Magnetic resonance of atomic hydrogen at low temperatures

This article reviews the present state of magnetic resonance studies of atomic hydrogen gas at low temperatures. The various types of resonances that can be exploited are discussed and the paper ends with a review of the existing experimental data. It will be seen that up to the present, essentially all of the results have been derived from pulsed magnetic resonance of the 1420 MHz zero field hyperfine transition, and the many interesting results expected of the high field experiments are yet to appear.