Search results for "neutron"
showing 10 items of 2330 documents
host‐defect luminescence of stishovite
2005
a detailed study of the 4.75 eV luminescence band of stishovite single crystal (SiO2 with rutile structure) is reported. Kinetics of luminescence intensity is studied at durable (tens of minutes) X-ray excitation. The observed behaviour of the band intensity is explained by creation and destruction of luminescence centres depending on temperature both being determined by radiation stimulated diffusion of atomic particles. The luminescence decay is observed to last for minutes after X-ray irradiation while only for ns and hundreds of µs under pulsed e-beam irradiation suggesting a complicated recombination of the created defects. The UV band of stishovite is compared with the 4.9 eV luminesc…
Structural properties of phosphatidylcholine in a monolayer at the air/water interface
1991
Neutron reflectivities of phosphatidylcholine monolayers in the liquid condensed (LC) phase on ultrapure H 2 O and D 2 O subphases have been measured on a Langmuir film balance. Using a dedicated liquid surface reflectometer, reflectivities down to R = 10 -6 in the momentum transfer range Q z = 0–0.4A -1 were accessed. In a new approach, by refining neutron reflectivity data from chain-perdeuterated DPPC-d 62 in combination with x-ray measurements on the same monolayer under similar conditions it is shown that the two techniques mutually complement one another. This analysis leads to a detailed conception of the interface structure. It is found that in the LC phase (which is analogous to th…
Photoconversion and dynamic hole recycling process in anion vacancies in neutron-irradiated MgO crystals
1999
Optical spectroscopy and theory demonstrate that photon excitation of the positively charged anion vacancies (F{sup +} centers) at 5.0 eV in neutron-irradiated MgO crystals releases holes that are subsequently trapped at {ital V}-type centers, which are cation vacancies charge compensated by impurities, such as Al{sup 3+}, F{sup {minus}}, and OH{sup {minus}} ions. The concentration of trapped-hole centers was found to exceed that of available anion vacancies. The disproportionately large amount of holes produced is attributed to a dynamic recycling process, by which the F{sup +} center serves to release a hole to the {ital V}-type centers and subsequently trap a hole from an Fe{sup 3+} ion.…
Amorphous Ge15Te85: density functional, high-energy x-ray and neutron diffraction study
2011
The structure and electronic properties of amorphous Ge15Te85 have been studied by combining density functional (DF) simulations with high-energy x-ray and neutron diffraction measurements. Three models with 560 atoms have been constructed using reverse Monte Carlo methods constrained to (1) agree with the experimental structure factors S(Q), and have (2) energies close to the DF minimum and (3) a semiconducting band structure. The best structure is based on the melt-quenched DF structure and has a small number of Ge–Ge bonds. It shows interlocking networks of Te and GeTe with a significant fraction (22–24%) of voids (cavities). Ge occurs with both tetrahedral and 3 + 3 defective octahedral…
Crystal structure and magnetism of the double perovskites A2FeReO6 (A=Ca, Sr, Ba)
2004
Abstract We synthesized a series of double perovskites A 2 FeReO 6 (A=Ca, Sr, Ba) with Curie temperatures above room-temperature. Neutron and X-ray diffraction analysis have been performed in order to determine the structural and (local) magnetic properties of these materials. While Ba 2 FeReO 6 stays cubic over the whole temperature range we examined, the Sr-compound shows a tetragonal distortion of the perovskite structure which does not completely vanish up to about 520 K far above T C . Ca 2 FeReO 6 has a monoclinic unit cell at high temperatures. Below 400 K a phase separation in two monoclinic phases with identical cell volume is observed in neutron scattering.
Archaeometric Applications of X-Ray and Neutron Techniques
2009
Cultural Heritage is part of our everyday life and its conservation is extremely important not only from the cultural point of view, but also from a practical one. This is particularly true for Italy, a country which lists the highest number of World Heritage sites. Italian heritage, largely embodied in buildings and works of art, has a wider range of interests. For example information buried in sunk ships is very important when trying to gain information on commercial routes, exchange of technology and similar. In the case of stones authentication of works of art in museums is also of great concern, particularly as a number of rather expensive fakes have been acquired by museums from dubio…
Investigation of Wood Materials by Combined Application of X-ray and Neutron Imaging Techniques*
2014
Abstract Conservation of cultural heritage is extremely important not only from a cultural point of view, but also from a practical one. It is our duty to pass on to future generations the cultural heritage left to us by our ancestors. Wood is one of the most common materials used to generate works of art which are in a state of constant change and/or deterioration. In order to optimize the knowledge of artworks together with their conservation, it is necessary to use the most advanced scientific and technological tools. In the following paper, we will show the tomographic results which can be achieved by application of complementary techniques based on the combined use of X-ray and neutron…
Integrated multi-physics design tool for fusion breeding blanket systems - development and validation
2020
Il Breeding Blanket (BB) del reattore DEMO rappresenta un sistema complesso in un ambiente pericoloso. Infatti, esso deve soddisfare diversi requisiti e vincoli ingegneristici sia di tipo nucleare, termo-strutturale che di sicurezza. Per questi motivi, è necessaria una progettazione omnicomprensiva che preveda l'applicazione di strumenti avanzati di simulazione basati su approcci multi-fisici. Questi strumenti devono eseguire simultaneamente diversi tipi di analisi. Tre di esse possono essere considerate prioritarie e propedeutiche per lo studio di tutti gli altri fenomeni riguardanti il BB, vale a dire l´analisi nucleare, termo-fluidodinamica e strutturale. In questa tesi, è proposto un in…
Structural investigation of the confinement of finite amounts of trehalose in water-containing sodium bis(2-ethylhexyl)sulfosuccinate reversed micell…
2006
The structural effect of trehalose confined in water-containing sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reversed micelles at water to AOT molar ratio W = 5 and 10 as a function of the trehalose to AOT molar ratio T (0 < T < 0.1) has been investigated by small-angle neutron scattering (SANS). SANS data analysis is consistent with the hypothesis that trehalose is encapsulated within the quite spherical hydrophilic micellar cores of water-containing reversed micelles, causing an increase of the aggregate size and a decrease of the polydispersion. Moreover, SANS results suggest that the trehalose confinement in water-containing reversed micelles involves marked changes on the molecular pac…
Ultrafast Optical Demagnetization manipulates Nanoscale Spin Structure in Domain Walls
2012
During ultrafast demagnetization of a magnetically ordered solid, angular momentum has to be transferred between the spins, electrons, and phonons in the system on femto- and picosecond timescales. Although the intrinsic spin-transfer mechanisms are intensely debated, additional extrinsic mechanisms arising due to nanoscale heterogeneity have only recently entered the discussion. Here we use femtosecond X-ray pulses from a free-electron laser to study thin film samples with magnetic domain patterns. We observe an infrared-pump-induced change of the spin structure within the domain walls on the sub-picosecond timescale. This domain-topography-dependent contribution connects the intrinsic dem…