Search results for "neutron"
showing 10 items of 2330 documents
Amorphous polymorphis in ice investigated by inelastic neutron scattering
1997
Abstract High-density Ilda and low-density Ilda amorphous have been investigated by inelastic neutron scattering (INS) with emphasis on the energy window from 0.5 to 20 meV. At variance with earlier measurements the spectra in the Ilda phase show a simple ω2 behaviour in the acoustic region and the temperature dependence is found to be harmonic. Ilda converts with a strongly temperature-dependent rate towards Ilda ice. We have investigated in detail the time evolution of both the static and dynamic response functions at several temperatures. Elastic small-angle signals indicate the presence of strong heterogeneties at the early stages of the conversion process. At least two different time s…
Dynamic heterogeneity in polymer electrolytes. Comparison between QENS data and MD simulations
2001
Abstract We have investigated the dynamics of poly(ethylene oxide) (PEO) lithium-based salt electrolytes (PEO–LiBETI) using quasi-elastic neutron scattering (QENS). Measurements were carried out on the spectrometer NEAT (HMI, Berlin) above the melting temperature of PEO ( T m ≈65°C). The experimental data fully support the Molecular Dynamics (MD)-derived model of a heterogeneous dynamics in dilute PEO-salt electrolytes. In agreement with MD simulations carried out on PEO–LiPF 6 , we find evidences for the existence of two dynamic processes: (a) a faster process that is described in terms of the pure PEO dynamics and (b) a second component which we identify with the slower motion of the PEO …
Fractal approach in petrology: Combining ultra small angle (USANS), and small angle neutron scattering (SANS)
2000
Ultra small angle neutron scattering instruments have recently covered the gap between the size resolution available with conventional intermediate angle neutron scattering and small angle neutron scattering instruments on one side and optical microscopy on the other side. Rocks showing fractal behavior in over two decades of momentum transfer and seven orders of magnitude of intensity are examined and fractal parameters are extracted from the combined USANS and SANS curves.
Spherical microgel colloids - Hard spheres from soft matter
1998
While gels are usually considered to be soft materials, we demonstrate that it is possible to model hard sphere behaviour when the gel structure is confined to spherical objects of sizes in the colloidal range. We have measured the static structure factor of microgel spheres dispersed in good solvents, differing in size, crosslink density and swelling behaviour, by light scattering and small angle neutron scattering. Comparing with theoretical calculations for polydisperse hard spheres we show how the interactions in highly concentrated dispersions of spherical microgel colloids are determined by an interplay of the relative length of dangling polymer ends at the surface (determined by the …
Mesoscopic structural organization in fluorinated room temperature ionic liquids
2018
The presence of fluorous tails in room-temperature ionic liquids imparts new properties to their already rich spectrum of appealing features. The interest towards this class of compounds that are of ionic nature with melting point less than 25 degrees C is accordingly growing; in particular, compounds bearing relatively long fluorous tails have begun to be considered. In this invited presentation, we show recent results arising from the systematic study of structural properties of a series of fluorinated room temperature ionic liquids, with growing fluorous chain length. At odd with the current understanding of this class of compounds, we show experimentally that they are characterized by t…
Nanoscale organization in the fluorinated room temperature ionic liquid: Tetraethyl ammonium (trifluoromethanesulfonyl)(nonafluorobutylsulfonyl)imide
2018
Fluorinated Room Temperature Ionic Liquids (FRTILs) are a branch of ionic liquids that is the object of growing interest for a wide range of potential applications, due to the synergic combination of specifically ionic features and those properties that stem from fluorous tails. So far limited experimental work exists on the micro-and mesoscopic structural organization in this class of compounds. Such a work is however necessary to fully understand morphological details at atomistic level that would have strong implications in terms of bulk properties. Here we use the synergy between X-ray and neutron scattering together with molecular dynamics simulations to access structural details of a …
Neutronic and photonic analysis of the single box water-cooled lithium lead blanket for a DEMO reactor
1998
Abstract The water-cooled Pb–17Li demonstration plant (DEMO) breeding blanket line was selected in 1995 as one of the two EU lines to be further developed in the next decade. In this paper the results of a neutronic and photonic analysis of the `single box' concept is presented. A full three-dimensional model, including the whole assembly and many of the DEMO reactor components, has been developed, together with a three-dimensional neutron source. A tritium breeding ratio (TBR) value of 1.16, with no ports and a Li6 enrichment of 90%, has been obtained and a further analysis has been performed to determine Li6 enrichment that would still ensure tritium breeding self-sufficiency. Selected po…
The commensurate-incommensurate transition of hydrogen monolayers physisorbed on graphite
1987
We present a neutron diffraction study of the commensurate-incommensurate (C-IC) transition of hydrogen monolayers physisorbed on the basal planes of exfoliated graphite. It is shown that the solid intermediate phase detected by specific-heat measurements can be described in terms of a striped domain-wall phase with superheavy walls. Comparison with simple models with fixed domain sizes is made. The results are in agreement with recent LEED experiments of Cui and Fain and provide an experimental realization of C-IC transition theories.
Electronically induced trapping of hydrogen by impurities in niobium
1984
The binding energies of hydrogen and its isotopes to substitutional impurities Ti, Cr, and V in niobium have been calculated. The hydrogen-metal interaction is based on the effective-medium theory. The wave mechanics of the hydrogenic interstitials are explicity dealt with, and the lattice distortion created by the hydrogen is incorporated through the method of lattice statics. The difference in the electronic structure between impurity and host atoms is shown to be largely responsible for the binding of hydrogen to the impurities. The results are in agreement with recent inelastic neutron scattering experiments. Peer reviewed
Simulation of H- ion source extraction systems for the Spallation Neutron Source with Ion Beam Simulator.
2012
A three-dimensional ion optical code IBSimu, which is being developed at the University of Jyväskylä, features positive and negative ion plasma extraction models and self-consistent space charge calculation. The code has been utilized for modeling the existing extraction system of the H(-) ion source of the Spallation Neutron Source. Simulation results are in good agreement with experimental data. A high-current extraction system with downstream electron dumping at intermediate energy has been designed. According to the simulations it provides lower emittance compared to the baseline system at H(-) currents exceeding 40 mA. A magnetic low energy beam transport section consisting of two sole…