CN114942468B - A method and device for non-contact rapid detection of special nuclear materials - Google Patents

Abstract

The invention relates to a nuclear material detection method and device, in particular to a non-contact type rapid detection method and device for special nuclear materials, which solve the technical problem that the conventional neutron detector is difficult to effectively realize the requirements of high-efficiency detection and high-sensitivity detection on neutrons after moderation. According to the method for non-contact rapid detection of the special nuclear material, provided by the invention, neutrons released by spontaneous fission of the nuclear material are detected by combining the metal organic framework scintillator with the fission substances containing ²³⁵ U, so that the primary screening, screening and detection of the nuclear material are realized. The device comprises a transparent matrix, a metal organic framework scintillator, a fissile material containing ²³⁵ U, a photoelectric conversion device and a signal amplitude discrimination circuit; the method is used for detecting and screening the sensitive nuclear material wrapped or specially shielded by a large amount of cargoes.

Description

A method and device for non-contact rapid detection of special nuclear materials

Technical Field

The present invention relates to a nuclear material detection method and device, and in particular to a non-contact rapid detection method and device for special nuclear materials, which are suitable for the detection and identification of sensitive nuclear materials wrapped in a large amount of goods or after special shielding.

Background Art

The development of detection and testing technology for special nuclear materials (SNM) is of great significance to preventing the proliferation of nuclear devices and resisting terrorist nuclear threats. Detecting heavily shielded special nuclear materials (such as plutonium or uranium) in containers loaded with large quantities of cargo faces very great technical challenges. Since the energy and flux of gamma rays released by special nuclear materials are low and they are also easily shielded by high atomic number (high Z) materials, it is not feasible to use gamma rays to detect such nuclear materials. Since neutrons have strong penetrating power and are difficult to be completely shielded, it is feasible to use neutron detection to achieve special nuclear material detection. However, since heavy shielding can cause neutron slowing and partial loss of directional and energy spectrum information, high technical requirements are placed on neutron detection methods and devices.

Special nuclear materials can spontaneously fission and release neutrons. Neutrons are uncharged, have strong penetrating power, and are difficult to be completely shielded. Therefore, even if special nuclear materials are well hidden in well-shielded cargo containers, they can be detected. To detect escaped neutrons slowed down by shielding materials, a large number of low-cost, high-efficiency, and high-sensitivity neutron detectors are required. However, the ³ He tube materials used for neutron detection in the world are currently in short supply, expensive, and in short supply. BF ₃ detectors and liquid scintillators are toxic and flammable, and ¹⁰ B counter tubes have low detection efficiency. All of these cannot meet the low-cost, high-efficiency, and high-sensitivity neutron detection needs of special nuclear materials.

The scintillation detection method is one of the important methods for realizing neutron detection. It has the characteristics of a two-stage amplification structure of scintillator and photoelectric device, so it has high sensitivity to neutrons. Since the size of the scintillator material can be very large, the thickness can be as high as several centimeters to several meters, which is significantly higher than the thickness of the sensitive area of the semiconductor, it is the first choice for realizing high neutron detection efficiency. In recent years, metal organic framework scintillators have been often used in medical human imaging research, but there have been no research reports on neutron detection and special nuclear material detection.

Summary of the invention

The purpose of the present invention is to solve the technical problem that existing neutron detectors are difficult to effectively realize the requirements of high-efficiency and high-sensitivity detection of slowed-down neutrons, and to provide a method and device for non-contact rapid detection of special nuclear materials to achieve preliminary detection of special nuclear materials.

In order to solve the above technical problems, the technical solution adopted by the present invention is:

A non-contact method for rapid detection of special nuclear materials, which is special in that it includes the following steps:

1) Filling the pores of the metal organic framework scintillator with fissile material containing ²³⁵ U;

2) placing a metal organic framework scintillator on a transparent substrate to obtain a light emitting device;

3) placing the light-emitting device obtained in step 2) around the special nuclear material to be detected, so that the light-emitting device and the neutrons generated in the special nuclear material to be detected undergo nuclear fission reaction to generate secondary charged substances;

4) transferring the energy of the secondary charged substance to the light-emitting unit in the metal organic framework scintillator, so that the metal organic framework scintillator emits visible light;

5) using a photoelectric conversion device to convert the visible light emitted in step 4) into an electrical signal;

6) The electrical signal is input into the signal amplitude discrimination circuit to discriminate and record the neutron signal, thereby detecting special nuclear materials.

Furthermore, in step 2), the fissile material containing ²³⁵ U is a fissile material containing ²³⁵ UO ₂ .

Furthermore, in step 3), the secondary charged matter is fission fragments or protons.

Furthermore, a step of encapsulating the metal organic framework scintillator is included between step 2) and step 3).

At the same time, the present invention also provides a non-contact rapid detection device for special nuclear materials, which is used to implement the above-mentioned non-contact rapid detection method for special nuclear materials, and its special features are: comprising a transparent matrix, a metal organic framework scintillator, a fission material containing ²³⁵ U, a photoelectric conversion device and a signal amplitude discrimination circuit;

The fissile material containing ²³⁵ U is placed in the pores of the metal organic framework scintillator;

The metal organic framework scintillator is arranged on a transparent matrix, or dispersed in the transparent matrix, and the metal organic framework scintillator and the transparent matrix constitute a light emitting device;

The photoelectric conversion device is arranged on the light emitting path of the light emitting device;

The signal amplitude discrimination circuit is connected to the photoelectric conversion device.

Furthermore, the fissile material containing ²³⁵ U is fissile material containing ²³⁵ UO ₂ .

Further, it also includes a reflective layer;

The photoelectric conversion device is arranged on one side of the metal organic framework scintillator;

The reflective layer is arranged on the other five side surfaces of the metal organic framework scintillator.

Furthermore, it also includes an optical coupling component, which is arranged between the metal organic framework scintillator and the photoelectric conversion device.

Furthermore, the transparent matrix is a solid transparent matrix, and its material is epoxy resin;

The emission wavelength of the metal organic framework scintillator is greater than 440nm;

The photoelectric conversion device is an arrayed silicon PM photoelectric conversion device;

The signal amplitude discrimination circuit is a high-frequency signal amplitude discrimination device.

Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

1. The non-contact rapid detection method of special nuclear materials of the present invention detects neutrons released by spontaneous fission of nuclear materials by combining metal organic framework scintillators with fission materials containing ²³⁵ U, thereby realizing the initial screening, identification and detection of nuclear materials.

2. The pores of the metal organic framework scintillator used in the present invention are filled with fission materials containing ²³⁵ U and hydrogen atoms in the metal organic framework scintillator, which can simultaneously achieve the moderation and detection of fission neutrons released by nuclear materials, and a high signal-to-noise ratio can be obtained by combining with a high-frequency signal amplitude discrimination device; it is expected to be used for the effective detection of heavily shielded special nuclear materials in containers carrying a large amount of cargo.

3. The hydrogen atoms in the metal organic framework scintillator and the metal organic framework scintillator containing ²³⁵ U fission material are the media for neutron detection. After the neutrons are slowed down, they will undergo nuclear reactions with the fission material containing ²³⁵ U, releasing secondary charged matter (high-energy fission fragments). The secondary charged matter transfers energy to the light-emitting unit in the metal organic framework scintillator, causing it to emit visible light. The visible light is converted into an electrical signal by the photoelectric conversion device, and the electrical signal enters the high-frequency signal amplitude discrimination device. The high-frequency signal amplitude discrimination device can effectively discriminate and record the large-amplitude signal of the neutron-induced fission fragments.

4. Since the metal organic framework scintillator contains hydrogen atoms and its pores are filled with fission materials containing ²³⁵ U, the location where the secondary charged material is generated is near the organic molecules or pores of the metal organic framework scintillator, which is very close to the light-emitting unit (i.e., the organic molecules of the metal organic framework scintillator), only within a few nanometers, so efficient and rapid energy transfer can be achieved, so that the metal organic framework scintillator can obtain high luminescence efficiency under the action of neutrons; the luminescence wavelength of the metal organic framework scintillator is greater than 440nm, which can match most of the photoelectric conversion devices on the market and achieve high photoelectric conversion efficiency. Therefore, the special nuclear material detection device based on the metal organic framework scintillator can realize the effective detection of neutrons.

5. The present invention can achieve a high signal-to-noise ratio. The fission fragments released by neutron-induced fission of fissionable materials containing ²³⁵ U have high energy, with an average energy greater than 40 MeV, which is much higher than the energy of gamma rays released by special nuclear materials and alpha particles released by spontaneous decay of ²³⁵ U. Therefore, the signal amplitude generated by neutron-induced fission fragments is much higher than the signal amplitude of radiation background interference and environmental interference. By selecting a signal amplitude discrimination circuit and selecting and recording large-amplitude signals induced by neutrons, a high signal-to-noise ratio can be achieved.

6. Applicable to the detection of shielded nuclear materials. The neutrons released by special nuclear materials have strong penetrating power and can penetrate the cargo and shielding materials wrapped around them, and can be effectively detected by the non-contact rapid detection device of special nuclear materials of the present invention. The present invention is applicable to the detection of nuclear materials wrapped by shielding materials and nuclear materials wrapped by cargo in large containers.

7. The non-contact rapid detection device for special nuclear materials of the present invention has stable performance and is less affected by the environment. The metal organic framework scintillator has strong irradiation stability, can stably convert neutron signals into visible light when used for a long time, has good environmental stability, and the luminescence characteristics do not change with the influence of humidity, oxygen fluctuations in the environment, etc. After encapsulating the metal organic framework scintillator, this performance can be enhanced.

8. The present invention is a non-contact nuclear material detection method that does not require an additional radiation source and achieves nuclear material identification by detecting the neutrons released by the nuclear material's own decay.

9. Rapid nuclear material detection. Since the decay time of the metal organic framework scintillator is fast, at the sub-nanometer to nanometer level, the neutron detection speed of the present invention is high; since the thickness of the metal organic framework scintillator can reach several centimeters, combined with the arrayed silicon PM photoelectric conversion device, high-efficiency neutron detection can be achieved, and the detection efficiency of the present invention is high; the metal organic framework scintillator can be wrapped with a reflective layer, which can be in close contact with or separated from the photoelectric conversion device. Adding a coupling agent material between the metal organic framework scintillator and the photoelectric conversion device can optimize the light transmission characteristics and further improve the sensitivity of neutron detection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic structural diagram of an embodiment of a non-contact rapid detection device for special nuclear materials according to the present invention;

FIG2 is a detection schematic diagram of an embodiment of a non-contact rapid detection device for special nuclear materials according to the present invention;

FIG3 is a detection principle diagram of a method for non-contact rapid detection of special nuclear materials according to Embodiment 1 of the present invention;

FIG. 4 is a schematic diagram of identifying neutron signals according to Embodiment 1 of a method for non-contact rapid detection of special nuclear materials of the present invention.

The accompanying drawings in the figure are marked as follows:

1-metal organic framework scintillator, 2-photoelectric conversion device, 3-signal amplitude discrimination circuit, 4-cargo, 5-special nuclear material, 6-shielding material, 7-container, 8-neutron, 9-non-contact rapid detection device for special nuclear materials.

DETAILED DESCRIPTION

The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the technical solution in the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

Embodiment 1

Referring to FIG. 2 and FIG. 3 , a method for non-contact rapid detection of special nuclear materials includes the following steps:

1) Filling the pores of the metal organic framework scintillator 1 (i.e., MOF scintillator) with fissionable material containing ²³⁵ U;

2) Arranging a metal organic framework scintillator 1 on a transparent substrate (in other embodiments, the metal organic framework scintillator 1 may also be uniformly diffused in the transparent substrate) to obtain a light-emitting device;

3) placing the light-emitting device obtained in step 2) around the special nuclear material 5 to be detected, so that the light-emitting device and the neutrons 8 generated in the special nuclear material 5 to be detected undergo nuclear fission reaction to generate secondary charged substances;

4) transferring the energy of the secondary charged substance to the light-emitting unit in the metal organic framework scintillator 1, so that the metal organic framework scintillator 1 emits visible light;

5) Using the photoelectric conversion device 2 to convert the visible light into an electrical signal;

6) The electrical signal obtained in step 5) is input into the signal amplitude discrimination circuit 3 to discriminate and record the neutron 8 signal.

The MOF scintillator presents a special structure. Neutrons 8 undergo nuclear fission reactions with the fissionable materials containing ²³⁵ U in the MOF scintillator, and at the same time undergo nuclear recoil with the hydrogen atoms in the MOF scintillator, producing secondary charged materials, which are fission fragments or protons. The secondary charged materials transfer energy to the light-emitting units of the MOF scintillator, causing it to emit visible light. Since the location where the secondary charged materials are produced is in the channels or pores of the MOF scintillator, the distance between the secondary charged materials and the light-emitting units (i.e., organic molecules) of the MOF scintillator is very close, only within 1 nanometer, so the secondary charged materials quickly and effectively transfer energy to the light-emitting units, achieving high luminescence efficiency of the MOF scintillator under the action of neutrons 8. The luminescence wavelength of the MOF scintillating material is greater than 440nm, which can match most of the photoelectric conversion devices 2 on the market, achieving high photoelectric conversion efficiency. Therefore, the special nuclear material detection device based on the metal organic framework scintillator 1 can achieve effective detection of neutrons 8.

In this embodiment, the pores of the metal organic framework scintillator 1 are filled with fissionable materials containing ²³⁵ UO _2. The organic molecules of the metal organic framework scintillator 1 and the hydrogen atoms in the metal organic framework scintillator 1 are moderators of the neutrons 8, so that the neutrons 8 and the hydrogen atoms are slowed down and their energy is reduced after multiple collisions.

The fission material containing ²³⁵ UO ₂ and the hydrogen atoms of the metal organic framework scintillator 1 are the detection media of neutron 8; when neutron 8 is slowed down, neutron 8 will react with the fission material containing ²³⁵ UO ₂ in the metal organic framework scintillator 1, and the cross section of the nuclear reaction is larger and the sensitivity to neutron 8 is higher. Nuclear reaction or nuclear recoil releases secondary charged matter (secondary charged matter is fission fragments or protons, etc.), which transfers energy to the light-emitting unit in the metal organic framework scintillator 1, causing it to emit visible light, which is converted into an electrical signal by the photoelectric conversion device 2. The electrical signal enters the signal amplitude discrimination circuit 3, and the large signal of the fission fragment will be effectively discriminated and recorded by the signal amplitude discrimination circuit 3, obtaining the schematic diagram of the neutron 8 signal as shown in Figure 4. The dotted line is the neutron 8 discrimination threshold. It can be seen from the figure that neutron 8, above the neutron 8 discrimination threshold dotted line is the neutron 8 signal.

As shown in FIG1 , the present invention also provides a non-contact rapid detection device for special nuclear materials, which is used to implement the above-mentioned method for non-contact rapid detection of special nuclear materials, comprising a transparent matrix, a metal organic framework scintillator 1, a fission material containing ²³⁵ U, a photoelectric conversion device 2, and a signal amplitude discrimination circuit 3;

The fissionable material containing ²³⁵ U is arranged in the pores of the metal organic framework scintillator 1;

The metal organic framework scintillator 1 is disposed on a transparent substrate, or dispersed in a transparent substrate, and the metal organic framework scintillator 1 and the transparent substrate constitute a light emitting device;

The photoelectric conversion device 2 is arranged on the light-emitting path of the metal organic framework scintillator 1;

The signal amplitude discrimination circuit 3 is connected to the photoelectric conversion device 2 .

In this embodiment, the metal organic framework scintillator 1 is a rectangular structure, and its luminous wavelength is greater than 440nm; one side of the metal organic framework scintillator 1 is arranged opposite to the photoelectric conversion device 2, and the other five sides of the metal organic framework scintillator 1 are wrapped with a reflective layer. The transparent matrix is a solid transparent matrix (in other embodiments, the metal organic framework scintillator 1 can also be evenly diffused in the transparent matrix), its size can reach several centimeters, and its material is epoxy resin; the photoelectric conversion device 2 is a combined arrayed silicon PM device, and its size is much smaller than that of a photomultiplier tube, etc.; the signal amplitude discrimination circuit 3 is a high-frequency signal amplitude discrimination device. An optical coupling component can also be provided, and the optical coupling component is specifically provided between the metal organic framework scintillator 1 and the photoelectric conversion device 2. The metal organic framework scintillator 1 is in close contact with the photoelectric conversion device 2 (in other embodiments, the metal organic framework scintillator 1 and the photoelectric conversion device 2 can also be separated). When in close contact, the effect of detecting neutrons 8 is better, and the effect can be enhanced when in close contact and an optical coupling component (or optical coupling material) is used.

The fission fragments released by neutron 8-induced fission of fissionable material containing ²³⁵ U have very high energy, with an average energy greater than 40MeV, which is much higher than the energy of gamma rays released by special nuclear material 5 and alpha particles released by spontaneous decay of ²³⁵ U. Therefore, the signal amplitude generated by neutron 8 is much higher than the signal amplitude of radiation background interference and environmental interference. Selecting high-frequency signal amplitude discrimination devices and recording large-amplitude response signals induced by neutron 8 can achieve an ultra-high signal-to-noise ratio.

The device can also be used to detect special nuclear materials 5 hidden in a large amount of cargo 4 and a container 7 loaded with cargo, wherein the container 7 is wrapped with shielding materials with high atomic numbers. The non-contact rapid detection device 9 of the present invention for special nuclear materials can effectively detect heavily shielded special nuclear materials 5.

Embodiment 2

The difference between the second embodiment and the first embodiment is that after the fission material containing ²³⁵ U is filled into the pores of the metal organic framework scintillator 1, the metal organic framework scintillator 1 is encapsulated and encapsulated using a transparent film (in other embodiments, it can also be encapsulated using a reflective film, which is arranged on the non-luminous side). After encapsulation, the metal organic framework scintillator 1 can stably convert the neutron 8 signal into visible light when used for a long time, has good environmental stability, and the luminescence characteristics are not degraded by the influence of humidity, oxygen fluctuations, etc. in the environment.

The rest of the content of the second embodiment is the same as that of the first embodiment.

The above descriptions are merely embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings, or directly or indirectly applied in other related technical fields, are included in the patent protection scope of the present invention.

Claims (7)

1. A method for non-contact rapid detection of special nuclear materials, comprising the steps of:

1) Filling a ²³⁵ U-containing fissile material into the pores of the metal organic framework scintillator (1);

The fissile material containing ²³⁵ U is the fissile material containing ²³⁵UO₂;

2) Arranging a metal organic framework scintillator (1) on a transparent matrix to obtain a light-emitting device;

3) Placing the light-emitting device obtained in the step 2) around the special nuclear material (5) to be detected, and enabling the light-emitting device and neutrons (8) generated in the special nuclear material (5) to be detected to undergo nuclear fission reaction to generate secondary charged substances;

The secondary charged species are fission fragments or protons;

4) Transmitting energy of the secondary charged substance to a light emitting unit in the metal-organic frame scintillator (1), so that the metal-organic frame scintillator (1) emits visible light;

5) Converting the visible light emitted in the step 4) into an electric signal by using a photoelectric conversion device (2);

6) The electric signal is input into a signal amplitude discrimination circuit (3) to discriminate and record neutron (8) signals, and then the special nuclear material (5) is detected.

2. A method for non-contact rapid detection of specialty nuclear materials according to claim 1, wherein:

The step of packaging the metal organic framework scintillator (1) is further included between the step 2) and the step 3).

3. A device for non-contact rapid detection of special nuclear material, for realizing a method for non-contact rapid detection of special nuclear material according to any one of claims 1-2, characterized in that: comprises a transparent matrix, a metal organic framework scintillator (1), a fissile material containing ²³⁵ U, a photoelectric conversion device (2) and a signal amplitude discrimination circuit (3);

The fissile material containing ²³⁵ U is arranged in the pores of the metal organic framework scintillator (1);

the metal organic framework scintillator (1) is arranged on the transparent matrix or dispersed in the transparent matrix, and the metal organic framework scintillator (1) and the transparent matrix form a light-emitting device;

the photoelectric conversion device (2) is arranged on a light-emitting light path of the light-emitting device;

The signal amplitude discrimination circuit (3) is connected with the photoelectric conversion device (2).

4. A device for the non-contact rapid detection of particularly sensitive materials as claimed in claim 3, wherein: the fissile material containing ²³⁵ U is the fissile material containing ²³⁵UO₂.

5. The device for non-contact rapid detection of special nuclear materials according to claim 4, wherein: the light reflecting layer is also included;

The photoelectric conversion device (2) is arranged on one side surface of the metal organic framework scintillator (1);

The reflecting layer is arranged on the other side surfaces of the metal organic framework scintillator (1).

6. The device for non-contact rapid detection of special nuclear materials according to claim 5, wherein: the photoelectric conversion device further comprises an optical coupling assembly, wherein the optical coupling assembly is arranged between the metal organic framework scintillator (1) and the photoelectric conversion device (2).

7. A device for the non-contact rapid detection of special nuclear materials according to any one of claims 3 to 6, characterized in that:

The transparent matrix is a solid transparent matrix, and the material of the transparent matrix is epoxy resin;

the luminescence wavelength of the metal organic framework scintillator (1) is more than 440nm;

The photoelectric conversion device (2) is an arrayed silicon PM photoelectric conversion device;

the signal amplitude discrimination circuit (3) is a high-frequency signal amplitude discrimination device.