The diffraction detector for the EMD of the CSNS

On 23rd August 2018, the China Spallation Neutron Source (CSNS) located in Dongguan operated 4 neutron instruments. In the future, twenty neutron spectrometers will be built to provide multidisciplinary platforms for scientific research by national institutions, universities, and industries. Engineering Material Diffractometer (EMD), which will be used for strain measurements in engineering materials and components, will be constructed at the Beamline 8 in 2022. A novel thermal neutron detector, which will comply with the requirements of EMD application, is being developed. This detector will consist of 6LiF/ZnS(Ag) scintillation screens, wavelength shifting fiber (WLSF) arrays, a silicon photomultiplier (SiPM) and Application Specific Integrated Circuit (ASIC) read-out electronics. Each scintillation screen will be inclined with respect to the incident neutron beam at a grazing angle θ = 17°. Such geometry will not only improve the spatial resolution of detectors but also the neutron detection efficiency. The prototype of detector module has been tested at the neutron Beamline 20 at the CSNS. The experimental results obtained for this prototype illustrate that the pixel size of detector module is 3 mm and the detection efficiency exceeds 40% at the neutron wavelength of 1 Å. Based on these results, we design and manufacture the final version of the detector for the EMD application, which is characterized by low power consumption, highly integrated and easy to install. 70 such detectors will be installed till the end of 2021.

Clustering of Diamond Nanoparticles, Fluorination and Efficiency of Slow Neutron Reflectors

Neutrons can be an instrument or an object in many fields of research. Major efforts all over the world are devoted to improving the intensity of neutron sources and the efficiency of neutron delivery for experimental installations. In this context, neutron reflectors play a key role because they allow significant improvement of both economy and efficiency. For slow neutrons, Detonation NanoDiamond (DND) powders provide exceptionally good reflecting performance due to the combination of enhanced coherent scattering and low neutron absorption. The enhancement is at maximum when the nanoparticle diameter is close to the neutron wavelength. Therefore, the mean nanoparticle diameter and the diameter distribution are important. In addition, DNDs show clustering, which increases their effective diameters. Here, we report on how breaking agglomerates affects clustering of DNDs and the overall reflector performance. We characterize DNDs using small-angle neutron scattering, X-ray diffraction, scanning and transmission electron microscopy, neutron activation analysis, dynamical light scattering, infra-red light spectroscopy, and others. Based on the results of these tests, we discuss the calculated size distribution of DNDs, the absolute cross-section of neutron scattering, the neutron albedo, and the neutron intensity gain for neutron traps with DND walls.

First measurements with the new 3He-filled Monoblock Aluminium Multitube neutron detector developed at the ILL for ANSTO PLATYPUS reflectometer

A detector upgrade was carried out on the PLATYPUS instrument dedicated to neutron reflectometry at the Australian Nuclear Science and Technology Organisation (ANSTO). The new detector, developed in the framework of a research collaboration between the ILL and ANSTO, is based on the Monoblock Aluminium Multi-tube (MAM) detector design already in use on several reflectometers and SANS instruments at the ILL. This article provides a technical description of the mechanical design and read-out electronics of the PLATYPUS detector and its commissioning on the PLATYPUS instrument. The main detector performance parameters have been measured and are presented here as well as the characterisation methods and the results of several reflectometry measurements. These measurements show an improvement in experimental data quality resulting from high positional resolution, high detection efficiency and reduced neutron scattering background in the 2.5–19 Å neutron wavelength range used in PLATYPUS instrument.

First Experiment of Spin Contrast Variation Small-Angle Neutron Scattering on the iMATERIA Instrument at J-PARC

Recently, we have developed a novel dynamic nuclear polarization (DNP) apparatus with a magnetic field of 7 T and a sample temperature of 1 K. High proton spin polarizations from −84% to 76%, for TEMPO doped polystyrene samples, have been demonstrated. This DNP apparatus satisfies the simultaneous requirement for quick and easy sample exchange and high DNP performance. On the iMATERIA (BL20) instrument at J-PARC, the first beam experiment using this DNP apparatus has been performed. For this experiment, the beamline was equipped with a supermirror polarizer. The stray magnetic field due to the superconducting magnet for DNP was also evaluated. The stray magnetic field plays an important role for in maintaining the neutron polarization during the transportation from the polarizer to the sample. The small-angle neutron scattering (SANS) profiles of silica-filled rubber under dynamically polarized conditions are presented. By applying our new analytical approach for SANS coherent scattering intensity, neutron polarization (PN) as a function of neutron wavelength was determined. Consequently, for the neutron wavelength, range from 4 Å to 10 Å, |PN| was sufficient for DNP-SANS studies.

Comment on “Giant electromechanical coupling of relaxor ferroelectrics controlled by polar nanoregion vibrations”

Manley et al. (Science Advances, 16 September 2016, p. e1501814) report the splitting of a transverse acoustic phonon branch below TC in the relaxor ferroelectric Pb[(Mg1/3Nb2/3)1−xTix]O3 with x = 0.30 using neutron scattering methods. Manley et al. argue that this splitting occurs because these phonons hybridize with local, harmonic lattice vibrations associated with polar nanoregions. We show that splitting is absent when the measurement is made using a different neutron wavelength, and we suggest an alternative interpretation.

Calibration of the Suanni small-angle neutron scattering instrument at the China Mianyang Research Reactor

A series of calibration measurements have been performed on Suanni – the first small-angle neutron scattering spectrometer entering into routine user operation in China – aiming to characterize instrument performance and to provide a reference for user experiments. Various calibration standards were used to verify the precise association of the scattering intensity I with the scattering vector magnitude q at short and medium sample–detector distances. The measurements recorded for silver behenate powder revealed a slight shift of the neutron wavelength (λ) at the sample position as compared to the nominal λ calculated by the selector constant. The deviation was more significant with λ > 0.8 nm owing to the shape of the incoming neutron spectrum incident on the selector. The measured dead time for the entire detection system is 2.7 µs, as determined by measurements with varying fluxes. A protonated/deuterated polystyrene blend was employed as the primary standard to calibrate the secondary standard H2O. The instrument covers an effective q range between 0.013 and 5 nm−1, as demonstrated by scattering curves obtained from a monodisperse poly(methyl methacrylate) nanoparticle suspension and a glassy carbon plate.

Three Dimensional Numerical Simulation of Thermal-Hydraulic Behaviors of CSNS Decoupled Poisoned Hydrogen Moderator With Non-Uniform Heat Source

The Chinese Spallation Neutron Source (CSNS) is the national major scientific equipment, which will be completed around 2018. The moderator is the core of the CSNS parts, and CSNS uses three types of moderator to meet the requirements of different neutron wavelength and pulse shapes, and the structure and flow field of Decoupled Poisoned Hydrogen Moderator (DPHM) is the most complicated. Currently, Computational Fluid Dynamics (CFD) is the primary tool for thermal design of DPHM to ensure the reliability of calculation result and precision of the engineering requirements. In the current work, three-dimensional simulation of fluid-solid conjugate heat transfer and flow for container pipe, poisoned plate and moderator material were carried out, by compiling corresponding UDF program for ANSYS FLUENT to describe the non-uniform heat source distribution accurately. Thermal-Hydraulic behaviors such as pressure disturbance, pressure rise and temperature distribution cooling capacity are investigated.