CN216669794U - Passive nuclear material fast neutron multiplicities measurement system based on spherical symmetrical structure - Google Patents
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Abstract
The utility model relates to a passive nuclear material fast neutron multiplicities measuring system based on a spherical symmetrical structure. The utility model aims to solve the problems of the existing column layout model of the fast neutron multiple measurement system built by simulation and experiment at home and abroad, such as low detection efficiency of the system and different detection efficiency corresponding to any point in the internal space, but in actual measurement, the measurement result of the system has large deviation due to various shapes and sizes of nuclear materials, so that the subsequent data processing and correction are more difficult. The utility model changes the detection efficiency of the system by controlling the radius of the system or controlling the increase and decrease of the detectors, and simultaneously, the spherical symmetrical structure can ensure uniform detection efficiency in a certain radius range and adapt to the measurement requirements of samples to be detected with different radioactive intensities. The utility model comprises a plurality of detectors and a shielding body, wherein the detectors are symmetrically and uniformly distributed in the shielding body in a spherical shape. The utility model belongs to the technical field of nuclear security research.
Description
Technical Field
The utility model relates to the technical field of nuclear security research, in particular to a passive nuclear material fast neutron multiplicities measuring system based on a spherical symmetric structure.
Background
Nuclear neutron measurement techniques are used to analyze samples by detecting neutrons emitted by spontaneous or induced fission in plutonium/uranium containing samples. The method mainly comprises three methods: total neutron measurement techniques, coincidence neutron measurement techniques, and neutron multiplicities measurement techniques. Compared with the former two technologies, the neutron multiplicities technology has high measurement accuracy and high measurement speed, and is applied to the fields of nuclear security, nuclear weapon military control verification and the like.
The neutron multiplicities measuring technology measures the multiplicities counting rate (a counting rate S, a counting rate D and a counting rate T) of neutrons, and then solves the ratio alpha of the reaction rate of unknown parameters (sample (alpha, n) and the emissivity of fission neutrons (spontaneous or induced)) through the relation between the unknown parameters and the measured parameters of the sample, the neutron multiplication coefficient M of the sample and the spontaneous fission rate F of the samplef) To obtain the nuclear material (e.g. from240Pu).
Neutron multiplicities measurement techniques are mainly divided into two main categories: (1) slow neutron multiplicities measurement techniques and (2) fast neutron multiplicities measurement techniques. Among them, the conventional slow neutron multiplicities measurement technology has been developed for many years and has been a mature commercial product. The detector of the technique adopts3He counter tube, but since now3Extreme shortage of He gas, resulting in3The price of the He counting tube is higher; the fast neutron multiplicities measurement technology is internationally researched in recent yearsInstead of a neutron-gamma detector, such as a liquid scintillator detector3New technology of He counting tube. Because the neutron-gamma discrimination detector, such as a liquid flash detector, has lower price3The He counting tube can directly measure fission (fast) neutrons, so that the system does not need an additional slowing-down body, the cost and the system complexity are reduced, meanwhile, the influence of background counting is reduced, and in addition, the dead time of the fast neutron-based multiple system is short, so that the fast neutron multiple measurement technology has higher cost performance and also improves the measurement precision.
At present, fast neutron multiplicities measurement system models constructed by foreign and domestic simulation and experiments are all in cylindrical layout, so that the detection efficiency of the system is low, and the detection efficiency corresponding to any point of an internal space is different.
SUMMERY OF THE UTILITY MODEL
Aiming at the defects in the prior art, the utility model aims to provide a solution for a passive nuclear material fast neutron multiplicities measurement system based on a spherical symmetric structure. Within a certain space range in the system, the detection efficiency can not change along with the change of the size and the shape of the sample, and the detection efficiency of the system can be changed by controlling the radius of the system or controlling the increase and decrease of the detector.
In order to achieve the purpose, the technical scheme adopted by the utility model is as follows:
a passive nuclear material fast neutron multiplicities measurement system based on a spherical symmetric structure, the system comprising: a plurality of probes and shields; the plurality of detectors are symmetrically and uniformly distributed in the shielding body in a spherical manner.
Further, the detector has neutron-gamma discrimination properties, such as a liquid scintillator detector.
Further, the number of detectors is determined by the spherical symmetry formula (1), such as the exemplary thirty-two.
Furthermore, the (thirty-two) detectors forming the detection system are uniformly arranged in a spherical symmetry manner.
Further, the shield is spherical shell shaped.
Furthermore, the shielding body is made of (high density) polyethylene.
Furthermore, a plurality of holes for placing the detector are arranged on the shielding body.
Compared with the traditional slow neutron multiplicities measurement system, the measurement system disclosed by the utility model has shorter dead time, 10ns vs 10 μ s, so that the technology can detect higher-order multiple coincidence events and can detect a measured sample with a high (alpha, n) reaction event, and meanwhile, the measurement time is shorter under the same measurement precision.
The coincidence gate width of the utility model is less than 100ns, which is equivalent to the fission time, the miscoincidence probability is very low, while the slow neutron technology is three orders of magnitude larger than the utility model, the miscoincidence probability is increased, therefore, when other conditions are the same, the utility model is helpful to improve the signal-to-noise ratio of the detection system, which further has higher detection precision.
The system disclosed by the utility model comprises a shielding body made of (high-density) polyethylene material, can increase the neutron scattering rate to improve the detection efficiency, and can shield background neutron signal interference, fix and support the detector;
compared with a fast neutron multiple measuring system in cylindrical arrangement, the measuring system disclosed by the utility model has higher detection efficiency, the detection efficiency can not change along with the change of the size and the shape of a sample and the change of the placing position of the sample within a certain space range in the measuring system, and the detection efficiency of the system can be changed by controlling the radius of the system or controlling the increase and decrease of the detectors.
Drawings
FIG. 1 is a diagram illustrating simulation results of a fast neutron multiplicities measurement system in accordance with an exemplary embodiment of the present invention;
FIG. 2 is a schematic diagram of a fast neutron multiplicities measurement system;
FIG. 3 is a schematic diagram of the layout of the detector shown in FIG. 2
Fig. 1 to 3:
1-detector, 2-shield.
Detailed Description
The utility model is described in further detail below with reference to the drawings and the detailed description.
Referring to fig. 1 to 3, the present embodiment provides a passive nuclear material fast neutron multiplicities measurement system based on a spherical symmetric structure, which includes a plurality of detectors 1 and a shield 2; a plurality of detectors 1 are uniformly distributed in the shielding body 2.
In some embodiments, the detector 1 has neutron-gamma discrimination capabilities, such as a liquid scintillator detector.
In some embodiments, the number of the detectors 1 is not limited, and is at least four, and thirty-two detectors 1 are taken as an example in the present embodiment.
The number of detectors 1 is determined by an algorithm of spherical symmetrical layout (number of vertices and number of faces of a regular polyhedron), as exemplified in this patent on the basis of thirty-two (sum of number of vertices and number of faces of a regular icosahedron).
Where V is the number of vertices of the regular polyhedron, F is the number of faces, E is the number of edges, m is the number of edges corresponding to each vertex, and n is the number of edges for each face.
In some embodiments, thirty-two detectors 1 are arranged uniformly in a spherical symmetry. The arrangement mode of the detector 1 uses the external sphere of the regular icosahedron for reference, the radius of the sphere (the distance from the vertex of the regular icosahedron to the body center) is used as the distance from the center of the detector to the center of the system, the detectors are respectively placed at the positions of all the vertexes of the regular icosahedron, the detectors are respectively placed at the positions of the intersection points of the extension lines of the connecting lines of the centers of all the surfaces of the icosahedron and the body center and the spherical surface, and thirty-two detectors are formed. The arrangement is mainly to improve the detection efficiency and enable the detection efficiency to achieve the goal of spherical symmetry, so that the detection efficiency can not change along with the change of the size and the shape of a sample within a certain space range in the system.
In some embodiments, the shield 2 is spherical shell shaped.
In some embodiments, the shield 2 is made of (high density) polyethylene.
In some embodiments, the shield 2 is provided with a plurality of holes for receiving the detectors 1.
Principle of operation
Taking a liquid scintillator detector as an example for illustration, a sample nuclear material (such as plutonium) can be obtained by detecting neutrons emitted by (spontaneous) fission of a nuclear material sample using the liquid scintillator detector, and performing a multiplicity analysis240Pu).
Taking a point source as an example, by using the fast neutron multiplicity measurement system, simulating the distance that a neutron emitted at a certain point in space passes through each detector through the software of Geant4, calculating the fraction of the neutron subjected to nuclear reaction in each detector by using the following formula, and then summing the fractions of all detectors, wherein the obtained value can be approximated to the detection efficiency of the system corresponding to the certain point in space, so as to verify that the detection efficiency of the fast neutron multiplicity measurement system is independent of the space position.
P＝1-e-∑x
In the above formula, P is the probability of a neutron reacting after passing through a material with a thickness of x, Σ is the probability of a neutron reacting with a nuclear reaction in a unit distance, and x is the thickness of the material.
Taking the center of the detector to be 20cm away from the center of the system as an example, point sources are respectively placed on the center of the system and spherical surfaces with the radius of 2cm, 4cm, 6cm, 8cm, 10cm, 12cm, 14cm and 16cm, and are distributed according to the azimuth angle of a spherical coordinate of 0-355 DEG at intervals of 5 DEG, the polar angle of 0-175 DEG at intervals of 5 deg. The distribution of the total neutron generation nuclear reaction share (approximately the detection efficiency of the system) corresponding to each position is calculated as shown in fig. 1, and it can be seen that when the point sources are on a spherical surface with the same radius and the radius is less than or equal to 14cm, the detection efficiency of the system is independent of the position.
Table 1 shows the average value and standard deviation of the total fraction (approximately detection efficiency) of the neutron nuclear reaction of the point source on the spherical surfaces with different radii, and it can be seen that the detection efficiency slightly increases as the spherical radius becomes larger, and when the spherical radius is less than or equal to 8cm, the detection efficiency increases slowly and the relative standard deviation is basically unchanged, which indicates that the detection efficiency is relatively flat within this range.
TABLE 1
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the utility model. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is intended to include such modifications and variations.
Claims (7)
1. A passive nuclear material fast neutron multiplicities measurement system based on spherical symmetry structure, characterized in that, the system includes: a plurality of detectors (1) and shields (2); a plurality of detectors (1) are symmetrically and uniformly distributed in the shielding body (2).
2. The system for measuring the fast neutron multiplicities of the passive nuclear materials based on the spherical symmetrical structure is characterized in that the detector (1) is a detector with neutron-gamma discrimination performance.
3. The system for measuring the fast neutron multiplicities of the passive nuclear materials based on the spherical symmetrical structure is characterized in that the number of the detectors (1) is determined by an algorithm of the spherical symmetrical layout.
4. The system for measuring the fast neutron multiplicities of the passive nuclear materials based on the spherical symmetrical structure is characterized in that the detectors (1) are arranged on a spherical shell with the radius R in a spherical symmetrical and uniform mode.
5. The system for measuring the fast neutron multiplicities of the passive nuclear materials based on the spherical symmetrical structure is characterized in that the shielding body (2) is in a spherical shell shape.
6. The system for measuring the fast neutron multiplicities of the passive nuclear materials based on the spherical symmetrical structure is characterized in that the shielding body (2) is made of high-density polyethylene (HDPE) and is used for measuring the fast neutron multiplicities of the passive nuclear materials based on the spherical symmetrical structure.
7. The system for measuring the fast neutron multiplicities of the passive nuclear materials based on the spherical symmetrical structure is characterized in that a plurality of holes for installing the detector (1) are formed in the shielding body (2).
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116184482A (en) * | 2023-03-02 | 2023-05-30 | 中国人民解放***箭军工程大学 | Helium-3-based neutron multiple self-adaptive measurement device and measurement method |
| CN116736364A (en) * | 2023-05-12 | 2023-09-12 | 中国工程物理研究院材料研究所 | Neutron measurement system background count rate suppression system and suppression method |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116184482A (en) * | 2023-03-02 | 2023-05-30 | 中国人民解放***箭军工程大学 | Helium-3-based neutron multiple self-adaptive measurement device and measurement method |
| CN116184482B (en) * | 2023-03-02 | 2023-07-07 | 中国人民解放***箭军工程大学 | Helium-3-based neutron multiple self-adaptive measurement device and measurement method |
| CN116736364A (en) * | 2023-05-12 | 2023-09-12 | 中国工程物理研究院材料研究所 | Neutron measurement system background count rate suppression system and suppression method |
| CN116736364B (en) * | 2023-05-12 | 2023-12-29 | 中国工程物理研究院材料研究所 | Neutron measurement system background count rate suppression system and suppression method |
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