Search results for "Instrumentation"
showing 10 items of 4914 documents
Colour centres in LiBaF3 crystals
1998
Abstract The origin of the absorption bands in LiBaF 3 created by X-ray irradiation at RT has been investigated. It is found that three absorption bands at 270, 320 and 430 nm represent different electron transitions within a radiation defect effectively created in LiBaF 3 single crystals. Following the Mollwo–Ivey relation we discuss investigations of optical dichroism, magnetic optical dichroism, as well as the assumptions regarding the accumulation kinetics of these absorption bands, the F centre being the main radiation defect created by X-rays in undoped LiBaF 3 crystals at RT.
Transient absorption spectra and relaxation kinetics in Nb-doped PbWO4 scintillating crystals
2001
Abstract The spectra and relaxation kinetics of absorption induced by a pulsed electron beam were studied for undoped and Nb-doped PbWO 4 single crystals. A significant influence of Nb doping on transient absorption was found. The influence of Nb doping on the relaxation kinetics is proposed to be due to an oxygen vacancy involving electron–hole recombination. A delay was observed (35– 50 ns ) between the growth of F-centers and the irradiation pulse. A large portion of the F-centers decays within ∼16 μs due to recombination with mobile holes. The prolonged recombination processes are responsible for the decrease of the scintillation yield in PbWO 4 : Nb crystals.
Synthesis and crystal structures of two novel triazolopyridine compounds solved by local L.S. minimizations from powder diffraction data
2014
The heteroaryl-substituted triazolopyridines 3-phenyl-7-(pyrazin-2-yl)-[1,2,3]triazolo[1,5-a]pyridine (2) and 3-[6-(pyridazin-3-yl)-pyridin-2-yl]-[1,2,3]triazolo[1,5-a]pyridine (4) have been synthesized and characterized (by HRMS, IR,1H and13C NMR, XRPD, melting point). The crystal structures have been solved from laboratory powder X-ray diffraction data with the direct-space strategy TALP for molecular compounds based on fast local least-squares minimizations. The crystal structure confirmed the formation of the tridentate compound4from a ring chain isomerization process. The almost planar arrangement of atoms in both the structures favors the presence of intermolecularπ–πinteractions, alt…
Pitfalls in the powder diffraction analysis of zeolites ZSM-5 and ZSM-8
1994
Crystal structure analyses by the Rietveld method have shown that the framework structures of zeolites ZSM-5 and ZSM-8 are essentially identical. Therefore, it is difficult to distinguish the two phases especially when the template-free H forms are studied. In addition, some inconsistencies in publications on the two zeolites aggravate the correct interpretation of the powder diagrams. A powder pattern published for ZSM-8 which indicates significant differences between the lattice constants of ZSM-8 and ZSM-5 is shown to be incorrectly indexed. Correct reindexing gives lattice constants for ZSM-8 matching average ZSM-5 values. Peak splitting of a ZSM-8 reflection at 2θ≈23° (CuKα) has been u…
X-ray powder diffraction data for some transition metal phosphites and hypophosphites
1994
A set of nine transition metal oxophosphorous compounds, consisting of four hypophosphites and five phosphites has been synthesized and studied using X-ray powder diffraction techniques. The compounds are α-Mn(H2PO2)2·H2O, Co(H2PO2)2 ·0.53H2O, MCl(H2PO2)2·H2O (M = Co2+, Ni2+), M2(HPO3)2·2H2O (M = Co2+, Ni2+), and M11 (HPO3)8(OH)6 (M = Zn2+, Co2+, Ni2+). Unit cells and X-ray powder patterns are reported.
X-ray powder diffraction study of the stability of solid solutions in (La1−xGdx)OCl
1996
The formation of the solid solutions in the (La1−xGdx)OCl series was studied by X-ray powder diffraction (XPD) at room temperature in the 2θ region between 6.5 and 120°. The Rietveld profile refinement analyses of the XPD patterns were carried out with the background, unit cell, atomic position, isotropic temperature, and Gaussian profile form parameters refined freely. All (La1−xGdx)OCl samples possessed the tetragonal PbFCl-type structure with P4/nmm as the space group (Z=2). The unit cell parameters a and c evolve smoothly through the series and no clustering of the Gd3+ ions was observed according to Vegard's law. The solid solubility exists throughout the whole series. The valence bond…
Contribution of X-Ray diffraction to the study of spin transitions in some iron (II) complexes
1991
Abstract A review of recent single crystal investigations under constraint of iron (II) spin crossover complexes is given. The systems covered are Fe L2 (NCS)2 complexes (L = Phen, Btz) and some analogous derivatives. Emphasis is laid on the correlations between structural changes associated with spin transitions and the experimentally determined characteristics of these transitions.
Powder X-ray diffraction data for potassium silver thiocyanate, AgK(SCN)2 and dipotassium silver thiocyanate, AgK2(SCN)3
2002
Previously unpublished powder X-ray diffraction data for potassium silver thiocyanate, AgK(SCN)2 and dipotassium silver thiocyanate, AgK2(SCN)3 are presented. F30 values for AgK(SCN)2 and AgK2(SCN)3 are 80(0.0075, 50) and 53(0.0089, 63), respectively. The Rietveld refinement of the patterns is also performed. For AgK(SCN)2Rp=6.98, Rwp=11.84, and RBragg=2.9. For AgK2(SCN)3Rp=7.22, Rwp=10.79, and RBragg=5.0.
Timing techniques applied to distributed modular high-energy astronomy: the H.E.R.M.E.S. project
2021
The HERMES-TP/SP (High Energy Rapid Modular Ensemble of Satellites -- Technologic and Scientific Pathfinder) is an in-orbit demonstration of the so-called distributed astronomy concept. Conceived as a mini-constellation of six 3U nano-satellites hosting a new miniaturized detector, HERMES-TP/SP aims at the detection and accurate localisation of bright high-energy transients such as Gamma-Ray Bursts. The large energy band, the excellent temporal resolution and the wide field of view that characterize the detectors of the constellation represent the key features for the next generation high-energy all-sky monitor with good localisation capabilities that will play a pivotal role in the future …
The HERMES-Technologic and Scientific Pathfinder
2020
HERMES-TP/SP (High Energy Rapid Modular Ensemble of Satellites Technologic and Scientific Pathfinder) is a constellation of six 3U nano-satellites hosting simple but innovative X-ray detectors, characterized by a large energy band and excellent temporal resolution, and thus optimized for the monitoring of Cosmic High Energy transients such as Gamma Ray Bursts and the electromagnetic counterparts of Gravitational Wave Events, and for the determination of their positions. The projects are funded by the Italian Ministry of University and Research and by the Italian Space Agency, and by the European Union Horizon 2020 Research and Innovation Program under Grant Agreement No. 821896. HERMES-TP/S…