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Persistent URL http://purl.org/net/epubs/work/37145
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Record Id 37145
Title He-4 adsorbed in cylindrical silica nanopores: Effect of size on the single-atom mean kinetic energy
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Abstract This paper reports a study of the short-time dynamics of helium confined in silica nanopores (xerogel powder), with average pore diameters of 24 and 160 angstrom. The longitudinal momentum distribution of helium adsorbed in xerogels has been determined via deep inelastic neutron scattering (DINS) measurements performed on the VESUVIO spectrometer at the ISIS spallation source. DINS measurements, in the attosecond time scale, (i.e., 10(-16)-10(-15) s), were performed at a temperature of T=2.5 K and saturated vapor pressure conditions, with 95% pore volume filling. The average wave-vector transfer q was about 130 angstrom(-1). For confined helium, significant changes in the values of the single-particle mean kinetic energies < E-K > are found in the bulk phase. These are 32.6 +/- 8.7 K for the 24 angstrom and 24.4 +/- 5.3 K for the 160 angstrom pore diameters, remarkably higher than < E-K >=16.2 +/- 0.4 K, the value of normal liquid He-4 at T=2.5 K and saturated vapor pressure conditions. The results are interpreted in terms of a model where He-4 atoms are arranged in concentric annuli along the cylindrical pore axis, with < E-K > mainly dependent on the ratio between the atomic "effective" diameter and the pore diameter. The number of solid layers close to pore surface is found to be strongly pore-size dependent with one single solid layer for 24 angstrom diameter pore and three solid layers for 160 angstrom diameter pore
Organisation CCLRC , ISIS , ISIS-VESUVIO
Keywords INELASTIC NEUTRON-SCATTERING , BOSE-EINSTEIN CONDENSATION , VESUVIO SPECTROMETER , DIFFRACTION , LIQUID-HE-4 , SYSTEMS , HELIUM , PORES , ISIS 2007
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Language English (EN)
Type Details URI(s) Local file(s) Year
Journal Article Phys Rev B 75, no. 6 (2007): 064515. doi:10.1103/PhysRevB.75.064515 2007
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