A method for measuring the cadmium ratio of a thermal neutron field

Abstract

An embodiment of the present application provides a method for measuring the cadmium ratio of a thermal neutron field, which includes placing a first object to be measured at a set position in the beam of the thermal neutron field, and monitoring the reactor power through a monitor. Placing the first object to be measured outside the beam, and measuring the quantity of activation products generated by the first object to be measured through a detector. Placing a second object to be measured at the set position, and monitoring the reactor power through a monitor. Placing the second object to be measured outside the beam, and measuring the quantity of activation products generated by the second object to be measured through a detector. One of the first object to be measured and the second object to be measured is a first material to be measured, and the other includes a second material to be measured and a cadmium material layer wrapped outside the second material to be measured, and the first material to be measured and the second material to be measured are of the same material. Calculating the cadmium ratio according to the measurement result of the detector and the monitoring result of the monitor. The method for measuring the cadmium ratio of the thermal neutron field in the embodiment of the present application has higher measurement accuracy.

Description

Technical Field

[0001] The present application relates to the technical field of neutron measurement, and particularly relates to a method for measuring the cadmium ratio of a thermal neutron field. Background Art

[0002] Since the energy of thermal neutrons is the typical energy when neutrons and matter reach thermal equilibrium at ambient temperature, there are a large number of instruments for measuring the thermal neutron dose rate outside the shielding of large nuclear facilities. The accurate measurement of these instruments requires calibration with a thermal neutron field. In places with relatively small spaces such as nuclear-powered ships, it is necessary to develop materials with low density, low cost, excellent mechanical and shielding properties for shielding thermal neutrons and γ-rays. The shielding performance of these materials for thermal neutrons needs to be tested with a thermal neutron field. Since the energy of thermal neutrons is the typical neutron reference energy, it is necessary to measure the thermal neutron cross-section of important isotopes with a thermal neutron standard field.

[0003] During the construction of a thermal neutron field, the gold cadmium ratio is an important parameter for the performance of the thermal neutron field. The higher the gold cadmium ratio, the purer the thermal neutron field and the fewer fast neutrons in the field.

[0004] Since it is difficult to directly measure the neutron intensity to obtain the gold cadmium ratio, in related technologies, a bare gold foil and a cadmium-coated gold foil are placed in a beam for irradiation, and the gold cadmium ratio is represented by measuring the ratio of the amounts of Au-198 generated by the two. However, since the actual thermal neutron field is not an ideal uniform beam, there are certain errors in the neutron fluence rate in different regions, which affects the accuracy of the gold cadmium ratio measurement. Summary of the Invention

[0005] In view of this, the main purpose of the embodiments of the present application is to provide a method for measuring the cadmium ratio of a thermal neutron field with higher measurement accuracy.

[0006] To achieve the above object, the technical solution of the embodiments of the present application is implemented as follows:

[0007] The embodiments of the present application provide a method for measuring the cadmium ratio of a thermal neutron field, including:

[0008] Placing a first object to be measured at a set position in the beam of the thermal neutron field, and monitoring the reactor power through a monitor;

[0009] Placing the first object to be measured outside the beam, and measuring the number of activation products generated by the first object to be measured through a detector;

[0010] Placing a second object to be measured at the set position, and monitoring the reactor power through the monitor;

[0011] Place the second object to be measured outside the beam, and measure the quantity of the activation products generated by the second object to be measured through the detector; wherein, one of the first object to be measured and the second object to be measured is a first material to be measured, and the other includes a second material to be measured and a cadmium material layer wrapped outside the second material to be measured, and the first material to be measured and the second material to be measured are of the same material;

[0012] Calculate the cadmium ratio according to the measurement result of the detector and the monitoring result of the monitor.

[0013] In one implementation, in the step of calculating the cadmium ratio according to the measurement result of the detector and the monitoring result of the monitor, the specific calculation formula of the cadmium ratio is:

[0014]

[0015] wherein, R cd is the cadmium ratio, n no is the quantity of the activation products generated by the first material to be measured per unit time measured by the detector; m no is the mass of the first material to be measured; n cd is the quantity of the activation products generated by the second material to be measured per unit time measured by the detector; m cd is the mass of the second material to be measured;

[0016] When the first material to be measured is placed at the set position, the monitor monitors the reactor power to obtain a count rate of mon no ;

[0017] When the second material to be measured is placed at the set position, the monitor monitors the reactor power to obtain a count rate of mon cd ;

[0018] In one implementation, both the first material to be measured and the second material to be measured are gold foils, the cadmium ratio of the thermal neutron field is the gold-cadmium ratio, and the activation product is Au-198.

[0019] In one implementation, the n no and the n cd both satisfy the following calculation formula:

[0020]

[0021] wherein, when the detector measures the first material to be measured, the n p is the n no; When the detector measures the second material to be measured, the n p is the n cd ;

[0022] N 198 is the number of Au-198 generated by the gold foil separated from the beam when the irradiation of the beam ends; λ is the decay constant; t is the irradiation duration of the beam.

[0023] In one embodiment, the detector is a high-purity germanium detector, and the high-purity germanium detector is used to measure the 411.8 keV γ-rays emitted by the Au-198 generated by the gold foil, and the N 198 The specific calculation formula of is:

[0024]

[0025] wherein, the N 412 is the net count of 411.8 keV γ-rays measured by the high-purity germanium detector; C 412 is the self-absorption correction coefficient of the gold foil; P γ is the emission probability of 411.8 keV γ-rays; ε is the efficiency of the high-purity germanium detector for measuring 411.8 keV γ-rays; t1 is the time for the high-purity germanium detector to measure 411.8 keV γ-rays; t2 is the time interval from the end of the irradiation of the beam to the start of the measurement by the high-purity germanium detector.

[0026] In one embodiment, both the first material to be measured and the second material to be measured are manganese foils, and the cadmium ratio of the thermal neutron field is the manganese-cadmium ratio; the activation product is Mn-56.

[0027] In one embodiment, the detector is a high-purity germanium detector.

[0028] In one embodiment, after placing the first object to be measured at the set position in the beam of the thermal neutron field, the cadmium ratio measurement method further includes: aligning the first object to be measured by a laser alignment instrument; and / or,

[0029] After placing the second object to be measured at the set position, the cadmium ratio measurement method further includes: aligning the second object to be measured by the laser alignment instrument.

[0030] In one embodiment, the set position is the center position of the beam.

[0031] In one embodiment, the thickness of the cadmium material layer is 1 mm.

[0032] An embodiment of the present application provides a method for measuring the cadmium ratio of a thermal neutron field. The cadmium ratio measurement method specifically includes placing a first object to be measured at a set position in the beam of the thermal neutron field, and monitoring the reactor power through a monitor; placing the first object to be measured outside the beam, and measuring the quantity of activation products generated by the first object to be measured through a detector; placing a second object to be measured at the set position, and monitoring the reactor power through a monitor; placing the second object to be measured outside the beam, and measuring the quantity of activation products generated by the second object to be measured through a detector; calculating the cadmium ratio according to the measurement results of the detector and the monitoring results of the monitor. Thus, on the one hand, since both the first object to be measured and the second object to be measured are irradiated at the set position in the beam rather than at different positions in the beam, the neutron fluence rates passing through the first object to be measured and the second object to be measured respectively are only related to the reactor power during irradiation, and thus the error caused by the non-uniformity of the thermal neutron field can be reduced, and the measurement accuracy can be improved. On the other hand, by monitoring the reactor power through a monitor, the measurement error caused by the change of the reactor power during the irradiation measurement of the first object to be measured and the second object to be measured can be reduced. Thus, the measurement accuracy can be further improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a flowchart of a method for measuring the cadmium ratio of a thermal neutron field according to an embodiment of the present application;

[0034] Figure 2 is the uniformity result of the thermal neutron field in the related art. DETAILED DESCRIPTION

[0035] In the related art, in order to ensure the mutual recognition of the neutron measurement values among countries, the International Organization for Standardization recommends the neutron energies and their generation methods for the energy and fluence responses of neutron measurement instruments, including thermal neutron energy, as shown in Table 1.

[0036] Table 1 Neutron radiation fields for determining the energy and fluence responses of neutron measurement instruments

[0037]

[0038]

[0039] During the construction of a thermal neutron field, the cadmium ratio can reflect the performance of the thermal neutron field. The higher the value, the purer the thermal neutron field and the fewer fast neutrons in the field. According to the definition, the cadmium ratio can be expressed as:

[0040]

[0041] where R cd is the cadmium ratio, and I is the neutron fluence rate; I cdThe neutron fluence rate after passing through 1 mm of cadmium.

[0042] In fact, it is not convenient to directly measure the neutron intensity, and the neutron fluence rate is proportional to the number of activation products generated due to irradiating the test object with a unit mass per unit time. Therefore, in this application, the cadmium ratio can be represented by the ratio of the number of activation products generated by the first test object and the second test object with a unit mass per unit time of irradiation.

[0043] An embodiment of this application provides a method for measuring the cadmium ratio of a thermal neutron field. Please refer to Figure 1 , the method for measuring the cadmium ratio of the thermal neutron field includes the following steps:

[0044] Step S1: Place the first test object at a set position in the beam of the thermal neutron field, and monitor the reactor power through a monitor.

[0045] Step S2: Place the first test object outside the beam, and measure the number of activation products generated by the first test object through a detector.

[0046] Step S3: Place the second test object at the set position, and monitor the reactor power through a monitor.

[0047] Step S4: Place the second test object outside the beam, and measure the number of activation products generated by the second test object through a detector; wherein, one of the first test object and the second test object is the first test material, and the other includes the second test material and a cadmium material layer wrapped outside the second test material, and the first test material and the second test material are the same material.

[0048] Step S5: Calculate the cadmium ratio according to the measurement result of the detector and the monitoring result of the monitor.

[0049] Specifically, the first test material and the second test material are of the same material, and both are materials that can be used for measuring the cadmium ratio of the thermal neutron field.

[0050] For example, both the first test material and the second test material are gold foils, the cadmium ratio of the thermal neutron field is the gold-cadmium ratio, and the activation product is Au-198 (gold-198).

[0051] Another example is that both the first test material and the second test material are manganese foils, the cadmium ratio of the thermal neutron field is the manganese-cadmium ratio, and the activation product is Mn-56 (manganese-56).

[0052] For the convenience of description, this application describes by taking both the first test material and the second test material as gold foils as an example.

[0053] It is possible that the first analyte to be measured is the first material to be analyzed, and the second analyte to be measured includes the second material to be analyzed and a cadmium material layer wrapped around the outside of the second material to be analyzed. It is also possible that the second analyte to be measured is the first material to be analyzed, and the first analyte to be measured includes the second material to be analyzed and a cadmium material layer wrapped around the outside of the second material to be analyzed. It can be understood that the first material to be analyzed and the second material to be analyzed are made of the same material, and different names are given only for the convenience of distinction. For example, both are gold or both are manganese.

[0054] That is to say, the difference between the first analyte to be measured and the second analyte to be measured is that one of them is not wrapped with a cadmium material layer on the outside, and the other is wrapped with a cadmium material layer on the outside. And, according to the actual situation, it is possible to first measure the analyte to be measured without the cadmium material layer wrapped on the outside, or it is also possible to first measure the analyte to be measured with the cadmium material layer wrapped on the outside.

[0055] Both the first analyte to be measured and the second analyte to be measured are measured at a set position in the beam, thereby reducing the measurement result error caused by the non-uniformity of the thermal neutron field itself and improving the measurement accuracy. In addition, the specific position of the set position can be set according to the actual situation.

[0056] For example, the set position is the center position of the beam. Thus, the measurement stability can be improved, and the required effect of the measurement can be better achieved.

[0057] It should be noted that the outside of the second material to be analyzed is wrapped with a cadmium material layer, which means that the second material to be analyzed is located inside the cadmium material layer, and its specific setting method is not limited. It can be to wrap a layer of cadmium material on the outer surface of the second material to be analyzed. It can also be to place the second material to be analyzed in a box made of cadmium material.

[0058] According to the internationally accepted standard, the thickness of the cadmium material layer is 1 mm. In addition, the sizes of the first material to be analyzed and the second material to be analyzed are not limited, and they can be set according to the actual situation.

[0059] For example, the diameters of the first material to be analyzed and the second material to be analyzed are greater than or equal to 6 mm and less than or equal to 2 cm. Thus, it is convenient for measurement. For example, both diameters are 6 mm or both are 2 cm.

[0060] The monitor can separately monitor the reactor power when the first object to be measured is in the beam current and the reactor power when the second object to be measured is in the beam current. It can be understood that since the reactor power is not stable and constant, the change in reactor power will cause a change in the neutron fluence rate, and the production rates of the activation products generated by the first object to be measured and the second object to be measured will also change. Therefore, in the process of comparing the quantities of the activation products generated by the first object to be measured and the second object to be measured respectively by the detector to obtain the cadmium ratio, by combining the monitoring result of the reactor power by the monitor, the measurement error caused by the change in the reactor power can be reduced, and thus the measurement accuracy can be further improved.

[0061] It should be noted that according to the actual situation, the specific implementation manner of combining the measurement result of the detector and the monitoring result of the monitor can be determined according to the actual situation. For example, based on the measurement result of the detector, a certain proportion of weighting is performed according to the monitoring result of the monitor to normalize the change in reactor power.

[0062] In addition, the specific type of the detector can be set according to the actual situation.

[0063] For example, the detector is a high-purity germanium detector.

[0064] In the related technology, the bare gold foil and the cadmium-coated gold foil are simultaneously placed at different positions in the beam current for irradiation, so as to represent the gold-cadmium ratio by measuring the quantity ratio of Au-198 generated by the two. This obviously does not consider the difference in neutron fluence rate between the positions of the bare gold foil and the cadmium-coated gold foil, thus resulting in a certain error in the measurement result. For example, the uniformity result of the thermal neutron field obtained by the China Advanced Research Reactor at the 12.5 cm single-crystal bismuth filter is as Figure 2 shown. The neutron fluence rate at the beam center and at 1 cm adjacent differs by 4.1% - 4.4%. If the uniformity correction is not performed, the measured cadmium ratio has an error of at least more than 4.1%. If the uniformity correction of the thermal neutron field is performed, an additional irradiation and measurement are required, which makes the measurement process complicated. In addition, due to the corresponding measurement uncertainty brought by the uniformity correction, the accuracy of the cadmium ratio measurement is affected.

[0065] The cadmium ratio measurement method for the thermal neutron field of the present application specifically includes placing a first object to be measured at a set position in the beam of the thermal neutron field, and monitoring the reactor power through a monitor; placing the first object to be measured outside the beam, and measuring the number of activation products generated by the first object to be measured through a detector; placing a second object to be measured at the set position, and monitoring the reactor power through a monitor; placing the second object to be measured outside the beam, and measuring the number of activation products generated by the second object to be measured through a detector; calculating the cadmium ratio based on the measurement results of the detector and the monitoring results of the monitor. Thus, on the one hand, since both the first object to be measured and the second object to be measured are irradiated at the set position in the beam, rather than at different positions in the beam, the neutron fluence rates passing through the first object to be measured and the second object to be measured respectively are only related to the reactor power during irradiation, and thus the error caused by the non-uniformity of the thermal neutron field can be reduced, the measurement accuracy can be improved, and it is also not necessary to measure the uniformity of the thermal neutron field beam. On the other hand, by monitoring the reactor power through a monitor, the measurement error caused by the change of the reactor power during the irradiation measurement of the first object to be measured and the second object to be measured can be reduced, and thus the measurement accuracy can be further improved.

[0066] In one embodiment, in the step of calculating the cadmium ratio based on the measurement results of the detector and the monitoring results of the monitor, the specific calculation formula of the cadmium ratio is:

[0067]

[0068] where, R cd is the cadmium ratio, n no is the number of activation products generated by the first material to be measured per unit time measured by the detector; m no is the mass of the first material to be measured; n cd is the number of activation products generated by the second material to be measured per unit time measured by the detector; m cd is the mass of the second material to be measured.

[0069] When the first material to be measured is placed at the set position, the monitor monitors the reactor power to obtain a count rate of mon no .

[0070] When the second material to be measured is placed at the set position, the monitor monitors the reactor power to obtain a count rate of mon cd .

[0071] Specifically, by measuring the first material to be measured through the detector, the number of activation products generated by the first material to be measured per unit time (i.e., n no ) can be obtained, and dividing it by the mass of the first material to be measured (i.e., m no) can obtain the number of activated products generated by the first material to be measured per unit mass per unit time.

[0072] By measuring the second material to be measured with a detector, the number of activated products generated by the second material to be measured per unit time can be obtained (i.e., n cd ). Dividing it by the mass of the second material to be measured (i.e., m cd ), the number of activated products generated by the second material to be measured per unit mass per unit time can be obtained.

[0073] It should be noted that if only the ratio of the number of activated products generated by the first material to be measured and the second material to be measured per unit mass per unit time is defined as the cadmium ratio, the difference in the reactor power during the measurement processes for the first material to be measured and the second material to be measured successively is ignored. Therefore, on the basis of the above ratio, removing the coefficient proportional to the change in the reactor power can reduce the measurement error caused by the change in the reactor power, thereby further improving the measurement accuracy.

[0074] It can be understood that the above coefficient is the ratio of m no to m cd , and through simple transformation, it is the above calculation formula.

[0075] It should be noted that the monitor can monitor the reactor power to form a counting rate proportional to the change in the reactor power, that is, the ratio of the counting rates obtained from two successive monitors is equal to the ratio of the reactor powers during the two successive monitors, so it can better reflect the change in the reactor power.

[0076] In addition, the specific method for the detector to obtain the number of activated products through measurement can be set according to the actual situation.

[0077] Exemplarily, take the first material to be measured and the second material to be measured as gold foils.

[0078] n no and n cd both satisfy the following calculation formula:

[0079]

[0080] Among them, when the detector measures the first material to be measured, n p is n no ; when the detector measures the second material to be measured, n p is n cd .

[0081] N 198The number of Au-198 generated from the gold foil separated from the beam at the end of the irradiation of the beam; λ is the decay constant; t is the irradiation duration of the beam.

[0082] Specifically, since the first material to be measured and the second material to be measured are of the same material, which is gold, the activation products produced by them are also the same, both being Au-198. Thus, the measurement principles of the detector for the first material to be measured and the second material to be measured are also the same. After separating the first material to be measured and the second material to be measured from the beam, by measuring the number of Au-198 and calculating through the above formula, n no and n cd .

[0083] Among them, the decay constant λ is 2.97682E-6 s -1 .

[0084] In one embodiment, the detector is a high-purity germanium detector, and the high-purity germanium detector is used to measure the 411.8 keV γ-rays emitted by the Au-198 generated from the gold foil. The calculation formula of N 198 is specifically:

[0085]

[0086] Among them, N 412 is the net count of 411.8 keV γ-rays measured by the high-purity germanium detector; C 412 is the self-absorption correction coefficient of the gold foil; P γ is the emission probability of 411.8 keV γ-rays; ε is the efficiency of the high-purity germanium detector for measuring 411.8 keV γ-rays; t1 is the time for the high-purity germanium detector to measure 411.8 keV γ-rays; t2 is the time interval from the end of the irradiation of the beam to the start of the measurement by the high-purity germanium detector.

[0087] Specifically, the Au-198 generated after the activation of the gold foil will emit 411.8 keV γ-rays, and the high-purity germanium detector can measure the 411.8 keV γ-rays. Thus, through the above formula, the number of Au-198 generated after the activation of the gold foil, that is, N 198 , can be deduced.

[0088] Among them, P γ is 0.9554.

[0089] In one embodiment, after placing the first object to be measured at the set position in the beam of the thermal neutron field, the cadmium ratio measurement method further includes: centering the first object to be measured through a laser alignment instrument. Thus, it can be ensured that the center of the first object to be measured is centered with the center of the set position, and further, the measurement accuracy can be improved.

[0090] In one embodiment, after placing the second object to be measured at the set position, the cadmium ratio measurement method further includes: aligning the second object to be measured with a laser alignment instrument. Thereby, it can be ensured that the center of the second object to be measured is aligned with the center of the set position, and thus the measurement accuracy can be improved.

[0091] In a specific embodiment, a bracket is installed at the set position in the beam direction of the thermal neutron field to position the first object to be measured and the second object to be measured, and then the first object to be measured and the second object to be measured are successively fixed to the bracket with transparent tape, thereby improving stability. It can be understood that the second object to be measured is installed on the bracket after the first object to be measured is detached from the beam.

[0092] In a specific embodiment, the first object to be measured is the first material to be measured, the second object to be measured includes the second material to be measured and a cadmium material layer wrapped outside the second material to be measured, and both the first material to be measured and the second material to be measured are gold foils.

[0093] By measuring the first object to be measured, the result data is shown in Table 2.

[0094] Table 2 Data of the first object to be measured

[0095] Parameter name Parameter value Gold foil diameter / cm 1.0 <![CDATA[Gold foil mass m no / mg]]> 14.986 Irradiation duration t / s 3615 <![CDATA[Time t2 / s from the end of irradiation to the start of measurement]]> 2976 <![CDATA[Measurement time t1 / s]]> 9953 High-purity germanium detector efficiency ε 2.21E-3 <![CDATA[Net count N of 411.8 keV γ-rays 412 > 180773 <![CDATA[Gold foil self-repair correction coefficient C 412 > 1.002 Monitor count 379365 Monitor measurement time / s 3605

[0096] It should be noted that the count rate obtained by the monitor is the ratio of the monitor count to the monitor measurement time.

[0097] By measuring the second object to be measured, the result data is shown in Table 3.

[0098] Table 3 Data of the second object to be measured

[0099]

[0100]

[0101] Thus, through the data in Table 2 and Table 3 combined with relevant formulas, the measured gold-cadmium ratio of the thermal neutron field is 41.62.

[0102] It can be understood that when measuring the manganese-cadmium ratio for a manganese foil, its calculation formula and measurement method are the same as those for measuring the gold-cadmium ratio for a gold foil.

[0103] In the description of the present application, the descriptions with reference to terms such as "in one embodiment", "in some embodiments", "in a specific embodiment", or "exemplary", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the embodiments of the present application. In the present application, the schematic expressions of the above terms are not necessarily directed to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine the different embodiments or examples described in the present application and the features of different embodiments or examples.

[0104] The foregoing are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, the present application may have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application are all included within the protection scope of the present application.

Claims

1. A method for measuring the cadmium ratio of a thermal neutron field, characterized in that, Comprising: Placing a first analyte to be measured at a set position in the beam of the thermal neutron field, and monitoring the reactor power by a monitor; Placing the first analyte to be measured outside the beam, and measuring the quantity of activation products generated by the first analyte to be measured by a detector; Placing a second analyte to be measured at the set position, and monitoring the reactor power by the monitor; Placing the second analyte to be measured outside the beam, and measuring the quantity of activation products generated by the second analyte to be measured by the detector; wherein, one of the first analyte to be measured and the second analyte to be measured is a first analyte material, and the other comprises a second analyte material and a cadmium material layer wrapped outside the second analyte material, and the first analyte material and the second analyte material are of the same material; Calculating the cadmium ratio according to the measurement result of the detector and the monitoring result of the monitor; In the step of calculating the cadmium ratio according to the measurement result of the detector and the monitoring result of the monitor, the specific calculation formula of the cadmium ratio is: wherein, R cd is the cadmium ratio, n no is the number of the activation products generated by the first material to be measured per unit time as measured by the detector; m no is the mass of the first material to be measured; n cd is the number of the activation products generated by the second material to be measured per unit time as measured by the detector; m cd is the mass of the second material to be measured; When the first material to be measured is placed at the set position, the monitor monitors the reactor power to obtain a count rate of mon no ; When the second material to be measured is placed at the set position, the monitor monitors the reactor power to obtain a count rate of mon cd ; Said n no and said n cd both satisfy the following calculation formula: Among them, when the detector measures the first material to be measured, the n p is the n no ; when the detector measures the second material to be measured, the n p is the n cd ; N is the quantity of activation products generated by the first analyte material and the second analyte material separated from the beam at the end of the irradiation of the beam; λ is the decay constant; t is the irradiation duration of the beam.

2. The cadmium ratio measurement method for the thermal neutron field according to claim 1, characterized in that, Both the first analyte material and the second analyte material are gold foils, the cadmium ratio of the thermal neutron field is the gold-cadmium ratio, and the activation product is Au-198.

3. The cadmium ratio measurement method of the thermal neutron field according to claim 2, wherein, The detector is a high-purity germanium detector, which is used to measure the 411.8 keV γ-rays emitted by Au-198 generated by the gold foil, and the N is N 198 , the N 198 The specific calculation formula is as follows: wherein, the N 198 is the quantity of Au-198 generated from the gold foil separated from the beam at the end of the irradiation of the beam, and the N 412 is the net count of 411.8 keV γ-rays obtained by measurement with the high-purity germanium detector; C 412 is the self-absorption correction coefficient of the gold foil; P γ is the emission probability of 411.8 keV γ-rays; ε is the efficiency of the high-purity germanium detector for measuring 411.8 keV γ-rays; t1 is the time for the high-purity germanium detector to measure 411.8 keV γ-rays; and t2 is the time interval from the end of the irradiation of the beam to the start of the measurement by the high-purity germanium detector.

4. The cadmium ratio measurement method for a thermal neutron field according to claim 1, characterized in that Both the first analyte material and the second analyte material are manganese foils, the cadmium ratio of the thermal neutron field is the manganese-cadmium ratio; the activation product is Mn-56.

5. The method for measuring the cadmium ratio of a thermal neutron field according to claim 1 or 2, characterized in that, The detector is a high-purity germanium detector.

6. The method for measuring the cadmium ratio of a thermal neutron field according to any one of claims 1-3, characterized in that, After placing the first analyte to be measured at the set position in the beam of the thermal neutron field, the cadmium ratio measurement method further comprises: aligning the first analyte to be measured by a laser alignment instrument; and / or, After placing the second analyte to be measured at the set position, the cadmium ratio measurement method further comprises: aligning the second analyte to be measured by the laser alignment instrument.

7. The cadmium ratio measurement method for a thermal neutron field according to any one of claims 1 to 3, characterized in that The set position is the central position of the beam.

8. The cadmium ratio measurement method for a thermal neutron field according to any one of claims 1-3, characterized in that, The thickness of the cadmium material layer is 1 mm.

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