Fast neutron multiplex measurement experiment method

Abstract

The invention discloses a fast neutron multiplex measurement experiment method, which belongs to the field of nuclear radiation detection and nuclear electronics, and comprises the following steps: S1, adjusting the high voltage and threshold value of a detector; s2, testing the n / gamma discrimination performance of each detector by using a 252Cf source with the activity of 75700Bq; s3, using a BC501A, an EJ301 and an OGS (One Glass Solution) to form a detection system; and S4, obtaining an optimal detection combination system. According to the fast neutron multiplex measurement experiment method provided by the invention, different detection systems can be constructed by changing the number, the variety, the distance and the combination mode of the liquid scintillator detectors on the basis of a digital acquisition card principle prototype, so that the detection system with the optimal detection efficiency is obtained. Experimental results show that when the combined optimal detection system is put into actual use, the detection efficiency of the detector on large-size objects can be remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear radiation detection and nuclear electronics, and in particular to a fast neutron multiplicity measurement experimental method. Background Art

[0002] With the development of the nuclear industry, there are more and more uranium and plutonium materials in the world, and preventing nuclear proliferation has become a common concern of the international community today. Since uranium and plutonium materials can produce fission neutrons, the use of neutron detection technology and combined with isotope abundance to conduct non-destructive analysis of them is the most commonly used method in the field of nuclear safeguards. In my country, the detection of uranium and plutonium materials in nuclear facilities and the classification and treatment of large amounts of radioactive solid waste generated during long-term operation and decommissioning have gradually become an arduous task. With the development of nuclear electronic detection technology, neutron measurement technology has become an important means of non-destructive analysis technology in the field of nuclear electronic detection technology, and is of great significance in the field of nuclear safeguards, especially in nuclear material balance.

[0003] Liquid scintillator detectors are important devices for fast neutron multiplicity measurement. Their main components are carbon and hydrogen elements. BC501A, EJ-301, and Stilbene are three common detectors for fast neutron detection. Organic glass scintillator (OGS) has become a research hotspot in recent years due to its unique optical and physical properties.

[0004] Due to the actual needs of nuclear electron detection, when facing large-volume measurement objects, the existing measurement equipment has the problem that the detector volume needs to be continuously increased to increase the detection efficiency, but the detector cost increases as the detector volume continues to increase. Summary of the invention

[0005] In order to solve the problem of detection efficiency existing in the above-mentioned prior art, the present invention provides a fast neutron multiplicity measurement experimental method.

[0006] To implement the above technical solution, the present invention provides a fast neutron multiplicity measurement experimental method, comprising the steps of:

[0007] S1: Adjust the high voltage and threshold of the detector, debug the high voltage of the detector, and use the activity of 1.037×

[0008] 10 6 of 137 The Cs point source adjusts the detector's trigger threshold to 1 / 4Cs;

[0009] S2: Using 75700Bq 252 The n / γ discrimination performance of each detector was tested by Cf source.

[0010] hour 252The Cf source is 50 cm away from the probe cross section, and each measurement lasts 10 min;

[0011] S3: Use BC501A, EJ301 and OGS to form a detection system;

[0012] S4: Obtain the best detection combination system.

[0013] Furthermore, when the trigger threshold is adjusted, 137 The Cs source and the detector are located at the center axis, with a distance of 10 cm, and each measurement takes 2 minutes.

[0014] Further, in step S3, 6 BC501A, 6 EJ301, 6 BC501A+2 EJ301, 6 BC501A+1 EJ301+1 OGS and 4 BC501A+4 EJ301 are used to form a detection system.

[0015] Furthermore, when 6 BC501A detectors were used for testing, the distance between two opposing BC501A detectors was 26 cm; when 6 EJ301 detectors were used for testing, the distance between two opposing EJ301 detectors was 17 cm; when 6 BC501A detectors + 2 EJ301 detectors were used for testing, the distance between opposing BC501A detectors was 32 cm, and the distance between opposing EJ301 detectors was about 32.5 cm; when 6 BC501A detectors + 1 EJ301 detector + 1 OGS detector were used for testing, the 6 BC501A detectors were opposed to each other, 29 cm apart, and the OGS and EJ301 detectors were opposed to each other, 24 cm apart.

[0016] Furthermore, when using 4 BC501A + 4 EJ301 for testing, the testing method is divided into two methods: placing 4 BC501A + 4 EJ301 on the same layer and placing 4 BC501A on the first layer and then placing 4 EJ301 on the second layer.

[0017] Furthermore, when 4 BC501A + 4 EJ301 are placed on the same floor, the system consists of 4 BC501A and 4 EJ031 detectors. The detectors are connected in pairs and arranged in a staggered manner. The distance between BC501A detectors is 27 cm, and the distance between EJ301 detectors is 30 cm.

[0018] Furthermore, when four BC501A detectors are placed on the first layer and four EJ301 detectors are placed on the second layer, the detectors are placed opposite to each other in pairs and staggered up and down, and the distance between the detectors is ensured to be 8 cm.

[0019] Furthermore, when the trigger threshold is adjusted, 137 The Cs source and the detector are located at the center axis, with a distance of 10 cm, and each measurement takes 2 minutes.

[0020] Furthermore, the measurement time is 100 s, each detection system measures 6 times in total; the measurement gate width is set to 0.8 μs; and the pre-delay is 0.04 μs.

[0021] In summary, the present invention has the following beneficial effects compared with the prior art:

[0022] The fast neutron multiplicity measurement experimental method provided by the present invention can construct different detection systems by changing the number, type, distance and combination of liquid scintillator detectors on the basis of the principle prototype of the digital acquisition card, thereby obtaining a detection system with the best detection efficiency. The experimental results show that putting the combined best detection system into practical use can significantly improve the detection efficiency of the detector for large-volume objects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0024] Figure 1 A flow chart of a fast neutron multiplicity measurement experimental method provided by the present invention;

[0025] Figure 2 This is the BC501An / γ discrimination performance image;

[0026] Figure 3 It is the EJ301 n / γ discrimination performance image;

[0027] Figure 4 It is the Stilbene n / γ discrimination performance image;

[0028] Figure 5 This is an image of the n / γ discrimination performance of the OGS detector. DETAILED DESCRIPTION

[0029] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0030] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form can also include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0031] See also Figure 1 As shown, the present invention provides a fast neutron multiplicity measurement experimental method, comprising the steps of:

[0032] S1: The high voltage and threshold of the detector are the basic requirements for its normal operation. The present invention uses BC501A detector, EJ301 detector, Stilbene detector and OGS detector, and adjusts the high voltage and threshold of each detector. First, the high voltage of each detector is debugged separately; then 137 Cs point source (activity 1.037×10 6 ) The trigger thresholds of different detectors are adjusted separately (1 / 4Cs), so that the backgrounds deducted by all detectors are consistent, which facilitates the subsequent acquisition of detection efficiency; the liquid scintillator detectors used in the present invention are shown in Table 1.

[0033] Table 1 Main properties of four scintillator materials

[0034]

[0035] S2: Using 75700Bq 252 The n / γ discrimination performance of each detector was tested by Cf source.

[0036] hour 252 The Cf source is 50 cm away from the probe cross section, and each measurement lasts 10 min;

[0037] S3: Use BC501A, EJ301 and OGS to form a detection system;

[0038] S4: Obtain the best detection combination system.

[0039] As a preferred embodiment, the detection system is composed of 6 BC501A, 6 EJ301, 6 BC501A+2 EJ301, 6 BC501A+1 EJ301+1 OGS and 4 BC501A+4 EJ301.

[0040] As a preferred embodiment, when 6 BC501A are used for testing, the distance between two opposite BC501A is 26cm; when 6 EJ301 are used for testing, the distance between two opposite EJ301 is 17cm; when 6 BC501A + 2 EJ301 are used for testing, the distance between opposite BC501A detectors is 32cm, and the distance between opposite EJ301 detectors is about 32.5cm; when 6 BC501A + 1 EJ301 + 1 OGS are used for testing, the 6 BC501A are opposite to each other, 29cm apart, and the OGS and EJ301 detectors are opposite to each other, 24cm apart.

[0041] (1) A detection system consisting of 6 BC501A liquid scintillation detectors is used to build the system. The BC501A detectors are connected in pairs, and the distance between two opposite detectors is 26 cm. 252 The Cf radiation source is located at the center of the detection system. 252 The Cf radioactive source sets the function of the system, and the multiplicity counts are shown in Tables 2 and 3. Among them, RPA represents the multiplicity distribution of the coincidence gate, and ACC represents the multiplicity distribution of the A gate.

[0042] Table 2 RPA multiplicity counts for the 6 BC501A detector system

[0043]

[0044] Table 3 ACC multiplicity counts of 6 BC501A detector systems

[0045]

[0046] (2) Detection system composed of 6 EJ301s. In order to compare the efficiency of the EJ301 and BC501A detection systems, the present invention uses 6 EJ301 detectors to build an identical system. Since the size of the BC501A liquid scintillator is larger than that of the EJ301, when the EJ301 detectors are connected in pairs, the relative detector distance is 17 cm. 252 The Cf radiation source is also located at the center of the detection system. The corresponding multiplicity counts are shown in Tables 4 and 5.

[0047] Table 4 RPA multiplicity counts of 6 EJ301 detector systems

[0048]

[0049]

[0050] Table 5 ACC multiplicity counts of 6 EJ301 detector systems

[0051]

[0052] From the results, the multiplicity count of the system composed of 6 EJ301 liquid scintillator detectors is much lower than that of the system composed of 6 BC501A liquid scintillator detectors. This is consistent with the efficiency of a single detector. Therefore, the present invention uses this system as a benchmark to examine the detection efficiency of the system under different detector types and quantities.

[0053] (3) The detection system consists of 6 BC501A + 2 EJ301. On the basis of 6 BC501A detectors, 2 EJ301 are added and placed symmetrically so that the relative positions of the 6 BC501A detectors are opposite to each other. The relative distance between the BC501A detectors is 32 cm, and the relative distance between the EJ301 detectors is about 32.5 cm. The corresponding multiplicity counts are shown in Tables 6 and 7.

[0054] Table 6 RPA multiplicity counts for the system built with 6 BC501A + 2 EJ301

[0055]

[0056] Table 7 RPA multiplicity counts for the system built with 6 BC501A + 2 EJ301

[0057]

[0058] Comparing Table 2 and Table 6, the change in multiplicity count is not obvious. Although the number of detectors is increased, the distance between the corresponding detectors is also increased, resulting in a decrease in the geometric factor of the detection system. The change in detection efficiency is the coupling effect of these two factors.

[0059] (4) A detection system consisting of 6 BC501A + 1 EJ301 + 1 OGS. In order to compare the performance of the OGS detector and the EJ301 detector, the present invention replaces one EJ301 detector in the previous system with one OGS detector. The 6 BC501A detectors are opposite to each other, 29 cm apart, and the OGS and EJ301 detectors are opposite to each other, 24 cm apart. The corresponding multiplicity counts are shown in Tables 8 and 9.

[0060] Table 8 RPA multiplicity counts of the system consisting of 6 BC501A+1 EJ301+1 OGS

[0061]

[0062] Table 9 ACC multiplicity counts of the system composed of 6 BC501A+1 EJ301+1 OGS

[0063]

[0064] Comparing Table 6 and Table 8, it is found that the change of a single detector type has little effect on the overall detection efficiency of the system. The present invention further increases the number of replaced detectors, increasing the number of EJ301 from 2 to 4, and examines the efficiency of the system.

[0065] As a preferred embodiment, when using 4 BC501A + 4 EJ301 for testing, the testing method is divided into two methods: placing 4 BC501A + 4 EJ301 on the same layer and placing 4 BC501A on the first layer and then placing 4 EJ301 on the second layer.

[0066] As a preferred method, when 4 BC501A + 4 EJ301 are placed on the same floor, the system consists of 4 BC501A and 4 EJ031 detectors, which are connected in pairs and arranged in a staggered manner. The distance between BC501A detectors is 27 cm, and the distance between EJ301 detectors is 30 cm. The multiplicity counts are shown in Tables 10 and 11.

[0067] Table 10 RPA multiplicity counts of a system consisting of 4 BC501A + 4 EJ301 (single layer)

[0068]

[0069] Table 11 ACC multiplicity counts of a system consisting of 4 BC501A + 4 EJ301 (single layer)

[0070]

[0071]

[0072] Comparing Table 6 and Table 10, it is found that as the number of BC501A detections decreases, the detection efficiency of the system gradually decreases. Instead of replacing more BC501A, we consider building a double-layer system. Since the number of BC501A detectors is less than 8, the present invention uses the 4 EJ301 detectors in the upper system as the second-layer detectors of the upper system to examine the efficiency of the system.

[0073] As a preferred method, four BC501As are placed on the first layer, and then four EJ301s are placed on the second layer, so that the detectors are opposite to each other, staggered up and down, and the distance between the detectors is 8 cm. The corresponding multiplicity counts are shown in Tables 12 and 13.

[0074] Table 12 RPA multiplicity counts of a system consisting of 4 BC501A + 4 EJ301 (double layer)

[0075]

[0076] Table 13 ACC multiplicity counts of a system consisting of 4 BC501A + 4 EJ301 (double layer)

[0077]

[0078] By comparing Tables 10 and 12, it can be found that when the number and type of detectors are the same, the efficiency of the two-layer system is much greater than that of the one-layer system. This may be because the more detectors there are on the same layer, the larger the space between the detectors, which reduces the overall detection efficiency.

[0079] In addition, the present invention uses a system consisting of 6 BC501A + 2 EJ301 to measure the background of the experimental environment. The multiplicity counts of the background are shown in Table 13 and Table 14.

[0080] Table 13 RPA multiplicity counts of background (second layer)

[0081]

[0082]

[0083] Table 14 ACC multiplicity counts of background

[0084]

[0085] The multiplicity analysis function of the digital analyzer prototype was used to perform multiplicity analysis. The total neutron count rate (S), double coincidence count rate (D) and triple coincidence count rate (T) of the background and each system are listed in Tables 15 and 16.

[0086] Table 15 Background measurement results

[0087]

[0088] Table 16 Multiplicity analysis results

[0089]

[0090] From the experimental results, it can be seen that compared with 6 EJ301 detectors, 6 BC501A detectors have higher detection efficiency because of their larger size; when 8 different detectors are combined in one layer, the detection efficiency is similar; when 8 different detectors are combined in 2 layers, the total number of neutrons detected is the largest, and the detection efficiency is the highest.

[0091] As a preferred embodiment, when the trigger threshold is adjusted, 137 The Cs source and the detector are located at the center axis, 10 cm apart, and each measurement is 2 minutes. The high voltage and threshold of the detector are shown in Table 17.

[0092] Table 17 High voltage and threshold settings for different detectors

[0093]

[0094]

[0095] The n / γ discrimination of the detector is achieved through pulse shape discrimination (PSD). The interaction mechanisms of neutrons and gamma rays in the scintillator are different, resulting in different time distributions of the scintillation light signals they produce. The n / γ discrimination results of BC501A, EJ301, Stilbene detectors and OGS detectors are shown in the figure below. Figure 2-4 As shown in the figure, each n / γ discrimination performance image consists of three parts, namely PSD-Counts, ADC Channel-Counts, and Energy-PSD. The n / γ discrimination performance is mainly judged by the Energy-PSD image. The clearer the Energy-PSD image, the better the n / γ discrimination performance of the detector. As can be seen from the figure, the Stilbene detector has the best n / γ discrimination performance.

[0096] As a preferred method, when using 252 When the Cf source performs functional verification on the detection system, the measurement time must be 100s, and each detection system is measured 6 times in total to eliminate statistical errors. The measurement gate width is set to 0.8μs; the pre-delay is 0.04μs.

[0097] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A fast neutron multiplicity measurement experimental method, characterized in that: Includes steps: S1: Adjust the high voltage and threshold of the detector, debug the high voltage of the detector, and use the activity of 1.037×10 6 of 137 The Cs point source adjusts the detector's trigger threshold to 1 / 4Cs; S2: Using 75700Bq 252 The n / γ discrimination performance of each detector was tested using a Cf source. 252 The Cf source is 50 cm away from the probe cross section, and each measurement lasts 10 min; S3: Use BC501A, EJ301 and OGS to form a detection system; S4: Obtain the best detection combination system.

2. The fast neutron multiplicity measurement experimental method according to claim 1, characterized in that: When the trigger threshold is adjusted, 137 The Cs source and the detector are located at the center axis, with a distance of 10 cm, and each measurement takes 2 minutes.

3. The fast neutron multiplicity measurement experimental method according to claim 1, characterized in that: In step S3, 6 BC501A, 6 EJ301, 6 BC501A+2 EJ301, 6 BC501A+1 EJ301+1 OGS and 4 BC501A+4 EJ301 are used to form a detection system.

4. The fast neutron multiplicity measurement experimental method according to claim 3, characterized in that: When 6 BC501A detectors were used for testing, the distance between two opposing BC501A detectors was 26cm; when 6 EJ301 detectors were used for testing, the distance between two opposing EJ301 detectors was 17cm; when 6 BC501A detectors + 2 EJ301 detectors were used for testing, the distance between opposing BC501A detectors was 32cm, and the distance between opposing EJ301 detectors was about 32.5cm; when 6 BC501A detectors + 1 EJ301 detectors + 1 OGS detector were used for testing, the 6 BC501A detectors were opposite to each other, 29cm apart, and the OGS and EJ301 detectors were opposite to each other, 24cm apart.

5. The fast neutron multiplicity measurement experimental method according to claim 3, characterized in that: When using 4 BC501A + 4 EJ301 for testing, the test method is divided into two methods: placing 4 BC501A + 4 EJ301 on the same layer and placing 4 BC501A on the first layer and then placing 4 EJ301 on the second layer.

6. The fast neutron multiplicity measurement experimental method according to claim 5, characterized in that: When 4 BC501A + 4 EJ301 are placed on the same floor, the system consists of 4 BC501A and 4 EJ031 detectors. The detectors are connected in pairs and arranged in a staggered manner. The distance between BC501A detectors is 27cm, and the distance between EJ301 detectors is 30cm.

7. The fast neutron multiplicity measurement experimental method according to claim 5, characterized in that: Place 4 BC501A on the first layer, and then place 4 EJ301 on the second layer, so that the detectors are opposite to each other, staggered up and down, and ensure that the distance between the detectors is 8cm.

8. The fast neutron multiplicity measurement experimental method according to any one of claims 1 to 7, characterized in that: When the trigger threshold is adjusted, 137 The Cs source and the detector are located at the center axis, with a distance of 10 cm, and each measurement takes 2 minutes.

9. The fast neutron multiplicity measurement experimental method according to any one of claims 1 to 7, characterized in that: The measurement time is 100s, and each detection system is measured 6 times in total; the measurement gate width is set to 0.8μs; and the pre-delay is 0.04μs.

Images