The spin diffusion coefficient of3He in3He-4He solutions |
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Authors: | D. C. Chang H. E. Rorschach |
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Affiliation: | (1) Rice University, Houston, Texas |
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Abstract: | The transport properties of3He in3He-4He solutions with molar concentrations of 5, 9, 14, and 24% have been studied for 0.9 KT2.5 K. The spin diffusion coefficientDs and the longitudinal relaxation timeT1 were measured by the spin-echo method for temperatures both above and below the solution lambda temperatureT. The spin-echo method measures the diffusion coefficient for magnetizationDs, which differs from the usual diffusion coefficient for particlesD belowT.Ds depends on the3He-3He scattering cross sectionFF and the3He-roton/phonon cross sectionFB, whileD depends only onFB. The distinction betweenDs andD is elaborated in terms of a simple mutual-friction model for diffusion. The two scattering mechanisms are clearly evident in the behavior ofDs as a function of concentrationx and temperature. The contribution due to the3He-3He scattering is inversely proportional tox, indicating that the3He can be treated in first approximation as a classical gas (the Pomeranchuk model). The predictions of various theoretical models are compared with the results, where possible, but most of the previous theoretical work is not applicable to the concentration range and temperatures of these measurements.Supported in part by the National Science Foundation and the U.S. Office of Naval Research. |
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