Measurements of the ^(107)Ag neutron capture cross sections with pulse height weighting technique at the CSNS Back-n facility

Silver indium cadmium(Ag–In–Cd) control rod is widely used in pressurized water reactor nuclear power plants,and it is continuously consumed in a high neutron flux environment. The mass ratio of ^(107)Ag in the Ag–In–Cd control rod is 41.44%. To accurately calculate the consumption value of the control rod, a reliable neutron reaction cross section of the ^(107)Ag is required. Meanwhile,^(107)Ag is also an important weak r nucleus. Thus, the cross sections for neutron induced interactions with ^(107)Ag are very important both in nuclear energy and nuclear astrophysics. The(n, γ) cross section of ^(107)Ag has been measured in the energy range of 1–60 eV using a back streaming white neutron beam line at China spallation neutron source. The resonance parameters are extracted by an R-matrix code. All the cross section of ^(107)Ag and resonance parameters are given in this paper as datasets. The datasets are openly available at http://www.doi.org/10.11922/sciencedb.j00113.00010.

Analytical computation of magnetic field in coil-dominated superconducting quadrupole magnets based on racetrack coils

Currently,three types of superconducting quadrupole magnets are used in particle accelerators:cos 2θ,CCT,and serpentine.However,all three coil configurations have complex spatial geometries,which make magnet manufacturing and strain-sensitive superconductor applications difficult.Compared with the three existing quadrupole coils,the racetrack quadrupole coil has a simple shape and manufacturing process,but there have been few theoretical studies.In this paper,the two-dimensional and three-dimensional analytical expressions for the magnetic field in coil-dominated racetrack superconducting quadrupole magnets are presented.The analytical expressions of the field harmonics and gradient are fully resolved and depend only on the geometric parameters of the coil and current density.Then,a genetic algorithm is applied to obtain a solution for the coil geometry parameters with field harmonics on the order of 10^(-4).Finally,considering the practical engineering needs of the accelerator interaction region,electromagnetic design examples of racetrack quadrupole magnets with high gradients,large apertures,and small apertures are described,and the application prospects of racetrack quadrupole coils are analyzed.

Generation of two-color polarization-adjustable radiation pulses for storage ring light source

To date, two-color pulses are widely used in pump–probe experiments. For a ring-based light source, the power of the spontaneous radiation fluctuates randomly in the longitudinal direction. It is difficult to produce twocolor double pulses by optical methods. In this paper, we introduce a method based on the echo-enabled harmonic generation scheme that generates two-color pulses in a storage ring light source. By adopting crossed undulators and a phase shifter, the polarization of the two-color pulses can be easily switched. A numerical simulation based on a diffraction-limited storage ring, the Hefei Advanced Light Source, suggests that the time delay and spectral separation of the two pulses can be adjusted linearly by changing the pulse duration and chirp parameters of the seed laser. A circular polarization degree above 80% could be achieved.

Neutron-based characterization techniques for lithium-ion battery research

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.

Measurement of ^(232)Th(n,γ)cross section at the CSNS Back-n facility in the unresolved resonance region from 4 keV to 100 keV

The neutron capture cross section of ^(232)Th was measured at the neutron time-of-flight facility Back-n of China Spallation Neutron Source(CSNS)for the first time.The measurement was performed with 4 hydrogen-free deuterated benzene C6D6 liquid scintillation detectors,in the ES#2 experiment station on the beam line,at a distance of about 76 m from the neutron-production assembly.The total energy detection principle in combination with the pulse height weighting technique(PHWT)was applied to analyze the measured data.Results of the ^(232)Th(n,γ)reaction cross section in the unresolved resonance region from 4 keV to 100 keV were obtained,which shows a good agreement with the existing experimental data from EXFOR,as well as with the evaluated data from the ENDF/B-VIII.0 and CENDL-3.1.In addition,the excitation function of ^(232)Th(n,γ)^(233)Th reaction in the unresolved resonance region was theoretically calculated by using the code TALYS-1.95.By fitting the experimental cross section and theoretical data,the average parameters in the unresolved resonance region were extracted.

Superconducting multipole wiggler with large magnetic gap for HEPS-TF

A 16-pole superconducting multipole wiggler with a large gap of 68 mm was designed and fabricated to serve as a multipole wiggler for HEPS-TF.The wiggler consists of 16 pairs of NbTi superconducting coils with a period length of 170 mm,and its maximum peak field is 2.6 Tesla.In magnet design,magnet poles were optimized.Furthermore,the Lorentz force on the coils and electromagnetic force between the upper and lower halves were computed and analyzed along with the stored energy and inductance at different currents.To enhance the critical current of the magnet coil,all the pole coils selected for the magnet exhibited excellent performance,and appropriate prestress derived from the coil force analysis was applied to the pole coils during magnet assembly.The entire magnet structure was immersed in 4.2-K liquid helium in the cryostat cooled solely by four two-stage cryocoolers,and the performance test of the superconducting wiggler was appropriately completed.Based on the measured results,the first and second field integrals on the axis of the superconducting wiggler were significantly improved at different field levels after the compensation of the corrector coils.Subsequently,the wiggler was successfully installed in the storage ring of BEPCII operation with beams.

Topological Confinement in Reversibly Interlocked Polymer Networks

Recently, we reported a series of reversibly interlocked polymer networks(RILNs), whose mechanical robustness and functionalities improvement was believed to be derived from topological interlocking of two sub-networks, although the direct evidence for the deduction is still lacking. Herein, a specially-designed RILNs system, in which the inter-component hydrogen bonds can be shielded as needed, was prepared and used to study the micro-structures of RILNs, aiming to verify the existence of mechanical interlocking in RILNs. By changing the pH of the swelling solvent, the effect exerted by the inter-component non-covalent bonds was eliminated, so detailed information of the networks structure was exposed. The small angle X-ray scattering(SAXS) and small-angle neutron scattering(SANS) results indicated that swelling-induced structural evolution of the two sub-networks mutually affected each other, even when the inter-component hydrogen bonds were absent, proving the presence of topological interlocking. The findings may help to draw a more accurate physical image and reveal the detailed structureproperty relationship of RILNs.

Flexible UV detectors based on in-situ hydrogen doped amorphous Ga_(2)O_(3) with high photo-to-dark current ratio

Amorphous Ga_(2)O_(3)(a-Ga_(2)O_(3))has been attracting more and more attention due to its unique merits such as wide bandgap(∼4.9 eV),low growth temperature,large-scale uniformity,low cost and energy efficient,making it a powerful competitor in flexible deep ultraviolet(UV)photodetection.Although the responsivity of the ever-reported a-Ga_(2)O_(3)UV photodetectors(PDs)is usually in the level of hundreds of A/W,it is often accompanied by a large dark current due to the presence of abundant oxygen vacancy(VO)defects,which severely limits the possibility to detect weak signals and achieve versatile applications.In this work,the VO defects in a-Ga_(2)O_(3)thin films are successfully passivated by in-situ hydrogen doping during the magnetron sputtering process.As a result,the dark current of a-Ga_(2)O_(3)UV PD is remarkably suppressed to 5.17×10^(-11) A at a bias of 5 V.Importantly,the photocurrent of the corresponding device is still as high as 1.37×10^(-3)A,leading to a high photo-to-dark current ratio of 2.65×107 and the capability to detect the UV light with the intensity below 10 nW cm^(-2).Moreover,the H-doped a-Ga_(2)O_(3)thin films have also been deposited on polyethylene naphtholate substrates to construct flexible UV PDs,which exhibit no great degradation in bending states and fatigue tests.These results demonstrate that hydrogen doping can effectively improve the performance of a-Ga_(2)O_(3)UV PDs,further promoting its practical application in various areas.

Development and prospects of Very Small Angle Neutron Scattering (VSANS) techniques

Very Small Angle Neutron Scattering （VSANS） is an upgrade of the traditional Small Angle Neutron Scattering （SANS） technique which can cover three orders of magnitude of length scale from one nanometer to one micrometer. It is a powerful tool for structure calibration in polymer science, biology, material science and condensed matter physics. Since the first VSANS instrument, Dll in Grenoble, was built in 1972, new collimation techniques, focusing optics （multi-beam converging apertures, material or magnetic lenses, and focusing mirrors） and higher resolution detectors combined with the long flight paths and long incident neutron wavelengths have been developed. In this paper, a detailed review is given of the development, principles and application conditions of various VSANS techniques. Then, beam current gain factors are calculated to evaluate those techniques. A VSANS design for the China Spallation Neutron Source （CSNS） is thereby presented.

Status of CSNS H-ion source

A new H^- ion source has been installed successfully and will be used to serve the China Spallation Neutron Source （CSNS）. In this paper, we report various components of the ion source, including the discharge chamber, temperature, cooling system, extraction electrodes, analyzing magnet, remote control system and so on. Compared to the previous experimental ion source, some improvements have been made to make the ion source more compact and convenient. In the present arrangement, the Penning field is generated by a pair of pole tip extensions on the 90° analyzing magnet instead of by a separate circuit. For the remote control system, F3RP61-2L is applied to the accelerator online control system for the first time. In the running of the ion source, a stable pulse H^- beam with a current of 50 mA at an energy of 50 keV is produced. The extraction frequency and pulse width is 25 Hz and 500 μs, respectively. Furthermore, an emittance scanner has been installed and measurements are in progress.

Research on radiation dose rate distribution in the backscattering neutron hall of CSNS

Purpose To evaluate the prompt and induced dose rate in backscattering neutron hall for radiation protection and safety management.Method The dose rates were calculated by Monte Carlo code FLUKA,with the"multi-step"simulation method based on traditional"two-step simulation"method.Conclusion Operation time of staff workers does not need to be restricted.But with the increase in beam power and irra-diation time,serious consideration might need to be taken as the dose rate of samples may be higher than the limit value.

Hall sensor angle error and relative position calibrations for cryogenic permanent magnet undulator of high energy photon source test facility(HEPS-TF)

Purpose A new in-vacuum three-dimensional Hall probe magnetic measurement system is under fabrication for characterizing the magnetic performance of the Cryogenic Permanent Magnet Undulator(CPMU).In order to fit the small gap(5 mm)of magnetic structure and vacuum environment,a small three-dimensional Hall probe has been manufactured.The angular and positional misalignment errors of the Hall sensors play an important role in the measurement accuracy of the CPMU.In order to minimize the misalignment errors,a method of calibrating angle error and relative assembly displacements of a three-dimensional Hall probe is carried out.Methods The angle error of Hall sensors will be calibrated by a standard dipole magnet and a five-dimensional Hall bench.The standard dipole magnet will generate a single direction and uniform magnetic field.And the fivedimensional Hall bench is used to rotate the Hall probe which is put in the center of magnet.Based on the relationship between angle and magnetic field strength,the angle error of each Hall sensor will be obtained.The relative position between the sensitive areas of the Hall sensors will be calibrated by a two-dimensional magnetic field undulator section.Based on Maxwell’s equations,through the calculation of measurement magnetic field strength,the relative assembly displacements of the three Hall sensors can be derived.Results The details of the calibration methods and the data processing of angle error and relative assembly displacements of a three-dimensional Hall probe are presented.The three-dimensional magnetic fields of a cryogenic permanent magnet undulator can be received accurately by correcting these angle errors and position errors of Hall sensors.Conclusions This paper illustrates the relative position and angle calibration procedures and the data processing of a three-dimensional Hall probe.Now the design of a smaller Hall probe is in process.The calibration of the angle errors and position errors will be carried out after the fabrication of the standard dipole magnet.

Achieving highest Young’s modulus in Al-Li by tracing the size and bonding evolution of Li-rich precipitates

For decades,it has been well accepted that every 1 wt.%Li addition to Al will reduce Al alloy’s density by 3%and increase its Young’s modulus by 6%.However,the fundamental mechanism of modulus improve-ments stays controversial though all studies agreed that the contribution of such a substantial boosting comes from Li-rich clusters either in solid solution or precipitations.In this study,we experimentally produce nano-sized Li-rich clusters by non-equilibrium solidification using centrifugal casting and trace their evolutions as a function of subsequent heat treatments.High-resolution transmission electron mi-croscopy(HRTEM)reveals a further decrease in the lattice constants of Li-rich regions from the as-cast(0.406 nm),solid solution(0.405 nm)to the aged state(0.401 nm),while Young’s modulus of the Al-Li al-loy reaches 89.16 GPa.Small-angle neutron scattering(SANS)experiments and first-principle calculations based on density functional theory have shown both the bond strength around precipitates and the size of those Li-rich region dominate Young’s modulus.At the beginning,it is volumetric compression due to Li addition that increases modulus,tightening the Al-Al potential curves.In the end,it is the Al-Al and Al-Li valence bonds in Al 3 Li at large size and high-volume fraction which increase its second derivative of internal energy and thus Young’s modulus.

Optimization of dynamic aperture by using non-dominated sorting genetic algorithm-Ⅱ in a diffraction-limited storage ring with solenoids for generating round beam

Purpose Round beam,i.e.,with equal horizontal and vertical emittance,is preferable than a horizontally flat one for some beamline applications in Diffraction-limited storage rings(DLSRs),for the purposes of reducing the number of photons getting discarded and better phase space match between photon and electron beam.Conventional methods of obtaining round beam inescapably results in a reduction of dynamic aperture(DA).In order to recover the DA as much as possible for improving the injection efficiency,the DA optimization by using Non-dominated sorting genetic algorithm-Ⅱ(NSGA-Ⅱ)to generate round beam,particularly to one of the designed lattice of the High Energy Photon Source(HEPS)storage ring,are presented.Method According to the general unconstrained model of NSGA-Ⅱ,we modified the standard model by using parallel computing to optimize round beam lattices with errors,especially for a strong coupling,such as solenoid scheme.Results and conclusion The results of numerical tracking verify the correction of the theory framework of solenoids with fringe fields and demonstrates the feasibility on the HEPS storage ring with errors to operate in round beam mode after optimizing DA.

纳米尺度非均匀性诱导自更新铁基非晶合金具有优异的长期反应活性（英文）

铁基非晶合金作为亚稳态新型零价铁,具有高活性亚稳态结构、较大的残余应力和高密度低配位点等特性,在催化和废水处理中引起了广泛的关注;但由于腐蚀产物沉淀覆盖活性位点,非晶合金的反应活性随着时间的推移而逐渐降低,导致耐用性差.腐蚀产物沉淀造成长期反应活性降低也是阻碍传统晶态零价铁技术在废水处理领域应用的主要问题之一.本文通过在铁基非晶合金中引入纳米尺度的化学不均匀性,有助于构成局部原电池效应,加速电子在降解过程中的转移,可以有效地克服这一问题.更重要的是,非晶合金中的零价铁被选择性腐蚀/脱合金,导致反应区域局部体积收缩和裂纹形成,裂纹扩展使沉淀腐蚀产物和反应区域自剥落.因此,可以连续提供新的低配位,消除质量传递和反应活性恶化的问题.本文所制备的具有成分不均匀的铁基非晶合金即使在中性溶液中也具有良好的长期反应活性和自更新性能.研究结果不仅为废水处理提供了一种新材料,而且为设计高活性零价铁材料提供了一种新思路.

Atomic pair distribution function research on Li_2MnO_3 electrode structure evolution

The mechanism research of structure-related reactions on Li_2MnO_3 is important to enhance the electrochemical performance of lithium-manganese-rich layered oxides.Although there are some reports on the structure evolution of Li_2MnO_3 during cycling process,the employed research techniques are very limited,mainly in/ex-situ X-ray diffraction,X-ray absorption and transmission electron microscopy.Here,atomic pair distribution function,a method to study the local atomic arrangement on the basis of average spectroscopic information,is used for the first time to study the local structure evolution of Li_2MnO_3 during electrochemical charge/discharge cycles.The results clearly demonstrate that Mn^(3+)/Mn^(4+) redox couple is activated and Mn ions are reduced during discharging process.Some Mn ions in Mn layers can significantly migrate to Li layers and occupy the octahedral sites.As a result,a portion of inserted Li ions can occupy the face-shared tetrahedron sites,accompanied by the formation of local spinel-like structure.This work provides an important and suitable method based on the average spectroscopic information to investigate the local structure of electrode materials of lithium-ion batteries as well as other advanced battery systems.

Analysis and experimental concepts of the vibrating wire alignment technique

The vibrating wire alignment technique is a method which, by measuring the spatial distribution of a magnetic field, can achieve very high alignment accuracy. The vibrating wire alignment technique can be applied to fiducializing magnets and the alignment of accelerator straight section components, and it is a necessary supplement to conventional alignment methods. This article gives a systematic summary of the vibrating wire alignment technique, including vibrating wire model analysis, system frequency calculation, wire sag calculation, and the relation between wire amplitude and magnetic induction intensity. On the basis of this analysis, this article outlines two existing alignment methods, one based on magnetic field measurement and the other on amplitude and phase measurements. Finally, some basic experimental issues are discussed.

Morphology Evolution of Polystyrene-core/Poly(N-isopropylacrylamide)-shell Microgel Synthesized by One-pot Polymerization

One-pot polymerization with macroinitiator is supposed to be a robust, facile way to synthesize well-defined core- shell nanoparticles with fixed shell thickness. To testify this, we investigated the temperature-depending morphology evolution of polystyrene （PS） core/poly（N-isopropylacrylamide） （PNIPAM） shell microgel synthesized by one-pot polymerization with PNIPAM-RAFT as macroinitiator in dimethylformamide （DMF） by transmission electron microscopy （TEM）, dynamic/static light scattering （DLS/SLS） and small angle neutron scattering （SANS）. It is revealed that the microgel has a core-shell structure, i.e., the core is made of pure PS, but the shell is composed of both PNIPAM-RAFT macroinitiator and crosslinked PS. In fact, there are 92.0 wt% D20, 6.7 wt% PNIPAM and 1.3 wt% PS in the shell in its aqueous dispersion at 21 ℃; therefore, its shell thickness is much larger than the extended chain length of the macroinitiator as revealed by both SANS and DLS observations. Competitive growth of styrene, divinylbenzene and PNIPAM macroinitiator as well as possible chain transfer from amine proton of PNIPAM side chain may lead to the larger shell thickness, compared with the extended chain length of the macroinitiator. Our work can shed light on the real morphology control in one-pot polymerization.

Uniform to Accelerated Crystal Twisting Transition in Deuterate Polyethylene/Poly(ethylene-alt-propylene) Blend Films

A uniform to accelerated crystal twisting transition is observed in deuterate polyethylene/poly（ethylene-alt- propylene） （d-PE/PEP） blend films. And the band period is a function of initial d-PE concentration, quench depth and annealing time of phase separation. As Keith and Padden suggested, twisting of lamella is due to the unbalanced stress on its both sides, which can supply a satisfying explanation to banded spherulites formed in homogeneous systems. When it comes to d-PE/PEP blend system, in homogeneous 99% d-PE/PEP （weight fraction of d-PE） blend film, the formation of banded spherulite is observed as a result of uniform twisting of ribbon like d-PE lamellae along the radial direction. With the amorphous PEP piling up, it transfers into accelerated edge-on to fiat-on twisting due to crystallization assisted phase separation. The mechanism can be interpreted as following： d-PE molecules must inter-diffuse to the twisting growth front to continue the secondary nucleation and growth process. Meanwhile, the amorphous PEP molecules are rejected and accumulated at the twisting growth front. Once the d-PE lamella begins to twist because of unbalanced stress on both sides, the accumulated rubber phase at the growth front strengthens the unbalance and accelerates the edge-on to flat-on twisting. The concentration wave propagates further away with constant speed, and leads to concentric ring pattern with periodic nonuniform twisting along the radial direction. Since this is a kinetic effect, the band period can be controlled through initial d-PE concentration, quench depth and annealing time of phase separation. Our result shows that crystallization assisted phase separation can modify lamella growth kinetic pathway, thereby assisting concentric ring pattern formation.

Mictomagnetism and suppressed thermal conduction of the prototype high-entropy alloy CrMnFeCoNi

High-entropy alloys are characteristic of extensive atomic occupational disorder on high-symmetric lattices,differing from traditional alloys.Here,we investigate the magnetic and thermal transport properties of the prototype face-centered-cubic high-entropy alloy CrMnFeCoNi by combining physical properties measurements and neutron scattering.Direct-current and alternating-current magnetizations measurements indicate a mictomagnetic behavior with coexisting antiferromagnetic and ferromagnetic interactions below room temperature and three anomalies are found at about 80,40,and 20 K,which are related to the paramagnetic to antiferromagnetic transition,the antiferromagnetic to ferromagnetic transition,and the spin freezing,respectively.The electrical and thermal conductivities are significantly reduced compared to Ni,and the temperature dependence of lattice thermal conductivity exhibits a glasslike plateau.Inelastic neutron scattering measurements suggest weak anharmonicity so that the thermal transport is expected to be dominated by the defect scattering.