Nuclear Spin-Lattice Relaxation in the Presence of Magnetic-Field Gradients

Brownian motion of a spin in the presence of a magnetic-field gradient can significantly influence the spin-lattice relaxation time. A theory is developed to describe this effect, and experiments on gaseous ${\mathrm{He}}^3$ which confirm the theory in detail are reported. Practical situations where this mechanism can dominate, such as in the construction and use of polarized ${\mathrm{He}}^3$ targets in nuclear-scattering experiments, are discussed. In a homogeneous magnetic field, relaxation times of approximately 7 h at low pressures permit us to establish an upper limit of $7\times {10}^{-15\mathrm{}}e$ cm for the electric-dipole moment of the ${\mathrm{He}}^3$ nucleus.