1,721,462 research outputs found
Roman bronze artefacts from Thamusida (Morocco): Chemical and phase analyses
No full textTwenty-six objects (1st to the 3rd century AD) found at the archaeological site of Thamusida (Morocco), which is a military settlement between the 1st and the 3rd century AD, have been investigated by means of portable X-ray fluorescence and time of flight-neutron diffraction. The combination of element-sensitive X-ray fluorescence and structure-sensitive neutron diffraction yields, in a totally non-destructive way, the necessary information to discriminate the copper alloy from corrosion and alteration layers. Results allowed dividing the repertory into five groups: (a) unalloyed copper, (b) binary alloys made of Cu and Sn, frequently leaded; (c) unleaded binary alloys made of Cu and Zn; (d) ternary alloys made of Cu, Sn and Zn, both leaded and unleaded; (e) quaternary alloys made of Cu, Sn, Zn and As. The choice of alloy is heterogeneous, mainly depending on availability and costs of raw and/or scrap materials and on technological constraints. Interestingly, the reconstruction obtained for Thamusida could either anticipate the important change in the Roman use of copper alloys generally referred as 'zinc decline', or more likely, indicate that brass never conspicuously entered the local metal-working activities of this military site
A comparative study of reconstruction methods applied to Neutron Tomography
No full textNeutron Tomography (NT) is an established technique to non-destructively investigate the inner structure of a wide range of objects. The major drawback of NT is the long acquisition time required to perform a tomographic scan compared to an X-ray Computed Tomography (CT) scan, due to the limited particle flux of the existing neutron sources. Therefore, in the NT field there is great interest in the reduction of scan time, dictated by the high neutrons production cost, aimed at optimizing the beamtime use at neutron imaging beamlines. A way for decreasing the total scan time is to reduce the number of projections. Generally, iterative reconstruction methods have advantages over analytical algorithms, such as the widely used Filtered Back-Projection (FBP), when data are noisy and limited. This research is focused on the comparative analysis of different reconstruction techniques, aimed at finding the data processing procedure suitable for NT, that reduces the scan time without reduction of the reconstructed image quality. For this purpose, a phantom sample was analysed by means of a white beam NT performed at the IMAT beamline, ISIS Neutron Source, U.K . Experimental data were used to test the performances of the FBP algorithm and different iterative reconstruction methods as a function of the number of projections and for different setups of the imaging system. The reconstructed images were quantitatively compared in terms of image quality indexes and the benefits of iterative methods for the limited data problem are discussed
Hydrogen atoms location in [Re4(μ3-H)4(CO)12] by joint X-ray single-crystal and neutron powder diffraction analysis
No full textThe hydrogen atom locations in [Re-4(mu(3)-H)(4)(CO)(12)] are accurately determined by joint X-ray single-crystal and time-of-flight neutron powder diffraction analysis; this new methodology does not require large crystals of several mm dimensions but only a sizeable amount of monophasic microcrystalline sample
Magnetic structure of Nd<sub>7</sub>Co<sub>6</sub>Al<sub>7</sub>
No full textTime-of-flight neutron powder diffraction has been used to determine the magnetic structure of the intermetallic compound Nd7Co6Al7. The thermodynamic, magnetic and electrical properties of this compound indicate that it undergoes a paramagnetic-ferromagnetic transition at 15.5 K, and possesses a magnetic refrigerant capacity of approximately 40 J/kg. The average value of the high field saturation magnetic moment per Nd atom at low temperatures is almost 50% below that of the free ion value. Neutron powder diffraction measurements have been performed at 300 K, in older to confirm the details of the crystal structure, and below the magnetic ordering temperature, at 6 it, in order to establish the nature of the magnetic structure. The high temperature data clearly confirm that Nd,Co,Al, crystallizes in the Pr7Co6Al7 structure (space group P4/mbm). The low temperature data show the presence of reflections at (100), (110), (200) and (210). reflections which are non-existent above the ordering temperature. The presence of the (100) reflection indicates the presence of antiferromagnetic configurations in this system. Models of the magnetic structure for Nd7Co6Al7 will be presented and discussed
Neutron diffraction study of Bronze Age tools from second millennium BC dwellings in Italy
Full text linkNeutron diffraction was utilized to characterise XX to XIII century BC bronze axes (Ancient to Late Bronze Age) from "Terramare" and other Bronze Age settlements near Modena, Italy. Archaeometric metallurgy issues have been addressed by means of phase and texture analysis from measurements carried out at the ROTAX and GEM beam lines of the neutron spallation source ISIS of the Rutherford Appleton Laboratory (UK), Neutron data provide accurate composition and structural information from the bulk of the alloy, with good grain statistics, without limitations due to surface alterations and with few limitations as to sample size. Bronze composition results are in good agreement with data obtained by micro-sampling and traditional analytical techniques thus confirming the validity of the method used for a totally non-destructive determination of the alloy composition from precise lattice parameter measurements. Phase analysis from diffraction profiles provides identification and quantification of surface alteration and corrosion products, free of interference with the analysis of the bulk alloy. Furthermore, texture analysis techniques may yield information on the ancient production methods of the artefacts. © Società Italians di Fisica
A study of the anti-ferromagnetic quadrupolar ordering in (DyB2C2)-B-11 through inelastic neutron scattering
No full textInelastic neutron scattering measurements have been carried out to investigate the crystal field (CF) excitations of DyB2C2 in order to understand the mechanisms of the quadrupolar ordering (TQ) observed at 24.7 K. Our analysis shows that the ground state is made up of nearly degenerate two Kramer doublets forming a ‘quasi-quartet’ ground state. This is consistent with heat capacity measurements, which have shown an estimated entropy of Rln2 at TN (15.3 K) and an additional Rln2 at TQ. A considerable shift and change in the width of the CF excitations and the splitting of the quasi-quartet ground state into two well-resolved doublets below TQ as well as a Zeeman splitting below TN have also been observed.<br/
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