Neutron moderation cylinder structure and neutron tube yield calibration method

Abstract

The invention relates to the technical field of oil and gas logging, and discloses a neutron moderation cylinder structure and a neutron tube yield calibration method.The outer side of a cylinder body is a sealed shell, and the cylinder body internally comprises a variable reduction ratio module and a deceleration detection module; the variable reduction ratio module comprises an internal cavity of the cylinder body, so that the variable reduction ratio module has variable reduction capacity for neutron rays, and the internal cavity is filled with a fluid medium with good reduction capacity for neutrons, so that the internal cavity has two different reduction ratios in the state of being filled with the reduction fluid medium and in the cavity state; the overall speed reduction and slowing-down capability of the neutron slowing-down cylinder is variable; a deceleration fluid medium inlet is formed in the upper end of the variable reduction ratio module cavity, and a deceleration fluid outlet is formed in the lower end, so that filling and discharging of a fluid medium are facilitated; and a neutron deceleration layer group is arranged in the deceleration detection module, so that the deceleration effect on neutron rays is realized, the neutron rays are transmitted to a neutron detector, and the calibration precision of the neutron tube is improved.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas well logging, in particular to a neutron moderator tube structure and a neutron tube yield calibration method. Background Art

[0002] At present, the closest existing technology is: controlled source neutron logging using deuterium-deuterium (DD) or deuterium-tritium (DT) neutron tubes is a new logging method. Compared with traditional chemical neutron sources, it has the characteristics of high neutron yield, good energy spectrum monochromaticity, no gamma background, almost zero pollution, and zero harm to operators. It can also generate pulsed neutrons. Therefore, it is becoming more and more popular. It has relevant applications in carbon-oxygen (C / O) ratio logging, element logging, neutron lifetime logging, cyclic activation logging, delayed and prompt neutron logging, neutron-gamma logging, etc.

[0003] Neutron yield is a key technical indicator for evaluating neutron tubes. For low-energy accelerators, neutron yield can be calculated using the companion particle method or the activation method, which measures the secondary radioactivity produced by neutron irradiation. However, due to the sealed structure of the neutron tube, the companion particle method cannot be used to determine the yield. If the activation method is used to measure neutron tube yield, the detection system is inefficient, and the activation plate must be placed very close to the neutron tube, typically 10-20 cm. Since the neutron tube target cannot be considered a point source, the neutron tube must be immersed in a certain thickness of insulating silicone oil during target calibration experiments. This results in large measurement errors due to the system's positioning accuracy, which cannot meet the requirements of neutron tube calibration.

[0004] Based on this, neutron tube yield calibration experiments currently use a neutron detector placed at a certain distance to determine the neutron yield through secondary calibration. Specifically, to accurately and effectively measure the neutron flux rate within a specific spatial incident angle and reduce the measurement error caused by scattered neutron radiation, the neutron detector is usually placed in a neutron moderator with a specific structure. This moderator shields most scattered neutrons, reducing the measurement error caused by scattered neutron radiation. Furthermore, because common neutron detectors are insensitive to fast neutrons and only sensitive to thermal or epithermal neutrons, the neutron moderator also has the effect of slowing down direct neutron radiation, slowing down incident fast neutrons to thermal neutrons. During yield calibration experiments, the neutron moderator is placed at a specific distance from the neutron tube and at the same height as the neutron tube target. To minimize the influence of scattered neutrons, the moderator should be kept as far away from the ground and walls as possible.

[0005] While the aforementioned neutron moderators have a defined internal structure, their ability to moderate incident neutrons is determined. However, due to the significant difference in neutron yield between DD and DT tubes (DT tube yield is approximately 102 times that of DD tubes), and the higher average neutron energy of DT tubes, at the same test distance, DD tubes produce fewer counts, leading to large errors in the final calibrated neutron yield due to statistical fluctuations. Meanwhile, DT tube counts are excessively high at the same distance, hindering measurement and calibration. Therefore, for these neutron moderators with a defined moderating capacity, different test distances are typically required when testing and calibrating DD and DT tubes.

[0006] During test calibration, the neutron moderator is typically placed on a stand at a certain height above the ground (generally, a support height of greater than 2 meters is recommended to minimize the impact of ground-scattered neutrons on the measurement). The stand is equipped with wheels. The difference in yield between DD and DT tubes creates a problem: the experimenter must frequently move the neutron moderator (along with the support stand), which is inconvenient. Furthermore, because the test distance requires manual adjustment, repeatable positioning accuracy is difficult to ensure, introducing new errors into the calibration accuracy of the entire system.

[0007] In summary, the problems existing in the prior art are:

[0008] (1) When testing and calibrating DD and DT tubes, the neutron moderator (detector) needs to be set at different test distances;

[0009] (2) Due to the different test distances, the entire test device (support frame, neutron moderator, detector and its circuit) needs to be moved frequently, which is inconvenient to operate. At the same time, since the test distance needs to be adjusted manually, the repeatable positioning accuracy is difficult to guarantee, which introduces new errors to the calibration accuracy of the entire system. Summary of the Invention

[0010] In order to overcome the above-mentioned defects of the prior art, the purpose of the present invention is to provide a neutron moderator tube structure for neutron tube yield calibration, so as to solve the technical problems in the prior art that the neutron moderator tube has low deceleration efficiency for neutron rays and cannot perform variable deceleration, and that the DD tube and DT tube need to be frequently moved during the calibration process, resulting in inconvenient operation and low calibration accuracy.

[0011] The present invention is achieved through the following technical solutions:

[0012] A neutron moderation cylinder structure includes a cylinder body and a neutron detector, the outer side of the cylinder body is a sealed shell, and the cylinder body includes a variable deceleration ratio module and a deceleration detection module; wherein the variable deceleration ratio module and the deceleration detection module are arranged in sequence along the cylinder direction of the cylinder body, and the variable deceleration ratio module and the deceleration detection module are separated to form two independent modules, a variable deceleration ratio module cavity is provided in the variable deceleration ratio module, which is used to contain a fluid medium, wherein the upper end of the variable deceleration ratio module cavity is provided with a deceleration fluid medium inlet through the sealed shell, and the lower end is provided with a deceleration fluid outlet through the sealed shell; a neutron deceleration layer group is provided in the deceleration detection module; the neutron detector is assembled in the neutron deceleration layer group through the end of the cylinder body.

[0013] Preferably, a heavy metal deceleration layer is provided at one end of the cylinder body close to the cavity of the variable reduction ratio module, and the size of the heavy metal deceleration layer is set corresponding to the cylinder diameter of the cylinder body.

[0014] Furthermore, a visual liquid level gauge is installed on the outer side of the heavy metal deceleration layer.

[0015] Preferably, the neutron deceleration layer group includes a scattered neutron deceleration layer and a neutron collimation deceleration layer, wherein the neutron collimation deceleration layer is arranged at the central axis of the cylinder body, the scattered neutron deceleration layer is wrapped around the outside of the neutron collimation deceleration layer, and the neutron detector is assembled in the neutron collimation deceleration layer through the end of the cylinder body.

[0016] Furthermore, the scattered neutron moderation layer is made of paraffin wax, and a stainless steel interlayer is provided on the inner side of the scattered neutron moderation layer for fixing the scattered neutron moderation layer.

[0017] Furthermore, a thermal neutron absorption layer is provided between the scattered neutron deceleration layer and the neutron collimation deceleration layer and on the side of the scattered neutron deceleration layer close to the variable deceleration ratio module, wherein the thermal neutron absorption layer is made of boric acid, boron carbide or metallic cadmium.

[0018] Furthermore, the neutron collimation and deceleration layer is made of polyethylene rods.

[0019] Preferably, support modules are respectively provided on both sides of the bottom of the cylinder body.

[0020] A neutron tube yield calibration method, based on the above-mentioned neutron moderator tube structure, includes the following steps:

[0021] Place the cylinder body and the neutron tube to be calibrated on the steel frame according to the calibration distance, and the extended axis of the cylinder body coincides with the target point of the neutron tube;

[0022] When measuring a deuterium-deuterium neutron tube, each electrode of the deuterium-deuterium neutron tube is connected to a corresponding excitation power supply lead, and the deuterium-deuterium neutron tube is immersed in an oil tank. The deceleration fluid outlet at the lower end of the variable reduction ratio module cavity is opened so that the variable reduction ratio module cavity is free of fluid medium. The anode voltage and current, target voltage and current are adjusted to rated operating values, and the operating state of the deuterium-deuterium neutron tube is observed through monitoring equipment. When the deuterium-deuterium neutron tube operating state is stable, the neutron count measured by the neutron detector is read, and the corresponding neutron yield is calculated based on the scale calibration when the variable reduction ratio module cavity is free of fluid medium.

[0023] When measuring a deuterium-tritium neutron tube, each electrode of the deuterium-tritium neutron tube is connected to a corresponding excitation power supply lead, and the deuterium-tritium neutron tube is immersed in an oil tank. The deceleration fluid outlet at the lower end of the variable reduction ratio module cavity is closed, the deceleration fluid medium inlet is opened, and the fluid medium is input. When the fluid medium in the variable reduction ratio module cavity is filled, the anode voltage and current, the target voltage and current are adjusted to rated operating values, and the operating state of the deuterium-tritium neutron tube is observed through a monitoring device. When the deuterium-tritium neutron tube operating state is stable, the neutron count measured by the neutron detector is read, and the corresponding neutron yield is calculated based on the scale calibration when the variable reduction ratio module cavity is filled with the fluid medium.

[0024] Preferably, the variable deceleration ratio module is used as the first deceleration layer in the cylinder body close to the neutron tube, and the deceleration detection module is used as the second deceleration layer. Neutron rays pass through the first deceleration layer and the second deceleration layer in sequence to reach the neutron detector.

[0025] Compared with the prior art, the present invention has the following beneficial technical effects:

[0026] The present invention provides a neutron moderator cylinder structure, wherein the outer side of the cylinder body is a sealed shell, and the cylinder body includes a variable deceleration ratio module and a deceleration detection module; wherein the variable deceleration ratio module includes an internal cavity of the cylinder body, and in order to enable the variable deceleration ratio module to have a variable deceleration ability for neutron rays, the internal cavity can be filled with a fluid medium with good deceleration ability for neutrons, so that the internal cavity has two different deceleration ratios when it is filled with the deceleration fluid medium and when it is empty, thereby realizing the variable deceleration and slowing down ability of the neutron moderator cylinder as a whole; and a deceleration fluid medium inlet is provided at the upper end of the variable deceleration ratio module cavity through the sealed shell, and a deceleration fluid outlet is provided at the lower end through the sealed shell, so as to facilitate the filling and discharge of the fluid medium; in the present invention, a neutron deceleration layer group is provided in the deceleration detection module, which can effectively achieve the deceleration effect on neutron rays, and transmit the neutron rays to the neutron detector, thereby improving the accuracy of neutron tube calibration.

[0027] Furthermore, a heavy metal deceleration layer is provided at one end of the cylinder body close to the cavity of the variable reduction ratio module. The size of the heavy metal deceleration layer is set corresponding to the diameter of the cylinder body. The inelastic scattering of heavy metal and neutron rays is used to decelerate the incident fast neutrons, thereby facilitating the deceleration of the neutron rays.

[0028] Furthermore, a visual liquid level gauge is installed on the outer side of the heavy metal deceleration layer to confirm the state of the fluid medium in the cavity of the variable reduction ratio module.

[0029] Furthermore, the neutron deceleration layer group includes a scattered neutron deceleration layer and a neutron collimation deceleration layer, wherein the neutron collimation deceleration layer is arranged at the central axis of the cylinder body, and the scattered neutron deceleration layer is wrapped around the outside of the neutron collimation deceleration layer. The neutron detector is assembled in the neutron collimation deceleration layer through the end of the cylinder body to effectively reduce the speed of the neutron rays.

[0030] Furthermore, the material of the scattered neutron deceleration layer is paraffin wax, and its main function is to decelerate the scattered neutrons scattered by the environment and entering the neutron moderator tube. A stainless steel interlayer is provided on the inner side of the scattered neutron deceleration layer. Since the paraffin wax of the scattered neutron deceleration layer is formed by melt casting, the inner stainless steel interlayer fixes the paraffin wax layer.

[0031] Furthermore, a thermal neutron absorption layer is provided between the scattered neutron deceleration layer and the neutron collimation deceleration layer, as well as on the side of the scattered neutron deceleration layer close to the variable deceleration ratio module. Its main function is to absorb the slowed-down thermal neutrons by neutron capture reaction to avoid interference of scattered neutrons on the detector. The thermal neutron absorption layer is made of boric acid, boron carbide or metallic cadmium. Boric acid, boron carbide or metallic cadmium are materials with large thermal neutron absorption cross-sections and are used as absorption materials.

[0032] Furthermore, the neutron collimation and deceleration layer is made of polyethylene rods, which decelerate and slow down the collimated neutron rays, and slow down the incident fast neutrons into thermal neutrons that can be received by the detector.

[0033] The present invention also provides a neutron tube yield calibration method, which can calibrate and measure deuterium-deuterium neutron tubes and deuterium-tritium neutron tubes respectively through a neutron moderator tube structure, and utilizes the presence or absence of a fluid medium in the cavity of a variable reduction ratio module to respectively realize laboratory yield calibration of two different types of neutron tubes, deuterium-deuterium neutron tubes and deuterium-tritium neutron tubes. This avoids the experimental operator from frequently moving the neutron moderator tube when conducting calibration experiments on different types of neutron tubes, and at the same time avoids the error caused to the calibration system by such frequent movement, which is conducive to improving the accuracy of the overall calibration system. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the neutron moderator structure of the present invention;

[0035] Figure 2 This is a schematic diagram of the interior of the neutron moderator in the present invention;

[0036] Figure 3 Schematic diagram of the neutron tube yield calibration process in the present invention.

[0037] In the figure: 1-sealed shell; 2-deceleration fluid medium inlet; 3-thermal neutron absorption layer; 4-scattered neutron deceleration layer; 5-neutron collimation deceleration layer; 6-neutron detector; 7-deceleration fluid outlet; 8-variable deceleration ratio module cavity; 9-heavy metal deceleration layer; 10-visual liquid level gauge; 11-variable deceleration ratio module; 12-deceleration detection module; 13-support module. DETAILED DESCRIPTION

[0038] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0039] The present invention is described in further detail below with reference to the accompanying drawings:

[0040] The object of the present invention is to provide a neutron moderator structure for neutron tube yield calibration, so as to solve the technical problems in the prior art of low deceleration efficiency of neutron rays by neutron moderators and inability to perform variable deceleration, and the need to frequently move DD tubes and DT tubes during the calibration process, resulting in inconvenient operation and low calibration accuracy.

[0041] Example 1

[0042] Specifically, according to Figure 1 and Figure 2As shown, the neutron moderation cylinder structure includes a cylinder body and a neutron detector 6, the outer side of the cylinder body is a sealed shell 1, and the cylinder body includes a variable deceleration ratio module 11 and a deceleration detection module 12; wherein the variable deceleration ratio module 11 and the deceleration detection module 12 are arranged in sequence along the cylinder direction of the cylinder body, and the variable deceleration ratio module 11 and the deceleration detection module 12 are separated to form two independent modules, and a variable deceleration ratio module cavity 8 is provided in the variable deceleration ratio module 1 for containing a fluid medium, wherein a deceleration fluid medium inlet 2 is provided at the upper end of the variable deceleration ratio module cavity 8 through the sealed shell 1, and a deceleration fluid outlet 7 is provided at the lower end through the sealed shell 1; a neutron deceleration layer group is provided in the deceleration detection module 12; the neutron detector 6 is assembled in the neutron deceleration layer group through the end of the cylinder body, and support modules 13 are respectively provided on both sides of the bottom of the cylinder body.

[0043] Specifically, a heavy metal deceleration layer 9 is provided at one end of the cylinder body close to the variable reduction ratio module cavity 8. The size of the heavy metal deceleration layer 9 is set corresponding to the diameter of the cylinder body. The inelastic scattering of heavy metal and neutron rays is used to decelerate the incident fast neutrons, thereby facilitating the deceleration of the neutron rays.

[0044] A visual liquid level gauge 10 is mounted on the outer side of the heavy metal deceleration layer 9 to confirm the state of the fluid medium in the cavity of the variable reduction ratio module.

[0045] Specifically, the neutron deceleration layer group includes a scattered neutron deceleration layer 4 and a neutron collimation deceleration layer 5, wherein the neutron collimation deceleration layer 5 is arranged at the central axis of the cylinder body, the scattered neutron deceleration layer 4 is wrapped around the outside of the neutron collimation deceleration layer 5, and the neutron detector 6 is assembled in the neutron collimation deceleration layer 5 through the end of the cylinder body.

[0046] Among them, the material of the scattered neutron deceleration layer 4 is paraffin, and a stainless steel interlayer is provided on the inner side of the scattered neutron deceleration layer 4 for fixing the scattered neutron deceleration layer 4. Since the paraffin of the scattered neutron deceleration layer is formed by melt casting, the inner stainless steel interlayer fixes the paraffin layer.

[0047] Among them, a thermal neutron absorption layer 3 is provided between the scattered neutron deceleration layer 4 and the neutron collimation deceleration layer 5, and on the side of the scattered neutron deceleration layer 4 close to the variable deceleration ratio module 11. Its main function is to absorb the slowed down thermal neutrons by neutron capture reaction to avoid the interference of scattered neutrons on the detector. The material of the thermal neutron absorption layer 3 is boric acid, boron carbide or metallic cadmium.

[0048] The neutron collimation and deceleration layer 5 is made of polyethylene rods, which decelerate and slow down the collimated incident neutron rays, and slow down the incident fast neutrons into thermal neutrons that can be received by the detector.

[0049] Example 2

[0050] according to Figure 3 As shown, the present invention also provides a neutron tube yield calibration method, based on the above-mentioned neutron moderator tube structure, including the following process:

[0051] Place the cylinder body and the neutron tube to be calibrated on the steel frame according to the calibration distance, and the extended axis of the cylinder body coincides with the target point of the neutron tube;

[0052] When measuring the deuterium-deuterium neutron tube, each electrode of the deuterium-deuterium neutron tube is connected to the corresponding excitation power supply lead, and the deuterium-deuterium neutron tube is immersed in an oil tank. The deceleration fluid outlet 7 at the lower end of the variable reduction ratio module cavity 8 is opened to ensure that the variable reduction ratio module cavity 8 is free of fluid medium. The anode voltage and current, target voltage and current are adjusted to rated operating values, and the operating state of the deuterium-deuterium neutron tube is observed through monitoring equipment. When the deuterium-deuterium neutron tube operating state is stable, the neutron count measured by the neutron detector 6 is read, and the corresponding neutron yield is calculated based on the scale calibration when the variable reduction ratio module cavity 8 is free of fluid medium.

[0053] When measuring the deuterium-tritium neutron tube, each electrode of the deuterium-tritium neutron tube is connected to the corresponding excitation power supply lead, and the deuterium-tritium neutron tube is immersed in an oil tank. The deceleration fluid outlet 7 at the lower end of the variable reduction ratio module cavity 8 is closed, the deceleration fluid medium inlet 2 is opened, and the fluid medium is introduced. When the fluid medium in the variable reduction ratio module cavity 8 is filled, the anode voltage and current, as well as the target voltage and current, are adjusted to the rated operating values, and the operating status of the deuterium-tritium neutron tube is observed through monitoring equipment. When the deuterium-tritium neutron tube operating state is stable, the neutron count measured by the neutron detector 6 is read, and the corresponding neutron yield is calculated based on the calibration when the variable reduction ratio module cavity 8 is filled with fluid medium.

[0054] Specifically, the variable deceleration ratio module 11 is used as the first deceleration layer in the cylinder body near the neutron tube, and the deceleration detection module 12 is used as the second deceleration layer. Neutron rays pass through the first and second deceleration layers in sequence to reach the neutron detector 6.

[0055] The variable reduction ratio module of the present invention is placed near the neutron tube and primarily comprises a sealed housing and an internal cavity. To enable the variable reduction ratio module to have variable deceleration capabilities for neutron radiation, the internal cavity can be filled with a fluid medium with excellent neutron deceleration capabilities. This allows the internal cavity to have two different reduction ratios when filled with the deceleration fluid and when empty, thereby achieving variable deceleration capabilities for the neutron moderator tube as a whole. To enable the filling and discharge of the fluid medium, the sealed housing should be provided with ports for the fluid medium to be filled and discharged.

[0056] From the analysis of the mechanism of the interaction between neutron rays and matter, when the incident neutron energy is high (when the incident fast neutron energy is >3MeV), the inelastic scattering cross section of fast neutrons with heavy elements is much larger than the elastic scattering cross section of fast neutrons with hydrogen nuclei, and the inelastic scattering cross section increases with the increase of the atomic weight of the target nucleus and the increase of the fast neutron energy. Therefore, the first layer of deceleration material of the entire neutron moderator should be made of materials with larger atomic weight. Common materials such as Cu, Fe, Pb, etc. can meet the requirements of the first layer of fast neutron deceleration. Considering economy and machinability, the entire shell of the neutron moderator is made of stainless steel, and the first layer of fast neutron deceleration is carried out through the inelastic scattering of fast neutrons with heavy elements. Generally, after several inelastic scatterings with Fe atoms, the energy of fast neutrons can be quickly reduced to <1MeV. When the fast neutron energy is reduced to 1MeV or below, the inelastic scattering cross section of Cu, Fe, Pb, etc. for neutrons (<2B) is much smaller than the elastic scattering cross section of Cu, Fe, Pb, etc. for neutrons (about 20B). Therefore, the second layer of deceleration material ( Figure 1 The mid-scattered neutron deceleration layer and the neutron collimation deceleration layer belong to the second layer of deceleration material and should be set as light hydrogen material. Commonly used deceleration materials for this layer include paraffin and polyethylene. Considering the location, processability and economy of the deceleration layer, Figure 1 The moderately scattered neutron deceleration layer is made of paraffin wax, and the neutron collimation deceleration layer is made of polyethylene rods.

[0057] In order to achieve two different deceleration ratios of the neutron moderator for neutron rays, the deceleration fluid medium may be a fluid medium rich in H element such as heavy water (D2O), water (H2O), or silicone oil.

[0058] In the present invention, the sealed shell is made of stainless steel. Since the energy of the incident neutron rays is relatively high, the front end of the sealed shell is made of thickened stainless steel. The incident fast neutrons are decelerated by utilizing the inelastic scattering of heavy metals and neutron rays. This deceleration layer is called the heavy metal deceleration layer 9.

[0059] The variable reduction ratio module cavity 8 of the present invention is made of stainless steel and has a hollow cylindrical structure. The variable reduction ratio module 11 is primarily designed to provide variable neutron deceleration capabilities. Cavity 8 can be filled with a fluid medium with excellent neutron deceleration capabilities, allowing the cavity 8 to have two different deceleration ratios when filled with the deceleration fluid and when empty, thereby achieving variable deceleration capabilities for the neutron moderator. For reasons of cost-effectiveness and neutron deceleration capabilities, the deceleration fluid is preferably water.

[0060] In the present invention, the variable reduction ratio module 11 and the rear end reduction detection module 12 are independent of each other, and the two modules are connected together by welding.

[0061] In the present invention, a cavity is provided on the neutron collimation and deceleration layer 5 for mounting a neutron detector 6. Optionally, the neutron detector 6 can be a BF3 detector or a He3 detector. Preferably, in this embodiment, the neutron detector 6 is a He3 detector.

[0062] Before the calibration test in the present invention, the manufactured neutron moderator is sent to the primary metering station for secondary calibration, and the total efficiency of the variable reduction ratio module cavity 8 in the empty state and the water-filled state is obtained respectively, and the total efficiency of the system in the two different states is obtained, that is, the neutron yield corresponding to one neutron count.

[0063] During the test experiment, the extended line of the cylindrical barrel axis coincided with the neutron tube target (when the distance is far, the neutron tube target can be regarded as a point source). During the actual experiment, the distance between the neutron source and the neutron moderator tube remained consistent with the distance during calibration.

[0064] In summary, the present invention provides a neutron moderator cylinder structure, the outer side of the cylinder body is a sealed shell, and the cylinder body includes a variable deceleration ratio module and a deceleration detection module; wherein the variable deceleration ratio module includes an internal cavity of the cylinder body, and in order to make the variable deceleration ratio module have a variable deceleration ability for neutron rays, the internal cavity can be filled with a fluid medium with good deceleration ability for neutrons, so that the internal cavity has two different deceleration ratios when it is filled with the deceleration fluid medium and in the cavity state, thereby realizing the variable deceleration and slowing down ability of the neutron moderator cylinder as a whole; and a deceleration fluid medium inlet is provided at the upper end of the variable deceleration ratio module cavity through the sealed shell, and a deceleration fluid outlet is provided at the lower end through the sealed shell, so as to facilitate the filling and discharge of the fluid medium; in the present invention, a neutron deceleration layer group is provided in the deceleration detection module, which can effectively achieve the deceleration effect on neutron rays, and transmit the neutron rays to the neutron detector, thereby improving the accuracy of neutron tube calibration.

[0065] The present invention also provides a neutron tube yield calibration method, which can calibrate and measure deuterium-deuterium neutron tubes and deuterium-tritium neutron tubes respectively through a neutron moderator tube structure, and utilizes the presence or absence of a fluid medium in the cavity of a variable reduction ratio module to respectively realize laboratory yield calibration of two different types of neutron tubes, deuterium-deuterium neutron tubes and deuterium-tritium neutron tubes. This avoids the experimental operator from frequently moving the neutron moderator tube when conducting calibration experiments on different types of neutron tubes, and at the same time avoids the error caused to the calibration system by such frequent movement, which is conducive to improving the accuracy of the overall calibration system.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A neutron moderator cylinder structure, characterized in that: The invention comprises a cylinder body and a neutron detector (6), wherein the outer side of the cylinder body is a sealed shell (1), and the cylinder body comprises a variable reduction ratio module (11) and a reduction detection module (12); wherein the variable reduction ratio module (11) and the reduction detection module (12) are arranged in sequence along the cylinder body direction of the cylinder body, and the variable reduction ratio module (11) and the reduction detection module (12) are separated and arranged to form two independent modules, wherein a variable reduction ratio module cavity (8) is arranged inside the variable reduction ratio module (1) for containing a fluid medium, wherein a reduction fluid medium inlet (2) is arranged at the upper end of the variable reduction ratio module cavity (8) through the sealed shell (1), and a reduction fluid outlet (7) is arranged at the lower end through the sealed shell (1); a neutron reduction layer group is arranged inside the reduction detection module (12); and the neutron detector (6) is assembled in the neutron reduction layer group through the end of the cylinder body.

2. A neutron moderator cylinder structure according to claim 1, characterized in that: A heavy metal deceleration layer (9) is provided at one end of the cylinder body close to the variable reduction ratio module cavity (8), and the size of the heavy metal deceleration layer (9) is set corresponding to the cylinder diameter of the cylinder body.

3. A neutron moderator cylinder structure according to claim 2, characterized in that: A visual liquid level meter (10) is mounted on the outer side of the heavy metal deceleration layer (9).

4. A neutron moderator cylinder structure according to claim 1, characterized in that: The neutron deceleration layer group comprises a scattered neutron deceleration layer (4) and a neutron collimation deceleration layer (5), wherein the neutron collimation deceleration layer (5) is arranged at the central axis of the cylinder body, the scattered neutron deceleration layer (4) is wrapped around the outside of the neutron collimation deceleration layer (5), and the neutron detector (6) is assembled in the neutron collimation deceleration layer (5) through the end of the cylinder body.

5. A neutron moderator cylinder structure according to claim 4, characterized in that: The material of the scattered neutron deceleration layer (4) is paraffin, and a stainless steel interlayer is provided on the inner side of the scattered neutron deceleration layer (4) for fixing the scattered neutron deceleration layer (4).

6. A neutron moderator cylinder structure according to claim 4, characterized in that: A thermal neutron absorption layer (3) is provided between the scattered neutron deceleration layer (4) and the neutron collimation deceleration layer (5) and on a side of the scattered neutron deceleration layer (4) close to the variable deceleration ratio module (11), wherein the thermal neutron absorption layer (3) is made of boric acid, boron carbide or metal cadmium.

7. A neutron moderator cylinder structure according to claim 4, characterized in that: The neutron collimation and deceleration layer (5) is made of polyethylene rods.

8. The neutron moderator cylinder structure according to claim 1, characterized in that: Support modules (13) are respectively provided on both sides of the bottom of the cylinder body.

9. A neutron tube yield calibration method, based on the neutron moderator tube structure according to any one of claims 1 to 7, characterized in that: The process includes the following: The cylinder body and the neutron tube to be calibrated are placed on the steel frame according to the calibration distance, and the extended axis of the cylinder body coincides with the target point of the neutron tube; When measuring the deuterium-deuterium neutron tube, each electrode of the deuterium-deuterium neutron tube is connected to the corresponding excitation power lead, and the deuterium-deuterium neutron tube is immersed in an oil tank, and the deceleration fluid outlet (7) at the lower end of the variable reduction ratio module cavity (8) is opened so that the variable reduction ratio module cavity (8) is free of fluid medium, and then the anode voltage and current, the target voltage and current are adjusted to the rated working values, and the working state of the deuterium-deuterium neutron tube is observed through a monitoring device; when the working state of the deuterium-deuterium neutron tube is stable, the neutron count measured by the neutron detector (6) is read, and the corresponding neutron yield is calculated according to the scale calibration when the variable reduction ratio module cavity (8) is free of fluid medium; When measuring the deuterium-tritium neutron tube, each electrode of the deuterium-tritium neutron tube is connected to the corresponding excitation power lead, and the deuterium-tritium neutron tube is immersed in an oil tank, the deceleration fluid outlet (7) at the lower end of the variable reduction ratio module cavity (8) is closed, the deceleration fluid medium inlet (2) is opened, and the fluid medium is input so that the fluid medium in the variable reduction ratio module cavity (8) is filled, and the anode voltage and current, the target voltage and current are adjusted to the rated working values, and the working state of the deuterium-tritium neutron tube is observed through a monitoring device. When the working state of the deuterium-tritium neutron tube is stable, the neutron count measured by the neutron detector (6) is read, and the corresponding neutron yield is calculated according to the scale calibration when the variable reduction ratio module cavity (8) is filled with the fluid medium.

10. A neutron tube yield calibration method according to claim 9, characterized in that: The variable deceleration ratio module (11) is used as the first deceleration layer in the cylinder body close to the neutron tube, and the deceleration detection module (12) is used as the second deceleration layer. Neutron rays pass through the first deceleration layer and the second deceleration layer in sequence to reach the neutron detector (6).

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