Ionization chamber beta activity measuring device

Abstract

The invention relates to the technical field of beta activity measurement, in particular to an ionization chamber beta activity measuring device which comprises a top cover and a handle, the handle is fixedly connected to the upper surface of the top cover, a plurality of grooves are formed in the top cover, nuts are in clearance fit with the interiors of the grooves, screws are fixedly connected to the lower portions of the nuts, and the screws are fixedly connected to the upper surface of the top cover. The outer wall of the screw rod is in threaded connection with the shell, and the upper end of the shell is attached to the top cover. The device adopts a beta activity measuring device designed by a small cylindrical ionization chamber, adopts the ionization chamber as a detector, designs a micro-current measuring system with an automatic range conversion function, also designs automatic compensation and current calibration functions, can deduct a background current value, and finally converts the background current value into the radioactive activity of the energy nuclide through automatic operation. The device can be installed in a hot chamber, a shielding chamber and a glove box for use, the beta activity of the radioactive material of 10 mCi to 20 Ci can be accurately measured, the measurement uncertainty is smaller than or equal to 5% (k = 1), and a user can conveniently and accurately master the beta activity in the measured sample material.

Description

Technical Field

[0001] This invention relates to the field of β activity measurement technology, specifically to an ionization chamber β activity measurement device. Background Technology

[0002] A beta activity measuring device is an activity meter that outputs activity measurement results in a digital direct-reading manner. It can be applied to fields such as isotope production, radiation detection, and nuclear medicine. With the rapid development of nuclear medicine, more and more short-lived or ultra-short-lived artificial nuclides are being used in clinical diagnosis and treatment. The rapid decay of these nuclides over time urgently requires a measuring device to quickly determine the radioactivity of nuclides. Summary of the Invention

[0003] The purpose of this invention is to solve the problem of rapid decay of nuclides over time, and to propose an ionization chamber β-activity measuring device.

[0004] To achieve the above objectives, the present invention provides the following technical solution: Design an ionization chamber β activity measuring device, including a top cover and a handle. The handle is fixedly attached to the upper surface of the top cover. Multiple grooves are provided inside the top cover. Nuts are fitted into the grooves with clearances. A screw is fixedly attached below the nut. The outer wall of the screw is threadedly connected to the outer shell. The upper end of the outer shell is in contact with the top cover.

[0005] Preferably, the lower end of the switch is in contact with the aviation plug, which is installed inside the housing.

[0006] Preferably, a composite shielding layer is fixed to the inner wall of the outer shell.

[0007] Preferably, the interior of the outer casing is provided with a β-ionization chamber.

[0008] Preferably, the first lead shielding layer is disposed inside the outer casing.

[0009] Preferably, a pre-ionization and electronic measurement processing module is installed inside the housing.

[0010] Preferably, the interior of the outer casing is provided with a second lead shielding layer.

[0011] Preferably, an indicator light is installed on the upper surface of the top cover.

[0012] Preferably, a first lead shielding layer is disposed above the β-ionization chamber.

[0013] Preferably, a switch is installed inside the top cover.

[0014] The ionization chamber β activity measuring device proposed in this invention has the following advantages: This device adopts a small cylindrical ionization chamber design for β activity measuring device, uses the ionization chamber as a detector, designs a micro-current measurement system with automatic range switching, and also designs automatic compensation and current calibration functions, which can deduct the background current value, and finally convert it into the radioactivity of the energy nuclide through automatic calculation.

[0015] Compared with conventional β activity meters that use a 4π well-type ionization chamber and liquid scintillation counting, this device has advantages such as small overall size, large activity measurement range, good repeatability of β radiation response, lower requirements for the preparation of the sample material, high detection efficiency, high result accuracy, and strong anti-interference ability. This device can be installed in a hot chamber, shielded room, or glove box and can accurately measure the β activity of radioactive materials ranging from 10 mCi to 20 Ci, with a measurement uncertainty of ≤5% (k=1), making it convenient for users to accurately determine the β activity in the sample material being tested. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a cross-sectional view of the structure of the present invention; Figure 3 This is a block diagram illustrating the principle of the electronic measurement and processing module in this invention. Figure 4 This is a schematic diagram of the working principle of the range switching circuit in this invention; Figure 5 This is a flowchart of the calibration function in this invention.

[0017] In the diagram: 1. Top cover, 2. Handle, 3. Groove, 4. Nut, 5. Screw, 6. Housing, 7. Switch, 8. Plug, 9. Composite shielding layer, 10. β ionization chamber, 11. First lead shielding layer, 12. Pre-ionization, 13. Second lead shielding layer, 14. Electronic measurement and processing module, 15. Indicator light. Detailed Implementation

[0018] The present invention will be further described below with reference to the accompanying drawings: See attached document Figure 1-5In this embodiment, an ionization chamber β activity measuring device includes a top cover 1 and a handle 2. The handle 2 is fixedly attached to the upper surface of the top cover 1, which facilitates the lifting of the device. The top cover 1 has multiple grooves 3 inside, and a through hole is provided below the groove 3 to facilitate the passage of the screw 5. The nut 4 cannot pass through the through hole. The nut 4 is fitted with a clearance inside the groove 3. The screw 5 is fixedly attached below the nut 4. The nut 4 and the screw 5 move together, and the screw 5 can be rotated through the nut 4. The outer wall of the screw 5 is threadedly connected to the outer shell 6. The top cover 1 and the outer shell 6 are connected and fixed through the screw 5, the nut 4 and the groove 3. The upper end of the outer shell 6 is in contact with the top cover 1. A switch 7 is installed inside the top cover 1, which is easy to press.

[0019] The lower end of switch 7 contacts the connector 8, allowing for easy control of the connector 8. The connector 8 is installed inside the housing 6. A composite shielding layer 9 is fixed to the inner wall of the housing 6. The composite shielding layer 9 uses a multi-layer composite shielding method, with an outer layer of 1cm low-carbon steel, a middle layer of 5cm low-background lead, and an inner layer of 3mm oxygen-free copper. It is integrally cast to avoid internal bubbling and ensure uniform density. This shielding design effectively absorbs X-rays and gamma rays while reducing background interference caused by external bremsstrahlung radiation, protecting key components and reducing radiation damage. The housing 1 is easy to clean and decontaminate. A β-ionization chamber 10 is installed inside the housing 6. A first lead shielding layer 11 is installed above the β-ionization chamber 10 and is located inside the housing 6. A pre-ionization 12 and an electronic measurement and processing module 14 are installed inside the housing 6. A second lead shielding layer 13 is installed inside the housing 6. An indicator light 15 is installed on the upper surface of the top cover 1. The indicator light 15 is electrically connected to the internal circuit system of the device.

[0020] The measuring device's outer shell is made of stainless steel, which is resistant to salt spray and corrosion. The composite shielding layer uses a multi-layer material composite shielding method. The outer material is 1cm of low carbon steel, the middle material is 5cm of low background lead layer, and the inner material is 3mm of oxygen-free copper. It is integrally cast to avoid internal bubbling and ensure uniform density. This shielding design effectively absorbs X-rays and gamma rays, while reducing background interference caused by external bremsstrahlung radiation, protecting key components and reducing radiation damage. The outer shell is easy to clean and decontaminate.

[0021] The β-ionization chamber is located at the bottom of the measuring device. A groove for placing the sample material is designed directly below the entrance window of the β-ionization chamber. The electronics module is placed above the β-ionization chamber. The push-button switches, status indicator lights, communication interfaces, and power interfaces are arranged on the same side for easy use, wiring, and monitoring of the device status.

[0022] The beta ionization chamber is the detector of this measuring device, which converts the high-intensity electron beam emitted by Sr-90 radioactive material into a measurable current signal. The beta ionization chamber uses a cylindrical shell and a concentric rod as the collecting electrode. To more accurately respond to the relationship between beta ray energy and dose, the ionization chamber uses a thin stainless steel shell with an energy compensation structure. Considering the nonlinear effect of carrier collection in the ionization chamber caused by high-intensity beta rays, the ionization chamber is small in volume and filled with He gas at 1 atmosphere. The chamber wall material is as free of alpha particle emitters as possible (such as those containing thorium, radium, uranium, potassium, etc.). Since beta rays have a long range, in order to make full use of the ionization effect of beta rays, the ionization chamber is enlarged to extend the ionization path of beta rays. In order to eliminate the influence of alpha rays, the ray window is made of ultra-thin stainless steel material to absorb alpha rays.

[0023] Description of main technical specifications of β-ionization chamber

[0024] 1. Interaction between alpha rays and thin windows Alpha ray characteristics: Typical energies 4–9 MeV (e.g.) 239 Pu's 5.15 MeV, 210 Po (5.3 MeV) Extremely short range: about 3–6 cm in He at 1 atmosphere, and only 10–20 μm in 20 μm stainless steel, before being completely absorbed.

[0025] The function of thin windows: 20μm stainless steel windows (density ≈ 8 g / cm³) 3 It has an extremely high linear stopping power (dE / dx) against alpha particles, and can completely block alpha rays from entering the ionization chamber.

[0026] The range of 5 MeV α particles in stainless steel is approximately 15 μm (SRIM simulation data), therefore a thickness of 20 μm is sufficient for shielding.

[0027] 2. The purpose of the He gas filling design Advantages of He gas: Its low density (0.1785 g / L, 1 atmosphere) significantly increases the range of alpha particles (compared to 2–3 cm in air), but alpha interference can still be avoided inside the ionization chamber through geometric design (pole spacing <3 cm).

[0028] He gas is much more efficient at detecting gamma / X-rays than alpha, therefore alpha is blocked by a thin window.

[0029] Mechanisms for eliminating the effects of alpha: Physical barrier: Alpha particles cannot penetrate stainless steel windows.

[0030] Signal discrimination: Even if a very small number of alphas enter (such as window defects), their ionization signal amplitude (high LET) can be eliminated by electronic thresholding.

[0031] The meticulously designed electrometer circuit and two-stage preamplifier circuit are key to micro-current measurement. Besides performing IV-to-IV conversion of the ionization current, the preamplifier circuit is crucial for impedance transformation of the input current, thereby enabling accurate measurement of a wide current range. This circuit mainly consists of an electrometer-stage operational amplifier ADA4530-1, multiple fixed resistors, and relays. The core component, the ADA4530-1 operational amplifier, has a maximum input bias current of 20fA and a maximum offset voltage of 50pV, effectively reducing IV-to-IV conversion errors. Multiple fixed resistors and relays form a switchable sampling resistor network for range switching, effectively reducing interference between digital and analog signals by isolating them.

[0032] The MCU controls the AD7172-2 analog-to-digital converter to realize the current calibration and automatic compensation functions of the measuring device. After the device is started, it first completes the initialization parameter configuration of each module. The operator can choose to enter the calibration compensation mode or the current measurement mode. The calibration compensation mode is divided into two modes: current calibration and automatic compensation. The current calibration mode includes zero-level calibration and full-scale calibration for each range. This mode requires the use of a standard current source. The automatic compensation mode does not require the use of a standard current source. When there is no current input (input current value is 0) or when the background current value needs to be subtracted, automatic compensation is activated. The device will adjust to each range in sequence and perform 64 measurements. Finally, the measured values ​​are processed and the results are written into an 8-byte compensation register. In subsequent measurements, the data in the compensation register is used to correct the measurement data, thereby achieving the function of automatic compensation of the current measurement value.

[0033] The total test uncertainty is calculated by combining the uncertainty of the radioactive source activity value, the uncertainty corrected for ionization recombination loss during ionization current collection in the β-ionization chamber, the uncertainty of the ionization current measurement, the uncertainty of the linear extrapolation of activity, and the uncertainty of repeated tests for the same activity.

[0034] The ionization chamber β activity measuring device underwent uncertainty testing at the National Institute of Metrology, China. The source used by the National Institute of Metrology was an imported Sr-90 plane source, whose activity uncertainty was 3.7% (K=2). The uncertainty converted to K=1 was μ1=3.7% / 2=1.85%.

[0035] For the ionization recombination loss of Sr-90 sources with different activities in the range of 0.1Ci to 20Ci, the test values ​​are corrected by substituting them into the current-activity conversion software. The measurement uncertainty after this correction is usually considered to be within 1%, i.e., μ2≤1.0%.

[0036] For sources with activity of 0.01 Ci to 20 Ci, the corresponding ionization current ranges from 10⁻⁷ A to 10⁻⁴ A. Within this range, the uncertainty of current measurement is ≤0.01%, i.e., μ³≤0.01%.

[0037] The activity of the tested sample material is linearly extrapolated within the range of 0.04 mCi to 0.27 mCi, with a relative measurement deviation not exceeding 4.76%. The measurement uncertainty is assessed using a uniformly distributed Type B uncertainty. for Therefore, for Sr-90 sources with a range of 0.1 mCi to 20 Ci, the uncertainty of linear extrapolation will not exceed 2.75%. The greater the activity, the smaller the relative deviation of the measured current, and the smaller the measurement uncertainty according to the same evaluation. Therefore, μ4 ≤= 2.75%.

[0038] When the distance between the source and the incident window of the β-ionization chamber is fixed, the uncertainty of the measurement device for repeated testing of the same activity is very small and can be ignored, i.e., μ5=0%.

[0039] The combined uncertainty is calculated from the following factors: uncertainty of the source activity value used in the activity calibration, uncertainty corrected for ionization recombination loss during ionization current collection in the β-ionization chamber, uncertainty of ionization current measurement, uncertainty of linear extrapolation of activity, and uncertainty of repeated testing of the same activity.

[0040] Therefore, it can be seen that the measurement device can test the Sr-90 source within the range of 0.01Ci to 20Ci, achieving the requirement of measurement uncertainty of 3.46% < 5% (K=1).

[0041] Increase experimental data on the thickness gradient of the shielding layer (e.g., when the lead layer is increased from 1 cm to 5 cm, the γ background interference is reduced by 40%).

[0042] Experimental data on gamma-ray attenuation of lead shielding of different thicknesses

[0043] In the table, the attenuation percentage = (1 - dose rate after shielding / dose rate without shielding) × 100%; Test conditions: Gamma source: 137 Cs (662 keV), 60 Co (1.25 MeV), 22 Na (511 keV, positron annihilation radiation).

[0044] Lead purity: ≥99.99%, seamless structure.

[0045] Theoretical calculations were performed on the gamma-ray attenuation of lead shielding of different thicknesses, using equivalent calculations with half-value layers (HVL) and ten-fold attenuation layers (TVL): 137 Cs (662 keV): HVL ≈ 0.65 cm Pb → 5cm lead ≈ 7.7 HVL (theoretical attenuation 99.95%).

[0046] 60 Co (1.25 MeV): HVL ≈ 1.2 cm Pb → 5 cm lead ≈ 4.2 HVL (theoretical attenuation 99.7%).

[0047] 22 Na (511 keV): HVL ≈ 0.5 cm Pb → 5 cm lead ≈ 10 HVL (theoretical attenuation 99.97%).

[0048] Supplement the energy compensation curves for thin windows (20 μm) to compare the differences in absorption efficiency of alpha rays for different materials (such as titanium windows). Working principle: This device employs a small cylindrical ionization chamber for beta activity measurement, using the ionization chamber as the detector. It incorporates a micro-current measurement system with automatic range switching, automatic compensation, and current calibration functions. It can subtract the background current value and finally convert the result into the radioactivity of the nuclide through automatic calculation. Compared with conventional beta activity meters using 4π well-type ionization chambers and liquid scintillation counting, this device has advantages such as smaller overall size, a larger measurement range, better repeatability of beta radiation response, lower requirements for sample preparation, higher detection efficiency, higher result accuracy, and stronger anti-interference ability. This device can be installed in a hot chamber, shielded room, or glove box and can accurately measure the beta activity of radioactive materials ranging from 10 mCi to 20 Ci, with a measurement uncertainty ≤5% (k=1), allowing users to accurately determine the beta activity in the sample material being measured.

[0049] Although the present invention has been illustrated and described with reference to preferred embodiments, those skilled in the art will understand that various changes in form and detail are possible within the scope of the claims.

Claims

1. An ionization chamber beta activity measuring device comprising a top cover (1) and a handle (2), the upper surface of the top cover (1) is fixed with a handle (2), characterized in that: The inside of the top cover (1) is provided with a plurality of recesses (3), the inside gap of the recess (3) is matched with a screw cap (4), the lower part of the screw cap (4) is fixedly connected with a screw rod (5), the outer wall of the screw rod (5) is threadedly connected with an outer shell (6), and the upper end of the outer shell (6) is attached to the top cover (1).

2. A device for measuring the activity of beta particles in an ionization chamber according to claim 1, characterized in that: The lower end of the switch (7) is in contact with a navigation plug (8), and the navigation plug (8) is installed in the inside of the outer shell (6).

3. A device for measuring the activity of beta particles in an ionization chamber according to claim 1, characterized in that: The inner wall of the outer shell (6) is fixedly connected with a composite shielding layer (9).

4. A device for measuring the activity of beta particles in an ionization chamber according to claim 1, characterized in that: The inside of the outer shell (6) is provided with a beta ionization chamber (10).

5. A chamber beta activity measurement device according to claim 4, characterised in that: The first lead shielding layer (11) is arranged in the inside of the outer shell (6).

6. A device for measuring the activity of beta particles in an ionization chamber according to claim 1, characterized in that: The inside of the outer shell (6) is installed with a pre-ionization (12) and an electronic measurement processing module (14).

7. A device for measuring the activity of beta particles in an ionization chamber according to claim 1, characterized in that: The inside of the outer shell (6) is provided with a second lead shielding layer (13).

8. A device for measuring the activity of beta particles in an ionization chamber according to claim 1, characterized in that: The upper surface of the top cover (1) is installed with an indicating lamp (15).

9. A beta activity measurement device for an ionization chamber according to claim 4, characterized in that: The upper part of the beta ionization chamber (10) is provided with the first lead shielding layer (11).

10. A device for measuring the activity of beta particles in an ionization chamber according to claim 1, characterized in that: The inside of the top cover (1) is installed with a switch (7).

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