Papers by Wai Tung Hal Lee
Magnetic Resonance Imaging, 2021
We report the design, construction, and initial tests of a hyperpolariser to produce polarised 12... more We report the design, construction, and initial tests of a hyperpolariser to produce polarised 129Xe and 3He gas for medical imaging of the lung. The hyperpolariser uses the Spin-Exchange Optical Pumping method to polarise the nuclear spins of the isotopic gas. Batch mode operation was chosen for the design to produce polarised 129Xe and polarised 3He. Two-side pumping, electrical heating and a piston to transfer the polarised gas were some of the implemented techniques that are not commonly used in hyperpolariser designs. We have carried out magnetic resonance imaging experiments demonstrating that the 3He and 129Xe polarisation reached were sufficient for imaging, in particular for in vivo lung imaging using 129Xe. Further improvements to the hyperpolariser have also been discussed.
Journal of Applied Crystallography, 2018
QUOKKA is a 40 m pinhole small-angle neutron scattering instrument in routine user operation at t... more QUOKKA is a 40 m pinhole small-angle neutron scattering instrument in routine user operation at the OPAL research reactor at the Australian Nuclear Science and Technology Organisation. Operating with a neutron velocity selector enabling variable wavelength, QUOKKA has an adjustable collimation system providing source–sample distances of up to 20 m. Following the large-area sample position, a two-dimensional 1 m2 position-sensitive detector measures neutrons scattered from the sample over a secondary flight path of up to 20 m. Also offering incident beam polarization and analysis capability as well as lens focusing optics, QUOKKA has been designed as a general purpose SANS instrument to conduct research across a broad range of scientific disciplines, from structural biology to magnetism. As it has recently generated its first 100 publications through serving the needs of the domestic and international user communities, it is timely to detail a description of its as-built design, perf...
Nature Communications, 2016
Magnonic devices that utilize electric control of spin waves mediated by complex spin textures ar... more Magnonic devices that utilize electric control of spin waves mediated by complex spin textures are an emerging direction in spintronics research. Room-temperature multiferroic materials, such as bismuth ferrite (BiFeO3), would be ideal candidates for this purpose. To realize magnonic devices, a robust long-range spin cycloid with well-known direction is desired, since it is a prerequisite for the magnetoelectric coupling. Despite extensive investigation, the stabilization of a large-scale uniform spin cycloid in nanoscale (100 nm) thin BiFeO3 films has not been accomplished. Here, we demonstrate cycloidal spin order in 100 nm BiFeO3 thin films through the careful choice of crystallographic orientation, and control of the electrostatic and strain boundary conditions. Neutron diffraction, in conjunction with X-ray diffraction, reveals an incommensurate spin cycloid with a unique [11"Equation missing"] propagation direction. While this direction is different from bulk BiFeO3,...
SPIE Proceedings, 2001
In this contribution, we summarize the optimization of the neutron guide optics of the Magnetism ... more In this contribution, we summarize the optimization of the neutron guide optics of the Magnetism Reflectometer, which is currently under construction at the Spallation Neutron Source. The guide system consists of a straight source tube, a polygonal curved multi-channel bender, and a converging guide section. The bender will be essential for high-energy neutron and g-ray background suppression, while the converging
SPIE Proceedings, 2001
In this contribution, we evaluate novel applications of an energy band-pass filter for thermal an... more In this contribution, we evaluate novel applications of an energy band-pass filter for thermal and cold neutron beams. Our proposal is based on the original concept of the Drabkin spin-resonance flipper, which had been considered as a tunable neutron energy filter at reactor ...
9th International Conference on Polarised Neutrons in Condensed Matter Investigations, 2013
Time-of-flight polarized neutron reflectometry on PLATYPUS: status and future Time-of-flight pola... more Time-of-flight polarized neutron reflectometry on PLATYPUS: status and future Time-of-flight polarized neutron reflectometry on PLATYPUS: status and future developments developments
Advances in Computational Methods for X-Ray and Neutron Optics, 2004
ABSTRACT Neutron guides are widely used for improving the angular aperture of neutron scattering ... more ABSTRACT Neutron guides are widely used for improving the angular aperture of neutron scattering instruments in a broad band of wavelength. However, the usual guides are not effective enough in the short wavelength range. This is especially critical for time-of-flight instruments, which cannot take advantage of focusing techniques designed for steady-state monochromatic instruments. We discuss alternative ways to shape the reflecting surfaces in order to obtain a maximum angular aperture at the sample position at the expense of beam cross-section reduction. An optimal piecewise solution is proposed and Monte Carlo simulations with the IDEAS package are presented. Simulations for General Purpose Powder Diffractometer (GPPD) at Argonne National Laboratory are presented and the impact of a vertically focusing multiple-stage tapered guide is discussed. The results obtained by simulating the guide system options of engineering diffractometer VULCAN at the Spallation Neutron Source (SNS) are also presented, including vertically and horizontally tapered guide sections. The optimal multi-stage tapered guide design is discussed in terms of instrument figure of merit corresponding to different experimental needs ranging from high Q resolution to high intensity and/or high spatial resolution.
Nanoscale Research Letters, 2014
Zn1 - x Mn x O nanoparticles have been synthesized by hydrothermal technique. The doping concentr... more Zn1 - x Mn x O nanoparticles have been synthesized by hydrothermal technique. The doping concentration of Mn can reach up to 9 at% without precipitation or secondary phase, confirmed by electron spin resonance (ESR) and synchrotron X-ray diffraction (XRD). Room-temperature ferromagnetism is observed in the as-prepared nanoparticles. However, the room-temperature ferromagnetism disappears after post-annealing in either argon or air atmosphere, indicating the importance of post-treatment for nanostructured magnetic semiconductors.
Physica B: Condensed Matter, 2009
In recent years, polarized 3 He gas has increasingly been used as neutron polarizers and polariza... more In recent years, polarized 3 He gas has increasingly been used as neutron polarizers and polarization analyzers. Two of the leading methods to polarize the 3 He gas are the spin-exchange optical pumping (SEOP) method and the meta-stable exchange optical pumping (MEOP) method. At present, the SEOP setup is comparatively compact due to the fact that it does not require the sophisticated compressor system used in the MEOP method. The temperature and the laser power available determine the speed, at which the SEOP method polarizes the 3 He gas. For the quantity of gas typically used in neutron scattering work, this speed is independent of the quantity of the gas required, whereas the polarizing time using the MEOP method is proportional to the quantity of gas required. Currently, using the SEOP method to polarize several bar-liters of 3 He to 70% polarization would require 20À40 h. This is an order of magnitude longer than the MEOP method for the same quantity of gas and polarization. It would therefore be advantageous to speed up the SEOP process. In this article, we analyze the requirements for temperature, laser power, and the type of alkali used in order to shorten the time required to polarize 3 He gas using the SEOP method.
Journal of Physics: Conference Series, 2010
We report here the construction and neutron transmission test results of an in-situ polarized 3 H... more We report here the construction and neutron transmission test results of an in-situ polarized 3 He-based neutron polarization analyzer system for the Magnetism Reflectometer at the Spallation Neutron Source, Oak Ridge National Laboratory. The analyzer uses the Spin-Exchange Optical Pumping method to polarize the 3 He nuclei of a cell of 3 He gas. Polarized neutrons scattered from the sample are intercepted by the polarized 3 He gas which strongly absorbs neutrons in one spin-state while allowing most neutrons in the other spin-state to pass through. To maintain a stable analyzing efficiency during an experiment, the 3 He gas is continuously polarized in-situ on the instrument. Neutron transmission measurements showed that 73% 3 He polarization was reached in this setup.
Journal of the Physical Society of Japan, Apr 15, 2019
We report a wide-range reciprocal space observation with neutron diffraction in an iron vacancy c... more We report a wide-range reciprocal space observation with neutron diffraction in an iron vacancy controlled YbFe2O4 crystal, which is proposed as a prototype of electronic ferroelectrics arising fro...
Inorganic Chemistry, 2019
Journal of the Physical Society of Japan, 2019
We report a wide-range reciprocal space observation with neutron diffraction in an iron vacancy c... more We report a wide-range reciprocal space observation with neutron diffraction in an iron vacancy controlled YbFe2O4 crystal, which is proposed as a prototype of electronic ferroelectrics arising fro...
Journal of physics. Condensed matter : an Institute of Physics journal, Jan 2, 2018
We present magnetic susceptibility, heat capacity, and neutron diffraction measurements of polycr... more We present magnetic susceptibility, heat capacity, and neutron diffraction measurements of polycrystalline Nd2Ru2O7 down to 0.4 K. Three anomalies in the magnetic susceptibility measurements at 146, 21 and 1.8 K are associated with an antiferromagnetic ordering of the Ru4+ moments, a weak ferromagnetic signal attributed to a canting of the Ru4+ and Nd3+ moments, and a long-range-ordering of the Nd3+ moments, respectively. The long-range order of the Nd3+ moments was observed in all the measurements, indicating that the ground state of the compound is not spin glass. The magnetic entropy of Rln2 accumulated up to 5 K, suggests the Nd3+ has a doublet ground state. Lattice distortions accompany the transitions, as revealed by neutron diffraction measurements in agreement with earlier synchrotron x-ray studies. The magnetic moment of the Nd3+ ion at 0.4 K is estimated to be 1.54(2)μB and the magnetic structure is all-in all-out as determined by our neutron diffraction measurements.
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Papers by Wai Tung Hal Lee