High-Resolution Measurements of the Thermal Conductivity and Boundary Resistance of HELIUM-4 Near the Lambda Point.

This thesis describes high resolution measurements of the thermal conductivity of bulk helium and the thermal boundary resistance between helium and copper in the region from 10^{-7} to 10 ^{-3} K above the lambda transition, using thermometry with a resolution better than 10 ^{-9} K. In this region both properties are predicted to exhibit singular behavior as the transition is approached. We separated the thermal conductivity of bulk helium from boundary resistance by subtraction of data from runs with cell spacings ranging from 0.073 cm to 0.012 cm. Extrapolating the data to zero spacing, we obtained the first measurements of the boundary resistance above the lambda transition. The results are compared with recent calculations using renormalization group analysis. When the effect of gravity is taken into account, the thermal conductivity data agrees with the renormalization group analysis to within a few percent over the whole range measured. However the boundary resistance data yields an exponent 3 times smaller than that predicted. Two completely independent data sets were obtained, and the results were consistent.