Portable wide-energy neutron detector

Abstract

The invention provides a portable wide-energy neutron detector which is arranged in an upper layer and a lower layer, the upper layer is a circuit structure, the lower layer is a detection structure, and a He-3 proportional counter of the detection structure is arranged at the center of a wide-energy neutron moderator structure. The wide-energy neutron moderator structure is a cylindrical structure and is divided into four layers of moderators, the moderators are sequentially a first polyethylene layer, a lead powder layer, a boron-doped polyethylene layer and a second polyethylene layer from outside to inside, meanwhile, the wide-energy neutron detector is provided, the performance of the moderator structure is redesigned, so that the wide-energy neutron moderator structure can meet the measurement range of high-energy neutrons (20MeV-400MeV), and the measurement range of the high-energy neutrons (20MeV-400MeV) can be met. The wide-energy neutron detector is convenient to use and light in weight, and integration of the detector, the moderator and the response circuit is achieved.

Description

Technical Field

[0001] The invention belongs to the field of radiation detection and relates to a portable wide-energy neutron detector. Background Art

[0002] Neutrons are not charged, so when they pass through matter, they do not interact with the electrons in the matter and cannot directly cause ionization. Instead, they can only be recorded by interacting with atomic nuclei to produce secondary particles that can cause ionization. The interactions between neutrons and atomic nuclei include nuclear reactions, nuclear recoil, nuclear fission, activation, etc.

[0003] Neutrons can be roughly divided into slow neutrons (<1keV), medium energy neutrons (1-100keV), fast neutrons (0.1-20MeV), and high energy neutrons (20MeV-400MeV) according to their energy. Neutrons with an energy of 0.0253eV are usually called "thermal neutrons". This type of neutron is in thermal equilibrium with a large number of molecules in the surrounding medium at room temperature, that is, its energy is equivalent to the energy of thermal motion of the surrounding medium molecules. Neutrons can be detected by selecting a nuclear reaction that can produce charged particles and recording the ionization excitation phenomenon caused by the charged particles.

[0004] The detection capability of existing neutron detectors is to obtain a relatively flat response within the energy range of 1eV-20MeV. For the detection of high-energy neutrons (20MeV-400MeV), a large-volume moderator is often required in order to obtain a relatively flat response characteristic for high-energy neutrons. Although the neutron fluence response is relatively ideal, it is large in size and heavy in mass, making it inconvenient to carry. Summary of the invention

[0005] The present invention provides a portable high-energy neutron detector, redesigns the structural performance of the moderator to enable it to meet the measurement range of high-energy neutrons (20MeV-400MeV), and provides an easy-to-use, lightweight wide-energy neutron detector to achieve integration of the detector, moderator and response circuit.

[0006] The technical solution of the present invention is: the present invention provides a portable wide-energy neutron detector, wherein the detector is arranged in two layers, the upper layer is a circuit structure, and the lower layer is a detection structure. The detection structure includes a He-3 proportional counter and a wide-energy neutron moderator structure, and the He-3 proportional counter is arranged at the center position of the wide-energy neutron moderator structure.

[0007] Furthermore, the circuit structure includes a main board and a preamplifier.

[0008] Furthermore, the preamplifier includes two stages of HA2620 operational amplifiers and one stage of LM111J-8 comparator.

[0009] Furthermore, the main board is a 89C58RDZ main chip.

[0010] Furthermore, a NOT gate circuit is also provided at the front end of the 89C58RDZ main chip.

[0011] Furthermore, the 89C58RDZ main chip is connected to the RS485 chip and can perform RS485 communication with the outside world.

[0012] The present invention also provides a wide-energy neutron moderator structure, which is a cylindrical structure divided into four layers of moderators, and the moderators are, from the outside to the inside, a first polyethylene layer with a thickness of 50-60 mm, a lead powder layer with a thickness of 8-10 mm, a boron-doped polyethylene layer with a thickness of 8-10 mm, and a second polyethylene layer with a thickness of 20-30 mm.

[0013] The present invention divides the moderator into four layers according to the different moderation efficiencies of light nuclei, medium-heavy nuclei and heavy nuclei for low-energy neutrons, medium-energy neutrons and high-energy neutrons respectively. The moderator has different moderation efficiencies for different energies, so that neutron beams with energies of thermal neutrons to 400MeV can be moderated into thermal neutrons for measurement by a He-3 proportional counter at the center of the wide-energy neutron moderator structure.

[0014] The present invention is provided with a preamplifier and a main board, and by verifying the circuit performance and observing the signal waveform when using a radiation source, it is determined that the signal / noise ratio meets the measurement requirements.

[0015] The He-3 proportional counter tube of the present invention is integrated with the moderator and the response circuit to record the pulses of critical events. When the dose rate reaches the alarm threshold, an alarm signal is issued. The alarm signal and the dose rate are transmitted over a long distance via RS485, and the transmission distance is 1000m. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the structure of the wide energy neutron detector of the present invention;

[0017] Figure 2 This is a schematic diagram of the structure of the wide energy neutron moderator of the present invention;

[0018] Figure 3 This is a schematic diagram of the connection principle between the preamplifier and the mainboard of the present invention;

[0019] Figure 4 This is a schematic diagram of the mainboard response circuit principle of the present invention.

[0020] Figure numerals: first polyethylene layer-1, lead powder layer-2, boron polyethylene layer-3, second polyethylene layer-4, He-3 proportional counter-5, preamplifier-6, main board-7, wide energy neutron moderator-8. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

[0022] like Figure 1 As shown, the wide energy neutron detector of the present invention adopts a cylindrical shape, with the circuit part on the top and the detection part on the bottom. The circuit part is divided into two parts, namely the main board 7 and the preamplifier 6 in the electrostatic collection box, which are arranged in two layers, with the main board on the top. The detection part is divided into a He-3 proportional counter 5 and a wide energy neutron moderator 8. The He-3 tube is placed at the geometric center of the moderator to achieve the best moderation and detection efficiency. All materials are selected from materials with radiation resistance.

[0023] Among them, the He-3 proportional counter tube uses the 252180 model of LND company.

[0024] like Figure 2 As shown, since the energy range of the neutron beam to be measured is thermal neutrons ~ 400MeV, a single-layer moderator cannot meet the moderation requirements and must be moderated by multiple layers. According to the different moderation efficiencies of light nuclei, medium-heavy nuclei, and heavy nuclei for low-energy neutrons, medium-energy neutrons, and high-energy neutrons, the moderator can be divided into four layers. From the outside to the inside, the moderator is the first polyethylene layer 1, with a thickness of 50-60mm, the lead powder layer 2, with a thickness of 8-10mm, the boron-doped polyethylene layer 3, with a thickness of 8-10mm, and the second polyethylene layer 4, with a thickness of 20-30mm. With such hierarchical moderation, and the different moderation of each layer for different energies, neutron beams with energies of thermal neutrons ~ 400MeV can be slowed down to thermal neutrons to be measured by a He-3 proportional counter 5.

[0025] Among them, the thickness of each layer of the moderator is determined. For neutron detectors, it is necessary to slow down the neutrons to the detectable area of ​​the He-3 proportional counter tube. At the same time, in order to ensure the optimization of detection efficiency, the optimal thickness of the moderator is determined.

[0026] The Monte Carlo simulation software was used to calculate the optimal thickness of the neutron moderator. The radioactive source was a Cf-252 neutron source, and the detector was a 4atm proportional counter tube. The sensitive zone length was 200mm. The optimal moderator thickness was determined by calculating the number of reactions in the proportional counter tube at different polyethylene moderator thicknesses. At the same time, the S (α, β) free gas processing method was used to correct the thermal neutron scattering effect. After simulation, when the moderation thickness of the second polyethylene layer was 3cm, the number of reactions in the He-3 proportional counter tube was the largest, and the efficiency of the neutron detector was the highest at this time.

[0027] like Figure 3 As shown, the preamplifier amplifies the input signal to a suitable level through two stages of HA2620 operational amplifiers, and then adjusts the waveform through a stage of LM111J-8 comparator.

[0028] like Figure 4 As shown in the figure, the signal after amplification and comparator processing enters the main board, and enters the 89C58RDZ main chip through the NOT gate circuit. Under the action of the main chip, the signal is collected, converted, and stored, and then RS485 communication with the outside world can be carried out through the RS485 chip.

[0029] The present invention divides the moderator into four layers according to the different moderation efficiencies of light nuclei, medium-heavy nuclei and heavy nuclei for low-energy neutrons, medium-energy neutrons and high-energy neutrons respectively. In particular, when the moderation thickness of the innermost second polyethylene layer is 3 cm, the number of reactions in the He-3 proportional counter tube is the largest. At this time, the efficiency of the neutron detector is the highest, and neutron beams with energies of thermal neutrons to 400MeV can be moderated into thermal neutrons for measurement by the He-3 proportional counter at the center of the wide-energy neutron moderator structure.

[0030] The present invention is provided with a preamplifier and a main board, and by verifying the circuit performance and observing the signal waveform when using a radiation source, it is determined that the signal / noise ratio meets the measurement requirements.

[0031] The He-3 proportional counter tube of the present invention is integrated with the moderator and the response circuit to record the pulses during critical events. When the dose rate reaches the alarm threshold, an alarm signal is issued. The alarm signal and the dose rate are transmitted over long distances via RS485, with a transmission distance of 1000m.

[0032] The above-described embodiments are merely descriptions of preferred implementation modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by radiation detection technicians in the field shall fall within the protection scope of the claims of the present invention.

Claims

1. A portable neutron detector, characterized in that: The detector is arranged in two layers, the upper layer is a circuit structure, and the lower layer is a detection structure. The detection structure includes a He-3 proportional counter and a wide-energy neutron moderator structure. The He-3 proportional counter is arranged at the center of the wide-energy neutron moderator structure.

2. A portable neutron detector according to claim 1, characterized in that: The circuit structure includes a main board and a preamplifier.

3. A portable neutron detector according to claim 1, characterized in that: The preamplifier includes two stages of HA2620 operational amplifiers and one stage of LM111J-8 comparator.

4. A portable neutron detector according to claim 1, characterized in that: The main board is 89C58RDZ main chip.

5. A portable neutron detector according to claim 4, characterized in that: The front end of the 89C58RDZ main chip is also provided with a NOT gate circuit.

6. A portable neutron detector according to claim 4, characterized in that: The 89C58RDZ main chip is connected to the RS485 chip and can perform RS485 communication with the outside world.

7. A portable neutron detector according to claim 1, characterized in that: The wide energy neutron moderator structure is a cylindrical structure divided into four layers of moderators, and the moderators are, from the outside to the inside, a first polyethylene layer with a thickness of 50-60 mm, a lead powder layer with a thickness of 8-10 mm, a boron-doped polyethylene layer with a thickness of 8-10 mm, and a second polyethylene layer with a thickness of 20-30 mm.

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