Combined x-ray and thermal conductivity study of hexagonal-close packed helium-4
Fain, Samuel Clark, Jr.
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https://hdl.handle.net/2142/25798
Description
Title
Combined x-ray and thermal conductivity study of hexagonal-close packed helium-4
Author(s)
Fain, Samuel Clark, Jr.
Issue Date
1969
Doctoral Committee Chair(s)
Lazarus, David
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
x-ray studies
thermal conductivity
hexagonal close packed helium-4
laue x-ray photography
Language
en
Abstract
Thermal conductivity measurements made on hexagonal-close-packed
helium-4 are reported for specimens whose quality and orientation were
determined directly by an x-ray method. The specimens, 2.2mmin
diameter by 23 mm long, were held in a nylon container. They were
obtained by unidirectional growth from the fluid at a constant pressure
of 290 atmospheres and by recrystallization. Laue x-ray photographs
taken over 17 mm of the total length proved to be a very sensitive
indicator of specimen quality. These photographs showed specimens
grown from the fluid in the nylon container to be of inferior quality
to those obtained by recrystallization of samples rapidly grown from
the fluid. The thermal conductivity was lower in the low temperature
and the umklapp regimes for the specimens of inferior quality. The
thermal conductivity was highest at all, temperatures for a single crystal
obtained by recrystallization. This crystal was oriented with the
c-axis perpendicular to the axis of the specimen and of the heat current.
The thermal conductivityKfor this specimen could be represented at
higher temperatures by the :equation K = A exp (9 /bT), where A = o
L 1 X 10 -4 watts/ cm-deg, e = 58 K, b = 3.0, and T is the absolute
temperature. This temperature dependence is the same as that observed
in previous work at higher densities, but not at lower densities.
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