Sampling type fission ionization chamber and method for measuring total number of fissions based on the same

Abstract

The present invention relates to a fission ionization chamber, and in particular to a sampling type fission ionization chamber and a method for determining the total number of fissions based on the same, which solves the problems of introducing large measurement uncertainty when measuring fission yields with an existing ionization chamber due to the existence of self-shielding in the ionization chamber and poor consistency of neutron energy spectrum, and being unable to measure gas fission products and short-lived fission products and having a great impact on the health of measurement personnel. The ionization chamber is special in that it includes a cathode support and a cathode coaxially arranged from bottom to top, and an anode support arranged in the cathode cavity and coaxial with the cathode; an annular sealing boss and an isolation boss are arranged on the bottom surface of the anode support, and the sealing boss is located outside the isolation boss; the lower end surface of the sealing boss is sealed and fixedly connected to the inner surface of the bottom of the cathode; there is a gap between the lower end of the isolation boss and the inner surface of the bottom of the cathode; a sampling anode and an annular anode are attached to the bottom surface of the anode support, and the sampling anode is located inside the isolation boss; the annular anode is located between the isolation boss and the sealing boss.

Description

Technical Field

[0001] The present invention relates to a fission ionization chamber, in particular to a sampling type fission ionization chamber and a method for measuring the total number of fissions based on the same. Background Art

[0002] The probability of producing fission product A per unit fission of nuclear materials such as uranium, plutonium, and neptunium is called the fission yield of A. Generally speaking, there are certain differences in the fission cross section and fission yield values ​​under different neutron fields. When developing advanced nuclear devices such as nuclear reactors, the relationship between the change of fission yield and neutron energy is an important basis for the determination of fission burnup and other work. The determination of fission yield requires the simultaneous measurement of the total amount of fission products and the total number of fissions of nuclear materials. For the measurement of the total amount of fission products, β measurement, γ spectrum or mass spectrometry analysis is generally used. When measuring, it is usually required that the total number of fissions per unit time is greater than 10 7 When the fission ionization chamber is used to measure the total number of fissions, the optimal counting rate range of the fission ionization chamber is 10~10 3 cps; therefore, for the measurement of the total amount of fission products and the total number of fissions, it is usually necessary to use different targets and then convert the ratio of fission numbers through the mass ratio.

[0003] There are usually three methods for measuring the fission number: activation method (Finn.EC et al., Cumulative fissionyields of short-lived isotopes under natural-abundance-boron-carbi-de-moderated neutron spectrum.Journal of Radioanalytical and Nuclear Chemistry, Vol. 306, No. 1, 2015), solid fission track density method (Wang Dongmei et al. 24.4 KeV neutron induced 235 U fission yield measurement, Nuclear Chemistry and Radiochemistry, Vol. 13, No. 4, 1991) and double fission chamber method (Feng Jing et al., 0.57, 1.0 and 1.5 MeV neutron induced 235 U fission 99 Absolute measurement of Mo yield, Atomic Energy Science and Technology, Vol. 47, No. 9, 2015). The first two methods have high uncertainties, so the third method is usually used.

[0004] The double fission chamber was first invented by an American (Leo R. Boy et al., Fission chamber assembly, U.S. Patent, Publication No.: US3043954A, Publication Date: July 10, 1962). The structure of the double fission chamber commonly used in China is basically the same as that of the American (Feng Jing, 0.57MeV, 1.0MeV and 1.5MeV neutron induced 235 U fission product yield measurement, Master's thesis of China Institute of Atomic Energy, 2006). Figure 1 As shown, the interior of the double fission chamber is similar to a sandwich structure, with the upper and lower layers being two fission chambers for measuring the total number of fissions, namely the upper ionization chamber 01 and the lower ionization chamber 03; and the middle being a thick target for measuring the total amount of fission products, namely the thick fission target 02. The upper ionization chamber 01 includes a first collecting anode 011 and a first target cathode 012 arranged in sequence from top to bottom; the lower ionization chamber 03 includes a second target cathode 032 and a second collecting anode 031 arranged in sequence from top to bottom. The first target cathode 012 and the second target cathode 032 are standard fission material metal thin targets or fission material coatings with metal sheets such as platinum, titanium, and high-purity aluminum as substrates; the thick fission target 02 is a fission material metal or plated sheet. The double fission chamber has an outer shell 04 on the outside, and the outer shell 04 is filled with a working gas 06. The double fission chamber is placed under the neutron field 05 for irradiation. After the irradiation is completed, the thick fission target 02 is taken out from the shell 04 for measuring the total amount of fission products and analyzing the target fission products; the fission number is calculated by counting the upper ionization chamber 01 and the lower ionization chamber 03, and then the total number of fissions of the middle thick fission target 02 is obtained by the method of converting the mass ratio to the ratio of the fission number and a series of corrections, and then the fission yield of the target fission product is obtained. The above method for measuring and calculating the fission yield has the following disadvantages:

[0005] (1) The dual fission chamber has a self-shielding problem with the neutron field. Since the upper ionization chamber 01 itself moderates and scatters the neutron field 05, the neutron energy spectrum reaching the thick fission target 02 and the lower ionization chamber 03 is different from the initial neutron energy spectrum of interest. When calculating the fission number from the counts of the upper ionization chamber 01 and the lower ionization chamber 03, a series of corrections need to be made, which introduces additional large uncertainties.

[0006] (2) The "sandwich" arrangement of the upper ionization chamber 01, the thick fission target 02, and the lower ionization chamber 03 will also cause differences in neutron flux. Since the neutron beam is generally not a completely uniform and parallel beam, the farther away from the neutron source, the lower the neutron flux. The upper ionization chamber 01, the thick fission target 02, and the lower ionization chamber 03 are arranged in sequence from near to far along the emission direction of the neutron field 05. There will be slight differences in the neutron flux at each position, which will also introduce uncertainty.

[0007] (3) After irradiation, the thick fission target 02 needs to be removed in time for radioactivity measurement. Due to its non-sealed nature and complicated operation, it is impossible to accurately measure gaseous fission products and short-lived fission products. Therefore, the above method is generally only used to measure the fission yield of solid fission products with a longer lifespan.

[0008] (4) When the above-mentioned double fission ionization chamber is used to measure and calculate the fission yield, it is necessary to disassemble the double fission ionization chamber and take out the thick fission target 02 for radioactivity measurement. During the process of disassembling the double fission ionization chamber and taking out the thick fission target 02, the personnel will be exposed to a large radiation dose, which has a great impact on the health of the measurement personnel. Summary of the invention

[0009] The purpose of the present invention is to provide a sampling fission ionization chamber and a method for determining the total number of fissions based on the same, so as to solve the technical problems that when using the existing double fission ionization chamber to measure the fission yield, due to the self-shielding of the ionization chamber and the poor consistency of the neutron energy spectrum, a large measurement uncertainty is introduced, and the gas fission products and short-lived fission products cannot be measured and the health of the measurement personnel is greatly affected.

[0010] The technical solution adopted by the present invention is a extraction type fission ionization chamber, which is special in that:

[0011] It includes a cathode holder and a cathode which are coaxially arranged and fixedly connected from bottom to top, an anode holder which is arranged in the cathode cavity and coaxial with the cathode, and also includes a sampling anode, a ring anode, a sampling cathode sleeve, a balancing cathode sleeve, a sampling anode column, a balancing anode column and a working gas introduction unit; the cathode is detachably connected by an upper and a lower part to form a chamber;

[0012] The lower bottom surface of the anode holder is provided with an annular sealing boss and an annular isolation boss, the sealing boss is located outside the isolation boss and is coaxial with the anode holder; the height of the sealing boss is greater than the thickness of the annular thick fission target to be measured, which is attached to the inner surface of the cathode bottom, coaxial with the cathode and located between the sealing boss and the isolation boss; the lower end surface of the sealing boss is sealed and fixedly connected to the inner surface of the bottom of the cathode; there is a gap between the lowermost end of the isolation boss and the inner surface of the bottom of the cathode;

[0013] The sampling anode is attached to the lower bottom surface of the anode holder and is located inside the ring of the isolation boss and is coaxially arranged with the anode holder; the radial dimension of the sampling anode is larger than the radial dimension of the sampled thin fission target to be measured attached to the center of the inner surface of the cathode bottom;

[0014] The annular anode is attached to the lower bottom surface of the anode holder and is located between the isolation boss and the sealing boss, and is coaxially arranged with the anode holder; the radial dimension of the annular anode is consistent with the radial dimension of the annular thick fission target to be measured; the thickness of the annular anode is the same as that of the sampling anode;

[0015] The anode holder is provided with a sampling anode hole and a balancing anode hole with parallel axes, and the sampling anode hole is coaxial with the anode holder, and the balancing anode hole is between the isolation boss and the sealing boss; the top plate of the cathode is provided with a first through hole coaxial with the sampling anode hole and a second through hole coaxial with the balancing anode hole;

[0016] The sampling cathode sleeve and the balancing cathode sleeve pass through the first through hole and the second through hole respectively, are coaxially arranged with the first through hole and the second through hole, and both are fixedly connected to the cathode;

[0017] The sampling anode column is electrically connected to the sampling anode after passing through the sampling cathode sleeve and the sampling anode hole; the balancing anode column is electrically connected to the annular anode after passing through the balancing cathode sleeve and the balancing anode hole;

[0018] There are annular gaps between the sampling anode column and the sampling cathode sleeve, the sampling anode column and the sampling anode hole, the balancing anode column and the balancing cathode sleeve, and the balancing anode column and the balancing anode hole, and insulating sealant is filled in the corresponding annular gaps;

[0019] The anode support and the cathode support are both made of solid insulating material;

[0020] The cathode, sampling anode, annular anode, sampling cathode sleeve, balancing cathode sleeve, sampling anode column, and balancing anode column are all made of solid conductive materials;

[0021] The working gas introduction unit is used to transport working gas to the sealed cavity surrounded by the bottom surface of the anode support, the sealing boss and the inner surface of the cathode bottom.

[0022] Further, the working gas introduction unit includes a gasket, a clamping screw, a syringe and a gas supply unit;

[0023] On the anode support, an air inlet hole parallel to the axis of the sampling anode hole is provided between the isolation boss and the sealing boss, and the air inlet hole is a stepped hole with a larger top and a smaller bottom; a third through hole coaxial with the air inlet hole is provided on the top plate of the cathode; and a fourth through hole coaxial with the air inlet hole is provided on the annular anode;

[0024] The radial dimension of the gasket is adapted to the aperture dimension of the large hole at the upper end of the air inlet;

[0025] The gasket and the clamping screw are sequentially arranged in the upper large hole of the air inlet from bottom to top, and the clamping screw is fixedly connected to the anode support through a thread; the gasket is compressed by the clamping screw to seal the air path; a guide hole is vertically arranged at the center of the upper end surface of the clamping screw;

[0026] One end of the syringe needle passes through the guide hole and the gasket and is connected with the small hole at the lower end of the air inlet hole; the other end of the syringe opposite to the needle is connected with the gas supply unit.

[0027] Further, the gas supply unit includes a first valve, a third valve, a working gas storage device, a second valve, a vacuum pump and a pressure gauge;

[0028] After the other end of the syringe opposite to the needle passes through the first valve, it is divided into three paths: the first path is connected to the working gas storage device through the third valve; the second path is connected to the vacuum pump through the second valve; and the third path is connected to the pressure gauge. In this way, it is convenient to control the size of the gas flow and the gas pressure.

[0029] Further, the air inlet hole is located at the outermost side along the radial direction between the isolation boss and the sealing boss;

[0030] The balanced anode hole and the air inlet hole are symmetrically arranged on both sides of the center of the anode support, so that the influence on the electric field distribution is minimal and the measurement is more accurate.

[0031] Furthermore, in order to facilitate the positioning of the syringe, the guide hole is a stepped hole that is larger at the top and smaller at the bottom, and the large hole at the upper end is a hexagonal hole; the radial dimension of the hexagonal hole is compatible with the radial dimension of the hexagonal wrench used to lock the clamping screw; the aperture size of the small hole at the lower end of the guide hole is compatible with the tube diameter size of the syringe.

[0032] Furthermore, the height of the sealing boss is at least 2 mm higher than the thickness of the annular thick fission target to be measured. In this way, after the fission material on the fission target fissions, there is enough distance for the energy of the fission electrons to be completely consumed, and the final measured signal is high and can be distinguished from noise, thereby improving the accuracy of the measurement.

[0033] Furthermore, in order to allow airflow to pass through and to make the available area of ​​the sampled thin fission target to be measured and the annular thick fission target to be measured large enough, the cross-sectional shape of the isolation boss is an inverted triangle with a larger upper portion and a smaller lower portion.

[0034] Furthermore, in order to facilitate the positioning and tiling of the sampling anode, the anode holder includes an anode holder body and an adapter;

[0035] The adapter is in the shape of a stepped shaft with a larger upper portion and a smaller lower portion, and the outer diameter of the lower end surface of the adapter is equal to the outer diameter of the sampling anode; a through hole is vertically arranged at the center of the upper end surface of the adapter; the through hole is the sampling anode hole;

[0036] An adapter mounting hole adapted to the adapter is vertically arranged at the center of the upper end surface of the anode support body; the adapter is arranged in the adapter mounting hole, and the lower end surface of the adapter is flush with the lower end surface of the anode support body; the anode support is composed of the anode support body and the adapter fixedly connected by sealing.

[0037] Furthermore, the anode support, cathode support and clamping screw are all made of organic glass;

[0038] The cathode is made of high-purity aluminum foil;

[0039] The sampling anode and the annular anode are made of pure aluminum;

[0040] The gasket is made of silicone material;

[0041] The insulating sealant is epoxy resin;

[0042] The upper part of the cathode is a cylindrical upper cover, and the lower part is a circular bottom plate, and the enclosed chamber is a cylindrical chamber. In this way, the radioactive dose of the activated product after neutron irradiation can be greatly reduced, and the structure of the cathode is simple.

[0043] The present invention also provides a method for measuring the total number of fissions based on the above-mentioned sampling fission ionization chamber, characterized in that it comprises the following steps:

[0044] Step 1: quantitatively weigh the fission target materials to be measured respectively and make them evenly adhere to the set positions of the sampled thin fission target to be measured and the annular thick fission target to be measured on the inner surface of the cathode bottom, so as to prepare the sampled thin fission target to be measured and the annular thick fission target to be measured; and the ratio of the mass of the fission materials contained in the annular thick fission target to be measured and the sampled thin fission target to be measured is recorded as R;

[0045] Step 2: stick the sampling anode and the ring anode to the set position on the bottom surface of the anode support; place the sampling cathode sleeve, the balancing cathode sleeve, the sampling anode column, and the balancing anode column at the set position, seal and fix them with epoxy resin, so that the sampling anode column is electrically connected to the sampling anode, and the balancing anode column is electrically connected to the ring anode;

[0046] Step 3: sealingly and fixedly connect the lower end surface of the sealing boss of the anode holder to the bottom inner surface of the cathode; sealingly and fixedly connect the upper surface of the cathode holder to the bottom outer surface of the cathode;

[0047] Step 4: Cover the upper part of the cathode and electrically connect the upper and lower parts of the cathode; electrically connect the cathode to the sampling cathode sleeve, and the cathode to the balance cathode sleeve; at this point, the main body of the ionization chamber is completed;

[0048] Step 5: first evacuate the sealed cavity surrounded by the bottom surface of the anode support, the sealing boss and the inner surface of the cathode bottom in the ionization chamber body through the working gas introduction unit, and then deliver the working gas;

[0049] Step 6: Place the ionization chamber body to which the working gas is delivered in step 5 in a neutron field for irradiation. The irradiation direction is from the cathode support to the anode support. Measure the total count N of the sampled anode pulse signal. According to the ratio R of the mass of the fissile material contained in the annular thick fission target to be measured and the sampled thin fission target to be measured in step 1, calculate that the total number of fissions of the annular thick fission target to be measured is 2R·N, and the total number of fissions of the nuclear material is (2R+2)N.

[0050] The beneficial effects of the present invention are:

[0051] (1) In the sampling type fission ionization chamber of the present invention, the sampled thin fission target to be measured and the annular thick fission target to be measured are concentric and located in the same plane, which effectively avoids the inconsistency of the neutron energy spectrum self-absorption of the ionization chamber and the thick fission target; the lower end surface of the sealing boss is sealed and fixedly connected with the bottom inner surface of the cathode, and insulating sealant is filled in the annular gaps between the sampling anode column and the sampling cathode sleeve, the sampling anode column and the sampling anode hole, the balance anode column and the balance cathode sleeve, and the balance anode column and the balance anode hole, so that the bottom surface of the anode support, the sealing boss and the bottom inner surface of the cathode form a A sealed cavity is provided, and such a sealing design can realize the simultaneous measurement of gaseous and solid fission products; the extractable fission ionization chamber of the present invention can be transferred as a whole after irradiation without disassembly, which is convenient for non-destructive measurement of γ and can greatly reduce the radioactive dose received by the workers; therefore, the present invention solves the technical problems that when the existing double fission ionization chamber is used to measure the fission yield, due to the self-shielding of the ionization chamber and the poor consistency of the neutron energy spectrum, a large measurement uncertainty is introduced, and the gaseous fission products and short-lived fission products cannot be measured, and the health of the measuring personnel is greatly affected.

[0052] (2) The extraction-type fission ionization chamber of the present invention preferably uses a large amount of insulating organic materials, which can significantly reduce the radioactive dose of the activated products after neutron irradiation. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a structural schematic diagram of a double fission ionization chamber in the background technology.

[0054] Figure 1 The descriptions of the labels are as follows:

[0055] 01-upper ionization chamber, 011-first collecting anode, 012-first target cathode, 02-thick fission target, 03-lower ionization chamber, 031-second collecting anode, 032-second target cathode, 04-outer shell, 05-neutron field, 06-working gas.

[0056] Figure 2 is a schematic structural diagram of an embodiment of the present invention;

[0057] Figure 3 is a three-dimensional appearance diagram of an embodiment of the present invention;

[0058] Figure 4 Schematic diagram of the gas path for inflating the embodiment of the present invention.

[0059] Figures 2 to 4 The descriptions of the labels are as follows:

[0060] 1-anode support, 101-adapter, 102-anode support body, 2-cathode support, 3-cathode, 4-sealing boss, 5-air inlet, 6-isolating boss, 7-sampling anode hole, 8-balancing anode hole, 9-sampling anode, 10-annular anode, 11-sampling thin fission target to be measured, 12-annular thick fission target to be measured, 13-pressing screw, 1301-guide hole, 14-gasket, 15-sampling anode column, 16-balancing anode column, 1701-sampling cathode sleeve, 1702-balancing cathode sleeve, 18-ionization chamber body, 19-injector, 21-first valve, 22-second valve, 23-third valve, 24-working gas storage device, 25-pressure gauge, 26-vacuum pump. DETAILED DESCRIPTION

[0061] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0062] See also Figure 2 and Figure 3 The present invention provides a sampling type fission ionization chamber, comprising a cathode holder 2 and a cathode 3 which are coaxially arranged and fixedly connected in sequence from bottom to top, an anode holder 1 which is arranged in the inner cavity of the cathode 3 and is coaxial with the cathode 3, and also comprises a sampling anode 9, a ring anode 10, a sampling cathode sleeve 1701, a balance cathode sleeve 1702, a sampling anode column 15, a balance anode column 16 and a working gas introduction unit. The cathode 3 is detachably connected by upper and lower parts to form a chamber. In this embodiment, the cathode holder 2 is preferably cylindrical; the upper part of the cathode 3 is a cylindrical upper cover, and the lower part is a circular bottom plate, and the chamber formed is a cylindrical chamber, and the upper and lower parts are connected by conductive glue; the cathode holder 2 and the cathode 3 are bonded by epoxy resin. And preferably, the anode holder 1 is also cylindrical.

[0063] The lower bottom surface of the anode holder 1 is provided with an annular sealing boss 4 and an annular isolation boss 6. The sealing boss 4 is located outside the isolation boss 6 and is coaxial with the anode holder 1. The height of the sealing boss 4 is greater than the thickness of the annular thick fission target 12 to be measured, which is attached to the inner surface of the bottom of the cathode 3, coaxial with the cathode 3 and located between the sealing boss 4 and the isolation boss 6. In this embodiment, the height of the sealing boss 4 is preferably at least 2 mm higher than the thickness of the annular thick fission target 12 to be measured. The lower end surface of the sealing boss 4 is sealed and fixedly connected to the inner surface of the bottom of the cathode 3. In this embodiment, the lower end surface of the sealing boss 4 is preferably sealed with the inner surface of the bottom of the cathode 3 by epoxy resin to ensure its sealing. There is a gap between the lower end of the isolation boss 6 and the inner surface of the bottom of the cathode 3. In order to allow the airflow to pass through and to make the available area of ​​the sampled thin fission target to be measured and the annular thick fission target to be measured large enough, in this embodiment, the cross-sectional shape of the isolation boss 6 is preferably an inverted triangle with a large top and a small bottom.

[0064] The sampling anode 9 is attached to the lower bottom surface of the anode holder 1 and is located inside the annular isolation boss 6, and is coaxially arranged with the anode holder 1; the radial dimension of the sampling anode 9 is larger than the radial dimension of the sampled thin fission target 11 to be measured which is attached to the center of the bottom inner surface of the cathode 3; the annular anode 10 is attached to the lower bottom surface of the anode holder 1 and is located between the isolation boss 6 and the sealing boss 4, and is coaxially arranged with the anode holder 1; the radial dimension of the annular anode 10 is consistent with (i.e., equal to or similar to) the radial dimension of the annular thick fission target 12 to be measured; the thickness of the annular anode 10 is the same as that of the sampling anode 9.

[0065] The anode holder 1 is provided with a sampling anode hole 7 and a balancing anode hole 8 with parallel axes, and the sampling anode hole 7 is coaxial with the anode holder 1, and the balancing anode hole 8 is between the isolation boss 6 and the sealing boss 4; the top plate of the cathode 3 is provided with a first through hole coaxial with the sampling anode hole 7 and a second through hole coaxial with the balancing anode hole 8; the sampling cathode sleeve 1701 and the balancing cathode sleeve 1702 respectively pass through the first through hole and the second through hole, and are coaxially arranged with the first through hole and the second through hole, and both are fixedly connected to the cathode 3; the sampling anode column 15 passes through the sampling After the cathode sleeve 1701 and the sampling anode hole 7, it is electrically connected to the sampling anode 9; after the balanced anode column 16 passes through the balanced cathode sleeve 1702 and the balanced anode hole 8, it is electrically connected to the annular anode 10; there are annular gaps between the sampling anode column 15 and the sampling cathode sleeve 1701, the sampling anode column 15 and the sampling anode hole 7, the balanced anode column 16 and the balanced cathode sleeve 1702, and the balanced anode column 16 and the balanced anode hole 8, and insulating sealant is filled in the corresponding annular gaps. In this embodiment, the insulating sealant is preferably epoxy resin. In order to facilitate the positioning and tiling of the sampling anode 9, in this embodiment, the above-mentioned anode support 1 preferably includes an anode support body 102 and an adapter 101; the adapter 101 is a stepped shaft shape with a larger upper part and a smaller lower part, and the outer diameter of the lower end face of the adapter 101 is equal to the outer diameter of the sampling anode 9; a through hole is vertically arranged at the center of the upper end face of the adapter 101; the above-mentioned through hole is the sampling anode hole 7; an adapter mounting hole that is compatible with the adapter 101 is vertically arranged at the center of the upper end face of the anode support body 102; the adapter 101 is arranged in the adapter mounting hole, and the lower end face of the adapter 101 is flush with the lower end face of the anode support body 102; the above-mentioned anode support 1 is composed of the anode support body 102 and the adapter 101 fixedly connected by sealing.

[0066] The anode holder 1 and the cathode holder 2 are both made of solid insulating materials; the cathode 3, the sampling anode 9, the annular anode 10, the sampling cathode sleeve 1701, the balanced cathode sleeve 1702, the sampling anode column 15, and the balanced anode column 16 are all solid conductive materials. In this embodiment, the anode holder 1 and the cathode holder 2 are preferably made of organic glass; the cathode 3 is a high-purity aluminum foil with a thickness of 0.1 mm and a purity of 99.99%; the sampling anode 9 and the annular anode 10 are both pure aluminum sheets with a thickness of 0.1 mm and a purity of 99.99%; the sampling cathode sleeve 1701, the balanced cathode sleeve 1702, the sampling anode 9, and the annular anode 10 all use standard MHV standard electrical connectors.

[0067] The working gas introduction unit is used to deliver working gas to the sealed cavity surrounded by the lower surface of the anode support 1, the sealing boss 4 and the inner surface of the bottom of the cathode 3.

[0068] The working gas introduction unit of this embodiment includes a gasket 14, a clamping screw 13, a syringe 19 and a gas supply unit. On the above-mentioned anode holder 1, an air inlet 5 parallel to the axis of the sampling anode hole 7 is provided at a position between the isolation boss 6 and the sealing boss 4, and the air inlet 5 is a stepped hole with a larger upper part and a smaller lower part; a third through hole coaxial with the air inlet 5 is provided on the top plate of the above-mentioned cathode 3; a fourth through hole coaxial with the air inlet 5 is provided on the annular anode 10; the radial size of the gasket 14 is adapted to the aperture size of the upper large hole of the air inlet 5; the gasket 14 and the clamping screw 13 are arranged in the upper large hole of the air inlet 5 from bottom to top, and the clamping screw 13 is fixedly connected to the anode holder 1 by a thread; the gasket 14 is compressed by the clamping screw 13 to seal the gas path. In this embodiment, the air inlet 5 is preferably located at the outermost side in the radial direction between the isolation boss 6 and the sealing boss 4; the above-mentioned balancing anode hole 8 and the air inlet 5 are symmetrically arranged on both sides of the center of the anode holder 1. A guide hole 1301 is vertically arranged at the center of the upper end surface of the clamping screw 13; in order to facilitate the positioning of the syringe 19, the guide hole 1301 is preferably a stepped hole with a larger upper portion and a smaller lower portion, and the upper large hole is a hexagonal hole; the radial dimension of the hexagonal hole is adapted to the radial dimension of the hexagonal wrench used to lock the clamping screw 13; the aperture size of the small hole at the lower end of the guide hole 1301 is adapted to the diameter size of the syringe 19. After one end of the syringe 19 needle passes through the guide hole 1301 and the gasket 14, it is connected to the small hole at the lower end of the air inlet 5; the other end of the syringe 19 opposite to the needle is connected to the gas supply unit. In this embodiment, the clamping screw 13 is made of organic glass, and the gasket 14 is made of silicone material. In order to facilitate the control of the air flow size and gas pressure, the gas supply unit preferably in this embodiment includes a first valve 21, a third valve 23, a working gas storage device 24, a second valve 22, a vacuum pump 26 and a pressure gauge 25. After the other end of the syringe 19 opposite to the needle passes through the first valve 21, it is divided into three paths: the first path is connected to the working gas storage device 24 through the third valve 23; the second path is connected to the vacuum pump 26 through the second valve 22; and the third path is connected to the pressure gauge 25.

[0069] The method for measuring the total number of fissions using the sampling fission ionization chamber of the present embodiment comprises the following steps:

[0070] Step 1: quantitatively weigh the fission target materials to be measured and make them evenly adhere to the set positions of the sampled thin fission target 11 to be measured and the annular thick fission target 12 to be measured on the upper surface of the bottom plate of the cathode 3 (i.e., the inner surface of the bottom of the cathode 3), so as to prepare the sampled thin fission target 11 to be measured and the annular thick fission target 12 to be measured; in this embodiment, specifically, a nitric acid system fission target solution (the fission material is natural uranium) is prepared, and the acid concentration is not more than 0.5 mol / L; quantitatively take part of the solution and evenly drop it into the corresponding positions of the annular thick fission target 12 to be measured and the sampled thin fission target 11 to be measured on the upper surface of the bottom plate of the cathode 3, and quickly dry them to prepare the annular thick fission target 12 to be measured and the sampled thin fission target 11 to be measured, and the ratio of the mass of the fission materials contained in the two is recorded as R.

[0071] Step 2: Attach the sampling anode 9 and the annular anode 10 to the set position on the lower bottom surface of the anode holder 1; in this embodiment, the sampling anode 9 is attached to the lower bottom surface of the adapter 101, and the annular anode 10 is attached to the lower bottom surface of the anode holder body 102. Place the sampling cathode sleeve 1701, the balancing cathode sleeve 1702, the sampling anode column 15, and the balancing anode column 16 at the set position, seal and fix them with epoxy resin, so that the sampling anode column 15 is electrically connected to the sampling anode 9, and the balancing anode column 16 is electrically connected to the annular anode 10; in this embodiment, the sampling cathode sleeve 1701 and the sampling anode column 15 are replaced by one MHV connector, and the balancing cathode sleeve 1702 and the balancing anode column 16 are replaced by another MHV connector. After sealing and fixing with epoxy resin, the central electrodes of the two MHV connectors are electrically connected to the sampling anode 9 and the annular anode 10 respectively. Place the gasket 14 and the clamping screw 13 at the set position, and lock the clamping screw 13.

[0072] Step 3: The lower end surface of the sealing boss 4 of the anode holder 1 is fixedly connected to the upper surface of the bottom plate of the cathode 3 (i.e. the bottom inner surface of the cathode 3) by epoxy resin sealing; the upper surface of the cathode holder 2 is fixedly connected to the lower surface of the bottom plate of the cathode 3 (i.e. the bottom outer surface of the cathode 3) by epoxy resin sealing.

[0073] Step 4: Cover the upper cover (upper part) of the cathode 3, and electrically connect the bottom plate (lower part) and the upper cover (upper part) of the cathode 3, for example, by using conductive glue; electrically connect the cathode 3 and the sampling cathode sleeve 1701, and the cathode 3 and the balance cathode sleeve 1702, for example, by using conductive glue; in this embodiment, the cathode 3 is respectively connected to the external shielding sleeves of the two MHV connectors; at this point, the ionization chamber main body 18 is completed.

[0074] Step 5: The sealed cavity surrounded by the bottom surface of the anode support 1, the sealing boss 4 and the bottom inner surface of the cathode 3 in the ionization chamber body 18 is first evacuated through the working gas introduction unit, and then the working gas is delivered; in this embodiment, specifically: see Figure 4, connect the ionization chamber body 18 to the inflation platform, and in this embodiment, Xe-129 is selected as the working gas. Open the first valve 21 and the second valve 22, turn on the vacuum pump 26 to evacuate the ionization chamber body 18 for 5 to 10 minutes, close the second valve 22, slowly open the third valve 23, observe the pressure gauge 25 reading until it is about 100 kPa, close the first valve 21 and the third valve 23, and pull out the syringe 19.

[0075] Step 6: Place the ionization chamber body 18 to which the working gas is delivered in step 5 in the neutron field for irradiation. The irradiation direction is from the cathode holder 2 to the anode holder 1. Measure the total number N of the pulse signal of the sampling anode 9. Based on the ratio R of the mass of the fissile material contained in the annular thick fission target 12 to be measured and the sampled thin fission target 11 to be measured in step 1, calculate that the total number of fissions of the annular thick fission target 12 to be measured is 2R·N, and the total number of fissions of the nuclear material is (2R+2)N.

[0076] The ionization chamber body 18 is removed as a whole, and the total amount of fission products can be measured by using β measurement, γ spectrum or mass spectrometry analysis to obtain the fission yield.

[0077] The extraction type fission ionization chamber of the present invention is not only suitable for the measurement of long-life solid fission products, but also suitable for the measurement of gas fission products and short-life solid fission products.

Claims

1. A extraction type fission ionization chamber, characterized in that: The invention comprises a cathode support (2) and a cathode (3) which are coaxially arranged and fixedly connected in sequence from bottom to top, an anode support (1) which is arranged in the inner cavity of the cathode (3) and is coaxial with the cathode (3), and further comprises a sampling anode (9), a ring anode (10), a sampling cathode sleeve (1701), a balancing cathode sleeve (1702), a sampling anode column (15), a balancing anode column (16) and a working gas introduction unit; the cathode (3) is composed of an upper part and a lower part which are detachably connected to form a chamber; The lower bottom surface of the anode holder (1) is provided with an annular sealing boss (4) and an annular isolation boss (6); the sealing boss (4) is located outside the isolation boss (6) and is coaxial with the anode holder (1); the height of the sealing boss (4) is greater than the thickness of the annular thick fission target (12) to be measured, which is attached to the inner surface of the bottom of the cathode (3), coaxial with the cathode (3) and located between the sealing boss (4) and the isolation boss (6); the lower end surface of the sealing boss (4) is sealed and fixedly connected to the inner surface of the bottom of the cathode (3); there is a gap between the lowermost end of the isolation boss (6) and the inner surface of the bottom of the cathode (3); The sampling anode (9) is attached to the bottom surface of the anode holder (1), and is located inside the annular isolation boss (6), and is coaxially arranged with the anode holder (1); the radial dimension of the sampling anode (9) is greater than the radial dimension of the sampled thin fission target (11) to be measured, which is attached to the center of the inner surface of the bottom of the cathode (3); The annular anode (10) is attached to the bottom surface of the anode holder (1), and is located between the isolation boss (6) and the sealing boss (4), and is coaxially arranged with the anode holder (1); the radial dimension of the annular anode (10) is consistent with the radial dimension of the annular thick fission target (12) to be measured; the thickness of the annular anode (10) is the same as that of the sampling anode (9); The anode holder (1) is provided with a sampling anode hole (7) and a balancing anode hole (8) with parallel axes, and the sampling anode hole (7) is coaxial with the anode holder (1), and the balancing anode hole (8) is between the isolation boss (6) and the sealing boss (4); the top plate of the cathode (3) is provided with a first through hole coaxial with the sampling anode hole (7) and a second through hole coaxial with the balancing anode hole (8); The sampling cathode sleeve (1701) and the balancing cathode sleeve (1702) pass through the first through hole and the second through hole respectively, are coaxially arranged with the first through hole and the second through hole, and are both fixedly connected to the cathode (3); The sampling anode column (15) is electrically connected to the sampling anode (9) after passing through the sampling cathode sleeve (1701) and the sampling anode hole (7); the balancing anode column (16) is electrically connected to the annular anode (10) after passing through the balancing cathode sleeve (1702) and the balancing anode hole (8); There are annular gaps between the sampling anode column (15) and the sampling cathode sleeve (1701), the sampling anode column (15) and the sampling anode hole (7), the balancing anode column (16) and the balancing cathode sleeve (1702), and the balancing anode column (16) and the balancing anode hole (8), and insulating sealant is filled in the corresponding annular gaps; The anode support (1) and the cathode support (2) are both made of solid insulating material; The cathode (3), sampling anode (9), annular anode (10), sampling cathode sleeve (1701), balancing cathode sleeve (1702), sampling anode column (15), and balancing anode column (16) are all made of solid conductive materials; The working gas introduction unit is used to deliver working gas to a sealed cavity surrounded by the lower surface of the anode support (1), the sealing boss (4) and the inner surface of the bottom of the cathode (3).

2. The extraction type fission ionization chamber according to claim 1, characterized in that: The working gas introduction unit comprises a gasket (14), a clamping screw (13), a syringe (19) and a gas supply unit; An air inlet hole (5) parallel to the axis of the sampling anode hole (7) is provided on the anode support (1) between the isolation boss (6) and the sealing boss (4), and the air inlet hole (5) is a stepped hole with a larger top and a smaller bottom; a third through hole coaxial with the air inlet hole (5) is provided on the top plate of the cathode (3); and a fourth through hole coaxial with the air inlet hole (5) is provided on the annular anode (10); The radial dimension of the gasket (14) is adapted to the aperture dimension of the large hole at the upper end of the air inlet hole (5); The gasket (14) and the clamping screw (13) are arranged in sequence from bottom to top in the upper large hole of the air inlet (5), and the clamping screw (13) is fixedly connected to the anode support (1) through a thread; the gasket (14) is compressed by the clamping screw (13) to seal the air path; a guide hole (1301) is vertically arranged at the center of the upper end surface of the clamping screw (13); After one end of the needle of the syringe (19) passes through the guide hole (1301) and the gasket (14), it is connected to the small hole at the lower end of the air inlet (5); the other end of the syringe (19) opposite to the needle is connected to the gas supply unit.

3. The extraction type fission ionization chamber according to claim 2, characterized in that: The gas supply unit comprises a first valve (21), a third valve (23), a working gas storage device (24), a second valve (22), a vacuum pump (26) and a pressure gauge (25); After the other end of the syringe (19) opposite to the needle passes through the first valve (21), it is divided into three paths: the first path is connected to the working gas storage device (24) through the third valve (23); the second path is connected to the vacuum pump (26) through the second valve (22); and the third path is connected to the pressure gauge (25).

4. The extraction type fission ionization chamber according to claim 2, characterized in that: The air inlet hole (5) is located at the outermost side in the radial direction between the isolation boss (6) and the sealing boss (4); The balanced anode hole (8) and the air inlet hole (5) are symmetrically arranged on both sides of the center of the anode holder (1).

5. The extraction type fission ionization chamber according to claim 4, characterized in that: The guide hole (1301) is a stepped hole that is larger at the top and smaller at the bottom, and the large hole at the top is a hexagonal hole; the radial size of the hexagonal hole is compatible with the radial size of the hexagonal wrench used to lock the clamping screw (13); the aperture size of the small hole at the lower end of the guide hole (1301) is compatible with the tube diameter size of the syringe (19).

6. The extraction type fission ionization chamber according to any one of claims 1 to 5, characterized in that: The height of the sealing boss (4) is at least 2 mm higher than the thickness of the annular thick fission target (12) to be measured.

7. The extraction type fission ionization chamber according to claim 6, characterized in that: The cross-sectional shape of the isolation boss (6) is an inverted triangle that is larger at the top and smaller at the bottom.

8. The extraction type fission ionization chamber according to claim 7, characterized in that: The anode support (1) comprises an anode support body (102) and an adapter (101); The adapter (101) is in the shape of a stepped shaft with a larger upper portion and a smaller lower portion, and the outer diameter of the lower end surface of the adapter (101) is equal to the outer diameter of the sampling anode (9); a through hole is vertically arranged at the center of the upper end surface of the adapter (101); the through hole is the sampling anode hole (7); An adapter mounting hole adapted to the adapter (101) is vertically arranged at the center of the upper end surface of the anode support body (102); the adapter (101) is arranged in the adapter mounting hole, and the lower end surface of the adapter (101) is flush with the lower end surface of the anode support body (102); the anode support (1) is composed of the anode support body (102) and the adapter (101) fixedly connected by sealing.

9. The extraction type fission ionization chamber according to claim 2, characterized in that: The anode support (1), cathode support (2) and clamping screw (13) are all made of organic glass; The cathode (3) is made of high-purity aluminum foil; The sampling anode (9) and the annular anode (10) are made of pure aluminum; The gasket (14) is made of silicone material; The insulating sealant is epoxy resin; The upper part of the cathode (3) is a cylindrical upper cover, and the lower part is a circular bottom plate, and the enclosed chamber is a cylindrical chamber.

10. A method for measuring the total number of fissions based on the sampling fission ionization chamber according to claim 1, characterized in that: The following steps are involved: Step 1: quantitatively weigh the fission target materials to be measured respectively and make them evenly adhere to the set positions of the sampled thin fission target (11) to be measured and the annular thick fission target (12) to be measured on the inner surface of the bottom of the cathode (3), thereby preparing the sampled thin fission target (11) to be measured and the annular thick fission target (12) to be measured; and the ratio of the mass of the fission materials contained in the annular thick fission target (12) to the sampled thin fission target (11) to be measured is recorded as R; Step 2: attach the sampling anode (9) and the annular anode (10) to the set position on the bottom surface of the anode holder (1); place the sampling cathode sleeve (1701), the balancing cathode sleeve (1702), the sampling anode column (15), and the balancing anode column (16) at the set position, seal and fix them with epoxy resin, so that the sampling anode column (15) is electrically connected to the sampling anode (9), and the balancing anode column (16) is electrically connected to the annular anode (10); Step 3: sealingly and securely connecting the lower end surface of the sealing boss (4) of the anode holder (1) to the inner surface of the bottom of the cathode (3); and sealingly and securely connecting the upper surface of the cathode holder (2) to the outer surface of the bottom of the cathode (3); Step 4: Cover the upper part of the cathode (3), and electrically connect the upper and lower parts of the cathode (3); electrically connect the cathode (3) and the sampling cathode sleeve (1701), and the cathode (3) and the balance cathode sleeve (1702); at this point, the ionization chamber main body (18) is completed; Step 5: first evacuate the sealed cavity surrounded by the lower bottom surface of the anode support (1), the sealing boss (4) and the inner bottom surface of the cathode (3) in the ionization chamber body (18) through the working gas introduction unit, and then deliver the working gas; Step 6: placing the ionization chamber body (18) to which the working gas is delivered in step 5 in a neutron field for irradiation, the irradiation direction being from the cathode support (2) to the anode support (1), measuring the total number N of pulse signals of the sampling anode (9), and calculating the total number of fissions of the annular thick fission target (12) to be measured as 2R·N based on the ratio R of the mass of fission materials contained in the annular thick fission target (12) to be measured and the sampling thin fission target (11) to be measured in step 1, and then calculating the total number of fissions of the nuclear material to be measured as (2R+2)N.

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