CN103267798B - Measuring device and measuring method of high-concentration tritium in gas - Google Patents

Abstract

The invention provides a device for measuring high-concentration tritium in gas and a measuring method thereof. The measuring device of the present invention is composed of two cylindrical ionization chambers with identical structures and materials but different sizes. The measurement method of the present invention is to pass the tritium-containing gas through the two ionization chambers in the measurement device of the present invention in sequence, and make the two ionization chambers in the tritium measurement device work in the compensation mode, and obtain the tritium in the gas by signal matching. concentration. The measuring device of the invention can completely eliminate the influence of the memory effect on the measurement result caused by the adsorption of tritium on the wall of the ionization chamber when measuring high-concentration tritium in gas, and realize long-term and accurate measurement of tritium in gas under high-concentration conditions. The invention fully meets the requirements of real-time and continuous measurement of high-concentration tritium in various places.

Description

Device for measuring high-concentration tritium in gas and its measuring method

technical field

The invention belongs to the technical field of radiation protection and environmental protection, and in particular relates to a measuring device for high-concentration tritium in gas and a measuring method thereof. It is suitable for real-time measurement of tritium concentration in tritium operating glove boxes, secondary containers and other tritium containing containers.

Background technique

Tritium is the only radioactive isotope of hydrogen. The maximum energy of beta rays emitted by tritium decay is 18.6keV, and its average energy is 5.65keV. Tritium may corrode containment materials or cause degradation of material properties (brittleness, aging). Moreover, tritium can also enter the human body through inhalation, ingestion, and infiltration through intact skin, and be absorbed by human tissue and cause it to be exposed to internal radiation hazards. Due to its radioactive hazards and its characteristics in the environment, in radiation protection monitoring, tritium Monitoring is receiving increasing attention.

Tritium’s low-energy β particles have very weak penetrating ability. The maximum range in water is 6 μm, and the maximum range in air is only 5mm. It is difficult to measure with ordinary β detectors. Therefore, to measure tritium, tritium-containing gas must be introduced into the detector. measurement inside.

At present, the method of ionization chamber is used for the measurement of high concentration tritium in gas. However, when the concentration of tritium is high, especially in the presence of tritiated water vapor, the background of the ionization chamber will be greatly increased due to the large amount of tritium adsorption by the chamber wall material (generally, it will increase by more than 2 orders of magnitude) , which will directly lead to high ionization chamber measurement results during continuous monitoring of tritium concentration, which cannot be accurately measured. In addition, it is difficult to decontaminate the ionization chamber after contamination, and it takes a long time to restore the background of the ionization chamber to normal.

Contents of the invention

In order to eliminate the memory effect caused by the adsorption of tritium on the wall of the ionization chamber in the prior art and improve the accuracy of high-concentration tritium measurement, the purpose of the present invention is to provide a high-concentration tritium measurement device in gas. Another purpose of the invention is to provide a method for measuring high concentration tritium in gas. The memory effect caused by the adsorption of tritium on the wall of the ionization chamber is eliminated by means of signal compensation, and the real-time measurement of high-concentration tritium in the gas is realized.

The method for measuring high-concentration tritium in gas of the present invention is based on the geometrical principle that the volumes of cylinders with different geometric structures are the same when the inner surface area is the same. Sensitive volume for measurement. The measuring device of the present invention is constructed based on two ionization chambers, both of which are cylindrical, have completely the same inner surface area, and are processed with the same material and process. During the measurement, the two ionization chambers are respectively applied with saturation voltages of opposite polarities, so that the two ionization chambers collect positive ions and electrons respectively, and then carry out the coincidence of the signals. Due to the same inner surface area, the adsorption of tritium on the wall of the ionization chamber is the same after high-concentration tritium, and this part can be completely eliminated when the signals of the two ionization chambers coincide, that is, the memory effect of the ionization chamber will be effectively eliminated, and the ionization chamber system The final output signal is the signal output by the volume difference of the two ionization chambers.

The technical solution adopted by the present invention to solve its technical problems is as follows:

The device for measuring high-concentration tritium in gas of the present invention is characterized in that the measuring device contains two cylindrical first ionization chambers and second ionization chambers with the same structure. Wherein, the first ionization chamber includes a shell, a first insulating member, an ionization chamber wall, a second insulating member, a first gas pipe, a first collector, a third insulating member, a fourth insulating member, a guard ring, and a fifth insulating member , the lower cover of the ionization chamber, the sixth insulator, the high-voltage terminal, the nut, the high-voltage cable head, the signal cable head, and the second gas pipe; the connection relationship is that the collector is located on the central axis of the first ionization chamber, and the collector The lower end of the collector is suspended in the first ionization chamber, the upper end is provided with a fourth insulator, the upper end of the collector is fixed with the fourth insulator by a nut; the fourth insulator is provided with a protection ring, and the protection ring is provided with a fifth insulator The fifth insulator is provided with the lower cover of the ionization chamber; the wall of the ionization chamber is connected to the lower cover of the ionization chamber; the high-voltage terminal is fixed on the lower cover of the ionization chamber; the first gas pipe is connected to the wall of the ionization chamber, and the first gas pipe A second insulator is arranged between the walls of the ionization chamber; the walls of the ionization chamber and the lower cover of the ionization chamber are both arranged in the casing, and a first insulating member is arranged between the walls of the ionization chamber and the casing; the lower cover of the ionization chamber is A sixth insulator is arranged between the bases; the high-voltage cable head and the signal cable head are fixed on the side of the base; the collector of the first ionization chamber, the wall of the ionization chamber, and the shell are concentrically arranged;

Both the shell of the first ionization chamber and the second ionization chamber are fixed on the base; the first ionization chamber is connected with the second ionization chamber through the second gas pipe, and a The third insulator, the seventh insulator is arranged between the second gas pipe and the lower cover of the ionization chamber of the second ionization chamber; the first collector of the first ionization chamber is connected with the second collector of the second ionization chamber through a signal cable .

The collector, the fourth insulating part, the protective ring, the fifth insulating part, and the lower cover of the ionization chamber are all interference fits; the second air pipe, the lower cover of the ionization chamber, and the third insulating part are all interference fits ; There is an interference fit between the first air pipe, the wall of the ionization chamber and the second insulating member.

The materials of the fourth insulating part and the fifth insulating part are polytetrafluoroethylene; the materials of the ionization chamber wall, collecting electrode, protective ring, and the lower cover of the ionization chamber are all 316L stainless steel.

The first ionization chamber and the second ionization chamber have the same inner surface area.

The materials used in the first ionization chamber and the second ionization chamber are the same.

The method for measuring high-concentration tritium in gas of the present invention is characterized in that comprising the following steps in sequence:

①. Calculation of equivalent volume of ionization chamber system

The sensitive volumes of the first ionization chamber and the second ionization chamber are respectively: and ,and , then the equivalent volume of the ionization chamber system is: (1)

②.Ionization chamber saturation working voltage measurement

Measure the saturation operating voltages of the first ionization chamber and the second ionization chamber in the ionization chamber system respectively;

Keep the tritium concentration, gas pressure, and gas temperature in the ionization chamber constant, apply different high voltages to the high-voltage electrodes of the ionization chamber, measure the current collected by the ionization chamber, obtain the saturation voltage range of the ionization chamber, and record the saturation working voltage range of the first ionization chamber for , the saturation working voltage interval of the second ionization chamber is ;

③. Equivalent saturation current measurement of ionization chamber system

Apply saturation operating voltages with opposite polarities to the first ionization chamber and the second ionization chamber respectively, and apply saturation operating voltage to the first ionization chamber , add saturation working voltage in the second ionization chamber , the saturation current signal collected by the ionization chamber system is measured by a weak current measuring instrument ;

④. Calculation of tritium concentration in gas

The saturation current collected in the measured ion chamber system After that, the tritium concentration in the gas can be calculated by formula (2):

(2)

In the formula:

E - is the average energy of beta rays of tritium, unit eV, take 5.65keV;

e - electronic charge, unit 1.6×10 ^-19 C;

- is the average ionization work of the gas in the sealed container, that is, the average energy required to generate a pair of ions in the gas in the sealed container, the unit is eV, and the value corresponding to air is 36.0eV/ion pair;

V _eff - is the sensitive volume of the ionization chamber, in m ³ ;

Bring the above parameters into the formula (2) to get the tritium concentration value in the gas.

The working principle of the present invention is to use a system composed of two ionization chambers to eliminate the memory effect produced by the adsorption of tritium on the walls of the chambers. When working, add high voltage with opposite polarity to the high-voltage electrodes of the two ionization chambers, so that the signals collected by the collectors of the ionization chambers are opposite, and the output signals of the two ionization chambers are directly connected to the collectors of the two ionization chambers. Conformity, completely eliminate the memory effect caused by the adsorption of tritium on the wall of the ionization chamber, and realize the accurate measurement of high-concentration tritium in the gas. The invention fully satisfies the requirements of continuous on-line measurement of high-concentration tritium in various places (such as glove boxes, secondary containers and other tritium containing containers).

Description of drawings

Fig. 1 is a schematic structural diagram of a device for measuring high-concentration tritium in gas according to the present invention.

In the figure: 1. Shell 2. First insulating part 3. Ionization chamber wall 4. Second insulating part 5. First gas pipe 6. First collector 7. Third insulating part 8. Fourth insulating part 9. Protection Ring 10. The fifth insulating piece 11. The lower cover of the ionization chamber 12. The sixth insulating piece 13. High voltage terminal 14. Nut 15. High voltage cable head 16. Signal cable head 17. Second gas pipe 18. Base.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings.

Example 1

Fig. 1 is a schematic structural diagram of a device for measuring high-concentration tritium in gas according to the present invention. In Fig. 1, the device for measuring high-concentration tritium in gas of the present invention contains two cylindrical first ionization chambers I and second ionization chambers II with the same structure. Among them, the first ionization chamber I includes a shell 1, a first insulating member 2, an ionization chamber wall 3, a second insulating member 4, a first gas pipe 5, a first collector 6, a third insulating member 7, and a fourth insulating member 8. Protective ring 9, fifth insulator 10, ionization chamber lower cover 11, sixth insulator 12, high-voltage terminal 13, nut 14, high-voltage cable head 15, signal cable head 16, second gas pipe 17; its connection The relationship is that the collector 6 is located on the central axis of the first ionization chamber I, the lower end of the collector 6 is suspended in the interior of the first ionization chamber I, the upper end is provided with a fourth insulating member 8, and the upper end of the collector 6 is insulated from the fourth The part 8 is fixed by a nut 14; the fourth insulating part 8 is provided with a protective ring 9, and the protective ring 9 is provided with a fifth insulating part 10, and the fifth insulating part 10 is provided with an ionization chamber lower cover 11; the ionization chamber wall 3 It is connected to the lower cover 11 of the ionization chamber; the high-voltage terminal 13 is fixed on the lower cover 11 of the ionization chamber; the first gas pipe 5 is connected to the wall 3 of the ionization chamber, and a second Insulator 4; the ionization chamber wall 3 and the ionization chamber lower cover 11 are all arranged in the shell 1, and a first insulating member 2 is arranged between the ionization chamber wall 3 and the shell 1; the ionization chamber lower cover 11 and the base 18 A sixth insulator 12 is arranged between them; the high-voltage cable head 15 and the signal cable head 16 are fixed on the side of the base 18; the collector 6 of the first ionization chamber, the wall 3 of the ionization chamber, and the shell 1 are all arranged concentrically;

Both the shells of the first ionization chamber I and the second ionization chamber II are fixed on the base 18; the first ionization chamber I is connected with the second ionization chamber II through the second gas pipe 17, and the second gas pipe 17 is connected with the A third insulator 7 is arranged between the lower cover 11 of the ionization chamber, and an insulating member is arranged between the second gas pipe 17 and the lower cover of the ionization chamber of the second ionization chamber II; the first collector 6 of the first ionization chamber I and the second The second collector of the second ionization chamber II is connected by a signal cable.

The collector 6, the fourth insulator 8, the guard ring 9, the fifth insulator 10, and the lower cover 11 of the ionization chamber are all interference fits; the second gas pipe 17, the lower cover 11 of the ionization chamber, and the third insulator 7 are all interference fits; the first air pipe 5, the ionization chamber wall 3, and the second insulating member 4 are interference fits.

The materials of the fourth insulating part 8 and the fifth insulating part 10 are polytetrafluoroethylene; the materials of the ionization chamber wall 3, the collector 6, the protection ring 9 and the lower cover 11 of the ionization chamber are all 316L stainless steel.

The first ionization chamber I and the second ionization chamber II have the same inner surface area but different volumes.

The materials used in the first ionization chamber I and the second ionization chamber II are the same.

A method for measuring high-concentration tritium in gas of the present invention comprises the following steps:

①. Calculation of equivalent volume of ionization chamber system

In this example, the volumes of the two ionization chambers are 1.4L and 1.0L respectively, then the equivalent volume .

②.Ionization chamber saturation working voltage measurement

Under the condition of keeping the tritium concentration gas pressure and gas temperature in the ionization chamber constant, the measured saturation working voltage intervals of the ionization chambers with effective volumes of 1.4L and 1.0L are respectively and .

③. Equivalent saturation current measurement of ionization chamber system

In this embodiment, the saturation operating voltage is applied to the first ionization chamber and the second ionization chamber respectively and , the equivalent saturation current of the ionization chamber system measured with a weak current measuring instrument nA.

④. Calculation of tritium concentration in gas

According to formula (2), the tritium concentration in this embodiment is:

            

After measuring the concentration of tritium-containing gas, flush with nitrogen for 15 minutes, and the ionization chamber system restores the background current.

The present invention is not limited to this embodiment, and all described in the present invention can be implemented and have good effects.

Claims (6)

1. A device for measuring high-concentration tritium in gas, characterized in that: the measuring device contains two cylindrical first ionization chambers and second ionization chambers with the same structure; wherein, the first ionization chamber includes a housing (1) , the first insulator (2), the wall of the ionization chamber (3), the second insulator (4), the first gas pipe (5), the first collector (6), the third insulator (7), the fourth Insulator (8), protective ring (9), fifth insulator (10), lower cover of ionization chamber (11), sixth insulator (12), high voltage terminal (13), nut (14), high voltage Cable head (15), signal cable head (16), and second gas pipe (17); the connection relationship is that the collector (6) is located on the central axis of the first ionization chamber, and the lower end of the collector (6) is suspended above Inside the first ionization chamber, the upper end is provided with a fourth insulator (8), and the upper end of the collector (6) and the fourth insulator (8) are fixed by a nut (14); the fourth insulator (8) is provided with The protective ring (9), the fifth insulating part (10) is arranged outside the protective ring (9), and the fifth insulating part (10) is provided with the lower cover of the ionization chamber (11); the wall of the ionization chamber (3) and the lower part of the ionization chamber The cover (11) is connected; the high-voltage terminal (13) is fixed on the lower cover (11) of the ionization chamber; the first air pipe (5) is connected to the wall (3) of the ionization chamber, and the first air pipe (5) is connected to the ionization chamber A second insulator (4) is arranged between the walls (3); the ionization chamber wall (3) and the ionization chamber lower cover (11) are all arranged in the shell (1), and the ionization chamber wall (3) and The first insulating piece (2) is arranged between the shells (1); the sixth insulating piece (12) is arranged between the lower cover of the ionization chamber (11) and the base (18); the high-voltage cable head (15) and the signal cable head (16) fixed on the side of the base (18); the collector (6), the ionization chamber wall (3), and the shell (1) of the first ionization chamber are all arranged concentrically; Both the shell of the first ionization chamber and the second ionization chamber are fixed on the base (18); the first ionization chamber is connected to the second ionization chamber through the second gas pipe (17), and the second gas pipe (17) is connected to the first ionization chamber The third insulator (7) is set between the lower cover (11) of the ionization chamber, and the seventh insulator is set between the second gas pipe (17) and the lower cover of the ionization chamber of the second ionization chamber; the first ionization chamber The first collector (6) is connected with the second collector of the second ionization chamber through a signal cable. 2. A device for measuring high-concentration tritium in gas according to claim 1, characterized in that: the collector (6), the fourth insulator (8), the protection ring (9), the fifth insulator (10 ), the lower cover of the ionization chamber (11) are all interference fits; the second air pipe (17), the lower cover of the ionization chamber (11), and the third insulating member (7) are all interference fits; the first air pipe (5) There is an interference fit between the ionization chamber wall (3) and the second insulating member (4). 3. A device for measuring high-concentration tritium in gas according to claim 1, characterized in that: the material of the fourth insulator (8) and the fifth insulator (10) are polytetrafluoroethylene; the ionization chamber The wall (3), collector (6), protective ring (9), and the lower cover of the ionization chamber (11) are all made of 316L stainless steel. 4. A device for measuring high-concentration tritium in gas according to claim 1, characterized in that: the first ionization chamber and the second ionization chamber have the same inner surface area. 5. A device for measuring high-concentration tritium in gas according to claim 1, characterized in that: the materials used in the first ionization chamber and the second ionization chamber are the same. 6. A measuring method for the high-concentration tritium measuring device in gas according to claim 1, characterized in that comprising the following steps successively: ①. Calculation of equivalent volume of ionization chamber system The sensitive volumes of the first ionization chamber and the second ionization chamber are respectively: and ,and , then the equivalent volume of the ionization chamber system is: (1) ②.Ionization chamber saturation working voltage measurement Measure the saturation operating voltages of the first ionization chamber and the second ionization chamber in the ionization chamber system respectively; Keep the tritium concentration, gas pressure, and gas temperature in the ionization chamber constant, apply different high voltages to the high-voltage electrodes of the ionization chamber, measure the current collected by the ionization chamber, obtain the saturation voltage range of the ionization chamber, and record the saturation working voltage range of the first ionization chamber for , the saturation working voltage interval of the second ionization chamber is ; ③. Equivalent saturation current measurement of ionization chamber system Apply saturation operating voltages with opposite polarities to the first ionization chamber and the second ionization chamber respectively, and apply saturation operating voltage to the first ionization chamber , add saturation working voltage in the second ionization chamber , the saturation current signal collected by the ionization chamber system is measured by a weak current measuring instrument ; ④. Calculation of tritium concentration in gas The saturation current collected in the measured ion chamber system After that, the tritium concentration in the gas can be calculated by formula (2): (2) In the formula: E - is the average energy of beta rays of tritium, unit eV, take 5.65keV; e - electronic charge, unit 1.6×10 ^-19 C; - is the average ionization work of the gas in the sealed container, that is, the average energy required to generate a pair of ions in the gas in the sealed container, the unit is eV, and the value corresponding to air is 36.0eV/ion pair; V _eff - is the sensitive volume of the ionization chamber, in m ³ ; Bring the above parameters into the formula (2) to get the tritium concentration value in the gas.