The dynamic behaviors of water contained in calcium-silicate-hydrate（C-S-H） gel with different water content values from 10%to 30%（by weight）,are studied by using an empirical diffusion model（EDM） to analyze the...The dynamic behaviors of water contained in calcium-silicate-hydrate（C-S-H） gel with different water content values from 10%to 30%（by weight）,are studied by using an empirical diffusion model（EDM） to analyze the experimental data of quasi-elastic neutron scattering（QENS） spectra at measured temperatures ranging from 230 K to 280 K.In the study,the experimental QENS spectra with the whole Q-range are considered.Several important parameters including the bound/immobile water elastic coefficient A,the bound water index BWI,the Lorentzian with a half-width at half-maximum（HWHM） Γ;（Q） and Γ;（Q）,the self-diffusion coefficients D;and D;of water molecules,the average residence times τ;and τ;,and the proton mean squared displacement（MSD）(u;) are obtained.The results show that the QENS spectra can be fitted very well not only for small Q（≤1 A;） but also for large Q.The bound/immobile water fraction in a C-S-H gel sample can be shown by the fitted BWI.The distinction between bound/immobile and mobile water,which includes confined water and ultra-confined water,can be seen by the fitted MSD.All the MSD tend to be the smallest value below 0.25 A;（the MSD of bound/immobile water） as the Q increases to 1.9 A;no matter what the temperature and water content are.Furthermore,by the abrupt changes of the fitted values of D;,τ;,and Γ;（Q）,a crossover temperature at 250 K,namely the liquid-to-crystal-like transition temperature,can be identified for confined water in large gel pores（LGPs） and/or small gel pores（SGPs） contained in the C-S-H gel sample with 30% water content.展开更多
A 9 Cr-oxide dispersion strengthened(ODS)steel was thermally aged at 873 K for up to 5000 h.The size distribution and chemical composition of the dispersed oxide nanoparticles were analyzed by small-angle neutron scat...A 9 Cr-oxide dispersion strengthened(ODS)steel was thermally aged at 873 K for up to 5000 h.The size distribution and chemical composition of the dispersed oxide nanoparticles were analyzed by small-angle neutron scattering under a magnetic field.Combined with transmission electron microscopy,Vickers micro-hardness tests and electron backscattered diffraction measurements,all the results showed that the thermal treatment had little or no effect on the size distributions and volume fractions of the oxide nanoparticles in the ferromagnetic matrix,which suggested excellent thermal stability of the 9 Cr-ODS steel.展开更多
An innovative monochromator shielding is designed and implemented for the cold neutron spectrometers XINGZHI and BOYA operated by Renmin University of China at China Advanced Research Reactor.Via Monte Carlo simulatio...An innovative monochromator shielding is designed and implemented for the cold neutron spectrometers XINGZHI and BOYA operated by Renmin University of China at China Advanced Research Reactor.Via Monte Carlo simulations and careful mechanical designs,a shielding configuration has been successfully developed to satisfy safety requirements of below 3μSv/h dose rate at its exterior,meanwhile fulfilling space,floor load and nonmagnetic requirements.Composite materials are utilized to form the sandwich-type shielding walls:the inner layer of boron carbide rubber,the middle layer of steel-encased lead and the outer layer of borated polyethylene.Special-shaped liftable shielding blocks are incorporated to facilitate a continuous adjustment of the neutron energy while preventing radiation leakage.Our work has demonstrated that by utilizing composite shielding materials,along with the sandwich structure and liftable shielding blocks,a compact and lightweight shielding solution can be achieved.This enables the realization of advanced neutron scattering instruments that provide expanded space of measurement,larger energy and momentum coverage,and higher flux on the sample.This shielding represents the first of its kind in neutron scattering instruments in China.Following its successful operation,it has been subsequently employed by other neutron instruments across the country.展开更多
During the past decades,Li-ion batteries have been one of the most important energy storage devices.Large-scale energy storage requires Li-ion batteries which possess high energy density,low cost,and high safety.Other...During the past decades,Li-ion batteries have been one of the most important energy storage devices.Large-scale energy storage requires Li-ion batteries which possess high energy density,low cost,and high safety.Other than advanced battery materials,in-depth understanding of the intrinsic mechanism correlated with cell reaction is also essential for the development of high-performance Li-ion battery.Advanced characterization techniques,especially neutron-based techniques,have greatly promoted Li-ion battery researches.In this review,the characteristics or capabilities of various neutron-based characterization techniques,including elastic neutron scattering,quasi-elastic neutron scattering,neutron imaging,and inelastic neutron scattering,for the related Li-ion-battery researches are summarized.The design of in-situ/operando environment is also discussed.The comprehensive survey on neutron-based characterizations for mechanism understanding will provide guidance for the further study of high-performance Li-ion batteries.展开更多
Amorphous materials are ubiquitous and widely used in human society, yet their structures are far from being fully understood. Metallic glasses, a new class of amorphous materials, have attracted a great deal of inter...Amorphous materials are ubiquitous and widely used in human society, yet their structures are far from being fully understood. Metallic glasses, a new class of amorphous materials, have attracted a great deal of interests due to their exceptional properties. In recent years, our understanding of metallic glasses increases dramatically, thanks to the development of advanced instrumentation, such as in situ x-ray and neutron scattering. In this article, we provide a brief review of recent progress in study of the structure of metallic glasses. In particular, we will emphasize, from the scattering perspective, the multiscale structures of metallic glasses, i.e., short-to-medium range atomic packing, and phase transitions in the supercooled liquid region, e.g., crystallization and liquid-to-liquid phase transition. We will also discuss, based on the understanding of their structures and phase stability, the mechanical and magnetic properties of metallic glasses.展开更多
A method is proposed to characterize the fast neutron scattering cross-section ( s f) quantitatively by the combina-tion of inelastic gamma rays and captured gamma rays, so as to realize the gas saturation evaluation ...A method is proposed to characterize the fast neutron scattering cross-section ( s f) quantitatively by the combina-tion of inelastic gamma rays and captured gamma rays, so as to realize the gas saturation evaluation of CO_(2)-injected heavy oilreservoirs based on the three-de tector pulsed neutron logging technology. Factors influencing of the evaluation effect of thismethod are analyzed and the effectiveness of this method is verified by a simulation example. By using the Monte Carlo simu-lation method and the physical model of bulk-volume rock, the relationship between s f and CO_(2) saturation is studied, and thesaturation interpretation model is established. The influences of formation temperature and pressure, heavy oil density, bore-hole fluid and reservoir methane content on the evaluation results of CO_(2) saturation are analyzed. The results show that thecharacterization of s f by the combination of secondary gamma information can eliminate the influence of formation lithology,borehole fluid and methane content are the main factors affecting the quantitative monitoring of CO_(2) saturation, and the ef-fects of formation temperature and pressure and heavy oil density are negligible. The simulation example verified the feasibilityof the method for evaluating the CO_(2) saturation of CO_(2)-injected heavy oil reservoirs.展开更多
The small-angle neutron scattering(SANS)instrument,one of the first three instruments of the China Spallation Neutron Source(CSNS),is designed to probe the microscopic and mesoscopic structures of materials in the sca...The small-angle neutron scattering(SANS)instrument,one of the first three instruments of the China Spallation Neutron Source(CSNS),is designed to probe the microscopic and mesoscopic structures of materials in the scale range 1–100 nm.A large-area ^(3)He tube array detector has been constructed and operates at the CSNS SANS instrument since August 2018.It consists of 120 linear position-sensitive detector tubes,each 1 m in length and 8 mm in diameter,and filled with ^(3)He gas at 20 bar to obtain a high detection efficiency.The ^(3)He tubes were divided into ten modules,providing an overall area of 1000 mm×1020 mm with a high count rate capability.Because each tube is installed independently,the detector can be quickly repaired in situ by replacing damaged tubes.To reduce air scattering,the SANS detector must operate in a vacuum environment(0.1 mbar).An all-metal sealing technique was adopted to avoid high-voltage breakdown by ensuring a high-voltage connection and an electronic system working in an atmospheric environment.A position resolution of 7.8±0.1 mm(full width at maximum)is measured along the length of the tubes,with a high detection efficiency of 81±2% at 2A.Operating over the past four years,the detector appears to perform well and with a high stability,which supports the SANS instrument to finish approximately 200 user scientific programs.展开更多
Despite the apparent ubiquity and variety of quantum spin liquids in theory,experimental confirmation of spin liquids remains to be a huge challenge.Motivated by the recent surge of evidences for spin liquids in a ser...Despite the apparent ubiquity and variety of quantum spin liquids in theory,experimental confirmation of spin liquids remains to be a huge challenge.Motivated by the recent surge of evidences for spin liquids in a series of candidate materials,we highlight the experimental schemes,involving the thermal Hall transport and spectrum measurements,that can result in smoking-gun signatures of spin liquids beyond the usual ones.For clarity,we investigate the square lattice spin liquids and theoretically predict the possible phenomena that may emerge in the corresponding spin liquids candidates.The mechanisms for these signatures can be traced back to either the intrinsic characters of spin liquids or the external field-driven behaviors.Our conclusion does not depend on the geometry of lattices and can broadly apply to other relevant spin liquids.展开更多
We report the physical properties, crystalline and magnetic structures of singe crystals of a new layered antiferromagnetic(AFM) material PrPd0.82Bi2. The measurements of magnetic properties and heat capacity indicate...We report the physical properties, crystalline and magnetic structures of singe crystals of a new layered antiferromagnetic(AFM) material PrPd0.82Bi2. The measurements of magnetic properties and heat capacity indicate an AFM phase transition at TN^7K. A large Sommerfeld coefficient of 329.23 m J·mol-1·K-2 is estimated based on the heat capacity data, implying a possible heavy-fermion behavior. The magnetic structure of this compound is investigated by a combined study of neutron powder and single-crystal diffraction. It is found that an A-type AFM structure with magnetic propagation wavevector k =(0 0 0) is formed below TN. The Pr3+ magnetic moment is aligned along the crystallographic c-axis with an ordered moment of 1.694(3) μBat 4K, which is smaller than the effective moment of the free Pr3+ ion of 3.58 μB.PrPd0.82Bi2 can be grown as large as 1 mm×1 cm in area with a layered shape, and is very easy to be cleaved, providing a unique opportunity to study the interplay between magnetism, possible heavy fermions, and superconductivity.展开更多
Inelastic incoherent neutron scattering spectra of D2O high-density amorphous （hda） ice, ice-Ⅷ and ice-Ⅱ mixed with small amount of H2O （（5%） have been measured recently on high-energy transfer spectrometer at ...Inelastic incoherent neutron scattering spectra of D2O high-density amorphous （hda） ice, ice-Ⅷ and ice-Ⅱ mixed with small amount of H2O （（5%） have been measured recently on high-energy transfer spectrometer at Rutherford Appleton Laboratory （UK）. The hydrogen atom on D2O ice lattices has three distinguished vibrational modes, two bending at low frequencies and one stretching at high frequencies, and their frequencies are slightly different for different phases of ice. It was found that the lower one of the bending modes is located at -95 meⅤ for hda-ice, at -95 meⅤ for ice-Ⅷ and at -96 meⅤ for ice-Ⅱ and they are all lower than the value of 104 meⅤ for ice-Ih. It was also measured that the O-D and O-H covalent bond stretching modes of ice-Ⅷ are at -315 and -425 meⅤ, ice-Ⅱ at 307 and -415 meⅤ, hda-ice at 312 and -418 meⅤ, respectively. They are significantly higher than the values of ice-Ih at -299 and -406 meⅤ, respectively.展开更多
When one wants to simply estimate tritium breeding ratio （TBR）, the TBR may be reduced from a ＂local＂ TBR for the breeding zones of a blanket module by multiplying the breeder coverage （= the surface area of effe...When one wants to simply estimate tritium breeding ratio （TBR）, the TBR may be reduced from a ＂local＂ TBR for the breeding zones of a blanket module by multiplying the breeder coverage （= the surface area of effective breeding region / the surface area of the first wall around plasma）. When blanket modules are arranged~ the gap between neighboring modules and the frames of the modules are regarded as nombreeding zones. On the other hand, neutrons scattered in the non-breeding zones can enter breeding zones, contributing to tritium production. This means that the estimation method mentioned above tends to underestimate TBR. In order to assess the scattering effect quantitatively, we carried out a three-dimensional Monte Carlo N-particle transport MCNP-5 calculation. It was found from the calculation that there is little decrease in TBR for gaps less than 4 cm when the blanket thickness is 70 cm. The result indicates that such a wide allowance of the gap will facilitate access of remote handling equipment for the replacement of blanket modules and improve access of diagnostics.展开更多
In this paper, we present a computational study of L-serine using ab initio molecular dynamics simulation based on density functional theory （DFT） within the ultrasoft pseudopotentials and generalized-gradient appro...In this paper, we present a computational study of L-serine using ab initio molecular dynamics simulation based on density functional theory （DFT） within the ultrasoft pseudopotentials and generalized-gradient approximation. Taking into account the intermolecular interactions, we can indeed simulate the features of the experimental results very well for L-serine zwitterions in its solid state. The vibrational spectrum of L-serine performed by DFT was in excellent agreement with our previous inelastic incoherent neutron scattering spectra measured at 20K for L-serine in the 10-200meV region on HET spectrometers at ISIS, Rutherford Appleton Laboratory.展开更多
The iron-chalcogenide superconductor FeTe_(1-x)Se_(x) displays a variety of exotic features distinct from iron pnictides.Although much effort has been devoted to understanding the interplay between magnetism and super...The iron-chalcogenide superconductor FeTe_(1-x)Se_(x) displays a variety of exotic features distinct from iron pnictides.Although much effort has been devoted to understanding the interplay between magnetism and superconductivity near x=0.5,the existence of a spin glass phase with short-range magnetic order in the doping range(x~0.1-0.3)has rarely been studied.Here,we use DC/AC magnetization and(quasi)elastic neutron scattering to confirm the spin-glass nature of the short-range magnetic order in a Fe_(1.07)Te_(0.8)Se_(0.2) sample.The AC-frequency dependent spin-freezing temperature T_(f) generates a frequency sensitivityΔT_(f)(ω)/[T_(f)(ω)Δlog_(10)ω]≈0.028 and the description of the critical slowing down withτ=τ0(T_(f)/T_(SG-1))^(-zv) gives T_(SG)≈22 K and zv≈10,comparable to that of a classical spin-glass system.We have also extended the frequency-dependent T_(f) to the smaller time scale using energy-resolution-dependent neutron diffraction measurements,in which the T_(N) of the short-range magnetic order increases systematically with increasing energy resolution.By removing the excess iron through annealing in oxygen,the spin-freezing behavior disappears,and bulk superconductivity is realized.Thus,the excess Fe is the driving force for the formation of the spin-glass phase detrimental to bulk superconductivity.展开更多
Phosphotungstic acid is an excellent proton conductor that can be incorporated into porous supports, and nanocomposite proton exchange membrane materials made from mesoporous silica impregnated with phosphotungstic ac...Phosphotungstic acid is an excellent proton conductor that can be incorporated into porous supports, and nanocomposite proton exchange membrane materials made from mesoporous silica impregnated with phosphotungstic acid have been suggested for use in fuels cells operating> 100 ℃. In this work, quasielastic neutron scattering was used to study proton self-diffusion in mesoporous disordered and P6 mm symmetry silica impregnated with two concentrations of phosphotungstic acid. Overall, the silica structure had a significantly greater effect on proton conduction and diffusion than phosphotungstic acid concentration, with higher proton conduction occurring for the P6 mm symmetry silica samples. Quasielastic neutron scattering revealed two populations of protons diffusing through each sample, and that proton conduction is limited by the slower of these populations, which diffuse via a jump-diffusion mechanism. Whilst the fundamental jump-diffusion mechanism by which these slower protons moved was found to be similar for both silica supports and phosphotungstic acid concentrations, the faster diffusion occurring in P6 mm structured silica arises from a lower residence time of protons moving between sites in the jump-diffusion model, suggesting a lower energy barrier.展开更多
Quantum spin liquids（QSLs） represent a novel state of matter in which quantum fluctuations prevent the conventional magnetic order from being established, and the spins remain disordered even at zero temperature. Th...Quantum spin liquids（QSLs） represent a novel state of matter in which quantum fluctuations prevent the conventional magnetic order from being established, and the spins remain disordered even at zero temperature. There have been many theoretical developments proposing various QSL states. On the other hand, experimental movement was relatively slow largely due to limitations on the candidate materials and difficulties in the measurements. In recent years, the experimental progress has been accelerated. In this topical review, we give a brief summary of experiments on the QSL candidates under magnetic fields. We arrange our discussions by two categories： i） Geometrically-frustrated systems, including triangularlattice compounds YbMgGaO4 and YbZnGaO4, κ-（BEDT-TTF）2 Cu2（CN）3, and EtMe3 Sb[Pd（dmit）2]2, and the kagom′e system ZnCu3（OH）6 Cl2; ii） the Kitaev material α-RuCl3. Among these, we will pay special attention to α-RuCl3, which has been intensively studied by ours and other groups recently. We will present evidence that both supports and rejects the QSL ground state for these materials, based on which we give several perspectives to stimulate further research activities.展开更多
INS （Inelastic Neutron Scattering） spectrum of methane hydrate was measured on MARI （a direct-geometry chopper spectrometer） at Ruther-ford Appleton Laboratory, UK. Compared with ice Ih, it is found that the whole...INS （Inelastic Neutron Scattering） spectrum of methane hydrate was measured on MARI （a direct-geometry chopper spectrometer） at Ruther-ford Appleton Laboratory, UK. Compared with ice Ih, it is found that the whole spectrum of methane hydrate moves toward high-energy by about 1.5 meV. Using lattice dynamical （LD） technique, computer simulations of methane hydrate were carried out. In the simulations, four potential models （BE TIP3P, TIP4P, MCY） were employed to calculate the phonon density of states （PDOS）. Comparing the calculated PDOS spectrum with the experimental spectrum, it is found that BF, TIP4P, and TIP3P potential lattices give out well-separated translational and librational bands while MCY potential lattice is unstable to do so and this model is not suitable to describe hydrate system.展开更多
文摘The dynamic behaviors of water contained in calcium-silicate-hydrate（C-S-H） gel with different water content values from 10%to 30%（by weight）,are studied by using an empirical diffusion model（EDM） to analyze the experimental data of quasi-elastic neutron scattering（QENS） spectra at measured temperatures ranging from 230 K to 280 K.In the study,the experimental QENS spectra with the whole Q-range are considered.Several important parameters including the bound/immobile water elastic coefficient A,the bound water index BWI,the Lorentzian with a half-width at half-maximum（HWHM） Γ;（Q） and Γ;（Q）,the self-diffusion coefficients D;and D;of water molecules,the average residence times τ;and τ;,and the proton mean squared displacement（MSD）(u;) are obtained.The results show that the QENS spectra can be fitted very well not only for small Q（≤1 A;） but also for large Q.The bound/immobile water fraction in a C-S-H gel sample can be shown by the fitted BWI.The distinction between bound/immobile and mobile water,which includes confined water and ultra-confined water,can be seen by the fitted MSD.All the MSD tend to be the smallest value below 0.25 A;（the MSD of bound/immobile water） as the Q increases to 1.9 A;no matter what the temperature and water content are.Furthermore,by the abrupt changes of the fitted values of D;,τ;,and Γ;（Q）,a crossover temperature at 250 K,namely the liquid-to-crystal-like transition temperature,can be identified for confined water in large gel pores（LGPs） and/or small gel pores（SGPs） contained in the C-S-H gel sample with 30% water content.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFB0702400)。
文摘A 9 Cr-oxide dispersion strengthened(ODS)steel was thermally aged at 873 K for up to 5000 h.The size distribution and chemical composition of the dispersed oxide nanoparticles were analyzed by small-angle neutron scattering under a magnetic field.Combined with transmission electron microscopy,Vickers micro-hardness tests and electron backscattered diffraction measurements,all the results showed that the thermal treatment had little or no effect on the size distributions and volume fractions of the oxide nanoparticles in the ferromagnetic matrix,which suggested excellent thermal stability of the 9 Cr-ODS steel.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12004426,U2030106,and 12304185)the National Key Scientific Instrument and Equipment Development Project of NSFC(Grant No.11227906)the National Key R&D Program of China(Grant No.2023YFA1406500)。
文摘An innovative monochromator shielding is designed and implemented for the cold neutron spectrometers XINGZHI and BOYA operated by Renmin University of China at China Advanced Research Reactor.Via Monte Carlo simulations and careful mechanical designs,a shielding configuration has been successfully developed to satisfy safety requirements of below 3μSv/h dose rate at its exterior,meanwhile fulfilling space,floor load and nonmagnetic requirements.Composite materials are utilized to form the sandwich-type shielding walls:the inner layer of boron carbide rubber,the middle layer of steel-encased lead and the outer layer of borated polyethylene.Special-shaped liftable shielding blocks are incorporated to facilitate a continuous adjustment of the neutron energy while preventing radiation leakage.Our work has demonstrated that by utilizing composite shielding materials,along with the sandwich structure and liftable shielding blocks,a compact and lightweight shielding solution can be achieved.This enables the realization of advanced neutron scattering instruments that provide expanded space of measurement,larger energy and momentum coverage,and higher flux on the sample.This shielding represents the first of its kind in neutron scattering instruments in China.Following its successful operation,it has been subsequently employed by other neutron instruments across the country.
基金Project supported by the National Key R&D Program of China(Grant No.2016YFA0401503)the National Materials Genome Project of China(Grant No.2016YFB0100106)the National Natural Science Foundation of China(Grant No.11675255)
文摘During the past decades,Li-ion batteries have been one of the most important energy storage devices.Large-scale energy storage requires Li-ion batteries which possess high energy density,low cost,and high safety.Other than advanced battery materials,in-depth understanding of the intrinsic mechanism correlated with cell reaction is also essential for the development of high-performance Li-ion battery.Advanced characterization techniques,especially neutron-based techniques,have greatly promoted Li-ion battery researches.In this review,the characteristics or capabilities of various neutron-based characterization techniques,including elastic neutron scattering,quasi-elastic neutron scattering,neutron imaging,and inelastic neutron scattering,for the related Li-ion-battery researches are summarized.The design of in-situ/operando environment is also discussed.The comprehensive survey on neutron-based characterizations for mechanism understanding will provide guidance for the further study of high-performance Li-ion batteries.
基金supported by Shenzhen Science and Technology Innovation Commission of China(Grant No.R-IND8701)the Croucher Foundation(Project No.City U 9500020)+2 种基金partially supported by the Fundamental Research Funds for the Central Universities of China(Grant No.30915015103)the National Natural Science Foundation of China(Grant No.51501090)partially supported by the National Natural Science Foundation of China(Grant No.51571170)
文摘Amorphous materials are ubiquitous and widely used in human society, yet their structures are far from being fully understood. Metallic glasses, a new class of amorphous materials, have attracted a great deal of interests due to their exceptional properties. In recent years, our understanding of metallic glasses increases dramatically, thanks to the development of advanced instrumentation, such as in situ x-ray and neutron scattering. In this article, we provide a brief review of recent progress in study of the structure of metallic glasses. In particular, we will emphasize, from the scattering perspective, the multiscale structures of metallic glasses, i.e., short-to-medium range atomic packing, and phase transitions in the supercooled liquid region, e.g., crystallization and liquid-to-liquid phase transition. We will also discuss, based on the understanding of their structures and phase stability, the mechanical and magnetic properties of metallic glasses.
基金Supported by the National Natural Science Foundation of China(41974127,41974155)China University of Petroleum(East China)Graduate Student Innovation Project Funding Project(YCX2020008)。
文摘A method is proposed to characterize the fast neutron scattering cross-section ( s f) quantitatively by the combina-tion of inelastic gamma rays and captured gamma rays, so as to realize the gas saturation evaluation of CO_(2)-injected heavy oilreservoirs based on the three-de tector pulsed neutron logging technology. Factors influencing of the evaluation effect of thismethod are analyzed and the effectiveness of this method is verified by a simulation example. By using the Monte Carlo simu-lation method and the physical model of bulk-volume rock, the relationship between s f and CO_(2) saturation is studied, and thesaturation interpretation model is established. The influences of formation temperature and pressure, heavy oil density, bore-hole fluid and reservoir methane content on the evaluation results of CO_(2) saturation are analyzed. The results show that thecharacterization of s f by the combination of secondary gamma information can eliminate the influence of formation lithology,borehole fluid and methane content are the main factors affecting the quantitative monitoring of CO_(2) saturation, and the ef-fects of formation temperature and pressure and heavy oil density are negligible. The simulation example verified the feasibilityof the method for evaluating the CO_(2) saturation of CO_(2)-injected heavy oil reservoirs.
基金supported by the National Key R&D Program of China(No.2021YFA1600703)the National Natural Science Foundation of China(No.12175254)+2 种基金the Youth Innovation Promotion Association CASthe China Spallation Neutron Source Projectthe Innovative Projects of the IHEP(No.E15459U210).
文摘The small-angle neutron scattering(SANS)instrument,one of the first three instruments of the China Spallation Neutron Source(CSNS),is designed to probe the microscopic and mesoscopic structures of materials in the scale range 1–100 nm.A large-area ^(3)He tube array detector has been constructed and operates at the CSNS SANS instrument since August 2018.It consists of 120 linear position-sensitive detector tubes,each 1 m in length and 8 mm in diameter,and filled with ^(3)He gas at 20 bar to obtain a high detection efficiency.The ^(3)He tubes were divided into ten modules,providing an overall area of 1000 mm×1020 mm with a high count rate capability.Because each tube is installed independently,the detector can be quickly repaired in situ by replacing damaged tubes.To reduce air scattering,the SANS detector must operate in a vacuum environment(0.1 mbar).An all-metal sealing technique was adopted to avoid high-voltage breakdown by ensuring a high-voltage connection and an electronic system working in an atmospheric environment.A position resolution of 7.8±0.1 mm(full width at maximum)is measured along the length of the tubes,with a high detection efficiency of 81±2% at 2A.Operating over the past four years,the detector appears to perform well and with a high stability,which supports the SANS instrument to finish approximately 200 user scientific programs.
基金Project supported by the National Key R&D Program of China(Grant Nos.2016YFA0301001,2018YFGH000095,and 2016YFA0300500)Shanghai Municipal Science and Technology Major Project,China(Grant No.2019SHZDZX04)the Research Grants Council of Hong Kong with General Research Fund,China(Grant No.17303819).
文摘Despite the apparent ubiquity and variety of quantum spin liquids in theory,experimental confirmation of spin liquids remains to be a huge challenge.Motivated by the recent surge of evidences for spin liquids in a series of candidate materials,we highlight the experimental schemes,involving the thermal Hall transport and spectrum measurements,that can result in smoking-gun signatures of spin liquids beyond the usual ones.For clarity,we investigate the square lattice spin liquids and theoretically predict the possible phenomena that may emerge in the corresponding spin liquids candidates.The mechanisms for these signatures can be traced back to either the intrinsic characters of spin liquids or the external field-driven behaviors.Our conclusion does not depend on the geometry of lattices and can broadly apply to other relevant spin liquids.
基金National Key Research and Development Program of China(Grant Nos.2017YFA0302901 and 2016YFA0300604)the National Natural Science Foundation of China(Grant No.11774399)+2 种基金Beijing Natural Science Foundation,China(Grant No.Z180008)the K.C.Wong Education Foundation(Grant No.GJTD-2018-01)the DAAD-PPP programme,and the joint German-Sino HGF-OCPC Postdoc Programme.
文摘We report the physical properties, crystalline and magnetic structures of singe crystals of a new layered antiferromagnetic(AFM) material PrPd0.82Bi2. The measurements of magnetic properties and heat capacity indicate an AFM phase transition at TN^7K. A large Sommerfeld coefficient of 329.23 m J·mol-1·K-2 is estimated based on the heat capacity data, implying a possible heavy-fermion behavior. The magnetic structure of this compound is investigated by a combined study of neutron powder and single-crystal diffraction. It is found that an A-type AFM structure with magnetic propagation wavevector k =(0 0 0) is formed below TN. The Pr3+ magnetic moment is aligned along the crystallographic c-axis with an ordered moment of 1.694(3) μBat 4K, which is smaller than the effective moment of the free Pr3+ ion of 3.58 μB.PrPd0.82Bi2 can be grown as large as 1 mm×1 cm in area with a layered shape, and is very easy to be cleaved, providing a unique opportunity to study the interplay between magnetism, possible heavy fermions, and superconductivity.
基金Project supported by the National Natural Science Foundation of China （Grant Nos 10274034 and 10474085）, and the Scientific Research Foundation for the Returned 0verseas Chinese Scholars, State Education Ministry, China.
文摘Inelastic incoherent neutron scattering spectra of D2O high-density amorphous （hda） ice, ice-Ⅷ and ice-Ⅱ mixed with small amount of H2O （（5%） have been measured recently on high-energy transfer spectrometer at Rutherford Appleton Laboratory （UK）. The hydrogen atom on D2O ice lattices has three distinguished vibrational modes, two bending at low frequencies and one stretching at high frequencies, and their frequencies are slightly different for different phases of ice. It was found that the lower one of the bending modes is located at -95 meⅤ for hda-ice, at -95 meⅤ for ice-Ⅷ and at -96 meⅤ for ice-Ⅱ and they are all lower than the value of 104 meⅤ for ice-Ih. It was also measured that the O-D and O-H covalent bond stretching modes of ice-Ⅷ are at -315 and -425 meⅤ, ice-Ⅱ at 307 and -415 meⅤ, hda-ice at 312 and -418 meⅤ, respectively. They are significantly higher than the values of ice-Ih at -299 and -406 meⅤ, respectively.
文摘When one wants to simply estimate tritium breeding ratio （TBR）, the TBR may be reduced from a ＂local＂ TBR for the breeding zones of a blanket module by multiplying the breeder coverage （= the surface area of effective breeding region / the surface area of the first wall around plasma）. When blanket modules are arranged~ the gap between neighboring modules and the frames of the modules are regarded as nombreeding zones. On the other hand, neutrons scattered in the non-breeding zones can enter breeding zones, contributing to tritium production. This means that the estimation method mentioned above tends to underestimate TBR. In order to assess the scattering effect quantitatively, we carried out a three-dimensional Monte Carlo N-particle transport MCNP-5 calculation. It was found from the calculation that there is little decrease in TBR for gaps less than 4 cm when the blanket thickness is 70 cm. The result indicates that such a wide allowance of the gap will facilitate access of remote handling equipment for the replacement of blanket modules and improve access of diagnostics.
基金Project supported by the National Natural Science Foundation of China （Grant No 10228511） and the State Key Development Program for Basic Research of China （Grant No 001CB610504）.
文摘In this paper, we present a computational study of L-serine using ab initio molecular dynamics simulation based on density functional theory （DFT） within the ultrasoft pseudopotentials and generalized-gradient approximation. Taking into account the intermolecular interactions, we can indeed simulate the features of the experimental results very well for L-serine zwitterions in its solid state. The vibrational spectrum of L-serine performed by DFT was in excellent agreement with our previous inelastic incoherent neutron scattering spectra measured at 20K for L-serine in the 10-200meV region on HET spectrometers at ISIS, Rutherford Appleton Laboratory.
基金Beijing Normal University is supported by the National Natural Science Foundation of China (Grant Nos. 11734002 and 11922402, X.L.)supported by the US Department of Energy (DOE),Basic Energy Sciences (BES),under Contract No. DE-SC0012311 (P.D.)
文摘The iron-chalcogenide superconductor FeTe_(1-x)Se_(x) displays a variety of exotic features distinct from iron pnictides.Although much effort has been devoted to understanding the interplay between magnetism and superconductivity near x=0.5,the existence of a spin glass phase with short-range magnetic order in the doping range(x~0.1-0.3)has rarely been studied.Here,we use DC/AC magnetization and(quasi)elastic neutron scattering to confirm the spin-glass nature of the short-range magnetic order in a Fe_(1.07)Te_(0.8)Se_(0.2) sample.The AC-frequency dependent spin-freezing temperature T_(f) generates a frequency sensitivityΔT_(f)(ω)/[T_(f)(ω)Δlog_(10)ω]≈0.028 and the description of the critical slowing down withτ=τ0(T_(f)/T_(SG-1))^(-zv) gives T_(SG)≈22 K and zv≈10,comparable to that of a classical spin-glass system.We have also extended the frequency-dependent T_(f) to the smaller time scale using energy-resolution-dependent neutron diffraction measurements,in which the T_(N) of the short-range magnetic order increases systematically with increasing energy resolution.By removing the excess iron through annealing in oxygen,the spin-freezing behavior disappears,and bulk superconductivity is realized.Thus,the excess Fe is the driving force for the formation of the spin-glass phase detrimental to bulk superconductivity.
基金support from Australian Research Council Discovery Project DP120102325the Centre forMicroscopy and Microanalysis at the University of Queensland+1 种基金Curtin Universitythe Australian Institute for Nuclear Science and Engineering for support through a Post-Graduate Research Award
文摘Phosphotungstic acid is an excellent proton conductor that can be incorporated into porous supports, and nanocomposite proton exchange membrane materials made from mesoporous silica impregnated with phosphotungstic acid have been suggested for use in fuels cells operating> 100 ℃. In this work, quasielastic neutron scattering was used to study proton self-diffusion in mesoporous disordered and P6 mm symmetry silica impregnated with two concentrations of phosphotungstic acid. Overall, the silica structure had a significantly greater effect on proton conduction and diffusion than phosphotungstic acid concentration, with higher proton conduction occurring for the P6 mm symmetry silica samples. Quasielastic neutron scattering revealed two populations of protons diffusing through each sample, and that proton conduction is limited by the slower of these populations, which diffuse via a jump-diffusion mechanism. Whilst the fundamental jump-diffusion mechanism by which these slower protons moved was found to be similar for both silica supports and phosphotungstic acid concentrations, the faster diffusion occurring in P6 mm structured silica arises from a lower residence time of protons moving between sites in the jump-diffusion model, suggesting a lower energy barrier.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11674157 and 11822405)the Fundamental Research Funds for the Central Universities(Grant No.020414380105)
文摘Quantum spin liquids（QSLs） represent a novel state of matter in which quantum fluctuations prevent the conventional magnetic order from being established, and the spins remain disordered even at zero temperature. There have been many theoretical developments proposing various QSL states. On the other hand, experimental movement was relatively slow largely due to limitations on the candidate materials and difficulties in the measurements. In recent years, the experimental progress has been accelerated. In this topical review, we give a brief summary of experiments on the QSL candidates under magnetic fields. We arrange our discussions by two categories： i） Geometrically-frustrated systems, including triangularlattice compounds YbMgGaO4 and YbZnGaO4, κ-（BEDT-TTF）2 Cu2（CN）3, and EtMe3 Sb[Pd（dmit）2]2, and the kagom′e system ZnCu3（OH）6 Cl2; ii） the Kitaev material α-RuCl3. Among these, we will pay special attention to α-RuCl3, which has been intensively studied by ours and other groups recently. We will present evidence that both supports and rejects the QSL ground state for these materials, based on which we give several perspectives to stimulate further research activities.
基金supported by the National Natural Science Foundation of China (Grant No. 10474085)
文摘INS （Inelastic Neutron Scattering） spectrum of methane hydrate was measured on MARI （a direct-geometry chopper spectrometer） at Ruther-ford Appleton Laboratory, UK. Compared with ice Ih, it is found that the whole spectrum of methane hydrate moves toward high-energy by about 1.5 meV. Using lattice dynamical （LD） technique, computer simulations of methane hydrate were carried out. In the simulations, four potential models （BE TIP3P, TIP4P, MCY） were employed to calculate the phonon density of states （PDOS）. Comparing the calculated PDOS spectrum with the experimental spectrum, it is found that BF, TIP4P, and TIP3P potential lattices give out well-separated translational and librational bands while MCY potential lattice is unstable to do so and this model is not suitable to describe hydrate system.
