ISSN:
1573-7357
Source:
Springer Online Journal Archives 1860-2000
Topics:
Physics
Notes:
Abstract We propose a θ1-t1-θ2 pulse-NMR experiment to detect the spin-diffusion anisotropy, Δ=D∥-D⊥, in degenerate spin-polarized3He-4He mixtures, where D⊥ and d∥are the transverse and longitudinal spin diffusion coefficients. In such an experiment the nonlinearity of the dynamics produces multiple spin echoes (MSE). At the 3He concentration x3 ≈ 4% the spinrotation parameter vanishes (μM →0), so that the nonlinearity of the equations of motion is entirely due to the anisotropy. In this situation, detection of MSE amounts to observation of ΔD. For slight anisotropy, i.e. ΔD/D∥ ≲0.25, we use a perturbation scheme similiar to that developed by Einzel et al. (in that case, for small μ M and small demagnetizing field) to calculate the second and third echo heights. For larger anisotropy we numerically calculate the echo heights. We find that for ΔD/D∥ = 0.5 the heights are ≈ 2 % of the first echo, and should be detectable. The (θ1, θ2) tip-angle dependence of the ΔD echoes is different from that of the μM and demagnetization echoes, and furthermore, they occur at right angles to these echoes (in spin space). Thus, even when small spin-rotation and demagnetization effects are present, the θ1-t1-θ2 experiment provides a sensitive means of detecting the anisotropy.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00755124
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