Apparatus and method for multi-detector combination output long neutron counter
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NANJING UNIV OF AERONAUTICS & ASTRONAUTICS
- Filing Date
- 2023-04-03
- Publication Date
- 2026-07-21
Smart Images
Figure CN116559931B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of neutron measurement technology, and specifically to a device and method for a multi-detector combined output long neutron counter. Background Technology
[0002] The accurate transfer of fluence standards for reference neutron radiation fields recommended by the International Organization for Standardization (ISO) is a crucial aspect of neutron metrology. It is applied in nuclear parameter measurement, reactor design and operation, neutron nuclear technology applications, and the calibration of neutron metrology instruments, and is therefore of great significance. Due to the advantages of small size, low cost, and ease of preparation, isotopic neutron fields established using isotopic neutron sources are the most widely used reference neutron radiation fields. The energy spectrum of isotopic neutron fields typically spans 3-5 orders of magnitude. Detectors with uniform neutron detection efficiency across a wide energy range have a significant advantage in fluence standard transfer for such neutron fields.
[0003] Existing neutron detectors can be broadly classified into thermal neutron detectors and fast neutron detectors, both of which have limited neutron energy measurement ranges. To detect neutrons across a wider energy range, a moderator is typically added to the thermal neutron detector. In this moderator, some low-energy neutrons lose energy within the moderator and cannot reach the detector, while some high-energy neutrons lose energy within the moderator and become low-energy neutrons, i.e., thermal neutrons, which are then detected by the thermal neutron detector. For example... Figure 1 The diagram shows the response function of the thermal neutron detector before and after the addition of a moderator; that is, the response function is formed by connecting the detector's response values at different energies. Figure 1 As shown, the thermal neutron detector with the addition of a moderator can detect a wider range of neutron energies. However, two problems still exist: 1) the detected neutron energy range is not wide enough; 2) the response value still fluctuates significantly with the change of incident neutron energy, that is, the response function curve is still not flat enough.
[0004] Therefore, the most widely used flat-response detector in the neutron standard laboratory is currently the long neutron counter, such as... Figure 2 As shown, the principle is to use a moderator to modulate the response function of the thermal neutron detector, which follows a near-1 / v law, making the overall detection efficiency of the counter change slowly with energy. Most existing designs for long neutron counters revolve around moderators, aiming to obtain a flat response function by changing the type of moderator material and its geometric parameters. Despite the design of complex, large-volume moderators to modulate the response function, the flat response characteristics of existing long neutron counters are still not ideal. Furthermore, large-volume moderators are not only less portable but also disturb the original neutron radiation field to some extent, adversely affecting the measurement results. Summary of the Invention
[0005] To address the problems of complex geometry and large volume of the moderator, which disturbs the original neutron radiation field and adversely affects the measurement results, this application provides a device for a multi-detector combined output long neutron counter, used to detect the neutron fluence in the neutron radiation field formed by a neutron radiation source. The device includes: a moderator to reduce the energy of the neutrons, forming thermal neutrons; multiple thermal neutron detectors arranged in the moderator in a first depth order along the same direction to record the response values of the thermal neutrons; a metallic material layer disposed between the moderator and the multiple thermal neutron detectors to compensate for neutron responses with energies above MeV; and a shielding layer disposed between the metallic material layer and the moderator to shield scattered neutrons.
[0006] Furthermore, the aforementioned device also includes an air layer disposed on the surface of the moderator where neutrons are incident, making it easier for neutrons to enter the moderator and reach the thermal neutron detector.
[0007] Furthermore, the aforementioned moderating material is polyethylene or paraffin.
[0008] Furthermore, the aforementioned thermal neutron detector is a third-generation semiconductor detector containing a thermal neutron converter.
[0009] Furthermore, the aforementioned third-generation semiconductor detector is a silicon carbide detector, a gallium nitride detector, or a diamond detector.
[0010] Furthermore, the aforementioned thermal neutron converter material is 6 LiF or B4C4.
[0011] This application also relates to a method for outputting a long neutron counter using a multi-detector combination of the above-described device. The method involves recording the response values of the thermal neutrons recorded by the plurality of thermal neutron detectors arranged in the first depth order, and the response functions formed by the incident neutron energies. For different incident neutron energies, the method calculates the product of the response values with the linear combination coefficients corresponding to the plurality of thermal neutron detectors to obtain weighted response values. The method then calculates the sum of the weighted response values at the same incident neutron energy within the incident neutron energy range to obtain the total fluence response of the long neutron counter at the same incident neutron energy, thus forming the total fluence response function within the incident neutron energy range.
[0012] Furthermore, the calculation method for the first depth order of the aforementioned thermal neutron detectors and the aforementioned linear combination coefficients is as follows: The Monte Carlo method is used to calculate the original response functions of multiple thermal neutron detectors arranged at different depths; the product of the original response functions of n thermal neutron detectors within a certain neutron energy range and the corresponding n undetermined linear combination coefficients is set as the weighted response function; the sum of the aforementioned weighted response functions is set as a constant; the least squares solution of the overdetermined equation system formed by the original response function, the aforementioned undetermined linear combination coefficients, and the sum of the aforementioned weighted response functions is obtained as the n undetermined linear combination coefficients; the sum of the weighted response functions of n thermal neutron detectors arranged at different depths within a certain neutron energy range is calculated respectively; the number and position of the aforementioned thermal neutron detectors corresponding to the relative standard deviation of the sum of the aforementioned weighted response functions within the aforementioned energy range are recorded; the number and position of the aforementioned thermal neutron detectors n corresponding to the minimum relative standard deviation are selected as the first depth order of the aforementioned thermal neutron detectors and the corresponding undetermined linear combination coefficients as the aforementioned linear combination coefficients.
[0013] This invention provides a device and method for a multi-detector combined output long neutron counter, which solves the problem that traditional long neutron counters can only modulate the response function by changing the type of moderator material and the moderator's geometric parameters, thus requiring a large-volume moderator with complex geometry and failing to achieve ideal flat response characteristics. The long neutron counter designed by this method has a flat neutron fluence response, small size and weight, and is portable and easy to use. It can be used as a portable secondary neutron fluence rate standard instrument in reference neutron radiation fields recommended by the International Organization for Standardization.
[0014] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description
[0015] Figure 1 The provided response functions for the thermal neutron detector before and after the addition of the moderator.
[0016] Figure 2 Schematic diagram of a flat-response detector;
[0017] Figure 3 This is a schematic diagram of the structure of the multi-detector combined output long neutron counter device provided in an embodiment of the present invention;
[0018] Figure 4 The statistical graph of the response values of the long neutron counter to neutrons of different energies and the matrix calculation graph of the linear combination coefficients when the neutron detector is 3, provided for embodiments of the present invention;
[0019] Figure 5The total fluence response diagram of the long neutron counter provided in the embodiment of the present invention. Detailed Implementation
[0020] The specific embodiments of the present invention will be described in more detail below with reference to the accompanying drawings and examples, so as to better understand the solution of the present invention and its advantages in various aspects. However, the specific embodiments and examples described below are for illustrative purposes only and are not intended to limit the present invention.
[0021] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.
[0022] The following disclosure provides many different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.
[0023] Figure 3 This is a schematic diagram of the structure of a multi-detector combined output long neutron counter device provided in an embodiment of the present invention. In the diagram, 1 is a moderator, 2 is a thermal neutron detector, 3 is a metal material layer, 4 is a shielding layer, and 5 is an air layer.
[0024] like Figure 3As shown, this application provides a device for a multi-detector combined output long neutron counter, used to detect the neutron fluence in a neutron radiation field formed by a neutron radiation source. It includes a moderator 1, multiple thermal neutron detectors 2, a metallic material layer 3, a shielding layer 4, and an air layer 5. The moderator 1 reduces the energy of incident neutrons, forming thermal neutrons. Multiple thermal neutron detectors 2 are arranged in the moderator 1 in a first depth order according to the neutron's incident depth within the moderator 1, used to record the thermal neutron response value. The metallic material layer, disposed between the moderator 1 and the multiple thermal neutron detectors 2, is used to compensate for the neutron response. Its principle is to utilize the (n,xn) multiplication reaction between the metallic material and high-energy neutrons to improve the response value of the long neutron counter's response function in the energy range greater than MeV. The shielding layer, disposed between the metallic material layer and the moderator, is used to shield scattered neutrons. Its principle is to absorb scattered neutrons incident from the side and rear, only accepting neutrons incident orally from the front surface, thus improving statistical accuracy. In this application, the moderator is configured as a cylinder, and multiple thermal neutron detectors are arranged on the axis of the moderator. The metal material layer and the shielding layer are parallel to the axis of the moderator. That is, both the metal material layer and the shielding layer are designed as rings and nested within the moderator.
[0025] An air layer 5 is also provided on the surface of the moderator where neutrons are incident, that is, a part of the surface of the moderator is removed to make it easier for low-energy neutrons to enter the moderator and reach the thermal neutron detector, thereby improving the response value of the long neutron counter response function at the low-energy range.
[0026] This application also discloses that the moderator material is polyethylene or paraffin. The shielding layer material is boron-containing polyethylene. The metallic material layer is a third-generation semiconductor detector containing a thermal neutron converter, such as a 4H-SiC detector. The thermal neutron converter here is... 6 LiF or B4C are arranged close to the surface of the detector.
[0027] The method for using the above-described device to perform a multi-detector combined output long neutron counter is as follows:
[0028] S1: Calculate the response values recorded by multiple thermal neutron detectors arranged in the first depth order and the response functions formed by the incident neutron energy, respectively;
[0029] S2: When calculating different incident neutron energies, the above response values are multiplied by the linear combination coefficients corresponding to multiple thermal neutron detectors to obtain weighted response values;
[0030] S3: Calculate the sum of the above weighted response values at the same incident neutron energy within the incident neutron energy range. This sum is the total fluence response of the long neutron counter at that energy, ultimately forming the total fluence response function within the incident neutron energy range.
[0031] The number and arrangement of thermal neutron detectors in the apparatus and method of this application, as well as the linear combination coefficients in the usage method, need to be determined by a certain method.
[0032] The raw response functions of multiple thermal neutron detectors arranged at different depths were calculated using the Monte Carlo method.
[0033] The product of the original response functions of n thermal neutron detectors within a certain neutron energy range and the corresponding n undetermined linear combination coefficients is set as the weighted original response function. The sum of the weighted response functions is set as a constant fixed value. The least squares solution of the overdetermined equation system formed by solving the original response function, the undetermined linear combination coefficients and the sum of the weighted response functions is used as the n unknown linear combination coefficients.
[0034] Calculate the sum of weighted response functions of n thermal neutron detectors arranged at different depths within a certain neutron energy range, and select the number and position of the thermal neutron detectors corresponding to the relative standard deviation of the sum of the weighted response functions within the energy range.
[0035] The number and location of thermal neutron detectors corresponding to the minimum relative standard deviation are selected as the first depth order of thermal neutron detectors and the corresponding undetermined linear combination coefficients are used as linear combination coefficients.
[0036] The thermal neutron detectors are modulated using their arrangement and number, as well as the linear combination coefficients corresponding to each thermal neutron detector.
[0037] This application utilizes the above method to design a device for a multi-detector combined output long neutron counter of a specific size, and a method for counting using this device.
[0038] Example 1
[0039] This application specifically discloses the dimensions of the aforementioned multi-detector combined output long neutron counter device, such as... Figure 3As shown. The moderator 1, made of cylindrical polyethylene material, is divided into three parts by a metal material layer and a shielding layer: an outer moderator 1.1, an intermediate moderator 1.2, and an inner moderator 1.3. The outer moderator is a barrel-shaped structure open at one end, with a bottom height of 6 cm, a total height of 30 cm, and an outer diameter of 30 cm. The annular shielding layer 4, coaxial with the cylindrical moderator, has dimensions of a barrel-shaped bottom height of 1 cm, a total height of 24 cm, an outer diameter of 18 cm, and an inner diameter of 16 cm, and is at the same height as the moderator on the plane of neutron incidence. The intermediate moderator 1.2 has a height of 23 cm, an outer diameter of 16 cm, and an inner diameter of 12 cm; the metal material is made of Cu material, with a height of 13 cm, an outer diameter of 12 cm, and an inner diameter of 10 cm. The air layer 5 has a height of 10 cm, an outer diameter of 12 cm, and an inner diameter of 10 cm. The inner moderator has a height of 23 cm and a diameter of 10 cm. The thermal neutron detector is a 4H-SiC detector containing a thermal neutron converter. Twenty 4H-SiC detectors are staggered 1 cm apart along the axis of a cylindrical moderator. The detector dimensions are 5 mm x 5 mm. The thermal neutron converter in this application is... 6 LiF is arranged close to the surface of the detector. 6 The LiF conversion body has a thickness of 5 μm. 6 The enrichment level of Li atoms is 90%.
[0040] The neutron source in this application is a conveniently countable monoenergetic neutron source, specifically a disk-shaped neutron source with a diameter of 30 cm, incident parallel to the cylindrical axis, and spaced 10 cm from the front surface of the moderator. Figure 3 The apparatus in the diagram shows a neutron source incident on the paper from the right side. In this embodiment, the energy of the monoenergetic neutron is 10... -10 Within the energy range of MeV to 100MeV, 121 equally spaced neutron energy points were obtained on a logarithmic coordinate axis. Statistical analysis was performed on the response values recorded by a thermal neutron detector after the incident neutrons were incident on the device of this application within this energy range.
[0041] According to an embodiment of the present invention, the linear combination coefficient is calculated by selecting an incident neutron energy range of 10 eV-25 MeV, within which there are 71 response value recording points. The product of the response values detected by n thermal neutron detectors at the 71 energy nodes and the linear combination coefficient is set, and then summed to obtain a fixed constant representing the flat response function. For example, when n is 3, ... Figure 4 As shown, selecting 3 out of 20 thermal neutron detectors results in 1140 possible combinations. The goal is to solve for the linear combination coefficients in each of these combinations. That is, to solve for... Figure 5The matrix. In summary, the method for calculating the linear combination coefficients is to take the 71 response values of each response function in the selected response function combination between 10eV and 25MeV as the columns of the coefficient matrix, set the constant term as a fixed value to represent the ideal flat response function, and solve the least squares solution of the overdetermined equation system as the linear combination coefficients of each detector.
[0042] According to an embodiment of the present invention, the method for selecting the optimal combination of response functions is to select 2 to 10 response functions from 20 thermal neutron detectors and calculate the linear combination coefficients of all possible combinations of response functions. Then, these coefficients are linearly combined to obtain the flat response function, and the relative standard deviation of its response value in the energy range of 10 eV-25 MeV is calculated. Among combinations with the same number of response functions, the combination with the smallest relative standard deviation is selected, and the curve of the smallest relative standard deviation as a function of the number of thermal neutron detector response functions is plotted.
[0043] The 71 response values of each response function in the selected response function combination between 10eV and 25MeV are used as columns of the coefficient matrix. The constant term is set to a fixed value to represent the ideal flat response function. The least squares solution of the overdetermined equation system is used as the linear combination coefficient of each detector.
[0044] According to an embodiment of the present invention, the curve showing the change of the minimum relative standard deviation with the number of response functions no longer decreases significantly after the number of response functions exceeds four. Therefore, a suitable number of detectors is four, with the distances between the front surface of the detector and the front surface of the moderator being 2.9 cm, 9.9 cm, 15.9 cm, and 18.9 cm, respectively.
[0045] According to embodiments of the present invention, the weight values corresponding to the detectors described above are 0.62, 1.25, -6.47, and 10.23, respectively.
[0046] Please see Figure 5 The multi-detector combined output long neutron counter, which is made using the above method, selects appropriate response functions from the calculated response function matrix and combines them with certain weights to obtain a flat neutron fluence response. The total fluence response is relatively stable in the energy range of 10eV to 25MeV with small fluctuations.
[0047] According to an embodiment of the present invention, the total fluence response has a relative standard deviation of 1.78% in the energy range of 10 eV to 25 MeV. This demonstrates high accuracy and meets the requirements for neutron counting.
[0048] Obviously, the above embodiments are merely examples for clearly illustrating the present invention and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.
Claims
1. A device for outputting a long neutron counter using a multi-detector combination, used to detect the neutron fluence in a neutron radiation field formed by a neutron radiation source, characterized in that, include: Moderators reduce the energy of neutrons, forming thermal neutrons; Multiple thermal neutron detectors are disposed in the moderator and arranged in a first depth order along the same direction to record the response values of the thermal neutrons; the same direction is along the axis of the cylindrical moderator; A metallic material layer is disposed between the moderator and the plurality of thermal neutron detectors to compensate for neutron responses with energies above MeV; A shielding layer is disposed between the metal material layer and the moderator to shield scattered neutrons; The number of thermal neutron detectors and their first depth order were obtained using the following calculation method: The raw response functions of the multiple thermal neutron detectors arranged at different depths were calculated using the Monte Carlo method; The product of the original response function recorded by n thermal neutron detectors within a certain neutron energy range and the corresponding n undetermined linear combination coefficients is set as the weighted response function. The sum of the weighted response functions is set as a constant fixed value. The least squares solution of the overdetermined equation system formed by the original response function, the undetermined linear combination coefficients and the sum of the weighted response function is the n undetermined linear combination coefficients. Calculate the sum of weighted response functions of n thermal neutron detectors arranged at different depths within a certain neutron energy range, and record the number and position of the thermal neutron detectors corresponding to the relative standard deviation of the sum of the weighted response functions within the energy range; The number and position of the thermal neutron detectors corresponding to the minimum relative standard deviation are selected as the first depth order of the thermal neutron detectors, and the corresponding undetermined linear combination coefficients are used as the linear combination coefficients.
2. The apparatus as claimed in claim 1, characterized in that, Also includes: An air layer is provided on the surface of the moderator where neutrons are incident, making it easier for neutrons to enter the moderator and reach the thermal neutron detector.
3. The apparatus as described in claim 2, characterized in that, The moderating material is polyethylene or paraffin.
4. The apparatus as described in claim 3, characterized in that, The thermal neutron detector is a third-generation semiconductor detector containing a thermal neutron converter.
5. The apparatus as described in claim 4, characterized in that, The third-generation semiconductor detector is a silicon carbide detector, a gallium nitride detector, or a diamond detector.
6. The apparatus as claimed in claim 5, characterized in that, The thermal neutron converter material is 6LiF or B4C.
7. A method for using a multi-detector combination output long neutron counter based on any one of the devices described in claims 1-6, characterized in that, Calculate the response values of the thermal neutrons recorded by the plurality of thermal neutron detectors arranged in the first depth order and the response functions formed by the incident neutron energy, respectively; When calculating different incident neutron energies, the response value is multiplied by the linear combination coefficients corresponding to the plurality of thermal neutron detectors to obtain a weighted response value; The sum of the weighted response values at the same incident neutron energy within the incident neutron energy range is calculated to form the total fluence response of the long neutron counter at the same incident neutron energy, thus forming the total fluence response function within the incident neutron energy range.
8. The method as described in claim 7, characterized in that, The calculation methods for the first depth order of the thermal neutron detector and the linear combination coefficients are as follows: The raw response functions of the multiple thermal neutron detectors arranged at different depths were calculated using the Monte Carlo method; The product of the original response function recorded by n thermal neutron detectors within a certain neutron energy range and the corresponding n undetermined linear combination coefficients is set as the weighted response function. The sum of the weighted response functions is set as a constant fixed value. The least squares solution of the overdetermined equation system formed by the original response function, the undetermined linear combination coefficients and the sum of the weighted response function is the n undetermined linear combination coefficients. Calculate the sum of weighted response functions of n thermal neutron detectors arranged at different depths within a certain neutron energy range, and record the number and position of the thermal neutron detectors corresponding to the relative standard deviation of the sum of the weighted response functions within the energy range; The number and position of the thermal neutron detectors corresponding to the minimum relative standard deviation are selected as the first depth order of the thermal neutron detectors, and the corresponding undetermined linear combination coefficients are used as the linear combination coefficients.