Spin Transport in Very Dilute 3He-4He at Very High B/T

We report preliminary results for pulsed-NMR measurements on a very dilute 3 He- 4 He mixture (x 3 =900 ppm) in a 14.74 T field at temperatures down to 3 mK. The aim of the project is to investigate low temperature transverse spin relaxation and possible spin diffusion anisotropy. Spin-echo and T1-type measurements were employed to measure the transverse and longitudinal spin diffusion coefficients. At high temperatures both spin diffusion coefficients are well explained assuming a quasiparticle interaction consistent with previous experiments. Conversely, at low temperatures the measured value of |(lambda)(omega) (tau)…| is apparently limited to about ten by a poorly-understood process that accelerates spin-echo decay. This hampers an accurate determination of the transverse diffusion coefficient at the lowest temperatures reached.