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1993 (2)
1Author    RalphO. SimmonsRequires cookie*
 Title    Single-Particle Momentum Distributions from Deep Inelastic Neutron Scattering (DINS)  
 Abstract    Single-particle longitudinal momentum distributions in condensed matter are now accessible to direct measurement using eV neutrons. Some systems of particular interest include a) quantum solids and fluids, formed from "Hie, 4 He, and H 2 , b) prototype molecular crystals, formed from noble gases, c) fluids such as H 2 and Ne, which show deviations from classical behavior and d) mixed systems, in which guest-host interactions may be important. Quantum solids can be investigated at substan-tially different densities, for different structures, and further, can be compared to the corresponding fluids, with which they have significant similarities in their single-particle properties such as their momentum distributions. Noble gas solids comprise a graduated family with progressively varying importance of zero-point energy, of phonon anharmonicity, and of multi-body forces. They have also been very useful for matrix isolation studies, and eV neutron scattering can yield their center-of-mass motions, not previously seen directly. Finally, noble gas fluids can be used to investigate the nature and extent of final-state effects in the neutron scatttering. Such effects are defined to be the difference between the longitudinal "neutron Compton profile" and the longitudinal momentum distribution. 
  Reference    Z. Naturforsch. 48a, 415—424 (1993); received December 27 1991 
  Published    1993 
  Keywords    Momentum distribution, Dynamics, Neutron scattering 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0415.pdf 
 Identifier    ZNA-1993-48a-0415 
 Volume    48 
2Author    R. C. Blasdell, D. M. Ceperley, R. O. SimmonsRequires cookie*
 Title    Neutron and PIMC Determination of the Longitudinal Momentum Distribution of HCP, BCC and Normal Liquid 4 Het  
 Abstract    Deep inelastic neutron scattering has been used to measure the neutron Compton profile (NCP) of a series of condensed 4 He samples at densities from 28.8 atoms/nm 3 (essentially the minimum possible density in the solid phase) up to 39.8 atoms/nm 3 using a chopper spectrometer at the Argonne National Laboratory Intense Pulsed Neutron Source. At the lowest density, the NCP was measured along an isochore through the hep, bcc, and normal liquid phases. Average atomic kinetic energies are extracted from each of the data sets and are compared to both published and new path integral Monte-Carlo (PIMC) calculations as well as other theoretical predictions. In this prelimi-nary analysis of the data, account is taken of the effects of instrumental resolution, multiple scatter-ing, and final-state interactions. Both our measurements and the PIMC theory show that there are only small differences in the kinetic energy and longitudinal momentum distribution of isochoric helium samples, regardless of their phase or crystal structure. 
  Reference    Z. Naturforsch. 48a, 433—437 (1993); received December 27 1991 
  Published    1993 
  Keywords    Momentum distribution, Neutron, Helium 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0433.pdf 
 Identifier    ZNA-1993-48a-0433 
 Volume    48