Abstract
The A-phase of superfluid 3He is the equilibrium phase at temperatures well below Tc only when a magnetic field in excess of about 0.35 T is applied. As a preliminary experiment in 3He-A at very low temperatures, we have measured the effective boundary resistance between 3He-A, stabilised by a field, and sintered silver at temperatures between 230 and 600 μK at 0 bar pressure, using a heat pulse method. Vibrating wire resonators in 3He-B "contacts" serve as thermometers. The boundary resistance is found to vary exponentially with temperature as exp [Δ/kT], where Δ is about half the maximum A-phase gap.