DIRECT MEASUREMENT OF SPIN DIFFUSION FROM SPIN RELAXATION-TIMES IN SOLID HE-3

We show that the spin-diffusion coefficient in solid He-3 may be obtained unambiguously from measurements of spin relaxation at low magnetic fields. For long times, the dipolar autocorrelation function decays as t-3/2. This follows purely as a consequence of the hydrodynamics of the system. From this we show that the low-frequency form of the dipolar spectral density function is J(omega) = J(0) - A-omega-1/2, where the constant A depends on the diffusion coefficient and is independent of the microscopic details of the system. Values of the spin-diffusion coefficient thus obtained are in good agreement with those obtained by conventional means. Moreover this method permits extension to higher densities and lower diffusion coefficients.