respectively:

[0118]

[0119] Where: H E,α —Personal dose equivalent (rate) readings measured by monitoring equipment;

[0120] H 0,α —Personal dose equivalent H p (3) The agreed value of personal dose equivalent (rate) given by the secondary standard ionization chamber.

[0121] The personal dose equivalent H provided by the present invention p (3) Secondary standard ionization chamber and personal dose equivalent H p (3) Method of value transfer: my country has not yet established a personal dose equivalent H p (3) The problem of lack of reference for the value transfer specification and relevant test methods of monitoring equipment provides a high-precision and accurate measurement of β radiation personal dose equivalent H p (3) The secondary standard ionization chamber was used to establish a conversion method from absorbed dose to personal dose equivalent based on the ionization chamber, and the personal dose equivalent H was formed. p (3) A series of test methods for the transmission of measurement values ​​of monitoring equipment can ensure that the measurement results of radiation monitoring equipment are accurate and reliable, and at the same time fill the gap in the current domestic personal dose equivalent H p (3) The gaps in the measurement value transfer specifications and related test methods of monitoring equipment are of great significance to the improvement of my country's personal dose equivalent H p (3) The traceability / transfer system of measurement values ​​is of great significance.

[0122] The above embodiments are merely illustrative of the present invention, and the present invention may also be implemented in other specific ways or in other specific forms without departing from the gist or essential characteristics of the present invention. Therefore, the described embodiments are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is to be determined by the appended claims, and any variations equivalent to the intent and scope of the claims are intended to be within the scope of the present invention.

Claims

1. A personal dose equivalent H p (3) A secondary standard ionization chamber, characterized in that: The ionization chamber comprises: An anti-scattering phantom (1) is cylindrical in shape and is used to simulate the backscattering of beta rays by a human head. One end of the anti-scattering phantom (1) has a cavity, and the cavity includes an upper cavity and a lower cavity. A collecting electrode (2), the collecting electrode (2) being arranged in the middle of the bottom surface of the lower cavity and used for collecting and reading signals, the collecting electrode (2) being connected to an electrometer via a signal lead wire; A protective ring (3), the protective ring (3) being a hollow circular ring structure made of PMMA material, is sleeved outside the collecting electrode (2), and the outer circle of the protective ring (3) is matched with the inner wall of the lower cavity; A metal ring having the same size as the protective ring (3) is provided between the lower cavity and the upper cavity, and an incident window (6) is attached in the middle of the metal ring; The upper end surface of the backscatter phantom (1) is provided with a protective cover (7) for simulating the tissue absorption dose at a depth of (3) mm in the human body, and the space between the metal ring and the protective cover (7) is free air; The incident window (6) and the collecting electrode (2) together constitute a sensitive area (5) of the detection area; the metal ring and the protective ring (3) together constitute an air-filled cavity (4); the metal ring and the collecting electrode (2) provide a parallel electric field detection high voltage for the ionization chamber via a high-voltage lead wire; when beta radiation enters the sensitive area (5), it ionizes free air and generates positive and negative charges, wherein the positive charges drift to the collecting electrode (2) under the action of the electric field to generate a current signal.

2. The personal dose equivalent H according to claim 1 p (3) A secondary standard ionization chamber, characterized in that: The anti-scattering phantom (1) is a cylinder with a diameter of Φ80-100 mm and a height of 15-30 mm, and is made of a high polymer material with good tissue equivalence.

3. The personal dose equivalent H according to claim 1 p (3) A secondary standard ionization chamber, characterized in that: The collecting electrode (2) is a copper-clad gold-plated PCB board with a diameter of Φ35-45 mm and a thickness of 0.5-1 mm; the protective ring (3) is a PMMA hollow ring with an outer diameter of 55-65 mm and a thickness of 0.5-1 mm, and the inner diameter of the protective ring is spaced 0.4-0.6 mm from the collecting electrode (2).

4. The personal dose equivalent H according to claim 3 p (3) A secondary standard ionization chamber, characterized in that: The incident window (6) is a graphite film with a diameter of 35 to 45 mm and a thickness of 30 to 35 μm.

5. The personal dose equivalent H according to any one of claims 1 to 4 p (3) A secondary standard ionization chamber, characterized in that: A truncated cone structure with an inclination angle of 45° is adopted between the metal ring and the protective cover (7).

6. A beta radiation personal dose equivalent H p (3) A method for transferring a quantity value, wherein the method is to use the personal dose equivalent H as described in any one of claims 1 to 5. p (3) The secondary standard ionization chamber is realized, and the method comprises the following steps: S1. Using a simulation method, establish physical models of human tissue and a backscatter phantom, and obtain a database of absorbed dose-to-personal dose equivalent conversion coefficients for typical β nuclides under the backscatter phantom within an incident angle range of -45° to +45° through simulation calculations; S2. The personal dose equivalent H p (3) The secondary standard ionization chamber is placed under the β radiation field, and an antiscattering phantom is placed next to the rear end of the ionization chamber to ensure that the average incident direction of the β ray enters the sensitive area of ​​the ionization chamber vertically. The corresponding absorbed dose D at the measurement point is calculated based on the current reading measured by the electrometer T , the calculation formula is: In the above formula: J a —Accumulated charge; —average ionization energy of air; —Ratio of the average mass stopping power of PMMA and air; —Air quality in sensitive areas; k PT —Temperature and pressure correction factor, where P and T are the pressure and temperature at ambient conditions, respectively; S3. Multiply the absorbed dose measurement result in step S2 by the conversion coefficient of the corresponding β nuclide at the corresponding incident angle in the absorbed dose-personal dose equivalent conversion coefficient database to obtain the personal dose equivalent H at the measurement point. p (3) the agreed value; S4. The individual dose equivalent to be measured H p (3) The monitoring equipment is placed under the β radiation field, and the personal dose equivalent H p (3) The monitoring device is placed on the backscatter phantom, so that the reference point of the monitoring device is located at a measurement point in the β radiation field where the agreed value of the personal dose equivalent is known. The personal dose equivalent reading of the monitoring device at the measurement point is measured, and the personal dose equivalent H is obtained by calculating the relative inherent error, statistical fluctuation and angular response of the monitoring device. p (3) Transmission of measurement values ​​of monitoring equipment.

7. The beta radiation personal dose equivalent H according to claim 6 p (3) A method for transferring value, characterized in that: Step S1 is specifically as follows: S11. Establishing a physical model of human tissue and a backscattering phantom using simulation modeling software, and injecting monoenergetic beta particles with a set fluence Φ and energy E into the physical model at an incident angle of 0°; S12. Take a small volume element at a depth of 3 mm inside the human tissue along the horizontal direction of the radiation field, simulate the energy deposition and mass in the small volume element, and calculate the personal dose equivalent H. p (3), the calculation formula is: Where: Q—β particle quality factor. For weakly penetrating β particles from external irradiation, Q=1Sv / Gy; dε—energy deposition in a small volume element; dm—mass of small volume element; S13, only the small volume element at the depth of 3mm is retained, and other structural models are removed, and the absorbed dose D of the monoenergetic β particles incident at 0° with the set fluence Φ, energy E, and angle is obtained by simulation. T ; S14, according to H p (3) and D T Obtain the conversion coefficient of absorbed dose-personal dose equivalent. The calculation formula of the conversion coefficient is: H p (3) / D T ; S15. Changing the incident angle of the beta particle, repeating steps S11-S14, and finally establishing a conversion coefficient between the absorbed dose of a monoenergetic beta particle with energy E at a specific incident angle of the small volume element and the personal dose equivalent; S16. Combined with the standard emission spectrum of typical β radionuclides, calculate the H emission of typical β nuclides under the backscattering phantom at an incident angle of -45° to +45°. p (3) and D T , thus obtaining H p (3) / D T Conversion coefficient database, the calculation formula is:

8. The beta radiation personal dose equivalent H according to claim 7 p (3) A method for transferring value, characterized in that: The method for determining the relative inherent error of the monitoring equipment in step S4 is: The dose equivalent rate measurement range covers at least 2 decimal levels within the effective measurement range of the monitoring equipment, and the dose equivalent measurement range covers at least 3 decimal levels within the effective measurement range of the monitoring equipment. There are at least 4 measurement points, and the number of repeated measurements of each measurement point is not less than 4 times. The measurement points within the lowest decimal level are repeated for not less than 7 times. The relative inherent error I of each measurement point is calculated according to the following formula: i : Where: —The average value of the readings at the i-th measurement point; H iC —The agreed value of the individual dose equivalent at the i-th measurement point.

9. The beta radiation personal dose equivalent H according to claim 8 p (3) A method for transferring value, characterized in that: The method for determining the statistical fluctuation of the monitoring device in step S4 is: Repeat the measurement at the selected measurement point for no less than 10 times, and calculate the statistical fluctuation V of the monitoring equipment according to the following formula: Where: n is the number of repeated measurements.

10. The beta radiation personal dose equivalent H according to claim 7 p (3) A method for transferring value, characterized in that: The method for determining the angular response of the monitoring device in step S4 is: The monitoring device is changed to an angle α in two perpendicular planes passing through its reference point and including the reference direction, α = ±15°, ±30°, ±45°, and the angular response R of the monitoring device at the corresponding angle is measured according to the following formula: Where: H E,α —Personal dose equivalent readings measured by monitoring equipment; H 0,α —Personal dose equivalent H p (3) The agreed value of personal dose equivalent given by the secondary standard ionization chamber.

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