Observation of Nuclear Spin Waves in Spin-Polarized Atomic Hydrogen Gas

We have observed narrow, distinct resonances in the NMR spectrum of dilute spinpolarized atomic hydrogen gas ($n\sim {10}^{16}$ atoms/${\mathrm{cm}}^3$). The dependence of the observed spectra on temperature, density, polarization, and magnetic field gradient is consistent with theoretical predictions for spin-wave excitations damped by diffusion. We have measured the parameter $\mu$, which is a measure of the importance of exchange effects in spin-transport processes, and the diffusion coefficient $D_0$, both of which are in reasonable agreement with theory.