Multi-sphere neutron spectrometer applied to pulsed neutron radiation field monitoring

Abstract

The invention discloses a multi-ball neutron spectrometer applied to pulsed neutron radiation field monitoring. The multi-ball neutron spectrometer comprises a 3He gas detector, a 4H-SiC semiconductor detector, a neutron moderation ball, a preamplifier, a spectrometer main amplifier, a high-voltage power supply and a multichannel analyzer. A 3He gas detector and a 4H-SiC semiconductor detector are designed in a neutron moderator of a set of multi-sphere neutron spectrometer, the double-detector multi-sphere neutron spectrometer is applied in pulsed neutron radiation fields, and neutron energy spectrum and dose measurement is carried out in the pulsed neutron radiation fields with the neutron flux of 101-104 n.cm <-2 > s <-1 > and the neutron flux of 103-106 n.cm <-2 > s <-1 > respectively. According to the invention, a dual-detector multi-ball neutron spectrometer data acquisition system based on a 3He gas detector and a 4H-SiC semiconductor detector is utilized to realize measurement of neutron energy spectrum distribution information and neutron dose in a wide energy region.

Description

Technical Field

[0001] The invention belongs to the technical field of radiation monitoring, and in particular relates to a multi-sphere neutron spectrometer used for pulse neutron radiation field monitoring. Background Art

[0002] Neutron detection technology is widely used in many fields, such as nuclear energy, radiation monitoring, geological exploration and medical diagnosis. Neutron detectors have important application value in many fields due to their high sensitivity and accurate measurement capabilities to neutron radiation. Since a wide neutron energy spectrum distribution from the thermal neutron region to 20MeV energy is formed in the pulsed neutron radiation field, the neutron dose monitoring results of conventional neutron monitors have a large deviation from the actual ambient dose equivalent. Summary of the invention

[0003] In order to solve the above problems in the prior art, the present invention provides a multi-sphere neutron spectrometer for monitoring pulsed neutron radiation field. 3 A set of He gas detectors as the central counting, 4H-SiC semiconductor detectors as thermal neutron counters, neutron moderators, preamplifiers, fast charge sensitive preamplifiers, spectrometer main amplifiers, high voltage power supplies, and multi-channel analyzers was proposed. 1 ~10 4 n cm -2 s -1 and a neutron flux of 10 3 ~10 6 n cm -2 s -1 The dual-detector multi-sphere neutron spectrometer is used to measure neutron energy spectrum and dose in an environment with high sensitivity. The Monte Carlo method is used to calculate the neutron energy spectrum and dose of eight neutron moderators under different detectors. -9 MeV to 20MeV wide energy range response matrix. The present invention is used for the energy spectrum and dose measurement of pulsed neutron radiation field, and can realize the measurement of neutron energy spectrum distribution information and neutron dose in a wide energy range without multiple sets of multi-sphere neutron spectrometers.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] A multi-sphere neutron spectrometer for monitoring pulsed neutron radiation fields, the multi-sphere neutron spectrometer comprising 3 He gas detector, 4H-SiC semiconductor detector, neutron moderator, preamplifier, fast charge sensitive preamplifier, spectrometer main amplifier, high voltage power supply, digital multi-channel analyzer, designed dual detector neutron moderator, in 10 -9The energy range from MeV to 20MeV is evenly divided into 60 energy points according to logarithmic coordinates. The response function of eight neutron moderators at each energy point under different detectors is calculated using the Monte Carlo method to obtain the response matrix of the entire multi-sphere neutron spectrometer. The maximum entropy principle and SAND-II algorithm are then used to inversely solve the neutron energy spectrum. 3 The He gas detector and the 4H-SiC semiconductor detector are both set in the neutron moderator sphere. A part of the neutrons entering the neutron moderator sphere enters the 4H-SiC semiconductor detector and interacts with the neutrons in the 4H-SiC semiconductor detector. 28 Si and 12 The ionization signal generated by the nuclear reaction of C nuclide is amplified by the fast charge sensitive preamplifier; another part of the neutrons entering the neutron moderation sphere enters 3 In He gas detectors, 3 He gas generation 3 He (n, p) T reaction, the generated proton p and tritium nucleus T release energy, causing 3 He gas detector counts, the preamplifier is used to convert 3 The counting signal generated by the He gas detector is preliminarily amplified, and the main amplifier of the spectrometer filters the electrical signal amplified by the preamplifier. The high-voltage power supply provides bias voltage for the preamplifier and the fast charge sensitive preamplifier. The multi-channel analyzer records and analyzes the amplitude of the pulse signal amplified by the fast charge sensitive preamplifier and the preamplifier, selectively counts the pulse signal amplitude, and then performs binary encoding, and then sorts the counted pulse signals in order from low to high, thereby forming a pulse amplitude spectrum, and then the neutron energy spectrum can be reversed based on the maximum entropy principle and the SAND-II algorithm.

[0006] The present invention has the following beneficial effects:

[0007] The present invention adopts 3 The data acquisition system of the dual-detector multi-sphere neutron spectrometer with He gas detector and 4H-SiC semiconductor detector enables a set of dual-detector multi-sphere spectrometer to measure different radiation environments, making it more portable. 3 The He gas detector and 4H-SiC semiconductor are placed in the same neutron moderator sphere, and the different sensitivity ranges of different detectors are used. 3 He gas detector count rate is usually 10 5 cps, signal accumulation is easy at high counting rate, 4H-SiC semiconductor detector has low detection efficiency and is applicable at high counting rate. The dual-detector multi-sphere neutron spectrometer with different sensitivity characteristics improves the accuracy and range of energy spectrum and dose monitoring of pulsed neutron radiation field; at neutron flux of 10 1 ~10 4 n cm-2 s -1 Under conditions (low neutron yield), use based on 3 He detectors are used to measure neutron energy spectrum and dose; 3 ~10 6 n cm -2 s -1 Under the condition of high neutron yield, the neutron energy spectrum and dose are measured by using a 4H-SiC semiconductor detector. 3 The data acquisition system of the dual-detector multi-sphere neutron spectrometer with He gas detector and 4H-SiC semiconductor detector realizes the measurement of wide neutron energy spectrum distribution information and neutron dose in the pulsed neutron radiation field. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a structural schematic diagram of a multi-sphere neutron spectrometer used for pulse neutron radiation field monitoring of the present invention;

[0009] Figure 2 It is a circuit diagram of a multi-sphere neutron spectrometer used for pulse neutron radiation field monitoring of the present invention;

[0010] Figure 3 It is a neutron moderator ball with an outer diameter of 30.48 cm in the pulsed neutron radiation field. 3 Pulse amplitude distribution spectrum of He detector;

[0011] Figure 4 It is the pulse amplitude distribution spectrum of the 10.16 cm neutron moderator sphere 4H-SiC detector in the pulse neutron radiation field;

[0012] Figure 5 for 3 Comparison of simulated and experimental energy spectra of pulsed neutron radiation field in He gas detector;

[0013] Figure 6 Comparison of simulated and experimental energy spectra of pulsed neutron radiation field of 4H-SiC semiconductor detector.

[0014] Among them, 1. Neutron moderator ball, 2. 4H-SiC semiconductor detector, 3. 4H-SiC semiconductor detector signal line slot, 4. tray, 5. tray bracket, 6. metal aluminum cylindrical head, 7. 3 He gas detector stainless steel housing, 8. 3 He gas detector, 9. 3 He gas detector signal wireway. DETAILED DESCRIPTION

[0015] 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.

[0016] The present invention provides a multi-sphere neutron spectrometer for monitoring pulsed neutron radiation fields, such as Figure 2 As shown, it is a 3 The data acquisition system of the dual-detector multi-sphere neutron spectrometer of He gas detector 8 and 4H-SiC semiconductor detector 2 improves the accuracy and range of the energy spectrum and dose monitoring of the pulse neutron radiation field; the multi-sphere neutron spectrometer of the present invention includes 3 He gas detector 8, 4H-SiC semiconductor detector 2, neutron moderator 1, preamplifier, fast charge sensitive preamplifier, spectrometer main amplifier, high voltage power supply, multi-channel analyzer; 3 The He gas detector 8 and the 4H-SiC semiconductor detector 2 are both arranged in the neutron moderation sphere 1; since the neutrons generated in the pulsed neutron radiation field will undergo various scattering reactions with various building structures in the pulsed neutron radiation field, they will be gradually moderated, forming a wide neutron energy spectrum distribution from the thermal neutron region to 14MeV energy; part of the scattered neutrons will enter the neutron moderation sphere, part of which will be slowed down by the neutron moderation sphere and disappear, and another part of the neutrons will enter the center of the sphere after being slowed down by the neutron moderation sphere. 3 He gas detector 8, enter 3 Neutrons from He gas detector 8 will react with 3 He gas generation 3 He (n, p) T reaction, the proton p and tritium nucleus T released by the reaction distribute the generated 765keV energy, the proton p obtains 574keV energy, and the tritium nucleus T obtains 191keV energy. The generated proton p and tritium nucleus T will cause 3 The 4H-SiC semiconductor detector 2 can directly pass neutrons to the detector. 28 Si and 12 C nuclide generation 28 Si(n,p) 28 A1, 28 Si(n, α) 25 Mg, 28 Si(n, n) 28 Si, 12 C(n, α) 9 Be, 12 C(n, n′) 12C and 12 C(n, n')3α and other nuclear reactions to detect fast neutrons. The surface of 4H-SiC crystal is coated with 6 The Li thermal neutron conversion material is used to detect thermal neutrons, and the charged particle products produced by the reaction generate ionization signals in the silicon carbide detector; the preamplifier is used to convert 3 The counting signal generated by the He gas detector 8 is preliminarily amplified, and the main amplifier of the spectrometer filters the electrical signal amplified by the preamplifier to reduce background noise and interference; the fast charge sensitive preamplifier is used to amplify the ionized nuclear signal generated in the 4H-SiC semiconductor detector 2; the multi-channel analyzer records and analyzes the amplitude of the pulse signal amplified by the fast charge sensitive preamplifier and the preamplifier, selectively counts the pulse signal amplitude, and then performs binary encoding, and then sorts the counted pulse signals from low to high, thereby forming a pulse amplitude spectrum.

[0017] Furthermore, the neutrons are slowed down by the neutron slowing ball and enter the 4H-SiC semiconductor detector 2. 6 LiF converter undergoes nuclear reaction: ; The 4.78 MeV of energy released by the reaction is in the product helium nucleus and tritium nuclei T, among which the helium nuclei The energy of the helium nucleus is 2.05MeV, and the energy of the tritium nucleus T is 2.73MeV. The two are emitted in opposite directions. The emitted helium nucleus or tritium nucleus enters the sensitive volume of silicon carbide, causing the electron to rise from the valence band to the conduction band. Due to the lack of electrons in the valence band, holes are generated. The formed electron-hole pairs are collected on electrodes with opposite polarities under the action of the electric field, forming experimental signals.

[0018] Furthermore, the fast charge sensitive preamplifier (CAEN A1426) is used to amplify the signal of the detector, and the bias voltage BV (Bias Voltage) used by the 4H-SiC semiconductor detector 2 is +45V.

[0019] Furthermore, the multi-channel analyzer uses an analog-to-digital converter to convert each pulse signal to a corresponding channel. Each channel corresponds to a very narrow voltage amplitude. As time accumulates, the multi-channel analyzer allocates many addresses in its storage to store the amplitudes of these signals. These signals are arranged in order of pulse amplitude, thereby forming a pulse amplitude spectrum, such as Figure 3 and Figure 4 As shown; then the neutron energy spectrum in the pulse radiation field is obtained by inverse solution based on the maximum entropy principle and the SAND-II algorithm, and compared with the neutron energy spectrum calculated using the Monte Carlo method, as shown Figure 5 and Figure 6 shown.

[0020] Furthermore, the model of the preamplifier is Ortec142pc, and the recommended high voltage is set to +700V to ensure the best signal-to-noise ratio and extend the life of the amplifier.

[0021] Furthermore, the neutron moderator balls are all made of high-density polyethylene material to moderate scattered neutrons. There are 8 neutron moderator balls, and the outer diameters of each neutron moderator ball are 7.62, 8.89, 10.16, 12.70, 15.24, 20.32, 25.40 and 30.48 cm, respectively, and the density is 0.94 g / cm 3 , including designing a suitable bracket to ensure that the center of all sizes of neutron moderator spheres are at the same vertical height. -9 The energy range from MeV to 20MeV is evenly divided into 60 energy points according to logarithmic coordinates. The Monte Carlo method is used to calculate the response function of eight neutron moderator spheres at each energy point under different detectors, and the response matrix of the whole multi-sphere neutron spectrometer is obtained. The neutron energy spectrum can be inversely solved using the maximum entropy principle and SAND-II algorithm.

[0022] Furthermore, the interior of the 4H-SiC semiconductor detector 2 is a Schottky barrier structure, and the silicon carbide surface coating area is , thickness 30 of 6 LiF thermal neutron converter.

[0023] like Figure 1 FIG. 1 is a schematic diagram of the structure of a multi-sphere neutron spectrometer for pulse neutron radiation field monitoring according to the present invention, wherein the neutron moderator sphere 1 is a hemispherical cross-section and is made of high-density polyethylene. 3 The He gas detector 8 is located at the center of the neutron moderation sphere 1. 3 A 4H-SiC semiconductor detector 2 is set at 1 mm from the He gas detector 8. Neutrons enter the 4H-SiC semiconductor detector 2 or 3 The He gas detector 8 undergoes a corresponding nuclear reaction to generate a pulse signal that can be counted and analyzed.

[0024] 4H-SiC semiconductor detector signal line slot 3 and 3 The He gas detector signal wire slot 9 is a wire slot that fits the detector signal wire, and its purpose is to prevent excessive gaps from affecting the detector's response.

[0025] The tray 4 and the tray bracket 5 are both made of metal aluminum material, and their function is to make the centers of the other seven neutron moderator balls be located on the same horizontal plane, avoiding neutron flux measurement errors caused by position reasons, ensuring that the neutrons have the same attenuation path, ensuring the reliability of the experimental results, and simplifying the data analysis process.

[0026] Aluminum cylindrical head 6 and 3 He gas detector stainless steel housing 7 can effectively seal 3 He gas detector 8 3 He gas and other components to prevent the external environment from affecting the interior of the detector, such as air, moisture or other substances that may cause gas leakage or corrosion, while also having a better protection of its structure and function, providing structural support and protection for the interior and reactions.

Claims

1. A multi-sphere neutron spectrometer for monitoring pulsed neutron radiation fields, characterized in that: The multi-sphere neutron spectrometer comprises 3 He gas detector, 4H-SiC semiconductor detector, neutron moderator, preamplifier, fast charge sensitive preamplifier, spectrometer main amplifier, high voltage power supply, digital multi-channel analyzer; in, 3 The He gas detector and the 4H-SiC semiconductor detector are both set in the same neutron moderator sphere. A part of the neutrons entering the neutron moderator sphere enters the 4H-SiC semiconductor detector and interacts with the neutrons in the 4H-SiC semiconductor detector. 28 Si and 12 The ionization signal generated by the nuclear reaction of C nuclides is amplified by the fast charge sensitive preamplifier; another part of the neutrons entering the neutron moderation sphere enters 3 He gas detector 3 He gas generation 3 He (n, p) T reaction, the generated proton p and tritium nucleus T release energy, causing 3 He gas detector counts, the preamplifier is used to convert 3 The counting signal generated by the He gas detector is preliminarily amplified, and the main amplifier of the spectrometer filters the electrical signal amplified by the preamplifier. The high-voltage power supply provides bias voltage for the preamplifier and the fast charge sensitive preamplifier. The multi-channel analyzer records and analyzes the amplitude of the pulse signal amplified by the fast charge sensitive preamplifier and the preamplifier, selectively counts the pulse signal amplitude, and then performs binary encoding, and then sorts the counted pulse signals in order from low to high, thereby forming a pulse amplitude spectrum.

2. A multi-sphere neutron spectrometer for pulsed neutron radiation field monitoring according to claim 1, characterized in that: There are 8 neutron moderator balls, each with an outer diameter of 7.62, 8.89, 10.16, 12.70, 15.24, 20.32, 25.40 and 30.48 cm, and the material selected has a density of 0.94 g / cm 3 A bracket is set for each neutron moderator sphere so that the centers of neutron moderator spheres of all sizes are at the same horizontal height.

3. The multi-sphere neutron spectrometer for pulsed neutron radiation field monitoring according to claim 1, characterized in that: 3 The He gas detector consists of a spherical stainless steel cavity, a hexagonal support and a cylindrical joint, located in the center of the moderator; the inner diameter of the cavity is about 32 mm, of which 3 The He gas pressure is 203 kPa, and the anode wire in the cavity is fixed inside the cylindrical joint.

4. The multi-sphere neutron spectrometer for pulsed neutron radiation field monitoring according to claim 1, characterized in that: The 4H-SiC semiconductor detector is located at 3 The He gas detector is located 1mm from the surface. The internal structure is a Schottky barrier structure, including: the surface coating area of ​​silicon carbide is , thickness 30 of 6 LiF thermal neutron converter.

5. The multi-sphere neutron spectrometer for pulsed neutron radiation field monitoring according to claim 1, characterized in that: A power supply is also included to provide 12V to the preamplifier and fast charge sensitive preamplifier.

6. The multi-sphere neutron spectrometer for pulsed neutron radiation field monitoring according to claim 1, characterized in that: The high voltage power supply is used to provide 700V bias voltage to the preamplifier and 45V bias voltage to the fast charge sensitive preamplifier.

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