Search results for "inelastic neutron scattering"
showing 10 items of 78 documents
Charged-pion cross sections and double-helicity asymmetries in polarizedp+pcollisions ats=200 GeV
2015
We present midrapidity charged-pion invariant cross sections, the ratio of the pi(-) to pi(+) cross sections and the charge-separated double-spin asymmetries in polarized p + p collisions at root s = p + 200 GeV. While the cross section measurements are consistent within the errors of next-to-leading-order (NLO) perturbative quantum chromodynamics predictions (pQCD), the same calculations overestimate the ratio of the charged-pion cross sections. This discrepancy arises from the cancellation of the substantial systematic errors associated with the NLO-pQCD predictions in the ratio and highlights the constraints these data will place on flavor-dependent pion fragmentation functions. The char…
Neutron scattering and crystal fields in Pr-hydrides
1978
The crystal field splittings of PrD2 and PrD2.5 have been determined by inelastic neutron scattering. While for PrD2 the crystal field experienced by the majority of Pr-ions is cubic, it is shown that in PrD2.5 the occupation of the octahedral interstitials occurs not in a statistical but rather in a well defined way which leads to an orthorhombic crystal field at the Pr-site.
Experimental studies of the liquid-glass transition in trimethylheptane
2000
The molecular glass former trimethylheptane was studied by calorimetric, dielectric, ultrasonic, neutron scattering, Brillouin scattering, and depolarized light-scattering techniques. The molecular structure appears to be nearly spherical optically as indicated by the low depolarization ratio and dielectric susceptibility values. A preliminary mode-coupling theory (MCT) analysis of the light-scattering and neutron-scattering data indicates that ${T}_{C}\ensuremath{\gtrsim}150 \mathrm{K},$ at least 25 K above ${T}_{G}.$ The susceptibility minima were analyzed with the MCT interpolation equation, and disagreement between the light and neutron results was observed despite the apparent isotropy…
Inelastic neutron and low-frequency Raman scattering in a niobium-phosphate glass for Raman gain applications
2011
Abstract We present measurements of the vibrational spectrum of a binary niobium-phosphate glass in the THz frequency range using inelastic neutron and Raman scattering. The spectra of these glasses show a low-frequency enhancement of the vibrational density of states (“boson peak”). Using a recently developed theory of vibrational excitations in disordered solids we are able to reconcile the measured neutron and Raman spectra using fluctuating elastic and Pockels constants as a model concept. As the spontaneous Raman susceptibility is a key parameter for Raman amplification our results suggest a significant gain profile for application of niobium-phosphate glasses in Raman amplifiers.
Inelastic neutron scattering measurements on Nd2Fe14B and Y2Fe14B single crystals
1992
Abstract Inelastic neutron scattering measurements have been carried out on Nd 2 Fe 14 B and Y 2 Fe 14 B single crystals. Temperature dependent acoustic magnon dispersion curves have been found along the high-symmetry directions [0,0,1] and [1,0,0] with a gap at (0,0,2). Soft mode behaviour at spin wave vector q = 0 was observed for Nd 2 Fe 14 B near the spin reorientation temperature. The inelastic scattering intensity decreases steeply for larger q . Therefore, the dispersion curves could be measured until the middle of the Brillouin zone only. The experimental results are discussed in the frame of a classical spin wave model.
Transport of Mobile Particles in an Immobile Environment: Computer Simulations of Sodium Silicates
2007
Molecular dynamics (MD) simulations of various sodium silicate melts, (Na2O)x(SiO2) with x=2, 3, 20, are presented. In these systems, the mobility of sodium ions is much higher, often by orders of magnitude, than that of the silicon and oxygen atoms forming a tetrahedral network structure. We show that the high mobility of sodium is intimately related to the chemical ordering in sodium silicates. A network of percolating sodium-rich channels is formed in the static structure that serve as diffusion channels for the sodium ions. This channel network is revealed in static structure factors by a prepeak at the wavenumber q=0.95 A-1. Inelastic neutron scattering experiments of sodium silicate m…
Ferroelastic transition in Kbr:Kcn studied by neutrons, x-rays and ultrasonic
1986
The ferroelastic phase transition of (KBr) 0 27 (KNC) 0.73 has been studied by X-ray diffraction, ultrasonics and inelastic neutron scattering. It is the first example of a cubic crystal where the elastic shear constant C 44 softens completely corresponding to the m = 2 universality class. C 44 and the Bragg intensities show a non-classical critical behaviour.
Antiferromagnetism and the node structure of the superconducting order parameter of UPd Al
2000
The node structure of the superconducting order parameter of the heavy-fermion system is analyzed within the weak-coupling theory. A pairing interaction induced by the exchange of antiferromagnetic spin excitations is assumed as suggested by recent inelastic neutron scattering experiments and tunneling spectroscopy. The multi-sheeted Fermi surface is taken into account. Based on a model susceptibility for the simple antiferromagnetic structure of , line nodes result at the rim of the magnetic Brillouin zone.
Superconductivity mediated by spin fluctuations in the heavy-fermion compound UPd2 Al3
1999
It is well known that any weak attractive electron–electron interaction in metals can in principle cause the formation of Cooper pairs, which then condense into a superconducting ground state1. In conventional superconductors, this attractive interaction is mediated by lattice vibrations (phonons). But for the heavy-fermion and high-temperature superconductors, alternative pairing interactions are considered to be possible2. For example, the low-temperature properties of heavy-fermion systems are dominated by antiferromagnetic spin fluctuations, which have been considered theoretically3 as a possible cause for Cooper-pair formation. This picture recently received some experimental support: …
Magnetic clusters from polyoxometalate complexes
1999
Abstract The present article highlights the increasing interest of polyoxometalates in molecular magnetism, providing at the same time a perspective of the state-of-the-art in this area. The main focus is the polyoxotungstates. The first aspect we discuss is that of the coordination chemistry of these metal–oxide ligands. We show that this chemistry leads to remarkable examples of well-insulated magnetic clusters of controlled nuclearity and topology. In these clusters detailed information on the nature of the magnetic exchange interactions can be extracted by using, in addition to the classical magnetic techniques (magnetic susceptibility, magnetization and EPR spectroscopy), other physica…