Long neutron counter with wide energy measurement range

Abstract

The invention relates to a long neutron counter with a wide energy measurement range. The long neutron counter comprises a thermal neutron detector, an inner moderation layer, a neutron multiplication array, an absorption layer, an outer moderation layer, a nuclear electronics signal acquisition and processing system and the like, wherein the thermal neutron detector, the inner moderation layer, the neutron proliferation array, the absorption layer and the outer moderation layer are sequentially spliced into a whole, and moderation and proliferation of high-energy neutrons and partial shielding of high-energy scattered neutrons can be achieved; the thermal neutron detector is composed of 3He gas and an aluminum tubular container shell and mainly achieves the functions of thermal neutron detection, pulse signal output and the like. The nuclear electronics signal acquisition and processing system comprises a low-voltage power supply, a high-voltage power supply, a pre-amplifier, a main amplifier, a discriminator and the like, and realizes low-voltage power supply of a nuclear electronics system, high-voltage power supply of a detector, amplification and transmission of pulse signals, removal of environmental noise and acquisition of pulse counting.

Description

Technical Field

[0001] The invention belongs to the field of radiation detection and relates to a long neutron counter with a wide energy measurement range. Background Art

[0002] Timely, effective and accurate detection of radiation is the prerequisite for all nuclear operations. In the field of neutron science application and research and development, high-energy neutron fluence monitoring is a necessary means for space neutron dose assessment and high-energy particle accelerator radiation protection. Due to the rigid conditions such as special locations and uncertain neutron energy ranges, the detector is required to achieve wide energy range detection, high and accurate neutron detection efficiency, relatively stable neutron response characteristics and excellent n / γ discrimination capabilities. Among them, the long neutron counter is a widely used secondary standard equipment for neutron fluence monitoring. It mainly uses a large volume of moderator to slow down the neutrons, and uses a high-sensitivity moderator to slow down the slowed neutrons. 3 He proportional counter tube detects the secondary charged particles it produces, thereby achieving indirect measurement of neutrons.

[0003] The neutron response sensitivity of most long neutron counters currently disclosed is almost the same below 5MeV, but its energy lower limit is relatively high and the response to energy above 5MeV drops sharply. The large volume of the moderator not only makes it difficult to portability, but also disturbs the original neutron radiation field to a certain extent, which has an adverse effect on the measurement results. In order to improve the energy response and portability of the long neutron counter, the present invention develops a compact long neutron counter measurement system. The measurement system consists of a long neutron counter and an electronics system. Compared with the traditional long neutron counter, the system has a smaller volume and a wider energy response range, and has a relatively flat response value from thermal neutrons to 20MeV. Summary of the invention

[0004] In order to solve the problems of narrow energy measurement range and large size of traditional long neutron counters, the present invention provides a long neutron counter device with a wide energy spectrum measurement range, which is used to detect the neutron flux in the neutron radiation field formed by a neutron radiation source.

[0005] The technical solution of the present invention is: a long neutron counter with a wide energy measurement range, comprising a thermal neutron detector, an inner moderator, a neutron multiplication array, an absorption layer, an outer moderator, and a nuclear electronics signal acquisition and processing system; the inner moderator contains 13 through holes, one of which is located in the center for placing the thermal neutron detector, and the remaining 12 are distributed in a circular array structure outside the central hole, the neutron multiplication array uses lead rods or tungsten rods, and is located in the circular array holes inside the inner moderator, the absorption layer is located outside the inner moderator, and the outer moderator is located outside the absorption layer, and the nuclear electronics signal acquisition and processing system is connected to the thermal neutron detector.

[0006] Beneficial effects:

[0007] Ultra-high molecular weight polyethylene is used as the neutron moderator material, 30% boron-containing polyethylene is used as the neutron absorption material, and lead rods are used as the neutron value-added material. The moderator shielding shell uses component splicing and a special structure. This not only makes the equipment portable and economical, but also further improves the energy range and flat response characteristics of the counter's neutron detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a schematic structural diagram of a long neutron counter with a wide energy measurement range of the present invention;

[0009] Figure 2 It is a cross-sectional schematic diagram of a long neutron counter with a wide energy measurement range of the present invention;

[0010] Figure 3 It is a schematic diagram of a nuclear electronics system of a long neutron counter with a wide energy measurement range according to the present invention.

[0011] In the figure, the reference numerals are: neutron detector 1, inner moderator 2, neutron breeding array 3, absorption layer 4, outer moderator 5, nuclear electronics signal acquisition and processing system 6. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above-mentioned purpose, the present invention adopts the following technical scheme.

[0013] See also Figure 1 and Figure 2 , is a wide energy range long neutron counter of the present invention, comprising: a thermal neutron detector ( 3 He), will 3 The He tube is inserted into the moderator shielding shell, which is composed of an inner moderator layer, a neutron multiplication array, an absorption layer and an outer moderator layer from the inside to the outside. The present invention adopts the method of fast neutron moderation, multiplication, scattered neutron shielding and deduction to measure the neutron flux in a wide energy range, wherein 3He's high thermal neutron capture reaction cross section, special moderation shielding shell structure, neutron multiplication array, and the moderation of high-energy neutrons by carbon and hydrogen nuclei in ultra-high molecular weight polyethylene can expand the energy range of neutron detection by the detector to 0.025eV-20MeV. In addition, the accuracy of the measured value can be further improved by pulse discrimination, shadow cone contrast subtraction, setting thresholds, and coefficient scales, achieving accurate real-time measurement of neutron injection in a wide energy range.

[0014] According to an embodiment of the present invention, Figure 1 , Figure 2 As shown, in one embodiment, the present invention is based on a wide energy range long neutron counter, including a thermal neutron detector 1, an inner moderator 2, a neutron breeding array 3, an absorption layer 4, an outer moderator 5, and a nuclear electronics signal acquisition and processing system 6.

[0015] Among them, the thermal neutron detector 1 is filled with 3 He gas, with an aluminum tubular container shell on the outside. A high voltage of 800V is added to both ends of the detector electrode to achieve proportional multiplication of the secondary ionization of the accelerated particles. The container shell can shield interference without affecting the detection; the inner moderation layer 2 made of ultra-high molecular weight polyethylene can elastically collide with direct neutrons to slow down the neutrons. It contains 13 through holes, one of which is used to place the thermal neutron detector 1 in the center, and the remaining 12 are distributed outside the central hole in a circular array structure. The neutron multiplication array 3 uses lead rods or tungsten rods and is located in the inner moderation layer. 2 internal circular array holes, this method can not only increase the probability of neutron proliferation, but also can cause inelastic scattering with high-energy neutrons to further slow down the neutrons and improve the detection efficiency. The absorption layer 4 is located outside the inner moderation layer 2 and is 30% boron-containing polyethylene or cadmium sheet, which can absorb the environmental scattered neutrons after being slowed down by the outer moderation layer 5. The outer moderation layer 5 is located outside the absorption layer 4 and is made of ultra-high molecular weight polyethylene, which can slow down the environmental scattered neutrons; the nuclear electronics signal acquisition and processing system 6 is connected to the thermal neutron detector 1 through an SHV connector. The nuclear electronics signal acquisition and processing system 6 is as follows Figure 3 As shown, it includes a preamplifier, a low-voltage module, a high-voltage module, a main amplifier, a discriminator, an MCU and a host computer software. The low-voltage module supplies power to the system, and the high-voltage module maintains the high-voltage environment at both ends of the detector electrodes. The preamplifier initially amplifies the signal output by the detector and can also improve the signal-to-noise ratio, reduce environmental interference, and enhance the flexibility of the system. The main amplifier further amplifies the signal and adjusts the shape and amplitude of the signal. The discriminator can eliminate the noise interference generated by the environment during signal transmission. The counter converts and integrates the signal and then transmits it to the host computer software for statistics and display.

[0016] Among them, due to the neutron divergence of the radioactive source, a large number of scattered neutrons will exist in the environment. The long neutron counter will also receive a certain proportion of scattered neutrons during use. Therefore, this device is assembled by splicing multiple components, which not only realizes the portability of the equipment, but also can be slowed down, absorbed and multiplied by the characteristics of various materials. Most of the scattered neutrons are slowed down by the outer moderation layer and then absorbed by the neutron absorption layer. The direct neutrons from the radioactive source are slowed down by the inner moderation layer, multiplied by neutrons, and then absorbed by the detector. 3 He gas reacts to produce pulse counts, achieving improvements in the overall performance of the detector.

[0017] Among them, the front end of the inner moderator 2 is in a boss style, which improves the detector's response to low-energy neutrons, and the (n, xn) multiplication reaction between neutrons and metal materials can improve the response of the long neutron counter to high-energy neutrons. Under the influence of both, the range of neutron energy detected by the long neutron counter is further broadened, and the flat response characteristics of the long neutron counter are greatly improved.

[0018] Among them, scattered neutrons need to be deducted when performing coefficient calibration. A conical cone with a metal lead front end and a boron-containing polyethylene back end is placed between the radiation source and the long neutron counter. The central axes of the three must be on the same straight line and at the same height. The detector's ambient scattered neutron ratio is obtained by dividing the detector's count with a shadow cone by the detector's count without a shadow cone. The integer 1 minus this ratio is used to obtain the detector's effective count percentage to calculate the neutron yield of the accelerator.

[0019] The thermal neutron detector 1 is in the shape of a hollow cylinder and is arranged at the center of the inner moderator layer 2, the absorption layer 4 and the outer moderator layer 5; the thermal neutron detector has an outer diameter of 12 mm, a wall thickness of 0.5 mm, a height of 360 mm, and a high-purity and high-pressure 3 He gas.

[0020] The outer moderation layer 5 and the inner moderation layer 2 are composed of high molecular polyethylene or paraffin, and the absorption layer 4 is composed of BC4 or cadmium.

[0021] The inner moderator 2 is cylindrical and has a boss-shaped front end, which is used to improve the low-energy neutron response characteristics of the detector; the neutron multiplication array 3 is embedded in the inner moderator 2 in a circular array, and utilizes the (n, xn) multiplication reaction between neutrons and metal materials to improve the response of the long neutron counter to high-energy neutrons. The above two structural designs can broaden the range of neutron energy detection of the long neutron counter and well improve the flat response characteristics of the long neutron counter.

[0022] The long neutron counter is formed as a whole by splicing components, the outer moderator layer 5 is in a groove shape, and the absorption layer 4, the inner moderator layer 2, and the thermal neutron detector 1 are placed in the outer moderator layer 5 in sequence.

[0023] The nuclear electronics system 6 is composed of a preamplifier, a low-voltage power supply, a high-voltage power supply, a main amplifier, a discriminator and a host computer software. The nuclear pulse signal is amplified, discriminated and transmitted to the host computer software. After the formula conversion processing, the accelerator neutron yield is obtained:

[0024] ,

[0025] Wherein, R1 represents the distance between the neutron source and the effective center point of the long neutron counter, n represents the effective count of the detector after deducting scattered neutrons, δ represents the angle coefficient between the long neutron counter and the counter, and ε represents the detection efficiency of the long neutron counter.

[0026] like Figure 3 As shown, the measurement method of the long neutron counter measurement system comprises the following steps:

[0027] The long neutron counter 3 The He proportional counter is connected with a nuclear electronics system, which includes a preamplifier, a main amplifier, high and low voltage power supplies, a discriminator, an MCU and host computer software.

[0028] The neutron source is placed in front of the long neutron counter. The neutrons emitted by the neutron source are incident on the long neutron counter and are 3 He proportional counter detects, 3 The He proportional counter converts the detected neutron signal into a pulse voltage signal and transmits the voltage signal to the nuclear electronics system; the voltage signal is amplified by the preamplifier and the main amplifier, and then the neutron signal is converted into a pulse level signal by the discriminator, and then sent to the MCU to record the number of neutrons recorded by the long neutron counter. The host computer software can be used to set the recording time and discrimination threshold in the MCU, and the host computer software can also read the number of neutrons recorded by the long neutron counter stored in the MCU, and obtain the neutron yield or neutron injection of the neutron source according to the corresponding calculation formula.

[0029] According to an embodiment of the present invention, the thermal neutron detector 1 3 The outer shell of the He tube is made of metal aluminum, and the internal use is high-purity and high-pressure 3 He gas, the internal space is a cylinder of 8×340mm, the external space is a cylinder of 12×360mm, and the closed parts are sealed with solder.

[0030] The inner moderator layer 2 according to the embodiment of the present invention is made of ultra-high molecular weight polyethylene, 380 mm long and 100 mm in diameter, with a circular groove with an inner diameter of 60 mm, an outer diameter of 100 mm and a depth of 50 mm at the front end of the cylinder, and a central through hole with a diameter of 13 mm for inserting 3The He tube has 12 circumferentially evenly distributed through holes at a distance of 75 mm from the central axis, with a diameter of 10 mm for inserting lead rods.

[0031] The neutron multiplication array 3 according to the embodiment of the present invention is composed of 12 metal solid lead rods with a diameter of 9 mm and a length of 310 mm.

[0032] According to the embodiment of the present invention, the absorption layer 4 is a cylindrical boron-containing polyethylene with an inner diameter of 101 mm, an outer diameter of 111 mm, a length of 380 mm, a thickness of 5 mm, and a boron content of 30%, and can absorb neutrons moderated by the outer moderation layer 5 .

[0033] The outer moderation layer 5 according to the embodiment of the present invention is made of ultra-high molecular weight polyethylene, is 420 mm long and 230 mm in diameter, and has a groove with a depth of 380 mm and a diameter of 102 mm in the center for inserting the neutron absorption layer.

[0034] The nuclear electronics system according to the embodiment of the present invention is an integrated circuit board, the preamplifier, main amplifier, discriminator, etc. are all implemented by integrated circuit chips, and the low-voltage power supply and high-voltage power supply models are Hamamatsu integrated modules. The host computer software is the development program code.

[0035] The present invention changes the single and cumbersome nature of the previous neutron fluence measurement, can realize the measurement of neutron fluence in a wide energy range, and has excellent flat response characteristics in the energy range of 0.025eV-20MeV, making the neutron fluence measurement simpler and further improving the comprehensive performance.

[0036] 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 long neutron counter with a wide energy measurement range, characterized in that: The invention comprises a thermal neutron detector (1), an inner moderator (2), a neutron multiplication array (3), an absorption layer (4), an outer moderator (5), and a nuclear electronics signal acquisition and processing system (6); the inner moderator (2) contains 13 through holes, one of which is located in the center for placing the thermal neutron detector (1), and the remaining 12 are distributed in a circular array structure outside the central hole; the neutron multiplication array (3) is made of lead rods or tungsten rods and is located in the circular array holes inside the inner moderator (2); the absorption layer (4) is located outside the inner moderator (2); the outer moderator (5) is located outside the absorption layer (4); and the nuclear electronics signal acquisition and processing system (6) is connected to the thermal neutron detector (1).

2. A long neutron counter with a wide energy measurement range according to claim 1, characterized in that: The thermal neutron detector (1) is in the shape of a hollow cylinder and is arranged at the center of the inner moderator layer (2), the absorption layer (4) and the outer moderator layer (5); the thermal neutron detector has an outer diameter of 12 mm, a wall thickness of 0.5 mm, a height of 360 mm, and is high-purity and high-pressure. 3 He gas.

3. A long neutron counter with a wide energy measurement range according to claim 1, characterized in that: The outer moderation layer (5) and the inner moderation layer (2) are composed of high molecular weight polyethylene or paraffin, and the absorption layer (4) is composed of BC4 or cadmium.

4. A long neutron counter with a wide energy measurement range according to claim 1, characterized in that: The inner moderator (2) is cylindrical and has a boss-shaped front end, and is used to improve the low-energy neutron response characteristics of the detector; the neutron multiplication array (3) is embedded in the inner moderator (2) in a circular array manner, and utilizes the (n, xn) multiplication reaction between neutrons and metal materials to improve the response of the long neutron counter to high-energy neutrons.

5. A long neutron counter with a wide energy measurement range according to claim 1, characterized in that: The long neutron counter is formed as a whole by splicing components together. The outer moderator layer (5) is in a groove shape. The absorption layer (4), the inner moderator layer (2), and the thermal neutron detector (1) are placed in the outer moderator layer (5) in sequence.

6. A long neutron counter with a wide energy measurement range according to claim 1, characterized in that: The nuclear electronics signal acquisition and processing system (6) is integrated in a cylindrical aluminum box, which is directly connected to the thermal neutron detector (1) in the long neutron counter using an SHV connector and is directly fixed to the outer moderator layer (5) using a nut, converting the detected neutron signal into a pulse voltage signal, and transmitting the voltage signal to the nuclear electronics signal acquisition and processing system (6).

7. A long neutron counter with a wide energy measurement range according to claim 6, characterized in that: The nuclear electronics signal acquisition and processing system (6) is composed of a preamplifier, a low-voltage module, a high-voltage module, a main amplifier, a discriminator and a host computer software. The low-voltage module supplies power to the system, and the high-voltage module maintains a high-voltage environment at both ends of the detector electrodes. The preamplifier performs preliminary amplification on the signal output by the detector, and the main amplifier further amplifies the signal and adjusts the shape and amplitude of the signal. The discriminator eliminates the noise interference generated by the environment during signal transmission, and the signal is converted and integrated before being transmitted to the host computer software for statistics and display.

8. A long neutron counter with a wide energy measurement range according to claim 7, characterized in that: The upper computer software obtains the accelerator neutron yield after formula conversion: ， Wherein, R1 represents the distance between the neutron source and the effective center point of the long neutron counter, n represents the effective count of the detector after deducting scattered neutrons, δ represents the angle coefficient between the long neutron counter and the counter, and ε represents the detection efficiency of the long neutron counter.

9. A long neutron counter with a wide energy measurement range according to claim 2, characterized in that: The thermal neutron detector (1) 3 The outer shell of the He tube is made of metal aluminum, and the internal use is high-purity and high-pressure 3 He gas, and the closed places are sealed with solder.

10. A long neutron counter with a wide energy measurement range according to claim 3, characterized in that: The absorption layer (4) is cylindrical and made of boron-containing polyethylene with a boron content of 30%.

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