最新刊期
卷 41 ， 期 12 ， 2018
- 摘要：BackgroundThe beam stability is very important to each beamline at synchrotron radiation facility, it is the premise for users to obtain high-quality experimental data. PurposeThis study aims to test the beam stability of BL16B1 at Shanghai synchrotron radiation facility (SSRF) by the beam position monitor (BPM) which is used to detect the beam center position and intensity. MethodsThe IC-500-50 position sensitive ionization chamber is installed near the sample stage, the real-time current is measured by the TetrAMM 4-channel fast interface bipolar picoammeter made by CAENels company. The position sensitivity and linearity of IC-500-50 and the beam stability of BL16B1 are measured by changing the relative position of the ionization chamber and the incident beam. ResultsThe results show that the standard deviation of the center beam position of the beam along the vertical direction is 0.8%, and the standard deviation of the light intensity is 0.44%. ConclusionThe analysis shows that the instability within 1% meets the design requirements of beam stability (within 10%).关键词：Synchrotron radiation;Small angle X-ray scattering;Beam stabilization;Position sensitive ionization chamber;Experimental physics and industrial control system
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发布时间：2021-05-19 - 摘要：BackgroundRecent researches focusing on seeking excellent ionic permeability and selectivity in a nanoscale or even sub-nanometer scale have made great progress. Notably, we have established a new technique to fabricate uniform-sized nanopores in polyethylene terephthalate (PET) films, which shows great performance in ion transport. PurposeThis study aims to apply small angle X-ray scattering (SAXS) measurement to investigate the track structures in different fabrication stages. MethodsNonporous membranes were fabricated by irradiating PET films with 9.5 MeV·u-1 Bi in the range of 5×109 cm-2 to 5×1011 cm-2 followed by UV treatment and adequate infiltration. Structures of fabricated samples were measured at SAXS beamline of Shanghai Synchrotron Radiation Facility (SSRF) to obtain scattering spectra. Modified hard cylinder model and core shell model were employed to fit and analyze scattering spectra of samples in and after all fabrication procedures. ResultsThe fitting results showed that the nanopore in the final fabrication stage has a fine structure of 0.5~0.6 nm and a shell of 7~8 nm in radius. ConclusionThe SAXS techniques can be used to obtain the structure information of polymeric sub-nanometer pores.关键词：SAXS;Nanopores;Ion irradiation;PET
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发布时间：2021-05-19
SYNCHROTRON RADIATION TECHNOLOGY AND APPLICATIONS
- 摘要：BackgroundCO oxidation is a very important prototypical reaction in heterogeneous process. The reaction mechanism of Pt-group metals under ultrahigh vacuum (UHV) conditions was studied in detail, and unambiguous evidence of Langmuir-Hinshelwood kinetics was found. However, the reaction mechanism of the Pt(110) surface under high pressure conditions was still controversial. PurposeThis study aims to clarify the reaction mechanism and active sites of CO oxidation on Pt(110). MethodsThe oxidation of CO on Pt(110) surface was studied under total pressures up to 100 Pa in different CO:O2 reaction mixtures. Surface species and composition of products were analyzed in situ by ambient pressure X-ray photoelectron spectroscopy (APXPS) and online gas analysis by mass spectra (MS). ResultsThe process of CO oxidation on Pt(110) fell into three regimes:1) low active regime with CO poisoned Pt(110) surface and low CO2 formation rate; 2) highly active regime with ignition reaction on Pt(110) surface companied by a large amount of heat release; 3) mass transfer rate limited regime, excessive O-rich Pt(110) surface, the CO2 formation rate controlled by CO diffusion rate. ConclusionThe active sites of CO oxidation reaction on Pt(110) surface are metallic Pt.关键词：CO oxidation;Pt(110) surface;Catalysis;APXPS;Mass spectra
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发布时间：2021-05-19 - 摘要：BackgroundThe inversion of gamma spectrum by maximum likelihood method can effectively improve the energy resolution of gamma spectrum. PurposeThis study aims to observe the ability of maximum likelihood method to retrieve the central channel of γ characteristic peaks. MethodsMonte Carlo simulation program MCNP (Monte Carlo N Particle Transport Code) was used to calculate the energy response matrix of a 10.16 cm×10.16 cm×40.64 cm NaI(Tl) detector. Energy response matrix, the simulated spectra contained 10 different peaks, and the 152Eu γ spectra obtained by the experiment were retrieved. Results & ConclusionsThe results showed that the maximum deviation of the peak center channel between the retrieved spectra and the simulated spectra was 1 channel, deviation between the retrieved spectrum and 152Eu γ spectrum measured in the lead shielding room was less than 2 channels, the deviation between the retrieved spectrum and 152Eu γ spectrum measured in the laboratory's natural environment was less than 4 channels.关键词：Maximum likelihood method;γ spectra;Deconvolution;Central of peak
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发布时间：2021-05-19
NUCLEAR PHYSICS, INTERDISCIPLINARY RESEARCH
- 摘要：BackgroundAtmospheric particulate pollution is one of topic issues for urban air pollution control and environmental improvement. PurposeThis study aims to investigate the pollution characteristics especially the elements characteristics and identify the main emission sources of fine particulate matter PM2.5 at Xinzhen area of Beijing. MethodsProton induced X-ray emission (PIXE) was used to analyze 140 atmospheric particulate matter samples. Positive matrix factorization model was used to analyze the source apportionment. ResultsThe concentrations of particulate matter for 16 elements of Mg, Al, Si, S, Cl, K, Ca, Sc, Ti, Mn, Fe, Ni, Cu, Zn, As, Pb were measured. S, Cl, Cu, Zn and Pb account for a large proportion in fine particulate matter and are highly correlated. Mg, Al, Si, Ca, Ti and Fe mainly exist in coarse particulate matter and have strong correlation with each other. Concentrations of S, Cl, K, Black carbon (BC) in fine particles and Si, Ca, Fe in coarse particles increased significantly during pollution weather period. Through positive matrix factor analysis, the six major pollution sources in this area were founded:secondary sulfur (34.70%), construction industry (24.39%), chlorine industry (13.05%), soil dust (12.81%), transportation emissions (11.63%) and other pollution (3.42%). ConclusionThe mass concentration and pollution elements' characteristics of particulate matter pollution in Xinzhen area were obtained, and six types of pollution sources and their contribution rates were analyzed.关键词：PIXE;Atmospheric particulate matter;Atmospheric elements;Source analysis;Positive matrix factor analysis
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发布时间：2021-05-19 - 摘要：BackgroundBandwidth-limited neutron chopper (BWL choppers) is one of the indispensable key equipments in the time-of-flight neutron scatter of China spallation neutron source (CSNS), which decide the neutron energy spectrum obtained by detectors. The main principle is to chop the neutron beam to limit the neutron wavelength bandwidth at the neutron detector, so as to reduce the background and improve the signal-to-noise ratio. PurposeThis study aims to design BWL chopper system reasonably and reduce faults. MethodsThe basis principle of BWL chopper was reviewed, Design method, basis configuration principle of BWL chopper and system layout were put forward. The formulas for calculating the physical parameters of BWL chopper were given. ResultsThe configuration numbers of bandwidth chopper should meet the requirement of neutron scatter. The background removing chopper should be inserted in the front end of the beam line so that the neutrons in the required band of the spectrometer could pass through without loss, while the bandwidth selecting chopper should be placed at the back end as far as possible. In addition, the flux can be increased by double disk chopper that satisfies same phase, same speed, same slit angle but counter-rotating. ConclusionThe work can guide the physical design of twenty neutron instruments of CSNS.关键词：Neutron chopper;Bandwidth limiting chopper system;Bandwidth limiting;Disk
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发布时间：2021-05-19
LOW ENERGY ACCELERATOR, RAY AND APPLICATIONS
- 摘要：BackgroundNeutron ambient dose equivalent is closely related to neutron energy. Acquisition of the energy spectrum is necessary to calculate the ambient dose equivalent accurately in the neutron radiation field. PurposeThis study aims at the ambient dose equivalent calculation by shakedown test of multi sphere neutron spectrometer (MNS). MethodsFirst of all, pulse height analysis (PHA) method was used for neutron/γ discrimination to precisely measure neutron count rate. Then the neutron energy spectrum was successfully obtained and carefully analyzed in three neutron radiation fields:laboratory background, Am-Be neutron source and DD tube emergency neutron. Neutron fluence was converted into ambient dose equivalent consulting the conversion coefficient recommended by International Commission on Radiological Protection (ICRP) report No.74, and dose contribution weight from neutron in different energy groups was analyzed. Finally, comparison test was made against three other instruments with mono moderator respectively, errors between MNS and them were analyzed theoretically. ResultsNeutron ambient dose equivalent converted from energy spectrum measured by MNS was consistent with the other three dose instruments. No matter what kind of the neutron radiation field is, fast neutrons are the main contributors to the dose. ConclusionPHA and pulse height spectrum monitoring is the critical point for neutron energy spectrum measurement. MNS can be used to measure and calculate neutron ambient dose equivalent directly, guide optimal reference radiation for other neutron dose instruments calibration, and radiation protection design against neutron of special energy groups.关键词：Multisphere neutron spectrometer;Neutron-γ discrimination;Neutron energy spectrum;Ambient dose equivalent;Radiation field measurement;Dose calibration
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发布时间：2021-05-19 - 摘要：BackgroundOne of the most attractive subjects in the astronomical observation is the γ-ray detection in space astronomy. Recent research shows that the spectrum and distribution of the high-energy γ-ray can be utilized to explore the dark matter's distribution and physical characteristics. Several detectors can be utilized to detect high energy γ-ray, and one of the most suitable candidates is the silicon strip detector which possesses very high position and energy resolution. Silicon strip detector can be used to accurately detect the traversing particle's track and energy, and can be easily assembled together to form a large detecting plane. PurposeThis study aims to explore key technologies of the silicon strip detector, including high-precision assembly techniques, front-end electronics design and data acquisition board design. MethodsFirst of all, a test system with a low leakage current was built to inspect the silicon strip sensor. Then, an automatic wire-bonder was employed to connect the wires of sensors and front-end electronics. The automatic bond-tester was used to test wires' firmness. Finally, a readout scheme based on the characteristics of the sensor was design, and the printed circuit board (PCB) layout of the front-end electronics was optimized. In order to design the data acquisition board, the logics in the key component field programmable gate array (FPGA) and the automatic data acquisition software in the host computer were implemented. ResultsA prototype silicon strip detector has been fabricated and tested. All 384 channels show a good linearity in the range of 0~180 fC and the non-linearity is less than 5%. The prototype's input equivalent noise is less than 0.16 fC. The cosmic ray test result shows a clear peak of the minimum ionizing particle of 2.8 fC and the spectrum matches the convoluted Landau and Gaussian fitting function. ConclusionThe well behaved prototype demonstrates the validity and feasibility of the key technologies, and these technologies can be applied to the practical silicon strip detector for space astronomy.关键词：Dark matter;γ-ray;Silicon strip detector
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发布时间：2021-05-19 - 摘要：BackgroundIt has become a new trend to use X-ray source instead of 137Cs source in density logging for development of oil logging. PurposeThis study aims to analyze the near detector-source spacing's change when using a lower energy X-ray source instead of 137Cs source in density logging. MethodsMonte Carlo simulation method is used to study the critical detector-source spacing of different energy X-ray sources during the formation of water saturated limestone with different porosity, in addition, the near detector-source spacing is analyzed according to those sensitivities of X-ray sources and 137Cs source. ResultsSimulation results show that low energy X-ray source's critical detector-source spacing is shorter compared with 137Cs source's density instrument. When the density sensitivity is the same, the near detector-source spacing of X-ray source is shorter than that of 137Cs source. ConclusionThis study provides a theoretical basis for the design of near detector-source spacing of instrument.关键词：X-ray source;Density logging;Monte Carlo method;Critical detector-source spacing;Density sensitivity;Near detector-source spacing
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发布时间：2021-05-19
NUCLEAR ELECTRONICS AND INSTRUMENTATION
- 摘要：BackgroundWhen the reactor core temperature changes, the reaction cross sections at different temperatures need to be generated with on-the-fly methods. Among the existing on-the-fly cross-section generation methods, the curve fitting method is becoming a common tool used in MCNP6, but the efficiency of this method is quite low. PurposeThis study aims to accurately simulate the interaction between neutrons and various materials at different temperatures in the reactor by developing an on-the-fly generation method of nuclear cross sections. MethodsIn order to overcome the low efficiency of Doppler broadening in the parameter fitting method of MCNP6, double exponential method and Gauss-Hermite method are combined to replace the original analytical integral method to increase the width of the cross section generate efficiency. ResultsThe typical nuclides test results showed that the curve fitting calculation efficiency of the numerical integration method is more than 10 times higher than the original one. Doppler reactivity coefficient benchmark example shows that the curve fitting of the numerical integration method is relative to the accuracy of the original method within 1.54%. ConclusionThis method can be used for multi-physics coupling calculation of reactors.关键词：Neutron cross section;Numerical integration;On-the-fly;Doppler broadening
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发布时间：2021-05-19 - 摘要：BackgroundTritium is one of emitted radioactive materials during the operation of nuclear facilities. Plants and soil are parts of the tritium ecological cycle. The distribution of tritium in plants and soil around nuclear facilities can be used to determine the short-term and long-term emissions of nuclear facilities. PurposeThis study aims to analyze activities of tissue free water tritium (TFWT) and OBT in grasses and surface soils around Qinshan nuclear power station, and obtain the influence of the tritium emissions from Qinshan nuclear power station on the environment. MethodsTritium activities of different forms (HTO, TFWT and OBT) in grasses and surface soils around the Qinshan nuclear power station were sampled in several sites around Qinshan nuclear power station and stored in strict conditions during two years period from 2015 to 2016. Liquid Scintillation Counting (LSC) was employed to measure the tritium activity three times for samples collected in the same site. ResultsIn the prevailing wind direction, the longer distance apart from the nuclear facility, the lower activities of TFWT in the grass and the tritiated water (HTO) in the surface soil. In the two-year grass samples' results, the total amount of OBT was in the same level and distribution of OBT was consistent. The OBT distribution in the surface soil was different from the HTO in the surface soil and the OBT in the grass. The ratio of OBT/HTO in the surface soil was significantly higher than the ratio in the grass, indicating that the source, formation, migration and transformation of OBT in the soil was different from those in the grass. ConclusionThe HTO activity in surface soil and TFWT activity in grassland can reflect the short-term tritium emissions from nuclear power plant. Meanwhile, the OBT activity in grassland can reflect the long-term tritium emissions from nuclear power plant.关键词：Grass;Surface soil;Tritiated water;TFWT;Distribution
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发布时间：2021-05-19 - 摘要：BackgroundDuring the oxidation operation of a reactor, the max active concentration of 58Co in the coolant and the time to the end of the oxidation operation (activity concentration < 25 GBq·t -1) are compulsory. The current chemical sampling method produces large amounts of radioactive waste liquid. PurposeThis study aims to reduce the current radioactive waste liquid by establishing an external γ spectrum monitoring system. MethodsThe HPGe γ measurement system is used to measure the γ spectrum of the coolant outside the pipeline. The net count rates of the 58Co characteristic peak varition with time were obtained after reactor shutdown. These data can be used to predict the time to reach the maximum active concentration of 58Co in the coolant and the time to reach the end of the oxidation operation, and then performed a sample analysis. ResultsDuring the oxidation operation of a nuclear power plant, this monitoring system was used to continuously measure the γ spectrum outside the pipeline. The time of the maximum activity concentration of 58Co was predicted to be 33 h and 39 min after shutdown, and the oxidation operation end time predicted to be 57 h after shutdown. By continuously coolant sampling data, the time of the maximum activity concentration of 58Co was 33 h and 34 min after shutdown, and the oxidation operation end time was 57 h and 9 min after shutdown. Two time errors are in normal range (less than 10 min). ConclusionsThe external monitoring method can reduce the sampling frequency significantly and reduce the amount of radioactive waste generated by sampling analysis.关键词：Oxidation operation;The activity concentration of 58Co;In situ gamma measurement;Chemical sampling
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发布时间：2021-05-19
NUCLEAR ENERGY SCIENCE AND ENGINEERING
- 摘要：BackgroundRecycling the chloride salt from the fission product fluoride and chloride salt mixture is important to the research and development of electrolytic separation technology for actinides and fission products fluoride. Low pressure distillation is a powerful technique, but the experimental data on the distillation behaviors of fluoride doped chloride salts are limited. PurposeThis study aims at the experimental results which provide a basic understanding on the behaviors of fluoride doped molten chlorides during low pressure distillation. MethodsThe distillation behaviors of various fluoride doped molten chlorides at 1050 K and 130 Pa were studied in a pipe furnace. Salt vapor was condensed and collected on stainless steel foil 5 cm away from the crucible. ResultsWith the increase of evaporation ratio, the decontamination coefficient of Ce decreases at 1050 K and 130 Pa in the salt collected by 5% CeF3-LiCl-KCl low pressure distillation. For the LiCl-KCl salts containing CeF3, NdF3, LaF3 and SrF2 respectively, the corresponding decontamination factors of the collected salts are on the order of 103 at the evaporation ratio of 95%. The decontamination factor of EuF3-LiCl-KCl system is very low, which may due to the presence of more volatile EuF2 at 1050 K, while the high vapor pressure of ZrF4is responsible for the low decontamination factor of zirconium in the case of ZrF4-LiCl-KCl. ConclusionThe distillation behaviors of LiCl-KCl are affected by the nature of fission product fluorides as well as the evaporation ratio of the salt mixtures. The collected chloride salt mixture from low pressure distillation of CeF3-LiCl-KCl has a similar composition with the LiCl-KCl eutectic, and the content of fluoride is low enough.关键词：Low pressure distillation;LiCl-KCl;Fluoride;Fission product;Decontamination factor
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发布时间：2021-05-19
NUCLEAR CHEMISTRY, RADIOCHEMISTRY, RADIOPHARMACEUTICALS AND NUCLEAR MEDICINE
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