Device for continuously monitoring concentration of tritium in air

Abstract

The invention discloses a device for continuously monitoring the concentration of tritium in air. The device can eliminate the influence of background gamma rays of an environment or a measurement place on tritium measurement during continuous monitoring. Comprising a monitor air inlet structure, a detector and a display processing unit, the detector comprises a first ionization chamber, a second ionization chamber and a detection circuit between the first ionization chamber and the second ionization chamber, the second ionization chamber is located below the first ionization chamber and is symmetrically installed relative to the detection circuit, and the structure of the second ionization chamber is completely the same as that of the first ionization chamber; except for the ionization chamber air inlet hole and the ionization chamber air outlet hole, the whole ionization chamber is airtight, so that sample air cannot leak out from other places except for the ionization chamber air inlet hole and the ionization chamber air outlet hole.

Description

Technical Field

[0001] This invention belongs to the field of radiation protection and environmental protection technology, and specifically relates to a device for continuous monitoring of tritium concentration in the air. Background Technology

[0002] Tritium is a low-energy beta nuclide with an average energy of only 5.65 keV. However, it exhibits strong physical and chemical adsorption, making the measurement and protection against tritium extremely important.

[0003] Because the ionization chamber also responds to gamma rays during tritium measurements, the measurement of any type of radiation inevitably involves the background problem—that is, how to distinguish and eliminate (or reduce) counts unrelated to the measured object. For low-level radioactivity measurements, the impact is not only on the system instrument and its performance, but also on the background of the surrounding workplace, Compton scattering, and interference from cosmic rays. The sources of background counts are mainly threefold: first, the background from particles produced by cosmic rays and their secondary effects; second, the background from radioactive elements present in the environment surrounding the measurement system; and third, the background from radioactive impurities contained in the materials of the measuring device and detector. Among these, the environmental background is objectively present, and appropriate measures must be taken to reduce its influence on the measurement results. Summary of the Invention

[0004] The purpose of this invention is to provide a device for continuous monitoring of tritium concentration in the air, so as to eliminate the influence of background gamma rays in the environment or measurement site on tritium measurement.

[0005] The technical solution adopted by this invention to solve its technical problem is as follows:

[0006] This invention provides a continuous monitoring device for tritium concentration in air, comprising an air intake structure, a detector, and a display processing unit. The air intake structure is connected to the detector, and the detector is connected to the display processing unit via an RS485 port. The detector includes a first ionization chamber, a second ionization chamber, and a detection circuit between the first and second ionization chambers. The first ionization chamber includes a shell and a first ionization chamber cavity, with a high-voltage electrode disposed between the shell and the first ionization chamber cavity. A first collecting electrode is disposed within the first ionization chamber cavity, with a base disposed at the lower end of the first collecting electrode. An insulating support is disposed between the first collecting electrode and the base. An insulator is disposed between the high-voltage electrode and the base. Both the high-voltage electrode and the first collecting electrode are led out to the outside of the ionization chamber and connected to the detection circuit via conductors.

[0007] The second ionization chamber is located below the first ionization chamber, is symmetrically installed with respect to the detection circuit, and has the same structure as the first ionization chamber.

[0008] The detection circuit is housed in a square shielded box.

[0009] The shielding box is installed inside the base.

[0010] Both the insulating support and the insulator are made of polytetrafluoroethylene (PTFE).

[0011] Both the first ionization chamber and the second ionization chamber are provided with an ionization chamber air inlet and an ionization chamber air outlet.

[0012] The ionization chamber inlet and outlet are respectively connected to the base inlet and outlet.

[0013] The detection circuit includes a signal terminal and a high-voltage terminal.

[0014] The signal terminal is led out and connected to the RS485 port of the display processing unit.

[0015] The high-voltage end is connected to the first collecting electrode of the first ionization chamber and the second collecting electrode of the second ionization chamber.

[0016] The high voltage applied to the first and second collector electrodes has opposite polarities.

[0017] To eliminate the influence of background gamma rays from the environment or measurement site on tritium measurement, this invention designs a second ionization chamber. The second ionization chamber has the same internal structure and dimensions as the first ionization chamber and is symmetrically positioned below the first ionization chamber (primarily to ensure airtightness). The high voltage applied to both chambers has opposite polarities. When an external gamma field is present, currents of the same magnitude but opposite polarities are generated at the collecting electrodes of both chambers, canceling each other out and providing compensation. Since the collecting electrodes of the second and first ionization chambers are not directly connected, a detection circuit generates the required positive and negative high voltage power supply for the ionization chamber. The detection circuit amplifies the fA-level current signal output from the collecting electrode of the ionization chamber, calculates the tritium activity concentration in the air, and sends the result to the display and processing unit.

[0018] The beneficial effects of this invention are:

[0019] To eliminate the influence of background gamma rays from the environment or measurement site on tritium measurements, this invention ensures that the entire ionization chamber is airtight, except for the inlet and outlet ports. All structural joints must be airtight. This includes the conductive leads of the collecting electrode, which must be sealed to prevent sample air from leaking out through any point other than the ionization chamber inlet / outlet ports. The detection circuit is first placed in a sealed shielded box, which is then placed inside a base. Dedicated insulators are designed for the signal and high-voltage leads of the circuit to ensure both insulation and airtightness. Attached Figure Description

[0020] Figure 1 Schematic diagram of a continuous air tritium concentration monitoring device;

[0021] Figure 2 A schematic diagram of the side structure of the detector in a continuous air tritium concentration monitoring device;

[0022] Figure 3 Schematic diagram of the bottom structure of the detector of the continuous air tritium concentration monitoring device;

[0023] Figure 4 Block diagram of the detector circuit of a continuous air tritium concentration monitoring device;

[0024] Reference numerals: First ionization chamber-1, Second ionization chamber-2, Detection circuit-3, Outer shell-4, High voltage electrode-5, First collecting electrode-6, Base-7, Insulating support-8, Insulator-9, Inlet / outlet port-10, Power supply port-11, Signal terminal-12, High voltage terminal-13. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to the accompanying drawings.

[0026] like Figure 1 As shown, a continuous air tritium concentration monitoring device includes an air intake structure, a detector, and a display processing unit. The air intake structure is connected to the detector, and the detector is connected to the display processing unit via an RS485 port. The detector includes a first ionization chamber 1, a second ionization chamber 2, and a detection circuit 3 between the first and second ionization chambers. The first ionization chamber 1 includes a shell 4 and a first ionization chamber cavity. A high-voltage electrode 5 is disposed between the shell 4 and the first ionization chamber cavity. A first collecting electrode 6 is disposed within the first ionization chamber cavity. A base 7 is disposed at the lower end of the first collecting electrode. An insulating support 8 is disposed between the first collecting electrode 6 and the base 7. An insulator 9 is disposed between the high-voltage electrode and the base. Both the high-voltage electrode 5 and the first collecting electrode 6 are led out to the outside of the ionization chamber and connected to the detection circuit via conductors. The second ionization chamber is located below the first ionization chamber, symmetrically installed with respect to the detection circuit, and its structure is exactly the same as that of the first ionization chamber.

[0027] It should be noted that in the air intake structure, under the suction of the air pump, the air sample to be tested enters through the air inlet / outlet 10, impurities are filtered out by the filter, and it enters the measurement ionization chamber through the flow sensor, and finally flows out through the air pump and outlet.

[0028] Within the sensitive volume of the first ionization chamber (measuring ionization chamber), tritium emits beta rays that ionize the air. The resulting charge is collected by the first collecting electrode of the ionization chamber. The output current of the first collecting electrode is proportional to the concentration of tritium radioactivity in the air and the sensitive volume of the ionization chamber. Since the first ionization chamber also responds to gamma rays, a second ionization chamber (compensating ionization chamber) is designed to eliminate the influence of background gamma rays from the environment or measurement site on tritium measurement. The second ionization chamber has the same internal structure and dimensions as the first ionization chamber, but the applied high voltages are of opposite polarity. When an external gamma field is present, currents of the same magnitude but opposite polarity are generated at the collecting electrodes of both the second and first ionization chambers, canceling each other out and providing compensation. To measure the compensated current, a detection circuit is used, comprising a signal terminal 12 and a high-voltage terminal 13. The power supply port 11 amplifies the fA-level current signal output from the collector of the ionization chamber, calculates the activity concentration of tritium in the air, and sends the result to the display processing unit, while maintaining insulation and airtightness in the environment throughout the process.

[0029] The processing unit communicates with the detector via RS485 to acquire, process, display, store, and query measurement data. The processing unit also controls the air pump and acquires flow data via an interface circuit, enabling continuous monitoring.

[0030] like Figure 2 As shown, the second ionization chamber is located below the detection circuit and symmetrical to the first ionization chamber, and its internal structure is exactly the same as that of the first ionization chamber.

[0031] The air sample entering the first ionization chamber first flows through a strong electric field region formed by a narrow slit between the outer shell and the high-voltage electrode, removing charged impurities from the sample. It then passes through the mesh surface at the top of the high-voltage electrode into the measurement chamber where it is measured, and finally flows out of the first ionization chamber. The high-voltage electrode and the base are insulated with polytetrafluoroethylene (PTFE); the collecting electrode and the base are also insulated with PTFE, with sufficiently high insulation resistance. Both the high-voltage electrode and the collecting electrode are led out of the ionization chamber through conductors.

[0032] like Figure 3 As shown, except for the ionization chamber inlet and outlet, the entire ionization chamber is airtight, and all structural joints must be airtight. This includes the conductive leads of the collecting electrode, all of which must be sealed to prevent sample air from leaking out through any point other than the ionization chamber inlet / outlet. The detection circuit is first placed in a sealed shielded box, which is then placed inside the base. Dedicated insulators must be designed for the signal and high-voltage leads of the circuit to ensure both insulation and airtightness.

[0033] like Figure 4As shown, within the sensitive region of the first ionization chamber, beta rays emitted by tritium in the sample air ionize the air. The collecting electrode of the first ionization chamber collects the ionized charge to form an output current. (Due to the compensating effect of the second ionization chamber...)

[0034] The output current of the tritium measurement ionization chamber is calculated using the following formula:

[0035] The output current of the tritium measurement ionization chamber is calculated using the following formula:

[0036]

[0037] E: The average energy deposited by each decay in air, measured in eV; average energy of tritium particle decay.

[0038] It is 5.65 keV;

[0039] C: Concentration of radioactive gases in the ionization chamber, in Bq / m³ 3 ;

[0040] e: electron charge, 1.6 × 10⁻⁶ -19 coulomb;

[0041] w: The average energy required to produce one pair of ions in the air, expressed in units of 33.7 eV;

[0042] Ve: Volume of the ionization chamber, in cubic meters (m³) 3 ;

[0043] Substituting the numbers above into the formula above, we get:

[0044]

[0045] Assuming the sensitive volume of the ionization chamber, Ve = 3 L, and the tritium activity concentration in the air is the lower limit of the instrument's measurement, then C = 0.037 MBq / M 3 ,but:

[0046] Is = 3.1 × 10 -15 A

[0047] At this point, the instrument outputs the current corresponding to the lower limit of measurement. Therefore, the detection circuit must accurately measure currents in the fA range and maintain insulation and airtightness in the environment throughout the process.

[0048] The circuit amplifies, acquires, and processes the current signal output from the ionization chamber to calculate the tritium activity concentration in the air, and sends the result to the processing unit. The processing unit communicates with the detector via RS485 to acquire, process, display, store, and query the measurement data. The processing unit also controls the air pump and acquires flow data via an interface circuit, enabling continuous monitoring.

Claims

1. A device for continuous monitoring of tritium concentration in air, comprising a monitoring instrument air inlet structure, a detector and a display processing unit, the air inlet structure being connected to the detector, and the detector being connected to the display processing unit via an RS485 port, characterized in that, The detector comprises a first ionization chamber and a second ionization chamber and a detection circuit between the first ionization chamber and the second ionization chamber, the first ionization chamber comprises a shell and a first ionization chamber cavity, a high-voltage electrode is arranged between the shell and the first ionization chamber cavity, a first collecting electrode is arranged in the first ionization chamber cavity, a base is arranged at the lower end of the first collecting electrode, an insulating support is arranged between the first collecting electrode and the base, an insulator is arranged between the high-voltage electrode and the base, and the high-voltage electrode and the first collecting electrode are both led out of the ionization chamber to be connected with the detection circuit through conductors. The second ionization chamber is arranged below the first ionization chamber and is symmetrically arranged relative to the detection circuit and has the same structure as the first ionization chamber.

2. The device for continuous monitoring of tritium concentration in air according to claim 1, characterized in that, The detection circuit is arranged in a square shielding box.

3. A device for continuous monitoring of tritium concentration in air according to claim 2, characterized in that, The shielding box is arranged in the base.

4. The device for continuous monitoring of tritium concentration in air according to claim 1, characterized in that, The insulating support and the insulator are both made of polytetrafluoroethylene material.

5. The device for continuous monitoring of tritium concentration in air according to claim 1, characterized in that, The first ionization chamber and the second ionization chamber are both further provided with an ionization chamber air inlet hole and an ionization chamber air outlet hole.

6. A device for continuous monitoring of tritium concentration in air according to claim 5, characterized in that, The ionization chamber air inlet hole and the ionization chamber air outlet hole are respectively connected with a base air inlet hole and a base air outlet hole.

7. The device for continuous monitoring of tritium concentration in air according to claim 1, characterized in that, The detection circuit comprises a signal end and a high-voltage end.

8. A device for continuous monitoring of tritium concentration in air according to claim 7, characterized in that, The signal end is led out to be connected with an RS485 port of a display processing unit.

9. The apparatus according to claim 7, wherein The high-voltage end is connected with a first collecting electrode of the first ionization chamber and a second collecting electrode of the second ionization chamber.

10. The apparatus according to claim 9, wherein The high-voltage polarity of the high-voltage end applied to the first collecting electrode and the second collecting electrode is opposite.

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