Anomalous kinetic energies of adsorbed⁴He on active carbon fibre (ACF)

Abstract

Direct measurements of the kinetic energies of He atoms adsorbed on active carbon fibre (ACF), at submonolayer coverage, are reported. The electronvolt spectrometer (eVs) of the ISIS neutron source, that utilizes the neutron Compton scattering technique, was employed. The specific adsorption area of the ACF was 3000 m 2 g −1 . The momentum distribution of adsorbed helium was measured at 4.6 K and 10.2 K and the average kinetic energy K s was found: 54.3±3.0 K. This value is 30% higher than that estimated by assuming slit-shaped pores of dimensions ∼0.7 nm together with a nearly monolayer coverage on a graphitic type adsorber.

Enhanced Bose–Einstein condensation and kinetic energy of liquid4He near a free surface

“…Within the precision of the current measurements, there appears to be a significantly larger condensate fraction at lower coverages, which is an exciting result, and is in agreement with modern theoretical predictions [25,28]. In addition, we find that the kinetic energy of the helium atoms increases when the number of layers is reduced in both the superfluid and normal phases, an effect which has also been observed for a monolayer of liquid 4 He adsorbed on activated carbon fibre [23]. This effect appears more pronounced in the normal phase.…”

“…This effect has been observed before in helium adsorbed on activated carbon fibres (ACFs) (see e.g. [23]). …”

He4adsorbed in cylindrical silica nanopores: Effect of size on the single-atom mean kinetic energy

“…Table II indicate that for both samples, values of ͗E K ͘ greatly exceed the value at equilibrium pressure of normal liquid 4 He, namely, ϳ16 K. 31 This finding is in agreement with previous determinations of mean kinetic energy of 4 He adsorbed in porous graphite and MgO. 1,6 Moreover, the ͗E K ͘ increases as the pore diameter is reduced. This is interpreted by considering that the experimental ͗E K ͘ values of Table II are average signals among helium atoms localized either in the bulk of the pores or close to the surface of the pores.…”

“…15 Recent experimental DINS measurements of 4 He, adsorbed in flat surface or slit-geometry porous substrates, have shown a large increase in ͗E K ͘ and n 0 , the condensate fraction of atoms with zero momentum. 1,6 This has been attributed to the strong localization effects induced by the helium-substrate interaction potential, which mainly influence the first two or three adsorbed layers. 6 At the same time, a reduction in the equilibrium pressure observed at low helium coverage has been attributed to a reduced local density of the adsorbate.…”

“…1,6 This has been attributed to the strong localization effects induced by the helium-substrate interaction potential, which mainly influence the first two or three adsorbed layers. 6 At the same time, a reduction in the equilibrium pressure observed at low helium coverage has been attributed to a reduced local density of the adsorbate. The latter determines smaller interatomic interactions and, consequently, an enhancement on the formation of the condensate.…”