| 1. |
- Perrichon, Adrien, 1988, et al.
(författare)
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A silicon analyser for the OSIRIS spectrometer: An analytical and Monte Carlo simulation study
- 2019
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Ingår i: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 947
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Tidskriftsartikel (refereegranskat)abstract
- The indirect time-of-flight near-backscattering spectrometer OSIRIS at the ISIS Facility is being upgraded with the addition of a silicon analyser. The new analyser bank will allow to increase the dynamic range, giving access to relaxation times up to 400 ps, and provide a further dimension in momentum transfer detection with the help of position-sensitive detectors. Here we present analytical calculations for the energy resolution and an extensive Monte Carlo simulation study to assess the performance of the new analyser bank. Simulation and calculation agree perfectly and confirm the initial design parameters of the spectrometer. The simulations predict similar detected intensity but with a higher resolution compared to the existing analyser setup using pyrolytic graphite crystals. Furthermore, the simulations stress the importance of the sample height for this setup and point toward a necessary further upgrade of the guide system. Further improvements of the energy resolution might be achieved with a pulse shaping chopper.
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| 2. |
- Perrichon, Adrien, 1988, et al.
(författare)
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Neutron Ray-Tracing Simulations of a New Supermirror Guide for the Osiris Spectrometer
- 2020
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Ingår i: Journal of Surface Investigation. - : PLEIADES PUBLISHING INC. - 1819-7094 .- 1027-4510. ; 14, s. S169-S174
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Tidskriftsartikel (refereegranskat)abstract
- A new supermirror guide has been proposed to replace the current neutron guide of the indirect time-of-flight near-backscattering spectrometer OSIRIS at the ISIS facility. Here we present an extensive Monte Carlo simulation study for the design and optimisation of a new guide system. Among the several guide geometry assessed, a curved guide with elliptical defocusing and focusing sections is shown to perform best. The estimated gain in intensity is a factor of 5–6 at the sample position with a homogeneous distribution of the divergence. The elliptic geometry results in a smaller beam spot and smaller samples will particularly benefit from this upgrade. The proposed guide replacement will ensure that the OSIRIS spectrometer will remain competitive in the years to come.
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| 3. |
- Adroja, D. T., et al.
(författare)
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Competing 4 f-electron dynamics in Ce(Ru1-xFex)(2)Al-10 (0
- 2013
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Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 87:22
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Tidskriftsartikel (refereegranskat)abstract
- We have carried out muon spin relaxation (mu SR), neutron diffraction, and inelastic neutron scattering (INS) investigations on polycrystalline samples of Ce(Ru1-xFex)(2)Al-10 (x = 0, 0.3, 0.5, 0.8, and 1) to investigate the nature of the ground state (magnetic ordered versus paramagnetic) and the origin of the spin-gap formation as evident from the bulk measurements in the end members. Our zero-field mu SR spectra clearly reveal coherent two-frequency oscillations at low temperature in x = 0, 0.3, and 0.5 samples, which confirm the long-range magnetic ordering of the Ce moment with Neel temperature T-N = 27, 26, and 21 K, respectively. On the other hand, the mu SR spectra of x = 0.8 and x = 1 down to 1.4 K and 0.045 K, respectively, exhibit a temperature-independent Kubo-Toyabe term, confirming a paramagnetic ground state. The long-range magnetic ordering in x = 0.5 below 21 K has been confirmed through the neutron diffraction study. INS measurements of x = 0 clearly reveal the presence of a sharp inelastic excitation near 8 meV between 5 K and 26 K, due to an opening of a gap in the spin excitation spectrum, which transforms into a broad response at and above 30 K. Interestingly, at 4.5 K, the spin-gap excitation broadens in x = 0.3 and exhibits two clear peaks at 8.4(3) and 12.0(5) meV in x = 0.5. In the x = 0.8 sample, which remains paramagnetic down to 1.2 K, there is a clear signature of a spin gap of 10-12 meV at 7 K, with a strong wave-vector-dependent intensity. Evidence of a spin gap of 12.5(5) meV has also been found in x = 1. The observation of a spin gap in the paramagnetic samples (x = 0.8 and 1) is an interesting finding in this study, and it challenges our understanding of the origin of the semiconducting gap in CeT2Al10 (T = Ru and Os) compounds in terms of a hybridization gap opening only a small part of the Fermi surface, gapped spin waves, or a spin-dimer gap.
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| 4. |
- Guccini, Valentina, 1988-, et al.
(författare)
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The Impact of Surface Charges of Carboxylated Cellulose Nanofibrils on the Water Motions in Hydrated Films
- 2022
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Ingår i: Biomacromolecules. - : NLM (Medline). - 1525-7797 .- 1526-4602. ; 23:8, s. 3104-3115
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose nanofibrils (CNFs) with carboxylated surface ligands are a class of materials with tunable surface functionality, good mechanical properties, and bio-/environmental friendliness. They have been used in many applications as scaffold, reinforcing, or functional materials, where the interaction between adsorbed moisture and the CNF could lead to different properties and structures and become critical to the performance of the materials. In this work, we exploited multiple experimental methods to study the water movement in hydrated films made of carboxylated CNFs prepared by TEMPO oxidation with two different surface charges of 600 and 1550 μmol·g-1. A combination of quartz crystal microbalance with dissipation (QCM-D) and small-angle X-ray scattering (SAXS) shows that both the surface charge of a single fibril and the films' network structure contribute to the moisture uptake. The films with 1550 μmol·g-1 surface charges take up twice the amount of moisture per unit mass, leading to the formation of nanostructures with an average radius of gyration of 2.1 nm. Via the nondestructive quasi-elastic neutron scattering (QENS), a faster motion is explained as a localized movement of water molecules inside confined spheres, and a slow diffusive motion is found with the diffusion coefficient close to bulk water at room temperature via a random jump diffusion model and regardless of the surface charge in films made from CNFs.
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| 5. |
- Lavén, Rasmus, 1994, et al.
(författare)
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Diffusional Dynamics of Hydride Ions in the Layered Oxyhydride SrVO 2 H
- 2021
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 1520-5002 .- 0897-4756. ; 33:8, s. 2967-2975
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Tidskriftsartikel (refereegranskat)abstract
- Perovskite-type oxyhydrides are hydride-ion-conducting materials of promise for several types of technological applications; however, the conductivity is often too low for practical use and, on a fundamental level, the mechanism of hydride-ion diffusion remains unclear. Here, we, with the use of neutron scattering techniques, investigate the diffusional dynamics of hydride ions in the layered perovskite-type oxyhydride SrVO2H. By monitoring the intensity of the elastically scattered neutrons upon heating the sample from 100 to 430 K, we establish an onset temperature for diffusional hydride-ion dynamics at about 250 K. Above this temperature, the hydride ions are shown to exhibit two-dimensional diffusion restricted to the hydride-ion sublattice of SrVO2H and that occurs as a series of jumps of a hydride ion to a neighboring hydride-ion vacancy, with an enhanced rate for backward jumps due to correlation effects. Analysis of the temperature dependence of the neutron scattering data shows that the localized jumps of hydride ions are featured by a mean residence time of the order of 10 ps with an activation energy of 0.1 eV. The long-range diffusion of hydride ions occurs on the timescale of 1 ns and with an activation energy of 0.2 eV. The hydride-ion diffusion coefficient is found to be of the order of 1 × 10-6 cm2 s-1 in the temperature range of 300-430 K, which is similar to other oxyhydrides but higher than for proton-conducting perovskite analogues. Tuning of the hydride-ion vacancy concentration in SrVO2H thus represents a promising gateway to improve the ionic conductivity of this already highly hydride-ion-conducting material.
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