The effect of [sup 4]He on the surface scattering of [sup 3]He

Thesis/Dissertation · Tue Dec 31 23:00:00 EST 1991

OSTI ID:7138593

Tholen, S M

This thesis documents the results of two separate experiments designed to investigate the nature of the scattering of [sup 3]He at a solid boundary. These experiments explored several questions: (1) Can the scattering, which is usually diffuse, be made specular for highly polished substrates (2) Does [sup 4]He induce specularity for both normal and superfluid [sup 3]He (3) How does surface [sup 4]He induce specularity, and how does the specularity depend on the phase and thickness of the [sup 4]He Both experiments were carried out using the well-known torsional oscillator technique. The first experiment was performed on normal [sup 3]He, where the nature of the surface scattering determines the amount of hydrodynamic slip, or velocity difference between the fluid and the substrate. These measurements were carried out first for pure [sup 3]He. For subsequent runs, various amounts of [sup 4]He were deposited before admitting the [sup 3]He. Because its zero-point motion is smaller than that of [sup 3]He, the [sup 4]He is preferentially coated onto the surfaces. The author was able to map out in detail the dramatic changes in slip which occur upon the addition of [sup 4]He. The second experiment was performed on superfluid [sup 3]He confined to a restricted geometry. Since diffuse scattering breaks superfluid pairs while specular scattering does not, the superfluid density near the walls can be suppressed in a system with diffuse scattering. The relative amounts of superfluid and normal fluid can be deduced by measuring the resonant frequency of the oscillator. As in the first experiment, [sup 4]He was added to the surfaces after measuring the pure [sup 3]He. The author verified that the increased specularity observed for the normal fluid also occurred for superfluid [sup 3]He. It was found that the solidification of the [sup 4]He film itself could be studied with this type of measurement.

• Research Organization: Cornell Univ., Ithaca, NY (United States)
• OSTI ID: 7138593
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360606 -- Other Materials-- Physical Properties-- (1992-)
665420* -- Superfluidity-- (1992-)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FILMS
HELIUM 3
HELIUM 4
HELIUM ISOTOPES
ISOTOPES
LIGHT NUCLEI
NUCLEI
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
SCATTERING
STABLE ISOTOPES
SUPERFLUIDITY
SURFACE PROPERTIES