Exponential Temperature Dependence of the Thermal Boundary Conductance between Sintered Silver andHe3-Bin the Region of Low Normal Fluid Density

We report the first direct measurements of the thermal boundary conductance between superfluid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$-$B$ and sintered silver in the temperature region well below $T_c$. The conductance is highly temperature dependent, being dominated by an $\exp (-\frac{\Delta }{\mathrm{kT}})$ dependence in the region $T<\mathrm{}0.3\mathrm{}{T}_c$. Measurements made at the three pressures 0, 4, and 12 bars also demonstrate the variation of the conductance with the energy gap, $\Delta$.