最新刊期
      卷 39 ， 期 3 ， 2016
      • Liping LI,Xin ZHOU,Qiang LI
        Vol. 39, Issue 3, Article number: 030401(2016) DOI: 10.11889/j.0253-3219.2016.hjs.39.030401
        摘要：Background:High resolution is of key importance for positron emission tomography (PET) devices. Modern PET scanners use a large number of crystals in detector blocks to improve their resolution. The extra crystals lead to a significant increase in workload of crystal identification in PET detector calibration. Hence the robustness of crystal identification algorithms becomes a challenge. Crystal identification is typically based on flood histograms obtained by irradiating the detector blocks with an annihilation photon flood source. More crystals of smaller size degrade the quality of flood histogram and generate more complex spatial distortions. Existing crystal identification methods are not robust enough to handle these cases.Purpose:Our study aims to improve the robustness and success rate of crystal identification on PET detectors of different-level quality and reduce the manual interaction in PET detectors calibration.Methods:In this study, we developed a hierarchical fusion approach to overcome the limitations of the existing methods for accurate PET detector calibration. We first implemented three complementary state-of-the-art crystal identification methods and then assessed the consistency of the three identification results based on the quality of detected crystal position and row/column label information. The results of higher consistency are considered more reliable. The hierarchical fusion approach integrated first the identification results of the highest consistency and then those of gradually lower consistencies.Results:The performance of the crystal identification method was evaluated with PET detectors of three different levels (normal, heavily distorted, and low signal-to-noise ratio (SNR)). Although the three crystal identification methods alone achieved over95% of success rate on normal quality detectors, they only achieved around 80% of success rate on detectors of heavy distortion and low SNR. Our hierarchical fusion approach consistently improved the success rate to 99.8%, 92.2% and 94.3% for detectors of normal, heavily distorted, and low SNR.Conclusion:Compared to three individual PET detector identification methods, the fusion-based approach consistently and significantly improved the success rate of PET detector identification, especially for heavily distorted and low SNR detectors.  
        关键词：Crystal identification;Crystal look-up table (CLT);Hierarchical fusion;Space distortion correction;PET   
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        发布时间：2021-05-24
      • Xiaqing SHI,Guobing YU,Xianbao GU,Yu ZHANG,Jun ZHAO,Zhi CHEN,Xie XU
        Vol. 39, Issue 3, Article number: 030402(2016) DOI: 10.11889/j.0253-3219.2016.hjs.39.030402
        摘要：Background:There are four common methods to prepare radioactive aerosol samples for the purpose of gamma-spectroscopy involving an HPGe detector:ashing method, compressing method, holing method, and folding method. However, their counting characteristics have never been studied and compared.Purpose:This study aims to provide a comprehensive evaluation of these four sample preparation methods.Methods:An HPGe gamma spectrometer was used in the study to evaluate and confirm the reliability of these four radioactive aerosol sample preparation methods. Monte Carlo simulations were used to calculate the gamma-spectroscopic counting efficiency.Results:The four preparation methods were found to be generally reliable, with assessed activity differing less than 5%. The ashing method was found to yield the highest counting efficiency, followed by compressing method, holing method, and folding method. For the 260mm&#215;210 mm and 570mm&#215;470 mm sized filter, the variation range of gamma detection efficiency was found to be 55% and 120%.Conclusion:The analyses of these sample preparation methods provide useful suggestions on the suitability and conditions, thus offering a useful reference on how to choose, prepare and count radioactive aerosols samples.  
        关键词：Aerosol sample;Sample preparation method;Detecting efficiency;Monte Carlo simulation;Minimum detectable activity (MDA)   
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        发布时间：2021-05-24
      • Junqiang ZHANG,Yajuan LIU,Shaopeng ZHONG,Lin LI,Yingmin LI,Qiang GU
        Vol. 39, Issue 3, Article number: 030403(2016) DOI: 10.11889/j.0253-3219.2016.hjs.39.030403
        摘要：Background:The photo-neutron source driven by 15-MeV electrons linac in Thorium molten salt reactor (TMSR) program was designed for nuclear data measurement.Purpose:To ensure the linac to provide stable and high quality beam bunches, a low level radio frequency (LLRF) control system based on field programmable gate array (FPGA) was developed.Methods:LLRF realized digital amplitude and phase feedback control by using up-down converter, IQ (In-phase and Quadrature) modulator and demodulator techniques.Results:After commission, the control accuracy of amplitude and phase is less than&#177;0.4% and&#177;0.6&#176;, respectively.Conclusion:Long time running indicates that the whole digital control loop has the properties of fast time response and good stability, which meets the demand of photo-neutron facility.  
        关键词：Linac;LLRF;FPGA;Waveform acquisition;Feedback control   
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        发布时间：2021-05-24
      • Xingchen NIE,Jia LI,Pinghui ZHAO,Qingjun ZHU
        Vol. 39, Issue 3, Article number: 030501(2016) DOI: 10.11889/j.0253-3219.2016.hjs.39.030501
        摘要：Background:For the detailed Monte Carlo radiation transport, which possesses global characteristics, traditional MCNP Localized Variance Reduction (LVR) methods can hardly perform well. Global Variance Reduction (GVR) method is an effective way.Purpose:This study aims to decrease the global variance of Monte Carlo radiation transport calculations for Chinese Fusion Engineering Testing Reactor (CFETR).Methods:According to different information of neutron distribution, six kinds of GVR methods were implied and compared in a cylinder CFETR neutronics model. Global figure of merit (FOMG), standard deviation (σ) and the percentage of scoring were analyzed. Based on predecessors' research, other kinds of new GVR methods (energy, tracks) were applied in this calculation.Results:In the point of GVR methods, FOMGincreased dramatically, spatial variation in relative errors was more gradual, and the scoring was higher, compared with AN. The GVR method based on neutron flux achieved the global calculation efficiency of 6.43 times that of AN. Apart from that, the GVR method based on neutron energy can also be a practical GVR kind, achieving the global calculation efficiency of 5.11 times that of AN.Conclusion:The GVR method based on neutron flux can performed best that has a well function of global variance reduction, achieving the global calculation efficiency.  
        关键词：Global variance reduction;Weight window;Monte Carlo;MCNP;Neutronics   
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        发布时间：2021-05-24
      • Li ZHANG,Huawei YU
        Vol. 39, Issue 3, Article number: 030502(2016) DOI: 10.11889/j.0253-3219.2016.hjs.39.030502
        摘要：Background:The controllable neutron source is used to replace the chemical gamma source to measure the formation density in oil exploration.Purpose:The effect of capture gamma counting on density is studied in the process of D-D source density measurement.Methods:Firstly, the principle of D-D source density measurement is analyzed, and the type of gamma-ray source in the process of D-D source and the formation is studied. In addition, the intensity of induced gamma between D-D and D-T source density measurement is compared using Monte Carlo simulation method.Results &amp; Conclusion:The capture gamma takes a large proportion on D-D induced gamma density measurement. Although neutron yield of D-D source is far lower than that of D-T source, the capture gamma counting of D-D source is higher than inelastic gamma counting of D-T source with the distance from the source more than 50 cm in the low porosity formation. In addition, the capture gamma counting can be obtained by adjusting the source size to meet the requirements of density measurement in high porosity formation. Therefore, the counting of D-D induced gamma can meet the statistical accuracy of the density measurement.  
        关键词：D-D source;Capture gamma;Density measurement;Monte Carlo simulation   
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        发布时间：2021-05-24
      • Minchao WANG,Xin LI,Xiufeng WENG,Xiaopeng ZHANG,Weiguo XIAO,Xufeng SHEN,Jiajia CUI
        Vol. 39, Issue 3, Article number: 030503(2016) DOI: 10.11889/j.0253-3219.2016.hjs.39.030503
        摘要：Background:In order to obtain high quality pulsed electron beam for large physical experimental facilities, it usually has higher requirement of the vibration of the foundation. Detailed geological vibration analysis is an important premise for the location of the experimental facilities.Purpose:Spectrum estimation method was applied to evaluate whether the location is reasonable through the actual vibration measurement for exploration area of different positions, different time-windows and different components.Methods:Firstly, the theories of traditional spectrum estimation were introduced. Then vibrations at different exploration positions, different time-windows, frequency bands and directions were analyzed according to the above methods, and amplitude spectrum and power spectrum of exploration area were given.Results & Conclusion:The data show that amplitude spectrum displacement of vertical component is 185 nm for exploration area which is 60 nm smaller than plane component, and give probability distribution of above result, providing the necessary basis for the mitigation measures to be taken in the process of further construction.  
        关键词：Large physical experimental facilities;Ground vibration;Spectrum estimation;Displacement spectrum;Amplitude spectrum   
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        发布时间：2021-05-24
      • Jianyu ZHU,Xuefeng XU,Jiahang SU,Wenxiong XIE
        Vol. 39, Issue 3, Article number: 030601(2016) DOI: 10.11889/j.0253-3219.2016.hjs.39.030601
        摘要：Background:Anti-neutrino detection, a promising tool for nuclear reactor monitoring by International Atomic Energy Agency (IAEA), is tested by several experiments. The effectiveness and limitation of the method should be studied by numerical simulations.Purpose:The aim is to study the effectiveness and limitation of monitoring nuclear reactor by anti-neutrino detection.Methods:A code was developed to calculate the counting of anti-neutrino generated by nuclear reactor based on MCNP code. The anti-neutron counting was simulated and analyzed with various nuclear reactor operation modes.Results:The anti-neutrino counting was related to the burn-up and isotope abundances of the reactor.Conclusion:It is possible to provide useful evidence on reactor operation to detect the count of anti-neutrino emitted by the reactor.  
        关键词：Monte Carlo method;Fission-antineutrino;Reactor monitoring;Non-proliferation safeguard technology   
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        发布时间：2021-05-24
      • Yu CHEN,Chundong HU,Yongjian XU,Ling YU,Xiang LI,Weitang ZHANG
        Vol. 39, Issue 3, Article number: 030602(2016) DOI: 10.11889/j.0253-3219.2016.hjs.39.030602
        摘要：Background:Water flow calorimetry is often used to measure the beam power of high intensity ion beam. There are some inevitable errors in water flow calorimetry system of Experimental Advanced Superconducting Tokamak (EAST) neutral beam injector, due to the position of the measuring instrument and acquisition time.Purpose:This study aims to correct these errors.Methods:This paper analyzes the factors inducing errors of the water flow calorimetry system, and then carries out quantitative calculation method for main error factors, and finally embeds the result into an existing data processing system.Results:Take the shot 58003 as an example, the deposition power is changed from 73.72% to 86.27% before and after correction.Conclusion:The accurate results lay a basis for the exact calculation of beam power deposition distribution and neutralization efficiency.  
        关键词：Neutral beam injector;Water flow calorimetry;Error correction   
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        发布时间：2021-05-24
      • Jianyu ZHU,Xuefeng XU,Jiahang SU,Wenxiong XIE
        Vol. 39, Issue 3, Article number: 030603(2016) DOI: 10.11889/j.0253-3219.2016.hjs.39.030603
        摘要：Background:Pebble Bed Reactor (PBR), most often used in Generation IV high-temperature gas-cooled nuclear reactor, employs pebble-shaped fuel elements. As pebbles flow through the reactor, they will slide and rotate against each other and the wall, causing generation of graphite dust.Purpose:This study aims to investigate the rotation angles and angular velocities of pebble-shaped fuel elements (PSFE).Methods:The rotation angle and angular velocity were studied by using a simulated transparent cylinder to replace the reactor core. A pebble-shaped detection system is employed to test the angular velocities and accumulated rotation angles of PSFEs with wireless interface. The generation of graphite particles by rotational abrasion was also studied.Results:The experimental results show that the initial seeding position has influence on rotation angles and angular velocities. The distribution of rotation angles and angular velocities from the center to the wall can be described as an inverted V-type distribution. The calculation results show that wear mass by rotation accounts for 11%-27% of the total graphite dust.Conclusion:Sliding abrasion is stronger than rotation abrasion in general, graphite generation tends to be overestimated if we only take sliding abrasion into consideration and ignore rotation abrasion.  
        关键词：Pebble-shaped fuel element;Rotation angles;Angular velocity;Rotation abrasion;Pebble-shaped detector system   
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        发布时间：2021-05-24
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